# Another proof why BIGGER brakes are NOT always best!



## alexb75 (Dec 29, 2002)

It was very interesting as I was watching this show on Speed Vision (don't remember its name - the one with the fat guy) that they modify cars, add aftermarket components and dyno/track it before and after.
Very interestingly, they modified this Honda, added a Mugen cat-back that is supposed to add more than 10HP and they also put a BIG braking system there with all the bells and whistles. 
They actually LOST POWER, dyno was less after the cat-back and brakes! The guys were totally confused themselves and I am actually amazed they even aired the show... they called Mugen and they said they lost power because of the brakes they installed...








On the braking performance side, their stopping distance DID NOT change and their track time was also the same or worse (multiple runs)...








So, this goes with almost what most knowledgeable people were saying on this forum about brakes and why bigger is *not *always better!


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## gehr (Jan 28, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

I saw that part of the show......it was interesting......rotational inertia's a bitch


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (gehr)*


_Quote, originally posted by *gehr* »_I saw that part of the show......it was interesting......rotational inertia's a bitch









Yes it is!
It just bugs me that people come here and try to go bigger and BIGGER and *BIGGER* and they don't believe that it's not really doing anything for them and if someone who knows tells them (like for a long time Racer_x) they just say, "so why XYZ did it!"
Oh well, if there are not people like that, many companies would be out of business


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## kdiver58 (Jan 25, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

Racer_X has stated this very same thing over and over. From what I see I'm guessing that 75% maybe more install bigger brakes for the looks.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (kdiver58)*


_Quote, originally posted by *kdiver58* »_Racer_X has stated this very same thing over and over. From what I see I'm guessing that 75% maybe more install bigger brakes for the looks. 

I think so, but they still claim all kinds of non-sense... and companies also advertise and market bigger brakes for performance! I hope one day people learn


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## kdiver58 (Jan 25, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

I've learned my lesson. After reading what people had to say and my observations that the stock brake system and stock pads did 90% of what I wanted it to I've decided to just replace my pads with a pad that will take the higher temps of a track day and not upgrade to the 312mm rotors. I'm going with an extra set of track rotors and pads.


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## Byron N. (Oct 20, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

If I recall correctly the brake comparisons were done with entirely different weather conditions. It was very cold and rainy after they installed the Stoptech brake kit, and they stated that their was a lack of grip to truly test them. I don't know if this was the same episode you saw. I didn't see any part with dyno runs so I'm not sure. The show is Sportscar Revolution I believe.


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## N'Syncro (Jul 27, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (Byron N.)*

The Big-Brake belief is probably one of the greatest misconceptions about performance parts that I ever see. Kinda like M4d tyte JDM VTEC yo!


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## Racer_X (Jul 14, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

I'll bet they put some 18" wheels and some Z or W or Y speed rated 215/35R18 tires on it, too. Like that Honda is ever going to go over 168mph (or even 150mph). Right!
This also points out another important detail in building up a car. Make one change at a time, then measure your results. Sounds like the crew on that show was clueless as to which things helped and which things hurt. 
In slight defense of the big brakes, I'll bet the wheels and tires they picked hurt performance a lot worse than the brakes themselves. And the tires were probably the big problem with stopping distance (and could have contributed to acceleration problems, both due to weight and grip). But a lot big brake kits require larger than stock wheels to clear, so you get that added penalty in addition to the weight of the brakes themselves. 
Still, if you want maximum performance, you want the *smallest* brakes that you can use that won't fade in your driving situation(s) and the *smallest* (or almost smallest) wheels that clear those brakes.


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## dcomiskey (Mar 13, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_It was very interesting as I was watching this show on Speed Vision (don't remember its name - the one with the fat guy) that they modify cars, add aftermarket components and dyno/track it before and after.
Very interestingly, they modified this Honda, added a Mugen cat-back that is supposed to add more than 10HP and they also put a BIG braking system there with all the bells and whistles. 
They actually LOST POWER, dyno was less after the cat-back and brakes! The guys were totally confused themselves and I am actually amazed they even aired the show... they called Mugen and they said they lost power because of the brakes they installed...








On the braking performance side, their stopping distance DID NOT change and their track time was also the same or worse (multiple runs)...








So, this goes with almost what most knowledgeable people were saying on this forum about brakes and why bigger is *not *always better!









How can you "lose power" from the brakes they installed? That makes no sense to me.
Also, why did these dumbasses install a cat-back on a NA car? That does nothing other than add the fart sound.


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## N'Syncro (Jul 27, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*

IIRC, that Catback they installed added something like 8 or 11whp. 
And you lose power from big brakes (or large / heavy wheels) b/c your engine now has to try and spin all this extra added weight when it accelerates. The engine still puts out the same amount of power, but it is not able to efficiently put it to the ground. 
Picture them throwing on a set of 45inch wheels that weigh 1000lbs each and 40inch brakes (that would also be insanely heavy).. Now imagine if they went on a dyno. The engine would barely be able to turn the wheels, thus, "robbing" it of power.


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## mydeathbynapalm (Feb 2, 2005)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*

Crank HP can increase with whatever engine mods...power to the ground (Wheel HP) will decrease (say if one remains stock or doesn't upgrade those engine mods when adding heavier rotors and/or wheels) with heavier rotors and/or wheels. Kinda like yeah, the ECS Stage 3 big brake front weighs LESS than stock...but the rotors actually weigh MORE than stock...most of the weight savings is from the caliper. The specs are right there...
As was said above...rotational inertia is the issue.


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## Racer_X (Jul 14, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*


_Quote, originally posted by *dcomiskey* »_How can you "lose power" from the brakes they installed? That makes no sense to me.
It all depends on how you measure horsepower. The two easiest and most common methods would be the G-TECH/Pro and an inertial chassis dyno. 
The G-Tech pro will show horsepower based on observed vehicle acceleration, vehicle weight and tire rotating radius. So, any losses to inertia in all 4 wheels will show as lost whp.
An inertial chassis dyno also reads hp based on the acceleration of the roller on the dyno. So it will show inertial losses from the weight of the wheels and brakes on the drive wheels as lost whp. 

_Quote, originally posted by *dcomiskey* »_Also, why did these dumbasses install a cat-back on a NA car? That does nothing other than add the fart sound.








Actually, a cat back system helps norally asthmatic cars too, just not as much as it helps on a turbo. It also depends on how good the manifold, donwpipe and cat flow. VW's can have fairly good flow through those parts, so a 2" (or 2.25") cat back system will give a bit of extra power over the stock 1.75" (or 2") system.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Racer_X)*

Ok, just to clarify what they did... got a stock car, dynoed it, did a stopping distance test, and tracked it... 
Then added a cat back exhaust, and bigger brakes... did it again. HP shown on the dyno was less than stock and their stopping distance did not change, and their track time also remained the same! So, all that trouble for nothing








They then called Mugen Honda to see why they lost power and they said it is because of the rotational mass of the bigger brakes (not made by mugen) even though the bigger brakes weighed the same as the stock brakes!!!!
BTW, they were NOT trying to prove that bigger brakes cause power loss and they actually tried to justify it somehow...
-----
I bet in most of the mods people do here, if they do the exact same test, the results will be exactly the same. I see people slam their cars to the ground, get 20" wheels, and huge brakes and biggest exhaust, etc.... I wish they tracked their car before and after to find out that they just got slower










_Modified by alexb75 at 10:31 AM 2-3-2005_


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## dcomiskey (Mar 13, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

That's pretty lame. Most BBKs don't reduce your stopping distance, contrary to popular belief. The main advantag is for fade resistance. I guess initial logic would tell you bigger brakes = shorter stopping distance but no. Did these tuning idiots try better tires?


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## Racer_X (Jul 14, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_Ok, just to clarify what they did... got a stock car, dynoed it, did a stopping distance test, and tracked it... 
Then added a cat back exhaust, and bigger brakes...
What about wheels? Same wheels? Or did they "upgrade" to clear the larger brakes?

_Quote, originally posted by *alexb75* »_ did it again. HP shown on the dyno was less than stock and their stopping distance did not change, and their track time also remained the same! So, all that trouble for nothing








They then called Mugen Honda to see why they lost power and they said it is because of the rotational mass of the bigger brakes (not made by mugen) even though the bigger brakes weighed the same as the stock brakes!!!!
 Total weight might be the same. But I'll bet it went from heavy cast iron calipers, small rotors to big heavy rotors, light weight aluminum calipers. 
Even if the rotors weighted the same, the added diameter will move the weight outward, increasing inertia.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Racer_X)*


_Quote, originally posted by *Racer_X* »_What about wheels? Same wheels? Or did they "upgrade" to clear the larger brakes?
Total weight might be the same. But I'll bet it went from heavy cast iron calipers, small rotors to big heavy rotors, light weight aluminum calipers. 
Even if the rotors weighted the same, the added diameter will move the weight outward, increasing inertia.



Not sure on the wheels... but they didn't mention anything, so I assume it was the same wheels and tires. 
You are bang on with second comment, the guy said Mugen told them although the brakes are lighter, but the rotational mass is the problem as it moves the weight outward (just as u said).


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*


_Quote, originally posted by *dcomiskey* »_That's pretty lame. Most BBKs don't reduce your stopping distance, contrary to popular belief. The main advantag is for fade resistance. I guess initial logic would tell you bigger brakes = shorter stopping distance but no. Did these tuning idiots try better tires?

They didn't try better tires, this just showed that bigger brakes don't help stopping distance.
Also, your point of fade resistance is not 100% true as the most important factor is pads+fluid and if u upgrade those on ur stock-size rotors, you will have no fade!


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## idunno (May 9, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_ but the rotational mass is the problem as it moves the weight outward (just as u said).

Yeah...and not in a linear fashion. The moment of inertia goes up
with the square of the radius....


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_They didn't try better tires, this just showed that bigger brakes don't help stopping distance.
Also, your point of fade resistance is not 100% true as the most important factor is pads+fluid and if u upgrade those on ur stock-size rotors, you will have no fade! 

I think a better term to describe the benefit of larger rotors is _added heat capacity_ rather than fade resistance. I definitely noticed an improvement in temperatures with the 11.3" -> 12.3" upgrade. I doubt it made any difference to my lap times, but its mainly for my peace of mind and not melting off the clear-coat on my wheels!!!
edit: spelling



_Modified by phatvw at 1:08 PM 2-4-2005_


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## machschnelGTI (Jun 28, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*

Stock brakes will lock up the wheels (on a non-abs car) without problem. Take them to a track that is very hard on brakes and several laps later, they won't lock up the wheels...or slow them down much for that matter. Big brakes will not increase stopping distances...only tires can do that. Big brakes are for fade resistance and heat dissipation, so they will last the whole race and not go away half way through.


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## Byron N. (Oct 20, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (machschnelGTI)*

I'm just curious how many people posting about how big brakes work have ever installed them on their car or drove a car with them. I'm not talking about driving on the street or an autocross course but rather on a real road course like Road America or Summit Point. I have driven many street cars with different levels of upgrades ranging from pads/fliud/rotors/Hoosier tires on a mk3 VR6 Jetta to a 97 Audi w/chipped 1.8T with manual dual masters, 13"x1 1/4" 2 piece front rotors w/Alcon 4 pistons and 12"x1" rear rotors w/Alcon 4 pistons. I can say from experience that the difference between the two cars was night and day. The Audi would stop from 60m.p.h. in less than 85 ft. on street tires (225-40-18 Bridgestone S0-3 and Pagid Orange pads fr.Pagid Blue rr.), and it could do it as many times as you asked it to. I know that talk is cheap but to me it sounds like one person makes what sound like a good argument against something on this forum and its repeated over and over again by people that have no clue what it means. I'm not the end all be all expert but I have had the opportunity to test out many different set-ups first hand at a shop I worked at for a while. There is always a trade off with upgrades, wether its cams,turbos,.... Its up to the individual to find what is most important for their applications.
The same people that bang on about wieght are the ones that knock carbon hoods when they save 20-35lbs. off the nose of your car. 
If you don't want to shell out the long dollars for big brakes don't, but stop bashing those that do by saying they really are just for looks.
There are a lot of factors in comparing brakes. You can have the best brakes in the world but if you don't bed the pads and rotors in properly or clean new rotors properly they may perform worse than a lesser quality brake set-up. Pad material, fluid, master cylinder size, tire compound, camber, tire pressure, wieght distribution, pedal ratios, the list goes on, they all effect overall performance.
I'm sure there are a lot of people here that have a very solid understanding of brakes and how they work and should take no offense to me posting my experiences. If what you know works for you thats cool, but I'm sure not everyone needs the same thing from their car.
I just like to see all possible side to any point, to ensure all information that is available is recieved. I think we need to start posting what we have on our cars,to weed out the "ya I heards and me toos". Sorry for the long post. Not trying to piss in anyones cheerios.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Byron N.)*

First of all, I am not against all bigger brakes, but as the title says, state that "bigger brakes are not ALWAYS the best"... 
Byron,
What kind of pads were on the other car? You mentioned Pagid orange pads and blue on that big brake setup that's a HECK of a pad! Pads are the MOST important factor for fading and as long as you get good pads, you are able to stop consistently during track sessions.
I have been in cars with big brakes and I do track my own car. I can tell you that with a set of Brembo stock-size rotors, Pagid pads, and Motul DOT 5.1 fluid, my car does 4*25min sessions in a very brake demanding track very easily! When I was on stock pads, I only had decent braking for 2/3 of each session and then I had to brake much much earlier... 
At the same time I have seen cars there with HUGE brakes, Brembo upgrades, etc... that fade (one got off the road mutliple times) while others dont, the culprit is pads/fluid! 
All we are trying to say is that in MOST applications bigger brakes make you slower while not providing much braking improvement. A better upgrade would be pads+fluid.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (machschnelGTI)*


_Quote, originally posted by *machschnelGTI* »_Stock brakes will lock up the wheels (on a non-abs car) without problem. Take them to a track that is very hard on brakes and several laps later, they won't lock up the wheels...or slow them down much for that matter. Big brakes will not increase stopping distances...only tires can do that. Big brakes are for fade resistance and heat dissipation, so they will last the whole race and not go away half way through. 

Put stock pads on bigger brakes and you fade just as fast!


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## Byron N. (Oct 20, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_First of all, I am not against all bigger brakes, but as the title says, state that "bigger brakes are not ALWAYS the best"... 
Byron,
What kind of pads were on the other car? You mentioned Pagid orange pads and blue on that big brake setup that's a HECK of a pad! Pads are the MOST important factor for fading and as long as you get good pads, you are able to stop consistently during track sessions.
I have been in cars with big brakes and I do track my own car. I can tell you that with a set of Brembo stock-size rotors, Pagid pads, and Motul DOT 5.1 fluid, my car does 4*25min sessions in a very brake demanding track very easily! When I was on stock pads, I only had decent braking for 2/3 of each session and then I had to brake much much earlier... 
At the same time I have seen cars there with HUGE brakes, Brembo upgrades, etc... that fade (one got off the road mutliple times) while others dont, the culprit is pads/fluid! 
All we are trying to say is that in MOST applications bigger brakes make you slower while not providing much braking improvement. A better upgrade would be pads+fluid.


The pads that I was running on the Jetta VR6 were Pagid Orange front and rear. I ran this car at Road America at an event and even with the rotor shields taken off the rear for better cooling I still warped the rotors and could not make full use of the power and top speed of the car for fear of running ot of brakes at the end of the long downhill. Now I will say that the pads were a big improvement over the stock but the limiting factor is still the standard size non-directional viened rotor and its limted ability to handle massive amounts of heat generated by the high friction pads. That car was less fun for me to drive than my 86 GTI even with all the extra power because I never felt confident in the brakes. I just like to know that no matter what speed I'm driving or how many times I hit the brakes that the car will be predictable. 
I'm sure that most people with the older and lighter mk1 and mk2 would find pads and fluid to be a good performance upgrade but once you get into the mk3 you are talking about a car that is close to 3000lbs. Thats a whole different ball game then.
Brake upgrades should always be carefully thought out to achieve a desired level of performance, the problem is that most average people do not know enough to do that. I would like to see more technical information when talking about such an important area as brakes.


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## kt'sg60 (Feb 1, 2005)

*Re: Another proof why BIGGER brakes are NOT always best! (Byron N.)*

to put my two cents in coming from kart racing wher we used to run the smallest and i mean small rotor caliper and pad to save on rotational wieght. we even used the smallest chain allowed by rules to save on rotational weight as we did 99% of our racing on 15 mile to 1/4 tracks were we were flat out the whole time. Few road course races we did i a friend cart we had front brake setup onthe karts, large vented rotor on the axle and quite big caliper for karts on too. My point is you should only go as big (or small) as you going to need for whatever your planning to do with your car. anything else is just quite a waste of money in my eyes.


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## dcomiskey (Mar 13, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_They didn't try better tires, this just showed that bigger brakes don't help stopping distance.
Also, your point of fade resistance is not 100% true as the most important factor is pads+fluid and if u upgrade those on ur stock-size rotors, you will have no fade! 

Yes, I forgot to mention fluid. Equally as important!
Just goes to show you how stupid these "tuners" are. You want better stopping power, get stickier tires.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*


_Quote, originally posted by *dcomiskey* »_
Yes, I forgot to mention fluid. Equally as important!
Just goes to show you how stupid these "tuners" are. You want better stopping power, get stickier tires.

And how many people do you see who spend THOUSANDS of dollars on suspension, wheels and brakes and use all-season tires on their cars


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## machschnelGTI (Jun 28, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

People building their cars for looks???? noooo that NEVER happens. 
Some do it for looks and some do it for function...Some do it for spirited canyon runs and some do it for the track. Some big brake kits are better than others. I highly doubt that the Mugen kit in question has as much engineering behind it as the STOPTECH kit. On our Mitsubishi, we went out on the track with a 13" brake setup on the front and Hawk blue pads...the brakes were gone in about 4 laps and when the car came in, the rotors were cracked in half...the only thing holding them together was the fact that the wheel was still bolted on. We changed to a 14 inch rotor that it almost twice as thick, and everything works fine. The brakes last a whole race now so in this case, bigger is better.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (machschnelGTI)*


_Quote, originally posted by *machschnelGTI* »_People building their cars for looks???? noooo that NEVER happens. 
Some do it for looks and some do it for function...Some do it for spirited canyon runs and some do it for the track. Some big brake kits are better than others. I highly doubt that the Mugen kit in question has as much engineering behind it as the STOPTECH kit. On our Mitsubishi, we went out on the track with a 13" brake setup on the front and Hawk blue pads...the brakes were gone in about 4 laps and when the car came in, the rotors were cracked in half...the only thing holding them together was the fact that the wheel was still bolted on. We changed to a 14 inch rotor that it almost twice as thick, and everything works fine. The brakes last a whole race now so in this case, bigger is better. 

The brakes were NOT made by Mugen, the exhaust was. Mugen is highly reputable company, they win races.
The reason they called Mugen was that they had no idea why after the upgrade their dyno showed less HP, so after talking to Mugen, they were asked what other mods they did, and after realizing the big brakes, they said that's the reason they lost power.
I actually think the brakes were Stoptech







but I am not sure (dont remember)...


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## 02GTI-VR6-same1 (Nov 18, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

Just because mugen is reputable (in the honda world) doesn't mean they arent capable of trying to cover their azz. If the brakes were stoptech they should have been lighter or of comparible weight to the stockers (having aluminum calipers and rotor hats). Furthermore the weight concentrated father out from the center is better as well. There could have been a thousand and one reasons why the modifications didn't make power and you go take the word of one dud who was called at mugen. Futhermore if the exhaust was suppose to make a claimed 8-10hp (dyno after dyno has shown a civic picks up about 5hp with a good exhaust regardless of manufacturers reputation. Is that claim mugens or yours) a brake upgrades weight isn't going to sap 10hp. even the weight of grossly heavy wheels only usually sap 4-5hp. No way a brake upgrade is responsible for no gain or less hp. There should have still been some gain. at least 2-3hp or more.
a) could have been the exhaust just didn't make any power. It wont be the 1rst or last time. From car to car and time to time it happens with the best companies.
b) could have been dyno variations (operator error, ambient temp variations, normal accepted 2-3hp dyno variations from run to run ect)
c) 101 car variables (car temp ,coolant temp tranny fluid temp, ECU adaptation ect) 
and big brakes often dont make a car stop any faster, the purpose of bigger brakes are fade resistance/heat management. Multi piston calipers are also suppose to enhance pedal feel by distributing pressure over a larger surface area. How many repeated stops did they make and did they do rotor/caliper temps. If they didn't just a few 80-0 or 60-0 stopping distances dont tell anyting.
I know like everybody else bigger isn't always better. IF you arent racing and dont need bigger brakes and IF aftermarket brakes are going to be heavier and you dont need the fade resistance they may be unnessessary, that doesn't mean they arent better, it means they were used in the wrong application. Perhaps the mugen exhaust is an example of unneccesary change of bigger isn't better,
Proof my arse!


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (02GTI-VR6-same1)*


_Quote, originally posted by *02GTI-VR6-same1* »_Furthermore the weight concentrated father out from the center is better as well.


I think you got that part backwards, but otherwise you have some valid points. Good discussion guys! http://****************.com/smile/emthup.gif


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (02GTI-VR6-same1)*


_Quote, originally posted by *02GTI-VR6-same1* »_Just because mugen is reputable (in the honda world) doesn't mean they arent capable of trying to cover their azz. If the brakes were stoptech they should have been lighter or of comparible weight to the stockers (having aluminum calipers and rotor hats). Furthermore the weight concentrated father out from the center is better as well. 

The larger brakes were actually LIGHTER!!! You just dont know what your talking about weight farther from center is better and I trust Mugen over you! 
As I mentioned MANY TIMES, bigger brakes help in some situations but not in most and a pad/fluid does help you more in many different applications!


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## Byron N. (Oct 20, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

I was watching the show last night and they were talking about a set of cams they were running (forget brand) that should have gained 20h.p. but only made 10h.p.. Thats 10h.p. less than expected not a lose of 10h.p., they contacted the cam manufacture and were told that they would have to run a race header as well to achieve the full 20h.p. They chose to keep the stock manifold and cat to keep the car street legal then had the car remapped to optimize that combination. Mugen made the body kit for the car Stoptech provided the brakes. The next someone wants to start a post like this make sure you are not suffering from A.D.D. Anyway its a good topic its just funny that almost everything in the first post is the wrong info.


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Byron N.)*

They SPECIFICALLY said, we lost power compared to stock!


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## Byron N. (Oct 20, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

Maybe we are just talking about 2 different episodes. Just sounds like the same one I saw. I'm just going to let it go. http://****************.com/smile/emthup.gif


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Byron N.)*


_Quote, originally posted by *Byron N.* »_Maybe we are just talking about 2 different episodes. Just sounds like the same one I saw. I'm just going to let it go. http://****************.com/smile/emthup.gif 

Maybe... if I catch it again on replay, will tape it or something. At the end of the day, we see eye to eye http://****************.com/smile/emthup.gif


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## FamTree (Dec 28, 2004)

This is an interesting thread.
From what I have gathered if I want to upgrade brakes, the best way is to get better pads that won't fade. Also to possible to take stock size rotors and have them crossdrilled.
Am I correct?


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## 02GTI-VR6-same1 (Nov 18, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_They SPECIFICALLY said, we lost power compared to stock! 

So I mixed up one piece of information but you still havent said anything to dispute the other points I brought up.
You dont know what your talking about if you are contributing the lighter brakes to a 10hp wheel loss Sorry buddy there is no way in hell a stoptech brake kit is responsible for a 10hp loss on top of whatever the mugen exhaust made (if it made any hp). I've dyno'd my car and been to enough to know that just doesn't happen. Even if your theory is right and they are responsible for some power loss their is no way in hell does it explain the amount of power they loss. If you believe the mugen exhaust makes 10hp you are suggesting the brakes were responsible for a 20hp loss. 




_Modified by 02GTI-VR6-same1 at 7:30 AM 2-5-2005_


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## Racer_X (Jul 14, 2002)

*Re: (FamTree,02GTI-VR6-same1)*


_Quote, originally posted by *FamTree* »_This is an interesting thread.
From what I have gathered if I want to upgrade brakes, the best way is to get better pads that won't fade. Also to possible to take stock size rotors and have them crossdrilled.
Am I correct?
Better pads on stock rotors is usally the way to go. Check around, there are some excellent pads available today. Hawk HPS is a great street/mild performance pad, much better than the stock pads. And there's a range all the way up to full race pads that work good enough cold that you can still use them on the street (Ferodo DS-2500 or Panther Plus). 
As for drilled rotors. Buy them from a reputable manufacturer of brake components (Brembo or Zimmerman). Check http://forums.vwvortex.com/zerothread?id=1812125 for more information about rotors.

_Quote, originally posted by *02GTI-VR6-same1* »_So I mixed up one piece of information but you still havent said anything to dispute the other points I brought up.
You dont know what your talking about if you are contributing the lighter brakes to a 10hp wheel loss

Are the brake rotors in this "upgrade" lighter weight and smaller in diameter than the stock rotors? The rotor is the main part that matters for inertia. It takes power from the engine to spin the rotor. If the rotor is heavier or larger in diameter, it's going to take more power to spin it. That's just the laws of physics in this universe. There's no way to get around that. 

_Quote, originally posted by *02GTI-VR6-same1* »_ Sorry buddy there is no way in hell a stoptech brake kit is responsible for a 10hp loss on top of whatever the mugen exhaust made (if it made any hp). I've dyno'd my car and been to enough to know that just doesn't happen. Even if your theory is right and they are responsible for some power loss their is no way in hell does it explain the amount of power they loss. If you believe the mugen exhaust makes 10hp you are suggesting the brakes were responsible for a 20hp loss. 
Depending on the type of dyno you use, you might or might not see an actual reduction in power from the larger brake rotors. If the dyno is an inertia based dyno, then it will show the losses from the rotors. If it's a brake type, torque measuring dyno, then it won't show any losses from the rotors because it measures torque and power with the engine in a steady state at constant speed (constant RPM's). The G-Tech Pro "horsepower" measurement is based no the inertia of the whole car and how the car accelerates. It calculates the horsepower necessary to make the entire vehicle accelerate as observed. This type of "horsepower" measurement will show a loss from heavier rotors (or larger diameter rotors or heavier wheels or larger diameter wheels). 
The other type of inertial dyno is a chassis dyno with a big heavy roller and only a speed sensor on the roller. On this type of dyno, you put the drive wheels on the roller and accelerate from idle to redline with the throttle wide open the whole time. The computer on the dyno calculates horsepower based on how quickly the heavy roller accelerates and nothing else. This type of dyno doesn't measure torque directly. It measures how much the speed of the roller changes and based on the known weight and inertia of the roller, the torque applied can be calculated (and with torque and speed, hp is easy to calculate). 
But even if you use a dyno that measures actual torque and calculates horsepower from that (this type of dyno won't show a horsepower loss from big heavy rotors or big heavy wheels), it doesn't change the absolute fact that larger diameter rotors (even if they weigh the same as the stock rotors) have more inertia than smaller diameter rotors, and heavier rotors have more inertia than lighter rotors. 
Most of the big brake kits I've seen have very light calipers and larger, heavier rotors. They hurt acceleration due to the larger, heavier rotor. The lighter caliper kind of evens out (or even improves) total unsprung weight, so the handling and suspension load aspects are improved (or at least not harmed).


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## Ceilidh (Jan 7, 2004)

*Re: (Racer_X)*

Hi Racer_X,
Just wanted to say that I very much enjoy your posts on this forum (and on the others too!). That was a good, complete, yet succinct explanation; it's nice to see technical expertise combined with real-world experience and an ability to communicate!
- C


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## 02GTI-VR6-same1 (Nov 18, 2004)

*Re: (Ceilidh)*

I'm not disputing its possible to lose wheel hp from big brakes, I'm disputing specifically the amount of hp loss mugen/tv show contributed to putting on a brake upgrade (one that was lighter than stock to boot).


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## alexb75 (Dec 29, 2002)

*Re: (Racer_X)*


_Quote, originally posted by *Racer_X* »_Better pads on stock rotors is usally the way to go. Check around, there are some excellent pads available today. Hawk HPS is a great street/mild performance pad, much better than the stock pads. And there's a range all the way up to full race pads that work good enough cold that you can still use them on the street (Ferodo DS-2500 or Panther Plus). 
As for drilled rotors. Buy them from a reputable manufacturer of brake components (Brembo or Zimmerman). Check http://forums.vwvortex.com/zerothread?id=1812125 for more information about rotors.

Are the brake rotors in this "upgrade" lighter weight and smaller in diameter than the stock rotors? The rotor is the main part that matters for inertia. It takes power from the engine to spin the rotor. If the rotor is heavier or larger in diameter, it's going to take more power to spin it. That's just the laws of physics in this universe. There's no way to get around that. 
Depending on the type of dyno you use, you might or might not see an actual reduction in power from the larger brake rotors. If the dyno is an inertia based dyno, then it will show the losses from the rotors. If it's a brake type, torque measuring dyno, then it won't show any losses from the rotors because it measures torque and power with the engine in a steady state at constant speed (constant RPM's). The G-Tech Pro "horsepower" measurement is based no the inertia of the whole car and how the car accelerates. It calculates the horsepower necessary to make the entire vehicle accelerate as observed. This type of "horsepower" measurement will show a loss from heavier rotors (or larger diameter rotors or heavier wheels or larger diameter wheels). 
The other type of inertial dyno is a chassis dyno with a big heavy roller and only a speed sensor on the roller. On this type of dyno, you put the drive wheels on the roller and accelerate from idle to redline with the throttle wide open the whole time. The computer on the dyno calculates horsepower based on how quickly the heavy roller accelerates and nothing else. This type of dyno doesn't measure torque directly. It measures how much the speed of the roller changes and based on the known weight and inertia of the roller, the torque applied can be calculated (and with torque and speed, hp is easy to calculate). 
But even if you use a dyno that measures actual torque and calculates horsepower from that (this type of dyno won't show a horsepower loss from big heavy rotors or big heavy wheels), it doesn't change the absolute fact that larger diameter rotors (even if they weigh the same as the stock rotors) have more inertia than smaller diameter rotors, and heavier rotors have more inertia than lighter rotors. 
Most of the big brake kits I've seen have very light calipers and larger, heavier rotors. They hurt acceleration due to the larger, heavier rotor. The lighter caliper kind of evens out (or even improves) total unsprung weight, so the handling and suspension load aspects are improved (or at least not harmed). 

GREAT explanation! As always Racer_x is the MAN! http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif 
I always learn from your posts man and I owe my braking setup from what I learned from you. I was about to purchase expensive bigger brakes for my track days and after learning a thing or two here I opted for well built stock size rotor, better pads and fluid, saved LOTS of money and did not fade on track at all! 
Just wanted to point out the same for the rest of the folks so they may save a buck or two, if they just need better braking for street or occasional track/autoX.


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## FamTree (Dec 28, 2004)

That info from Racer-X is valuable. When I get my GTI I will probibly do no more than upgrade the pads.
Now when I get either the R-36, or possibly a Lotus Esprit Turbo ( very used and many years old) who knows how far I will go.


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## VWChimera (Jul 9, 2004)

I realize I may be stepping in the line of fire but I have been back and forth on a TT upgrade I just purchased and was wondering if this falls under the same catagory as the "big brake kits" that are being discussed here. I guess I am curious as to whether the installation of this kit would be valuable or detrimental given the above debate?


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## gehr (Jan 28, 2004)

*Re: (detailer03)*


_Quote, originally posted by *detailer03* »_I realize I may be stepping in the line of fire but I have been back and forth on a TT upgrade I just purchased and was wondering if this falls under the same catagory as the "big brake kits" that are being discussed here. I guess I am curious as to whether the installation of this kit would be valuable or detrimental given the above debate?

Ya, I've been thinking of doing the same up grade (11.3 to 12.3) but the bottom line is........the farther you move the weight (even if you don't add any more weight then the stock size) from the axis of rotation the greater the rotational inertia. The TT up grade will look better







and will provide more fade resistance but initial braking distances will be the same until the stock size can't cope with the heat dissipation, with leads to fade! If you do track days maybe it's worth it. I'm sticking to stock size Zimmermann cross drilled with Pagid pads it has been a good set up! http://****************.com/smile/emthup.gif


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## phatvw (Aug 29, 2001)

*Re: (detailer03)*


_Quote, originally posted by *detailer03* »_I realize I may be stepping in the line of fire but I have been back and forth on a TT upgrade I just purchased and was wondering if this falls under the same catagory as the "big brake kits" that are being discussed here. I guess I am curious as to whether the installation of this kit would be valuable or detrimental given the above debate?

That is a valid question. If you're only driving on the street, then the TT upgrade is probably not the best idea. Better pads will give you more bang for the buck, and the true big brake kits look much prettier.
If you take your car on the track, then the added heat capacity of the TT rotors will add to the overall durability of your brake system, and is therefore a suitable upgrade - after proper pads have been chosen of course.



_Modified by phatvw at 10:31 PM 2-6-2005_


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## dcomiskey (Mar 13, 2002)

*Re: (phatvw)*

Ya, even with the TT upgrade, you'll still need better pads, racing fluid and ss lines.


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## VWChimera (Jul 9, 2004)

*Re: (phatvw)*

So my spirited driving isn't enough to condone this huh? I guess I need to find more ways to go faster!


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## 2 doors (Jun 18, 2003)

*Re: (detailer03)*

I ran my first track event (at VIR) with stock MkIV brakes using HP+ front pads and Super Blue fluid, a Shine RS suspension and Z-rated all-seaons on about 20lb 16" wheels. As it was my first time on track, my abilities were more of a limiting factor than my car. I had a great time, and never was nervous about my brakes. 
I went back to VIR later in the year with the same suspension, full 337 (TT) brakes front and rear, the same HP+ pads, stainless lines up front and Motul 600 fluid, and Kumho MX's on 14lb 16" wheels. With some more track time under my belt, I was able to run a lot faster. I was braking later and a lot harder. I always had confidence in my brakes and was even able to put a nice blue sheen on my front rotors. 
I knew going in I was adding both rotational mass and unsprung weight. I got a good deal on the complete set of brakes. I was surprised at how much heavier the 12.3" rotors were than the 11.x" rotors. 
This change might not have made significant differences in my braking performance, but it is my PERCEPTION they are better. I like the feel of the brakes. It's my money, so I'll buy what I like. Also, I like the way the brakes fill out the wheels better. And the factory red calipers look good on my red car.
It's great to ask for advice here (i've learned plenty). But at the end of the day, do what makes you happy for whatever reason you choose.


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## alexb75 (Dec 29, 2002)

*Re: (detailer03)*


_Quote, originally posted by *detailer03* »_So my spirited driving isn't enough to condone this huh? I guess I need to find more ways to go faster!









As phat just explained, in most cases for street driving, the TT upgrade is only good for looks. If you are really interested in improving the braking, make sure you upgrade your pads, as well as fluid when you do this as if you dont, it's a total waste of time/money.


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## Dicardo (Dec 14, 2003)

*Re: (alexb75)*

I will defer to other Vortexers who have the knowledge and experience, but from an outside perspective most of the feedback on this thread seems slanted. Now before reading further and getting all upset, I am admitting that I do NOT know much about brakes and my thoughts are all based on what seems like a logical train of thought.
Bigger brakes must stop the vehicle more quickly. Otherwise the R32 would get the same brakes as the Golf Diesel. M5's and standard 5 series would have the same brake as well. Ford Ranger's & F150's would also share the same brake platform....they certainly don't need "track use" brakes to help prevent fading after repetitive use.
I will agree that in order to get the COMPLETE performance value, most big brakes should be driven hard, but that does not mean there is no value in the upgrade. Just like adding 50hp to a motor, does not always directly correlate to increase 0-60 times, you may only get the resulting benefit in your midrange or top end.
Now, if the thought is that some BBK's are poorly engineered and are not specific to our vehicles, and so we don't get to take advantage of the performance they could offer, well then the next logical question would be what does it take to improve these systems?
Race cars weigh less, and stop more quicly, but not on smaller brakes than what is on their production counterpart, but larger. Now, if the underlying theme here is that if a BBK and a stock set-up are equally paired (pads, type of rotor, fluids) than yes, the BBK stops better, but not that much, well then that is an entirely different concept. Like the common thought that an NA 24V is to much money for the gain and go buy a S/C or Turbo.
Also, when speaking of BBK, is the line of thought based just on a kit which upgrades the front brakes only? I'm looking forward to hearing back on this, since I have read many of the threads here, and have purchased a BBK (front only/pending installation) and am curious as to what to expect, and if by purchasing the "full package" than I will "get it right". No matter, I am installing the BBK (if the butt-o-meter doesn't notice a change then I will change my stance)







As an aside I am looking for a 20th/TT rear set-up.
Also, I did read the Stop-tech article regarding the test of the 350Z brake packages offered that is elsewhere in this forum...very interesting read indeed.


_Modified by Dicardo at 4:53 PM 2-7-2005_


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## phatvw (Aug 29, 2001)

*Re: (Dicardo)*

Dicardo, you touch on some very interesting topics, but I suspect we won't be able to cover them fully in this thread, even with some of the very knowledgeable folks like Racer_x contributing. You ought to seek out some printed materials if you're really interested.
That being said, I can offer a few comments.

*R32 vs TDI Golf brakes*
The R32 is a good 500 pounds heavier, and has a much higher top speed than the base model TDI golf. This is why the brakes are larger. A heavier car and higher speeds means more kinetic energy, which means more heat.
Now, many R32 drivers would like to think they own a race car, but its really just a very nicely equipped passenger car which will cruise around a city 99% of the time. Volkswagen kept this in mind and didn't put racing brake pads on, they put regular (or perhaps a smidgen tougher than regular) brake pads which give users good rotor life and relatively squeak-free performance. In order to account for all that extra weight, they had to put bigger rotors on, otherwise the brakes would overheat and you would get brake fade. They could have put tougher pads on instead, but then customers would complain about the squeaks and the burning smell








Same goes for the trucks with extra towing capacity. They have hefty brakes because they have to stop the thousands of pounds of extra weight in tow. M5 vs 5-series? Ok the weight is just about the same, but the top speeds aren't even close. Think of how they are driven on the German Audobons.
So what can we learn from the wise VW engineers? Bigger brakes help when you add weight and/or top speed and when you do not have the luxury of choosing a more grippy brake pad. That is not to say that bigger brakes don't help in other situations, but this is the primary scenario.
You could also get into why the R32 has super-grippy Goodyear GSD3 tires as opposed to the TDI's measly Michelin MXM4's but then we're getting into another whole discussion. Suffice it to say that if it weren't for the Goodyear tires, the R32 would probably have a longer stopping distance than the TDI even with those big brakes!

*Race editions of production cars*
You can't just compare the brakes of these cars. You have to take vehicle weight and tire performance into account. The race editions generally weigh less through use of advanced materials and deletion of luxury items. The tires are often stickier which is the major contributor towards reduced stopping distances. The engine upgrades increase top speed which increases the kinetic energy - requiring better pads and/or bigger rotors.


_Modified by phatvw at 6:09 PM 2-7-2005_


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## Racer_X (Jul 14, 2002)

*Re: (phatvw)*

Good post. I'll add a few things though.

_Quote, originally posted by *phatvw* »_<snip>
You could also get into why the R32 has super-grippy Goodyear GSD3 tires as opposed to the TDI's measly Michelin MXM4's but then we're getting into another whole discussion. Suffice it to say that if it weren't for the Goodyear tires, the R32 would probably have a longer stopping distance than the TDI even with those big brakes!

A note about stickier tires. Stickier tires do allow for shorter stopping distances, and also for shorter stopping times. As a result, stickier tires will put the same amount of kinetic energy into the brakes, generating the same total amount of heat, but in a shorter time. That means less air will flow over the rotors to cool them during the course of the stop, leading to a higher heat load into the brakes. 


_Quote, originally posted by *phatvw* »_<snip> _(about racing cars)_ The tires are often stickier which is the major contributor towards reduced stopping distances. The engine upgrades increase top speed which increases the kinetic energy - requiring better pads and/or bigger rotors.

The higher speeds increase kinetic energy, which is converted to heat by the brakes. Kinetic energy (and heat) vary with the square of the speed. So slowing from 141mph to 100mph puts as much heat in the brakes as stopping from 100mph. And, as I mentioned above, stickier tires reduce the braking time (and distance travelled and cooling air volume overe the brakes). 
Still, many production based race classes require stock sized rotors. Almost any VW you see racing in SCCA club racing will be limited to stock rotors by the rules. One of the reasons that Audi TT's got bigger brakes is because German Touring Car rules limit brakes to stock rotor sizes, but engine preparation rules allow for significant modifications and very high horsepower, so top speeds are fairly extreme. The main reason that 332's got those brakes was because it was something that was marketable and was easy to do with off the shelf parts. 
But the best racers always try to run the smallest brakes they can without overheating and fading. 
Formula one cars run 10.9" rotors. These are lighter and they fit within the wheels that are specified by the rules. But they use pure carbon rotors and pads to deal with the heat generated by cars traveling at 200-215mph on some tracks. Also, formula one cars are fairly light weight.


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## Dicardo (Dec 14, 2003)

*Re: (Racer_X)*

Ok...so here is where I am at. Stock rotors w/ better heat dissapative qualities, pads that remain efficient under high heat loads, and fluids that have a higher effective temperature range can produce as good or better braking capabilities than a BBK? (taking tires out of the equation...in my instance tires will be the same).
Or, are you stating that because racing rules stipulate/restrict brake modifications, there are other ways around not upsizing your brakes? Effectively, putting in a more efficient/effective brake combination that "matches" your stock setting is a way of getting more from less (eg: utilizing a turbo in lieu of increasing engine displacement)?


_Modified by Dicardo at 8:53 PM 2-7-2005_


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## Byron N. (Oct 20, 2003)

*Re: (Racer_X)*

Well for all this talk about tires lets mention that the Speed world challange were using shaved Toyo street tires (not sure if they still do) a couple years back. Every car that was winning races had some sort of larger rotor and 4 piston caliper, so even on "street" tires they must have been able to drive the car beyond the factory set up. These cars are lighter than road cars and make modest amounts of h.p. compared to some of the 1.8T on the street these days. This is an area that plays a big role hear, h.p. on the street these days is getting insane and I believe thats what has started the whole brake upgrade frenzy in the first place. I know that there are a lot of classes that do not permit changing from factory parts, and you must use every combination possible but engine mods are also heavily restricted so everything balances out in the end and keeps cost down for the drivers.
One thing I will say in my opinion any kit that merely slaps a Porshe caliper on a larger factory rotor is a very poorly designed kit. Using an oem rotor does not offer the durability that a h.d. 2 piece rotor/hat combo benefits from.


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## Racer_X (Jul 14, 2002)

*Re: (Dicardo,Byron N.)*


_Quote, originally posted by *Dicardo* »_Ok...so here is where I am at. Stock rotors w/ better heat dissapative qualities, pads that remain efficient under high heat loads, and fluids that have a higher effective temperature range can produce as good or better braking capabilities than a BBK? (taking tires out of the equation...in my instance tires will be the same).
Correct. Stock rotors, cooling ducts (with open spoke wheels) and good pads and fluid can make a huge improvement in performance. Pads are the area where the biggest gains are possible. Cooling ducts are cheap and very light weight as well. In extreme cases where fade is still an issue with race compound pads, slotted or drilled rotors will help reduce fade without adding more weight and inertia. 

_Quote, originally posted by *Dicardo* »_Or, are you stating that because racing rules stipulate/restrict brake modifications, there are other ways around not upsizing your brakes? Effectively, putting in a more efficient/effective brake combination that "matches" your stock setting is a way of getting more from less (eg: utilizing a turbo in lieu of increasing engine displacement)?
Sometimes it's the rules that restrict things. Other times, the rules might allow bigger brakes, but a team might choose smaller at some tracks to maximize other performance factors. This is especially true if the car is light enough and the pads/rotors are good enough to give strong, fade free braking performance with smaller rotors. In that situation, you'll pick up a tenth or two from the added acceleration, plus you'll have more speed down the straights and have a chance of passing other cars with the added speed. 

_Quote, originally posted by *Byron N.* »_Well for all this talk about tires lets mention that the Speed world challange were using shaved Toyo street tires (not sure if they still do) a couple years back. Every car that was winning races had some sort of larger rotor and 4 piston caliper, so even on "street" tires they must have been able to drive the car beyond the factory set up. 
They ran on Toyo T1-S tires, shaved. Now they run on Toyo Proxes RA-1's, which is a DOT approved (street legal) race compound tire. Again, they generally run shaved tires for dry conditions.
And the rules in those classes now allow any 4 piston caliper and restrict rotors to 328mm(~12.9")x32mm for the Touring class and 355mm(~14")x33mm for the GT class. I did check http://www.waybackmachine.org/ and they were allowed 4 piston calipers and 14" maximum diameter rotors for GT or 12" maximum diameter rotors in Touring when they used the T1-S tires. 
Racing really punishes brakes, especially on tight temporary street circuits, and the Speed World Challenge cars do make a few street races every year. The type of abuse racing brakes get is orders of magnitude higher than anything a sane person would do on the street. The GT cars can go from 165mph to 65mph braking zone, and then 20 seconds later do a 120 to 50 brake application. And then 7 seconds later a 95mph to 50mph, and less than 7 seconds later another 95mph to 45mph. I could continue, but you get the picture. (BTW, that was just a third of a lap at one of the tracks they run at). 
Also, the rules don't require changing from the OEM brakes, and at some tracks, some of the cars will run OEM calipers, sometimes on stock rotors.

_Quote, originally posted by *Byron N.* »_These cars are lighter than road cars and make modest amounts of h.p. compared to some of the 1.8T on the street these days. This is an area that plays a big role hear, h.p. on the street these days is getting insane and I believe thats what has started the whole brake upgrade frenzy in the first place. 
Horsepower by itself is irrelevant. The only thing that horsepower does is give you more potential top speed. The speed itself is what matters for braking.
The two things that factor in to brake loads are top speed and total vehicle weight. Those determine kinetic energy, and that is what the brakes convert into heat. The speed (velocity) is squared in the kinetic energy equation, and weight (mass) is a first order (linear) factor. 

_Quote, originally posted by *Byron N.* »_I know that there are a lot of classes that do not permit changing from factory parts, and you must use every combination possible but engine mods are also heavily restricted so everything balances out in the end and keeps cost down for the drivers.
Sometimes that's true (SCCA improved touring has restrictive engine rules and very restrictive brake rules, including stock rotors, stock thickness, stock diameter, stock surface, not drilled or slotted unless the stock rotors were that way, and stock calipers), but sometimes it's not as true (SCCA production category allows some healthy horsepower mods, but still requires stock sized rotors)

_Quote, originally posted by *Byron N.* »_ One thing I will say in my opinion any kit that merely slaps a Porshe caliper on a larger factory rotor is a very poorly designed kit. Using an oem rotor does not offer the durability that a h.d. 2 piece rotor/hat combo benefits from. 
But 90% of the two piece rotors are crap as well. IMO, only a true floating design is worth the trouble of upgrading. Most of the two piece designs I've seen are just bolted together. These are cheap poseurs. Aluminum hats expand at different rates than cast iron rotors. This stresses the fasteners and can lead to serious problems (at worst case, breaking fasteners and separating the rotor from the hat, but even under the best conditions, coning is still a serious problem with bolted together rotors in extreme usage). Note that a lot of "race" rotors are the bolted together two piece designs. But the rotors and fasteners on these are changed at least every race event and that helps reduce the likelihood of failures. I still agree with Carroll Smith on that. He says bolted 2 piece rotors are a "crime against nature."
The only thing that saves them in a street application is the fact that these design abominations never see any real thermal loads from real heavy braking. People put these on street cars for looks, not because they are exceeding the capabilities of the stock brakes. If they were exceeding the capabilities of the stock brakes, they would also be tearing up most "big brake" kits.


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## Dicardo (Dec 14, 2003)

*Re: (Racer_X)*

Maybe I'm just being bone-headed but why are you seemingly so anti-BBK? Yes, I recognize that performance gains can be made w/ mild modifications to the stock braking system. 
However (and obviously you are not on trial here so please don't read my OPINIONS as such) you have not addressed whether a complete BBK (F&R) has a braking advantage or not. Now that is a sweeping statement on my part so lets say Stop-tech and Brembo's high end two-peice rotor kits w/ 4 piston calipers.
My vehicle is a S/C VR6 w/ a very heavy stereo box, amp rack, and speakers w/ wide 235/40 Toyo Proxis tires on 18" rims. Under extreme braking my ABS does not typically get involved until the last few feet. Now, my brakes are 100% stock, hence the Brembo & pending larger rear purchase.
So, although I am uncertain how the ABS system will "read" my new brake/wheel/tire combo, I certainly expect better braking than what I could get on upgraded pads alone. My suspicion was that pads that would provide me the performance I wanted would be very dusty, dirty, noisy and eat my rotors. Thanks.


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## dcomiskey (Mar 13, 2002)

*Re: (Dicardo)*

I don't think he's anti BBK. He's just trying to inject some reality for those who are hypnotized by BBKs. Look, even in tests done in magazines, the BBKs have been shown to NOT reduce braking distance over stock setups. Over time, yes, they have the advantage in that they will not fade. But, if you take the time to add better components to the stock systems, you will achieve the same results. But for 99% of the drivers out there, a BBK is overkill and money wasted. Many do it to reduce unsprung weight. If you want to do that, then just go with ECS' floating rotors.
Would I like to se a sweet, large BBK behind my wheels? Absolutely. They're hot and sexy. But, I'm not going to blwo $1000+ when they're not going to do anything for me and I can spend that $ on other performance parts that WILL make a difference in my driving.
So, do BBKs have an advantage? Against stock sets with upgraded pads and fluid, most of the time the answer is no.


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## 91gti20v (Jul 18, 2001)

*Re: (Racer_X)*


_Quote, originally posted by *Racer_X* »_

Are the brake rotors in this "upgrade" lighter weight and smaller in diameter than the stock rotors? The rotor is the main part that matters for inertia. It takes power from the engine to spin the rotor. If the rotor is heavier or *larger* in diameter, it's going to take more power to spin it. That's just the laws of physics in this universe. There's no way to get around that. 


Ok, I have read through most of this and I am still questioning the above fact in bold. Quite simply, once the rotor is mounted to the hub/bearing/axle assembly, it acts as one system. Ok, now, lets think about this. You aren't altering the distance from the drive point to where the rotor is mounted. The mass acts at the same point. The simple equation for inertia is I = ((r)*(r))*m, where r is the distance from the axis, or transmission in this case, and m is the mass of the object. R is staying constant, but m changes as you change rotors. Where this theory is true is if you just go to a larger rotor that is nothing special. Obviously if the rotor is larger it will be heavier, but if you go to a larger, lighter, 2 piece floating design, you are decreasing the mass, therefore decreasing the inertia acting on the same point as the smaller rotor.


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## Byron N. (Oct 20, 2003)

*Re: (dcomiskey)*

Let me just say that I feel Racer_X gives some of the best answers I've read, and I'm not afraid to say without a doubt that he knows way more about all the technical info on brakes than I care to learn. I don't want any of this to turn into a pissing contest. This has become rather informative and I want it to continue on this path.
All the brake testing I ever see is 60-0 distances. I don't spend much time looking at specs and tests these days so if I'm wrong here let me know. I don't think that someone pushing 300-400h.p. in their street car is concerned with how the car stops at legal speeds. I know that its not wise to push your car hard on the street but lets be honest their are a lot of people that do, and one panic stop from triple digit speeds could be the end of your car or life. As stated by Racer_X speed is more important than h.p. but that is pretty much my point, when a person is driving a big h.p. car their is always the temptation to drive it hard and it is very easy to exceed the range of a road pad. Some of the 1.8T cars can reach speeds over 170m.p.h.
The thing I like about running big brakes that are more than is usually needed is that I do not need to change pads for street or track and if I find myself driving fast and need the stopping power its there. I run oem Porshe pads, they don't make a lot of noise and the brake dust is easy to remove. I've used some brake pads (in paticular Pagid Oranges) that would destroy the finish on my wheels and would require hours of cleaning to remove. Another benefit is that I will not have to replace pads and rotors at reduced intervals for better performance. Its one of those deals were the cost get offset over time. I'm still driving on the same set of pads and rotors for 4 summers now and they still have no visible wear. I like low maintenance.


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## rpaller (Jan 5, 2001)

*Re: (91gti20v)*

This Moment of Inertia experiment should help explain it.


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## alexb75 (Dec 29, 2002)

*Re: (Dicardo)*


_Quote, originally posted by *Dicardo* »_Maybe I'm just being bone-headed but why are you seemingly so anti-BBK? Yes, I recognize that performance gains can be made w/ mild modifications to the stock braking system. 
However (and obviously you are not on trial here so please don't read my OPINIONS as such) you have not addressed whether a complete BBK (F&R) has a braking advantage or not. Now that is a sweeping statement on my part so lets say Stop-tech and Brembo's high end two-peice rotor kits w/ 4 piston calipers.
My vehicle is a S/C VR6 w/ a very heavy stereo box, amp rack, and speakers w/ wide 235/40 Toyo Proxis tires on 18" rims. Under extreme braking my ABS does not typically get involved until the last few feet. Now, my brakes are 100% stock, hence the Brembo & pending larger rear purchase.
So, although I am uncertain how the ABS system will "read" my new brake/wheel/tire combo, I certainly expect better braking than what I could get on upgraded pads alone. My suspicion was that pads that would provide me the performance I wanted would be very dusty, dirty, noisy and eat my rotors. Thanks.

As Byron just mantioned him or me are not against BBK, but want to maximize braking with least amount of money. Also try to educate that bigger is not always better, that's all. 
People have been told for years that in order to have better braking they need to spend thousands of dollars, and that's just not true. We wanna to get around that marketing hype.


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## dcomiskey (Mar 13, 2002)

*Re: (Byron N.)*


_Quote, originally posted by *Byron N.* »_
The thing I like about running big brakes that are more than is usually needed is that I do not need to change pads for street or track and if I find myself driving fast and need the stopping power its there. I run oem Porshe pads, they don't make a lot of noise and the brake dust is easy to remove. I've used some brake pads (in paticular Pagid Oranges) that would destroy the finish on my wheels and would require hours of cleaning to remove. Another benefit is that I will not have to replace pads and rotors at reduced intervals for better performance. Its one of those deals were the cost get offset over time. I'm still driving on the same set of pads and rotors for 4 summers now and they still have no visible wear. I like low maintenance.

I don't have to change anything when I go to the track either. I use my Hawk HPS full-time. They work great for me for both uses. I guess I don't see your point here.










_Modified by dcomiskey at 1:54 PM 2-8-2005_


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## NOVAdub (Jul 28, 2003)

*Re: (91gti20v)*


_Quote, originally posted by *91gti20v* »_
The simple equation for inertia is I = ((r)*(r))*m, where r is the distance from the axis, or transmission in this case, and m is the mass of the object. 
If you treat the brake rotor as a solid cylinder rotating about an axis through its center and perpendicular to the radius, the moment of inertia can be expressed as .5MR^2. The radius is the radius of the brake rotor, not the distance along the drive shaft to the transmission. (the drive shaft has its own moment of inertia that has to be overcome when accelerating or braking) If you look at this equation for moment of inertia (or resistance to rotational motion) you will see that the objects resistance to motion goes up with the square of the radius of the rotor. The end result of lwering the moment of inertia is that you can use more of the brakiing force to stop the car. This is the same reason why you wont see 18" wheels on an f1 car. (or why you may have seen stories of people not being able to accelerate or brake as well on a low power car when adding big wheels) Like racer X has been saying you want to use the smallest rotors you can get away with. The smallest rotor youc an get away with is going to depend on your applicaiton though. Street car needs are completely different from track car needs. 


_Modified by NOVAdub at 6:55 PM 2-8-2005_


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## 91gti20v (Jul 18, 2001)

*Re: (NOVAdub)*


_Quote, originally posted by *NOVAdub* »_If you treat the brake rotor as a solid cylinder rotating about an axis through its center and perpendicular to the radius, the moment of inertia can be expressed as .5MR^2. The radius is the radius of the brake rotor, not the distance along the drive shaft to the transmission. (the drive shaft has its own moment of inertia that has to be overcome when accelerating or braking) If you look at this equation for moment of inertia (or resistance to rotational motion) you will see that the objects resistance to motion goes up with the square of the radius of the rotor. The end result of lwering the moment of inertia is that you can use more of the brakiing force to stop the car. This is the same reason why you wont see 18" wheels on an f1 car. (or why you may have seen stories of people not being able to accelerate or brake as well on a low power car when adding big wheels) Like racer X has been saying you want to use the smallest rotors you can get away with. The smallest rotor youc an get away with is going to depend on your applicaiton though. Street car needs are completely different from track car needs. 

_Modified by NOVAdub at 6:55 PM 2-8-2005_

Ok, I see your point, but again, the rotor is not rotating about the axis through its center. If it rotated independently of the axle, this would be true. But it is rigidly mounted to the hub.


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## 91gti20v (Jul 18, 2001)

*Re: (rpaller)*


_Quote, originally posted by *rpaller* »_This Moment of Inertia experiment should help explain it.


That experiment doesn't explain why a cylinder of the same mass, but different diameter, would have a different moment of inertia at the same effective radius. It explains the simple concept of how different masses and radii affect the moment of inertia. My contention is still that the rotor does not rotate independently of the axle and is rigidly mounted, therefore it is just treated as mass at the end of the axle. Again, I am not arguing the fact that a larger heavier rotor would have an adverse affect on performance. I wholeheartedly agree with that statement. What point I am arguing is that for two different rotors of the same mass but diff. diameter, the moment if inertia would be the same. It does not rotate about the hub, but the whole axle rotates with the rotor rigidly attached.


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## phatvw (Aug 29, 2001)

*Re: (91gti20v)*


_Quote, originally posted by *91gti20v* »_That experiment doesn't explain why a cylinder of the same mass, but different diameter, would have a different moment of inertia at the same effective radius. It explains the simple concept of how different masses and radii affect the moment of inertia. My contention is still that the rotor does not rotate independently of the axle and is rigidly mounted, therefore it is just treated as mass at the end of the axle. Again, I am not arguing the fact that a larger heavier rotor would have an adverse affect on performance. I wholeheartedly agree with that statement. What point I am arguing is that for two different rotors of the same mass but diff. diameter, the moment if inertia would be the same. It does not rotate about the hub, but the whole axle rotates with the rotor rigidly attached. 

Stand upright, and spin around on the spot. Your body is spinning roughly rigidly just like a drive axle. Ok now stretch your arms out and keep spinning. Its a little harder to spin isn't it? Not convinced? Spin as fast as you can with your arms stretched out, then pull them in close to your body. You start spinning faster cause it is now easier to spin. The moment of inertia has been reduced with a smaller radius (like smaller radius brakes) but the mass has stayed the same. Consider that your arms are the brake rotors and the rest of your body is the drive axle. Also think about figure skaters...
Still reading? C'mon - don't be lazy, do the experiment for yourself. Its fun











_Modified by phatvw at 12:22 PM 2-8-2005_


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## NOVAdub (Jul 28, 2003)

*Re: (91gti20v)*


_Quote, originally posted by *91gti20v* »_
Ok, I see your point, but again, the rotor is not rotating about the axis through its center. If it rotated independently of the axle, this would be true. But it is rigidly mounted to the hub. 
Could you please explain why you feel that a rotor does not rotate about an axis through its center?


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## Byron N. (Oct 20, 2003)

*Re: (dcomiskey)*


_Quote, originally posted by *dcomiskey* »_
I don't have to change anything when I go to the track either. I use my Hawk HPS full-time. They work great for me for both uses. I guess I don't see your point here.









_Modified by dcomiskey at 1:54 PM 2-8-2005_

Like I stated, when I ran Pagid oranges they were not very friendly to my rims. I actually trashed a set of rims because the pad material would bake itself into the clearcoat on the rim. Those pads worked great on the track but day to day they were noisy and didn't work well when cold. The Porshe Big Reds I use now have oem pad compound, they cost me $80 and work fine in all conditions with out the trade off of running a super aggressive pad. Plus I van get pads without ordering them. There are tons of different pads but I don't care to spend hundreds of dollars testing them all out for myself. I built my brake kit, designed it to run oem pads and it does exactly what I wanted of it. How often do you replace pads and rotors? Like I said I have over 4 summers worth of hard driving with zero maintenace.
I will be honest and say that I really like the way the brakes look as well, but thats not the main reason I went this route.
The point of this discussion is to inform so lets try to make it a point to read all the info that is posted not just pick and choose.


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## Racer_X (Jul 14, 2002)

*Re: (91gti20v)*


_Quote, originally posted by *91gti20v* »_Ok, I see your point, but again, the rotor is not rotating about the axis through its center. If it rotated independently of the axle, this would be true. But it is rigidly mounted to the hub. 
I'm not sure where to begin here. You aren't swinging the rotor around on the end of the axle, the rotor is spinning. 
I'm going to try to explain. Please see if you can tell me where you don't follow any more. 
Let's start with some inertia you can understand. Take a ball on the end of a string, swing it around. The ball has inertia due to it's mass and speed. If you make the string longer, and swing it around so it takes the same amount of time to make a complete revolution, then the ball has to travel faster, and it's inertia goes up. The distance around the circle goes up proportional to the length of the string, so the velocity increase is proportional to the added lenght of the string. But kinetic energy (inertia) goes up with the square of the speed, so it goes up with the square of the length of the spring. 
Are you with me so far? 
Now, let's think about a bicycle wheel (with spokes). Essentially, there's a little piece fo the rim at the end of each spoke that's just like the ball, and the spoke is just like the string. So you have a bunch of pieces and strings spinning around the axle in formation. Again, if you lengthen all the strings, the velocity of the rim pieces at the end goes up (and if the thickness of the metal stays the same, they get a bit bigger to fill in the gaps, adding some mass as well). So, the spinning velocity of the wheel rim goes up in relation to the radius of the wheel. And the kinetic energy (inertial) of the spinning wheel goes up with the square of the radius. 
Does this still make sense? 
A brake rotor is the same thing, except that instead of individual spokes as strings, there's a fairly solid piece of metal. Still, if you wanted too, you could slice it up into a bunch of narrow pieces and see that each piece spins around the centerline of the axle and has kinetic energy like the ball on the end of the string. 
Do you understand? 
So, increasing the diameter of the rotor, even if it weighs about the same, still increases the spinning inertia of the rotor. Because the heavy parts get further from the center, and the kinetic energy of those parts goes up with the square of the radius of the circle they trace as they move around the center.


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## phatvw (Aug 29, 2001)

*Re: (Racer_X)*

Nice, but I liked my example better


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## Racer_X (Jul 14, 2002)

*Re: (Dicardo)*


_Quote, originally posted by *Dicardo* »_Maybe I'm just being bone-headed but why are you seemingly so anti-BBK? Yes, I recognize that performance gains can be made w/ mild modifications to the stock braking system. 
However (and obviously you are not on trial here so please don't read my OPINIONS as such) you have not addressed whether a complete BBK (F&R) has a braking advantage or not. Now that is a sweeping statement on my part so lets say Stop-tech and Brembo's high end two-peice rotor kits w/ 4 piston calipers.
Not sure exactly what the question is. There are several ways to interpret this, and several other questions that should be asked. Here's a rundown.
Will they give you an improvement? Probably.
Are these big brake kits the most cost effective way to get that improvement? No, that's probably the most expensive and wasteful way to get that improvement.
Will these big brake kits have other side effects that have negative effects on vehicle performance? Definitely. 
Would I recommend that as a first step for improving your braking system? Definitely not.

_Quote, originally posted by *Dicardo* »_My vehicle is a S/C VR6 w/ a very heavy stereo box, amp rack, and speakers w/ wide 235/40 Toyo Proxis tires on 18" rims.
So, performance isn't your sole goal. Your priorities might be a bit different than mine. 

_Quote, originally posted by *Dicardo* »_Under extreme braking my ABS does not typically get involved until the last few feet.
This sounds like something is definitely wrong with the brakes. The ABS should be easier to engage at higher speeds. At very low speeds, like at the end of a stop, the ABS will disengage completely. It has to or the car would never stop. The exact speed where the ABS deactivates varies from one vehicle manufacture to another, but 5 to 10 mph is commonly the lowest speed that the ABS will work. Not sure exactly where VW sets the cutoff, and it could vary with models and years as they have used different systems and different versions over the years. 

_Quote, originally posted by *Dicardo* »_ Now, my brakes are 100% stock, hence the Brembo & pending larger rear purchase.
So, although I am uncertain how the ABS system will "read" my new brake/wheel/tire combo, I certainly expect better braking than what I could get on upgraded pads alone. My suspicion was that pads that would provide me the performance I wanted would be very dusty, dirty, noisy and eat my rotors. Thanks.
If you run stock or similar to stock pads in the big brakes, you might be surprised at how little the bigger rotors and calipers will do for braking performance. If you run better pads, then you'll be having dust, dirty, noise and eating the expensive big rotors, so I'm guessing you don't plan to upgrade the pads much. 
I state this often, but with proper pad selection, the 11.3" brakes on the late A3 and A4 cars are good for about 3000 pounds at up to 150mph or so in racing conditions, and they can deliver a good fade free panic stop from about 120mph (starting close to cold). If you use crappy pads, those numbers will be lower. But if that is the problem, a better first step to upgrading would be to put better pads on.
Hawk HPS and Porterfield R4-S are both decent street compounds that aren't too dusty and are very rotor friendly. The Porterfields are a little higher performance than the Hawk HPS, but both are 30-35% better than stock for grip and much better for fade resistance. This would be a slightly bigger upgrade than upgrading to 13"-14" rotors under a stock caliper and pad setup. 
Also, you are right to be concerned about he ABS. Different ABS implementations react differently to changes in wheels, tires and brake components. You really need to do some test stops before and after to make sure you haven't completely confused the system. Generally, adding mass and rotating inertia to the wheels, tires, or rotors is a bad idea with newer ABS implementations. Increasing inertia of the spinning parts can lead to very long stopping distances. It depends on how the system is "trimmed" and what margin of safety/margin of error there is in the system. But really good ABS implementations try to time how quickly the wheels spin up after they start releasing brake pressure, and they use that time to attempt to estimate the grip available. Heavier wheels, tires and rotors take longer to spin up and will appear to be a much more slippery surface to the ABS computer. So it won't apply the brakes as hard under those conditions. This applies to the wheels that are designed to slip first, which is the rear wheels on later VW's with ABS. So, you'll usually get more back end lifting under braking in an ABS stop with heavier wheels, tires and brakes. 
I guess the biggest issue I have is people bashing the stock brakes and saying they aren't adequate as a way to justify or sell big brake kits. That's simply not true. The stock brakes on these cars are actually very good, and that should lessen the need and the market for big brake kits. But the marketeers are busy spinning things so that people think they need bigger. And then some wonder why they lost acceleration and "wheel horsepower" when they install the bigger brakes. That was the initial topic of this thread.


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## LSinLV (Nov 25, 2001)

*Re: (Racer_X)*

a question...
having gone to 18" wheels/tires, I know my rotational mass is substantially greater than the stock set-up....I did upgrade to the TT brakes with Ferrodo (DS??) pads, and there was a noticable difference....noticable.
Now, add to that a stg III s/c, and I can tell that when I get the car in higher rpms with the clutch dis-engaged (engine braking), I seem to have a much harder/difficult time getting the spinning mass to brake/slow.
Obviously, when the wheels are spinning, with a greater mass they have a "flywheel" effect,a nd require a greater breaking force.
Am I to understand that by up-ing the fronts to a BBK (lets say Stoptech), that I will not notice better braking; event though I am using a lighter rotor assembly, and a caliper with greater clamping force which is set out further (greater leverage)???
I am curious as to why the above with a greater pad area will not positively affect my vehicle breaking dynamics....not beating up on the TT brakes.
Thanks,
Larry


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## ck_1.8T (Sep 5, 2004)

*Re: (Racer_X)*


_Quote, originally posted by *Racer_X* »_...
So, increasing the diameter of the rotor, even if it weighs about the same, still increases the spinning inertia of the rotor. Because the heavy parts get further from the center, and the kinetic energy of those parts goes up with the square of the radius of the circle they trace as they move around the center. 

The theory recalled here is correct assuming that we're talking about solid rotors. However, the situation is different when "performance" rotors (drilled, slotted, or both) are considered, where the holes make the mass in the rotor periphery actually less compared to a solid rotor...








Again, the same holds true about bigger alloy wheels (18" and 17" with the respective low-profile tyres) over factory OEM wheels, with the latter being usually heavier (selection of the tyre according to weight is critical here; 225/40 Michellin PS2 or Continental ContiSport contact are lighter than their respective 205/55 tyres)...
After all these analyses, which are admittedly very helpful in deciding what to select in brakes & wheels in order not to affect performance, I find that we may be discussing about 1-2hp loss in the worst possible senario...










_Modified by ck_1.8T at 2:06 PM 2-8-2005_


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## Dicardo (Dec 14, 2003)

*Re: (Racer_X)*

In regards to inertia a more tangible example to consider (which is in line w/ the ones above) is BMX vs Mountain Bike. Strong BMX rims can weigh as much as light weight cross country rims. However, irrespective of weight a BMX will accellerate much faster than a mountain bike. It takes less energy to accelerate a smaller rim around a fixed point, than a larger one.
Same thing w/ my vehicles larger rims & brakes. Although they are lighter than stock, and the wheel/tire combo are also lighter than stock it still takes more energy to move the mass that is further out from the axis.
Racer_X: Thank you for your responses. As you put it most succinctly our intentions are different for our respective vehicles. I am not a purist when it comes to my car. I drive it every day, I commute regularly, I love music and I like performance. So I have compromised to what works for me.
I would agree 100% that there are cost effective means to obtain similar braking performance. Just as there are Jetta GL's & GLX's...both perform the same function but go about it differently. What I wanted to get a better handle on was how much difference existed between the two products (upgraded vs BBK). Some have posted that they noticed a marked improvement w/ their BBK (from the driver perspective) and others have stated the improvement is nominal for the cash.
My intent was to understand why "BIGGER brakes are NOT always best!" w/o the consideration of cost. Financial investment in a vehicle is very personal. Most would think I spent to much money on my car, and some would say, good attempt Grasshopper but you have much more to spend








In summation I believe it is accurate (please amend this conclusion if necessary) that the mechanical advantage of a larger brake system is not directly related to the improved performance of the vehicle as an entire system. Although it is reasonable to expect improvement in the braking of the vehicle, this improvement may/will be offset be decreased performance in other areas (steering reaction times, accelleration, power delivery). Although some may feel that the return on investment in a BBK is adequate most will feel that they have spent hundreds of dollars on improving their brake system only to have it fall short of their expectations. In the event that each dollar spent on your vehicle must return the maximum performance advantage, upgrading the stock braking system with improved pads, fluids and lines (in conjunction w/ upgrading to a tire w/ a higher coefficient of friction) will provide a cost effective braking advantage and will, more likely than not, provide a satisfactory brake system. For those who are not purists, a BBK may perform better, but the purchase of a BBK is not directly related to overall vehicle performance, and so the choice to upgrade or not must be weighed against both the performance advantage and other intrinsic values such as cost vs. performance and appearance. http://****************.com/smile/emthup.gif


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## ck_1.8T (Sep 5, 2004)

*Re: (lsinlv)*


_Quote, originally posted by *lsinlv* »_
...
1. Now, add to that a stg III s/c, and I can tell that when I get the car in higher rpms with the clutch dis-engaged (engine braking), I seem to have a much harder/difficult time getting the spinning mass to brake/slow.
Obviously, when the wheels are spinning, with a greater mass they have a "flywheel" effect,a nd require a greater breaking force.
2. Am I to understand that by up-ing the fronts to a BBK (lets say Stoptech), that I will not notice better braking; event though I am using a lighter rotor assembly, and a caliper with greater clamping force which is set out further (greater leverage)???
I am curious as to why the above with a greater pad area will not positively affect my vehicle breaking dynamics....not beating up on the TT brakes.
Thanks,
Larry

I'll try to give an answer to your points according to my experience on track:
1. When breaking with downshifting (engine braking) before cornering you actually abuse the clutch-flywheel and therefore when starting to accelerate at the exit of the corner you simply get clutch slipping and cannot accelerate effectively... http://****************.com/smile/emthdown.gif What would really be ideal here is left foot braking (in older car) since in our cars with ABS/ASRs & DBW this is not in effect possible. Then, braking before the corner or at corner entrance is the only way... There is the point where a "well studied & balanced" BBK most effectively makes the difference...!!!
2. My car, an Octavia 1.8T-RS (not available in the US-same platform as Golf/Jetta) with 240whp wears the brakes of Audi TT-225hp (front 312mm-rear 256mm vented rotors) on stock pads, and even with changing pads to Ferodos DS2500+fluid+ss breaklines didn't make a lot of difference in lap times on a particular ring where we test. While with stage 3 ECS kit (big reds) front & 308mm rear rotors (+OEM rear pads) made about 1-1.5 sec faster laps on the same ring, with late braking in corners making the largest part of the difference...








What we noticed was that another BBK-Brembo 4-pot calipers+323mm rotors (Brembo Gran Turismo) in a Seat Leon Cupra-R (1st generation with 210hp and same brake system as Audi TT225hp) made very little difference over the OEM brake system (with upgraded pads only)...








That's my own experience...







Comments are yours...







!


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## alexb75 (Dec 29, 2002)

*Re: (phatvw)*


_Quote, originally posted by *phatvw* »_
Stand upright, and spin around on the spot. Your body is spinning roughly rigidly just like a drive axle. Ok now stretch your arms out and keep spinning. Its a little harder to spin isn't it? Not convinced? Spin as fast as you can with your arms stretched out, then pull them in close to your body. You start spinning faster cause it is now easier to spin. The moment of inertia has been reduced with a smaller radius (like smaller radius brakes) but the mass has stayed the same. Consider that your arms are the brake rotors and the rest of your body is the drive axle. Also think about figure skaters...
Still reading? C'mon - don't be lazy, do the experiment for yourself. Its fun










Good example, you could be an ice skating instructor


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## Racer_X (Jul 14, 2002)

*Re: (lsinlv,ck_1.8T)*


_Quote, originally posted by *lsinlv* »_a question...
having gone to 18" wheels/tires, I know my rotational mass is substantially greater than the stock set-up....I did upgrade to the TT brakes with Ferrodo (DS??) pads, and there was a noticable difference....noticable.
 Noticeable in the feel of the pedal? Or measurable in stopping distance? I doubt that the stopping distances changed unless you changed tires to a grippier (or less grippy) tire. 

_Quote, originally posted by *lsinlv* »_Now, add to that a stg III s/c, and I can tell that when I get the car in higher rpms with the clutch dis-engaged (engine braking), I seem to have a much harder/difficult time getting the spinning mass to brake/slow.
Obviously, when the wheels are spinning, with a greater mass they have a "flywheel" effect,a nd require a greater breaking force.
Am I to understand that by up-ing the fronts to a BBK (lets say Stoptech), that I will not notice better braking; event though I am using a lighter rotor assembly, and a caliper with greater clamping force which is set out further (greater leverage)???
Again, it will change the pedal feel some, but probably won't change the distance it takes to stop. If it does change stopping distances, then it's because you were overheating the pads and getting fade issues. Better pads would address the fade issues (and grippier pads with higher operating temperature range would help pedal effort and address the fade issues). 

_Quote, originally posted by *lsinlv* »_I am curious as to why the above with a greater pad area will not positively affect my vehicle breaking dynamics....not beating up on the TT brakes.
Thanks,
Larry

Again, there are several ways to address fade and pedal feel issues. If you want to do it without hurting acceleration, then better pads and maybe better fluid is the way to go. Cooling ducts also help in extreme cases. All of those things are quite cost effective, too. 
If you have a few pounds of cash to burn, then big calipers and big rotors will also do the same thing. But you'll be using additional engine power to overcome the added inertia of the larger spinning parts. That means bigger brakes will slow you down more on acceleration, in addition to improving pedal feel and fade resistance. 


_Quote, originally posted by *ck_1.8T* »_The theory recalled here is correct assuming that we're talking about solid rotors. However, the situation is different when "performance" rotors (drilled, slotted, or both) are considered, where the holes make the mass in the rotor periphery actually less compared to a solid rotor...








The holes in a typical high quality cross drilled rotor removes less than 5% of the weight. It's generally in the 3% to 4% range. Slots remove even less material and less weight. So, going from 11.3" rotors to 12.3" rotors increases the mass of the rotor by about 18%, all of which is at the outer edge of the rotor. Drilling 4% of that total weight out of the rotor surface will bring that down to about a 14% increase in rotor mass, and the inertia gain will be closer to 20% due to the location of the added mass at the outer edge of the rotor. 
By the way, for comparison, the loss of material comparing a brand new stock rotor to a worn out to minimum thickness stock rotor is usually around 20%. So, drilling and slotting remove less than a quarter of the mass that normal wear will remove over the useful life of the rotor. 
Rotors actually can be drilled to make them lighter, but this is generally not done for streetable applications. It's only done on race cars where the rotor size is excessively larger for the weight/speed of the car and reducing the mass of the rotor won't negatively affect braking by reducing the thermal capacity of the rotor. 
And most drilled or slotted rotors (and all rotors that I've seen that are both drilled and slotted) aren't exactly "performance" rotors. Most of them are decorative poseurs, with performance that ranges from poor to dangerous in extreme use, but that's another discussion for another thread.

_Quote, originally posted by *ck_1.8T* »_Again, the same holds true about bigger alloy wheels (18" and 17" with the respective low-profile tyres) over factory OEM wheels, with the latter being usually heavier (selection of the tyre according to weight is critical here; 225/40 Michellin PS2 or Continental ContiSport contact are lighter than their respective 205/55 tyres)...
Again, it's inertia that counts, not absolute weight. And most aftermarket wheels that I've seen actually in use are cast wheels, similar to the factory alloys in construction and weight. The heaviest part of the wheel is the rim portion, and moving that out another half inch or inch from the center and adding enough material to fill out the larger circumference adds lots of inertia. Even if you go with lighter spokes and wheel centers to keep the total weight about the same as the smaller wheels (or even slightly lighter), the inertia will go up significantly. Forged wheels or spun rims with forged centers are lighter. The spun outer rims are particularly good for reducing the rotating inertia, but they are expensive and somewhat fragile for street use. 
With tires, everything is at least at the bead diameter, and the tread is the heaviest part and is farther out still. So, tires can have the same approximate inertia, even though there are minor differences in the actual weight. If the outer diameter of the tires are the same, the inertia is going to be very similar so long as the weights are close to the same. 

_Quote, originally posted by *ck_1.8T* »_After all these analyses, which are admittedly very helpful in deciding what to select in brakes & wheels in order not to affect performance, I find that we may be discussing about 1-2hp loss in the worst possible senario...









Well, it can sometimes be significant, especiallly on the older, underpowered cars. On my 1984 Jetta diesel, switching from the steelies with 175/70HR13 tires (34 pounds per corner) to alloys with lighter weight 175/70SR13 tires gave me about a half second quicker zero to 60mph times. And the car feels much more sure footed with the lighter wheels (using GTI stock springs and cheap gas shocks).


----------



## alexb75 (Dec 29, 2002)

*Re: (Dicardo)*


_Quote, originally posted by *Dicardo* »_My intent was to understand why "BIGGER brakes are NOT always best!" w/o the consideration of cost. Financial investment in a vehicle is very personal. Most would think I spent to much money on my car, and some would say, good attempt Grasshopper but you have much more to spend










That is a valid point and I think Recer_x has actually answered it 

_Quote, originally posted by *Racer_X* »_
I state this often, but with proper pad selection, the 11.3" brakes on the late A3 and A4 cars are good for about 3000 pounds at up to 150mph or so in racing conditions, and they can deliver a good fade free panic stop from about 120mph (starting close to cold). If you use crappy pads, those numbers will be lower. But if that is the problem, a better first step to upgrading would be to put better pads on.


So, if your braking requirements are more than what is stated above, then you probably gain from BBK. If your braking requirement is not as much, then a set of good pads and fluid on stock-sized rotor gives you optimal braking performance without side-effects of BBK.
On my car, I upgraded my rotor to a Brembo-made stock size rotor (solid), Pagid pads, and Motul brake fluid. I also did ss lines just for the feel (not improved braking performance). My brakes last 4 whole track sessions of 25 minutes each. Now, I do not go above 100-105 mph on this track and if I did get close to 120mph (engine limited), then I may need those bigger rotors to help cooling it down.


----------



## alexb75 (Dec 29, 2002)

*Re: (Racer_X)*


_Quote, originally posted by *Racer_X* »_ And most drilled or slotted rotors (and all rotors that I've seen that are both drilled and slotted) aren't exactly "performance" rotors. Most of them are decorative poseurs, with performance that ranges from poor to dangerous in extreme use, but that's another discussion for another thread.


That is totally true. When I was looking for a Brembo made solid rotor, I had an extremely hard time finding one. I had to pre-order one as almost all those rotors are machined (drilled or slotted) right after they get into the shop and is sold for 100-150% more money!
Now, I can tell you that those machining are done at local places by machinist with no engineering behind it.


----------



## ck_1.8T (Sep 5, 2004)

*Re: (Racer_X)*


_Quote, originally posted by *Racer_X* »_ The holes in a typical high quality cross drilled rotor removes less than 5% of the weight. It's generally in the 3% to 4% range. Slots remove even less material and less weight. So, going from 11.3" rotors to 12.3" rotors increases the mass of the rotor by about 18%, all of which is at the outer edge of the rotor. Drilling 4% of that total weight out of the rotor surface will bring that down to about a 14% increase in rotor mass, and the inertia gain will be closer to 20% due to the location of the added mass at the outer edge of the rotor. 
By the way, for comparison, the loss of material comparing a brand new stock rotor to a worn out to minimum thickness stock rotor is usually around 20%. So, drilling and slotting remove less than a quarter of the mass that normal wear will remove over the useful life of the rotor. 
Rotors actually can be drilled to make them lighter, but this is generally not done for streetable applications. It's only done on race cars where the rotor size is excessively larger for the weight/speed of the car and reducing the mass of the rotor won't negatively affect braking by reducing the thermal capacity of the rotor. 
And most drilled or slotted rotors (and all rotors that I've seen that are both drilled and slotted) aren't exactly "performance" rotors. Most of them are decorative poseurs, with performance that ranges from poor to dangerous in extreme use, but that's another discussion for another thread.
Again, it's inertia that counts, not absolute weight. And most aftermarket wheels that I've seen actually in use are cast wheels, similar to the factory alloys in construction and weight. The heaviest part of the wheel is the rim portion, and moving that out another half inch or inch from the center and adding enough material to fill out the larger circumference adds lots of inertia. Even if you go with lighter spokes and wheel centers to keep the total weight about the same as the smaller wheels (or even slightly lighter), the inertia will go up significantly. Forged wheels or spun rims with forged centers are lighter. The spun outer rims are particularly good for reducing the rotating inertia, but they are expensive and somewhat fragile for street use. 
With tires, everything is at least at the bead diameter, and the tread is the heaviest part and is farther out still. So, tires can have the same approximate inertia, even though there are minor differences in the actual weight. If the outer diameter of the tires are the same, the inertia is going to be very similar so long as the weights are close to the same. 
Well, it can sometimes be significant, especiallly on the older, underpowered cars. On my 1984 Jetta diesel, switching from the steelies with 175/70HR13 tires (34 pounds per corner) to alloys with lighter weight 175/70SR13 tires gave me about a half second quicker zero to 60mph times. And the car feels much more sure footed with the lighter wheels (using GTI stock springs and cheap gas shocks).

 
When a friend's 1.8T car (Seat Leon chipped+exhaust = 235whp) was dynoed on a rolling road dyno (of a car magazine) with 16" (205/55/R16 alloys) and after some minutes with 18" BBS-RC (225/40/R18) the power loss was 2 hp...







(tyres had the same air pressure between the 1st and 2nd wheel ste-up)...
For underpowered cars, I accept your point (putting 18" wheels you sentence it to death... http://****************.com/smile/emthdown.gif ), but who's talking for underpower in these forums...?


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## rpaller (Jan 5, 2001)

*Re: (ck_1.8T)*


_Quote, originally posted by *ck_1.8T* »_ 
When a friend's 1.8T car (Seat Leon chipped+exhaust = 235whp) was dynoed on a rolling road dyno (of a car magazine) with 16" (205/55/R16 alloys) and after some minutes with 18" BBS-RC (225/40/R18) the power loss was 2 hp...







(tyres had the same air pressure between the 1st and 2nd wheel ste-up)...
For underpowered cars, I accept your point (putting 18" wheels you sentence it to death... http://****************.com/smile/emthdown.gif ), but who's talking for underpower in these forums...?









What is impacted more by the change in rotational mass horsepower or torque? I am leaning towards torque but not certain.


----------



## dcomiskey (Mar 13, 2002)

*Re: (rpaller)*

I have to say that this is one of the best threads in here ever.














to everyone. 
Just one added thing, and maybe RacerX can talk about this. I think if you want to lighten the unsprung weight of your setups, regardless if it's stock, TT ior whatever, I think ECS Tuning's lightweight floating rotors offer a really good solution. I don't have them, and not sure I will because of the price. But, if I'm not mistaken, you will gain the benefits of lower weight and inertia (slightly) with these rotors. 
Again, It costs nearly double to get these as opposed to "stock" rotors from Brembo, etc, so.....


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## Racer_X (Jul 14, 2002)

I'm not sure about the weight of the ECS two piece rotors. The hat assembly is much lighter, but I'm not sure what the overall inertia picture is for the outer rotor ring. 
I am fairly certain that those are bolt together, two piece rotor assemblies. They call them "floating" rotors, but they aren't true floating rotors (mostly because they don't "float").
A real floating rotor setup is more complex, and floating rotors do have a big advantage for extreme racing use. But the ECS rotors look like they have bolts that are torqued down to hold the rotor pressed firmly to the center hat. I haven't actually had an ECS two piece rotor in my hand, I'm going on pictures I've seen and answers to questions I've asked about those rotors. 
True floating rotors use pins or cogged dog rings to hold the rotor so that it spins with the hat, but the rotor is free to move slightly in a direction parallel to the axis of the axle. Some kind of spring clip or other loose fitting fastener keeps the rotor loosely located, but it must be free to float (move). 
One thing I definitely do on the race car is machine the rotors down to near minimum thickness. This will reduce mass and inertia. The reduced inertia helps acceleration (and braking to a small extent), but the reduced mass can reduce thermal capacity, so you have to have better cooling and/or be prepared for higher operating temperatures when you do this. 


_Modified by Racer_X at 7:48 AM 2-9-2005_


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## 91gti20v (Jul 18, 2001)

*Re: (NOVAdub)*


_Quote, originally posted by *NOVAdub* »_Could you please explain why you feel that a rotor does not rotate about an axis through its center? 

I was referring to relative motion concerning the rotor in relation to the hub. It does spin on an axis through its center, but it acts as a mass with a certain geometry attached to the end of the axle. What I inferred out of the explanation prior was that it rotates on its own, which dynamically would change the situation. Bottom line is, I was just saying it acts as a mass at the end of the axle with a specific geometry. 
I see the point Racer_X is getting at, but I guess I want to see the hard numbers calculated which I am working on right now. I am bored at work and figured why not drag out the dynamics book


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## ck_1.8T (Sep 5, 2004)

*Re: (rpaller)*


_Quote, originally posted by *rpaller* »_
What is impacted more by the change in rotational mass horsepower or torque? I am leaning towards torque but not certain.

What dynos actually measure (whether load type--> Mustang, Dynojet, etc or non-load type--> Rolling Roads) is torque over an rpm range (Power = Torque x rpm x a numerical factor) ... Mustang dynos, which are indeed simulating and are the most close to real road conditions (virtual inertia) calculate torque by torque sensors on the single roller (load cells)...!
For the above reasons and what I've stated earlier, I wouldn't take much into account a dyno result on a simple rolling road (no load except that put by the mass of the rollers) and any power losses measured with bigger wheels-brakes (rotational masses) thereof ...


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## Banditt007 (Oct 23, 2002)

*Re: (ck_1.8T)*


_Quote, originally posted by *discardo* »_Under extreme braking my ABS does not typically get involved until the last few feet. 


_Quote, originally posted by *Racer_X* »_This sounds like something is definitely wrong with the brakes. The ABS should be easier to engage at higher speeds. At very low speeds, like at the end of a stop, the ABS will disengage completely. It has to or the car would never stop. The exact speed where the ABS deactivates varies from one vehicle manufacture to another, but 5 to 10 mph is commonly the lowest speed that the ABS will work. Not sure exactly where VW sets the cutoff, and it could vary with models and years as they have used different systems and different versions over the years. 

I have noticed the exact same thing, this is with shine suspension, stock MKIV gti brakes(caliper/rotor/lines) ds2500 pads up front, redbox in the rear, good fluid, and 225/45/17 falken azenis 215's all around. At high speed 125mph->zero stopping, the brakes feel like they are too weak, and that the tires have so much stick, the brakes cannot engauge/lock up the front tires. until speeds of 30mph or less are seen. The abs will (if it does) enguage at high speed in the rear (b/c it gets so light during such hard braking/over rear bias....which is why i use less grippy pads there) but the front will not enguage the abs. I thought maybe the rotors still werent at best temperature for the ds2500's so i did the same thing again, with the same result. So being that these have pretty much the highest friction of any streetable pad.....and i still need more clamping force. i'm looking at BBK's.....
But it seems to be pointed out that, there really isnt much more total area of say a 4 piston boxster caliper than the single piston caliper my car comes with. and if comparing the calipers clamping force with all things being equal, there is only a very slight advantage to the clamping force of the boxster caliper (this is what i've read, i havent measured) so you get a slight advantage there, and a slight advantage that the boxster caliper is used on a larger rotor giving you more leverage...........to me its not worth the cash then if thats the case. It seems like the boxster BBK (boxster caliper on 12.3" TT rotor) has these advantages :more heat capacity, better pedal feel/modulation(more pistons)....and just a tad bit more clamping force fromt he actual caliper, and a small mechanical advantage b/c its used on a larger rotor. I am lookign for clamping force, and more torque applied to the rotors. I know that fluid and pads are the way to deal with the heat....(in my case, wont need larger rotors/ducts ect)
So for actual clamping force what are the options then? raising the pressure of the brake system? (bigger master?)







Trying to find a caliper w/ significantly more square inch area of pistons to use on the 12.3" rotor? maybe if someone allows the big reds to fit onto a 12.3" rotor? I know i'm going to get the answer of better pads give you more friction.....but i tried them, and its still not enough braking. and i dont feel like dropping about $1K on a boxster BBK for just slight increases in actual power applied to the rotor.










_Modified by Banditt007 at 5:31 PM 2-9-2005_


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## phatvw (Aug 29, 2001)

*Re: (Banditt007)*


_Quote, originally posted by *Banditt007* »_I have noticed the exact same thing...

Yeah me too... well sort of.
*Track day*
Braking at high speeds like 125mph is a little touchy in a VW. I find that if I brake really aggressively, it is hard to keep the car going exactly straight. It seems that every road imperfection is amplified and the car shimmys left-to-right. I think if ABS kicked in at those speeds, the shimmying would be even worse. I assume all this is caused by the massive weight transfer to the front which compresses the relatively soft suspension and thus dynamically changes the toe & camber.
When this happened, my track driving instructor told me that I was just braking too hard. He said for fastest lap times, I should be well away from the limit where ABS kicks in. Only on racing tires and a properly prepped car can you really do braking at 9/10ths effectively and maintain good control for corner entry.
*What about emergencies on the street?*
Some say that slamming on the brakes and letting ABS stop you is the best way. I tend to think that steering out of the way and not having ABS enter the equation is the best way... but I guess there are some situations where that is not possible. Proper driver training makes these situations far less likely because you're trained to always leave yourself an out - just like in poker. 
*Dan's summary*
So my feeling is that having enough brake torque to have ABS kick in at those high speeds (125mph) isn't necessarily the best thing.
*More random thoughts*
If the brakes apply the same torque regardless of what speed you're going, then why does ABS kick in easier at lower speeds? (assuming we don't have a variable computer threshold)
Well I believe the answer, once again, lies in our grade 12 physics lessons. The car has kinetic energy (translational kinetic energy), but so do the rotors+driveshafts. Remember how kinetic energy was related to velocity squared? Well the faster the rotors spin, the more kinetic energy (rotational kinetic energy) they have. That rotational kinetic energy is like a torque acting on the rotor in the opposite direction of the brake torque. So your brake system really has to do two jobs at high speed:
- fight the torque exerted by the rotational kinetic energy of the rotors
- apply force via the tires to counteract the translational kinetic energy of the car
Since the brake torque is constant, the extra job of fighting the rotational kinetic energy means that its harder to reach the ABS threshold.
Anyway, those are my random thoughts of the day. Sorry if I've used the incorrect scientific terms. Grade 12 was a long time ago...










_Modified by phatvw at 4:18 PM 2-9-2005_


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## Banditt007 (Oct 23, 2002)

*Re: (phatvw)*

Hmmmm i may just try to get in a ride in a car with the ecs stage 2 version 1 brake conversion and see exactly how it is. I really dont have a budget for a much bigger brake conversion than that. ideally i would like to know how much more surface area of the pistons there are in the next largest caliper that porsche offers, and see if i can get custom caliper carriers to allow those to fit on 12.3" rotors. I know exactly what you are saying with the car not tracking straight at high speeds, i too have experienced that wandering within its lane during high speed braking. I also have no doubts that your instructor knows what he's talking about with using less braking for proper corner entry. Buttttttttttt, i guess i really just like the feeling of having enough brakes on tap that can lock the tires up at speed if i wanted to, even though using it would probably increase stopping distances.... sounds strange i know, but even at speeds that arent that fast like say 60mph, i feel like i could use alot more brake force, and have the tires able to transfer that force to the ground. I will probably get this kit anyway and just mess with all sorts of different pads until i find one that works for me, and if thats not enough i'll just deal with it, b/c i'm not going to spend more cash on brakes. Plus admitingly i really love the look of porshe brakes, and alittle more added modulation/feel i will take anyday.








I agree with you completly on the reason the brakes seem much less effective at speed. My heavy (24lbs or so) 17" tires ontop of my cast stock monte wheels must have ALOT of rotational weight at speed. the driveshafts/rotors must have alot less impact, but still are a factor for sure. With that being said, i'm sure some super light weight wheels (SSR comps) and some light tires (toyo ts-1's) would give you a very notable amount more felt braking at high speed. http://****************.com/smile/emthup.gif


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## ck_1.8T (Sep 5, 2004)

*Re: (Banditt007)*


_Quote, originally posted by *Banditt007* »_Hmmmm i may just try to get in a ride in a car with the ecs stage 2 version 1 brake conversion and see exactly how it is. I really dont have a budget for a much bigger brake conversion than that. ideally i would like to know how much more surface area of the pistons there are in the next largest caliper that porsche offers, and see if i can get custom caliper carriers to allow those to fit on 12.3" rotors. I know exactly what you are saying with the car not tracking straight at high speeds, i too have experienced that wandering within its lane during high speed braking. I also have no doubts that your instructor knows what he's talking about with using less braking for proper corner entry. Buttttttttttt, i guess i really just like the feeling of having enough brakes on tap that can lock the tires up at speed if i wanted to, even though using it would probably increase stopping distances.... sounds strange i know, but even at speeds that arent that fast like say 60mph, i feel like i could use alot more brake force, and have the tires able to transfer that force to the ground. I will probably get this kit anyway and just mess with all sorts of different pads until i find one that works for me, and if thats not enough i'll just deal with it, b/c i'm not going to spend more cash on brakes. Plus admitingly i really love the look of porshe brakes, and alittle more added modulation/feel i will take anyday.








I agree with you completly on the reason the brakes seem much less effective at speed. My heavy (24lbs or so) 17" tires ontop of my cast stock monte wheels must have ALOT of rotational weight at speed. the driveshafts/rotors must have alot less impact, but still are a factor for sure. With that being said, i'm sure some super light weight wheels (SSR comps) and some light tires (toyo ts-1's) would give you a very notable amount more felt braking at high speed. http://****************.com/smile/emthup.gif 

For your info, just have a look to the following link at ECS's site comparing total piston areas, breaking torques, etc between the various ECS stage kits and stock break system of an MkIV-1.8T:
http://www.ecstuning.com/stage...=1.8T
(have a look at the tables down on the html page and download pdfs of these)


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## idunno (May 9, 2001)

*Re: (91gti20v)*


_Quote, originally posted by *91gti20v* »_Ok, I have read through most of this and I am still questioning the above fact in bold. Quite simply, once the rotor is mounted to the hub/bearing/axle assembly, it acts as one system. Ok, now, lets think about this. You aren't altering the distance from the drive point to where the rotor is mounted. The mass acts at the same point. The simple equation for inertia is I = ((r)*(r))*m, where r is the distance from the axis, or transmission in this case, and m is the mass of the object. R is staying constant, but m changes as you change rotors. Where this theory is true is if you just go to a larger rotor that is nothing special. Obviously if the rotor is larger it will be heavier, but if you go to a larger, lighter, 2 piece floating design, you are decreasing the mass, therefore decreasing the inertia acting on the same point as the smaller rotor. 

I think it's a little misleading to use this equation (I = mr^2). It was
alluded to at various points, but I didn't see anyone come out and
specifically state that the equation is meant for concentrated masses 
at a distance "r" from the axis of rotation.
For instance, two brake systems:
a) 12" OD, 15lb total weight, one piece design
b) 12" OD, 15lb total weight, two piece design with light aluminum hat
System "a" should have lower inertia. Since they both weigh the same,
and we know the aluminum hat is lighter than it's steel counterpart, the
weight (mass in our case) of "b" lies further out (away from it's rotational
axis) which increases the moment of inertia.
Maybe that just confused things....








My point is just because you have two rotors of the same weight and
OD, doesn't mean they have the same MofI. Your MofI _could_ even
go down with an increase in mass and OD, depending on where the
weight is concentrated (note: I don't mean to imply that you're likely
to find this to be the case, just that it's possible). It's easier to spin that
mass closer to the axis (as in the ice skater example).


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## JoeVeeDubber (Mar 15, 2002)

I don't know if its been mentioned yet, but a benefit to a 2pc rotor is that a lot of heat from the disc is not being transferred to the hub assembly/wheel bearing. That reduced heat prolongs the life of the bearing and under extreme conditions could also prevent bearing failure.


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## Racer_X (Jul 14, 2002)

*Re: (JoeVeeDubber)*


_Quote, originally posted by *JoeVeeDubber* »_I don't know if its been mentioned yet, but a benefit to a 2pc rotor is that a lot of heat from the disc is not being transferred to the hub assembly/wheel bearing. That reduced heat prolongs the life of the bearing and under extreme conditions could also prevent bearing failure.
That's true for true floating rotor. On those, the contact between the rotor rings and the pins or dogs that transfer the torque to the hub is over a much smaller area. But for most bolt together two piece rotors ("crimes against nature and engineering"), the arear where the rotor is in contact with the aluminum hat is fairly significant. When you conisder that aluminum is a much better thermal conductor than cast iron or steel, that means that a lot of heat will still get to the hub and the wheel.
This isn't entirely bad. It's not good to put that heat into the bearings. But the aluminum alloy wheels also make excellent heat sinks. On my race car, I've considered getting a thermal barrier coating oh the hubs themselves (might actually do that for the next set of bearings I have pressed in). And on all my cars with alloy wheels, I always use a thin coating of dielectric grease/heat sink compound on the parts of the alloy wheel that contact the center hat of the rotors. You want to take heat out of the rotor and into the air by any means you can.


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## Ceilidh (Jan 7, 2004)

*Re: some random physics*

Hi Folks,
Really interesting thread -- please keep going!!








Some random physics info, just in case any of you find it useful:

_Quote, originally posted by *idunno* »_
I think it's a little misleading to use this equation (I = mr^2). It was
alluded to at various points, but I didn't see anyone come out and
specifically state that the equation is meant for concentrated masses 
at a distance "r" from the axis of rotation.
For instance, two brake systems:
a) 12" OD, 15lb total weight, one piece design
b) 12" OD, 15lb total weight, two piece design with light aluminum hat
System "a" should have lower inertia. Since they both weigh the same,
and we know the aluminum hat is lighter than it's steel counterpart, the
weight (mass in our case) of "b" lies further out (away from it's rotational
axis) which increases the moment of inertia.
Maybe that just confused things....








My point is just because you have two rotors of the same weight and
OD, doesn't mean they have the same MofI. Your MofI _could_ even
go down with an increase in mass and OD, depending on where the
weight is concentrated (note: I don't mean to imply that you're likely
to find this to be the case, just that it's possible). It's easier to spin that
mass closer to the axis (as in the ice skater example).

idunno makes a good point(!). For future reference, the equations that pertain to brake discs would be:
1) "I" (moment of inertia) of solid disc = (1/2) * (M_solid *R^2)
2) "I" of disc with center hole (i.e., a ring) = (1/2) * M_ring * (R_hole^2 + R^2)
where R_hole is the radius of the center hole, and R is the overall radius
of the disc.
Equation 1 would apply to idunno's Case (a - one piece design); his Case (b - two piece design) can be (crudely) approximated as a small solid aluminum disc (the hat) plus a larger iron disc-with-hole. In the latter case, the shift of mass away from the hat and into the disc would increase the moment of inertia for a given overall mass.


_Quote, originally posted by *phatvw* »_
If the brakes apply the same torque regardless of what speed you're going, then why does ABS kick in easier at lower speeds? (assuming we don't have a variable computer threshold)
Well I believe the answer, once again, lies in our grade 12 physics lessons. The car has kinetic energy (translational kinetic energy), but so do the rotors+driveshafts. Remember how kinetic energy was related to velocity squared? Well the faster the rotors spin, the more kinetic energy (rotational kinetic energy) they have. That rotational kinetic energy is like a torque acting on the rotor in the opposite direction of the brake torque. So your brake system really has to do two jobs at high speed:
- fight the torque exerted by the rotational kinetic energy of the rotors
- apply force via the tires to counteract the translational kinetic energy of the car
Since the brake torque is constant, the extra job of fighting the rotational kinetic energy means that its harder to reach the ABS threshold.
Anyway, those are my random thoughts of the day. Sorry if I've used the incorrect scientific terms. Grade 12 was a long time ago...










Hello Phat!
Always nice to read your posts!
Just a little note: Your reasoning shows a lot of insight, but I think you might want to be a little careful here.







The torque that the brake pads exert on the spinning wheel (hub, tire, rim, disc, etc.) is simply:
Brake torque = (effective pad friction force) * (effective distance from pad to hub axis)
....while the torque exerted by the road on the wheel is:
Road torque = (effective tire "grip" force) * (effective tire radius)
When these two torques equal each other, the brakes lock (or ABS is invoked). The velocities (or in other terms, the inertia) of the system don't really come into it, except in terms of the kinetic energy that has to be dissipated; in this context, the "fighting" you refer to will have more to do with energy dissipation than with torque.
Anyway, please keep this discussion going -- it's fascinating reading! All best! - C


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## dcomiskey (Mar 13, 2002)

*Re: (phatvw)*


_Quote, originally posted by *phatvw* »_Yeah me too... well sort of.
*Track day*
Braking at high speeds like 125mph is a little touchy in a VW. I find that if I brake really aggressively, it is hard to keep the car going exactly straight. It seems that every road imperfection is amplified and the car shimmys left-to-right. I think if ABS kicked in at those speeds, the shimmying would be even worse. I assume all this is caused by the massive weight transfer to the front which compresses the relatively soft suspension and thus dynamically changes the toe & camber.
When this happened, my track driving instructor told me that I was just braking too hard. He said for fastest lap times, I should be well away from the limit where ABS kicks in. Only on racing tires and a properly prepped car can you really do braking at 9/10ths effectively and maintain good control for corner entry.


Interesting, my instructors told me I want to be at the point where ABS engages, otherwise, you're braking too early. 
I've never experienced this problem during track days that you seem to have. Maybe I have a different setup, but mine seem to grab pretty well. I'm just running on the Michelin Pilot Sports and Hawk HPS pads.


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## Racer_X (Jul 14, 2002)

*Re: some random physics (Ceilidh,dcomiskey)*


_Quote, originally posted by *Ceilidh* »_Hello Phat!
Always nice to read your posts!
Just a little note: Your reasoning shows a lot of insight, but I think you might want to be a little careful here.







The torque that the brake pads exert on the spinning wheel (hub, tire, rim, disc, etc.) is simply:
Brake torque = (effective pad friction force) * (effective distance from pad to hub axis)
....while the torque exerted by the road on the wheel is:
Road torque = (effective tire "grip" force) * (effective tire radius)
When these two torques equal each other, the brakes lock (or ABS is invoked). The velocities (or in other terms, the inertia) of the system don't really come into it, except in terms of the kinetic energy that has to be dissipated; in this context, the "fighting" you refer to will have more to do with energy dissipation than with torque.
Anyway, please keep this discussion going -- it's fascinating reading! All best! - C

Actually, it's you that seem to be ignoring the inertia of the spinning wheel. 
Here's something to think about. Let's say you jack the car up with the wheels off the ground. Now, "drive" it up to 30mph and then hit the brakes to stop the wheels. The brakes will definitely get warm as they convert the kinetic energy of the spinning wheels, tires, rotors, etc. into heat. But they will also excert a force on the wheel, and there will be an equal and opposite force on the the brakes. You could express this in terms of the pounds of force on the pads times the effective radius to the center of the pads as a torque force. 
Now, "drive" it up to 120mph and hit the brakes to stop the wheel. The wheel will spin considerably longer, and the brakes will get much hotter than they did from the 30mph '"stop" (because the 120mph spinning wheel will have 16 times as much kinetic energy as the wheel spinning at 30mph). All of the braking force applied to stop the spinning wheel is lost before it gets to the tire tread. That braking force is not availble to stop the car. Consider it like a "drive train loss" for the brakes. The amount of the loss goes up with the square of your speed. So, at higher speeds, more of the brake force is being used to just stop the spinning parts from spinning and less is available to apply braking force at the tire-road contact patch to slow the car. With heavy wheels and tires and extremely high speeds, the effects of this loss can be quite significant. 

_Quote, originally posted by *dcomiskey* »_Interesting, my instructors told me I want to be at the point where ABS engages, otherwise, you're braking too early.
That depends a whole lot on your tires and the temperatures of the track surface and your tires. 
Most tires have an optimum temperature range where grip is best. Below this temperature, they lose grip (cold tires), but they also lose grip above the optimum temperature. 
If you brake so late and so hard that your tires go over the optimum temperature range, then you won't have as much grip available when you start turning, and you might have to go slower through the corner. 
If someone is trying to pass you under braking, the the latest, hardest braker is going to come out in front, but often at a cost of reduced speed through the middle of that turn you are braking for. In a racing situation, that doesn't matter much because the slower car is in front and there's no way for the car with more potential speed to get around. But from a pure lap time perspective, braking too late can hurt your times, too. 


_Modified by Racer_X at 7:46 AM 2-10-2005_


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## phatvw (Aug 29, 2001)

*Re: some random physics (Racer_X)*


_Quote, originally posted by *Racer_X* »_
If someone is trying to pass you under braking, the the latest, hardest braker is going to come out in front, but often at a cost of reduced speed through the middle of that turn you are braking for. In a racing situation, that doesn't matter much because the slower car is in front and there's no way for the car with more potential speed to get around. But from a pure lap time perspective, braking too late can hurt your times, too. 


Yeah I think thats exactly what my instructor was getting at, but he didn't describe it quite so well







It might not win races, but its good to build technique. I'm not interested in competition (yet) so thats what we focussed on.
I must say this thread is certainly developing and will no doubt turn out to be another VWVortex classic


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## Ceilidh (Jan 7, 2004)

*Re: some random physics (Racer_X)*


_Quote, originally posted by *Racer_X* »_
Actually, it's you that seem to be ignoring the inertia of the spinning wheel. 



Hi Racer_X
Actually, no, it's not me who seems to be a little confused.







Let's look at this step by step, shall we?

_Quote »_
Here's something to think about. Let's say you jack the car up with the wheels off the ground. Now, "drive" it up to 30mph and then hit the brakes to stop the wheels. The brakes will definitely get warm as they convert the kinetic energy of the spinning wheels, tires, rotors, etc. into heat. But they will also excert a force on the wheel, and there will be an equal and opposite force on the the brakes. You could express this in terms of the pounds of force on the pads times the effective radius to the center of the pads as a torque force. 


So far we're both on the same page (well, mostly, anyway*): excellent scenario; torque = pad force * moment arm; torque is independent of velocity, but energy dissipation's related to velocity squared. So far so good!....
(* the caveat is that the force on the wheel is not equal and opposite to the force on the brakes, as that would imply the net force is zero and the wheels don't decelerate! But that's peripheral to the main point thus far...)
_ edit: now that it's morning after a bit of sleep, I see that I misinterpreted what you wrote -- ignore the *caveat: we're in full agreement!_

_Quote »_
Now, "drive" it up to 120mph and hit the brakes to stop the wheel. The wheel will spin considerably longer, and the brakes will get much hotter than they did from the 30mph '"stop" (because the 120mph spinning wheel will have 16 times as much kinetic energy as the wheel spinning at 30mph).


.....and we're still on the same page (at least on why the brakes get much hotter; the spinning longer is something we'll address in a moment)....









_Quote »_
All of the braking force applied to stop the spinning wheel is lost before it gets to the tire tread. That braking force is not availble to stop the car. Consider it like a "drive train loss" for the brakes. The amount of the loss goes up with the square of your speed. So, at higher speeds, more of the brake force is being used to just stop the spinning parts from spinning and less is available to apply braking force at the tire-road contact patch to slow the car.


....but here things start to go a little awry. Are we talking about force, or are we talking about kinetic energy? It becomes dangerous when the two get confused!
Your argument appears to be that more force is proportionally required at high speeds, as more energy has to be dissipated. The problem with this sort of argument is perhaps subtle, so we'll hit it in three entirely different ways:
1) Let's use your 30 mph / 120 mph scenario. You point out that the 120 mph wheel will take longer to slow down -- but does that imply the braking force has somehow been "lost"? Absolutely not! Even if absolutely none of the force is "lost", the 120 mph wheel will take longer to slow: 4X longer, to be exact! If we apply a constant braking force to a spinning wheel, it will decelerate at a constant angular acceleration. And at constant angular acceleration, something that starts out 4X faster will take 4X longer to come to a stop. So yes, the faster wheel takes longer to slow -- but that doesn't mean that force has been lost.
("ooo, but Ceilidh, you fool!", one might say, "You've just stated that 'a constant braking force' will lead to 'a constant angular deceleration" -- but is that really true??" Well, let's read on....)








2) Ok, but what about the energy? If we're dissipating 16X the energy in going from 120 mph to 0 (as opposed to 30 mph to 0) but must do so in only 4X the time, doesn't that mean that we have to dissipate the energy at a 4X faster rate? (i.e., 4X faster rate * 4X longer time = 16X energy dissipated) And if so, doesn't that mean we have to apply more braking force, in order to get the 4X faster energy dissipation? The answer to the first question is Yes! (the average rate of energy dissipation is 4X greater); but the answer to the second question is No! (no, we don't need more braking force).
The key here lies in the definition of Work (= force * distance) and its attendant equation for power (= rate of energy dissipation = force * velocity). The 120 mph wheel must on average dissipate energy at a 4X faster rate -- but on average it's spinning 4X faster, and hence its power output is 4X greater even with a constant force. Hence the 120 mph wheel requires no more force to dissipate its 16X greater energy than does the 30 mph wheel. Indeed, if it's to dissipate 16X the energy while decelerating at the same rate, it must exert exactly the same force -- neither more nor less.
Or, to put it another way, if you must dissipate 16X the energy while exerting constant brake pedal force (neglecting the effects of air resistance, etc.), the equations require that you decelerate at exactly the same rate.
3) The third way to get past the force/energy confusion is to return to the torque balance that occurs about the wheel axis (which ultimately is the equation that tells us about ABS onset): What's the torque exerted by the road on the tire/wheel? It's the force exerted on the tire contact patch, multiplied by effective radius. What's the torque exerted by the brake? It's the brake pad force, multiplied by the distance from pad to wheel axis. Are these torques equal and opposite? No -- the sum of these torques gives us the angular acceleration, which in turn is related to moment of inertia, and formally it all looks like this: 
Tau = (pad force * pad-to-wheel-axis) - (tire force * tire radius) = I * alpha, where Tau = torque, I = moment of inertia, alpha = angular acceleration.
Notice that this equation does include moment of inertia -- which is in line with what you and Phatvw have been saying all along(!): heavy wheels and brakes make it hard to slow the car. But velocity doesn't enter into the equation at all, and hence it doesn't have an explicit effect on how much braking force is needed to slow the wheels (and car).
(Weird, huh? It seems like velocity should enter in, but it doesn't.







)
Anyway, the above principles are admittedly subtle, and the university students here regularly get them wrong on major exams even after protracted study, so hats off to you and Phatvw for even broaching them in the first place! In any case, I still stand by my original statements (which you might have missed, earlier): it's been a pleasure reading your and Phat's posts on this thread (in addition to all the practical advice, your explanations of moment of inertia have been wonderfully vivid and insightful!), and I look forward to reading and learning more from your wealth of competition experience!
All best,
-C
.
P.S. -- I almost forgot! Phat, are you reading along? I've been thinking about your report that the ABS seems much more reluctant to invoke at high speeds than it is at low, and that (for various unreported reasons) you're fairly sure that this isn't a fade-type effect having to do with hotter brakes when braking from higher speeds; if that observation still holds, here's another possible reason:
Although the above arguments imply that the *absolute* rate of acceleration might be fairly constant at high speeds and low (assuming no fade, aero effects, etc.), the *relative* rate is pretty different! That is, if we're slowing down at a rate of (to pick numbers straight out of a hat) 20 mph/ second, then when we're braking from 120 mph, we're slowing down 17% in one second (20 mph / 120 mph) -- but in braking from 30 mph, in one second we'll have slowed 67% ! (20 mph / 30 mph). This difference should have an effect on the ABS control algorithms.
Racer_X seems to have much more experience with ABS electronics, so he can comment on whether the following applies (my experience is with robotics control systems, and not with ABS, but the same general principles often apply), but in many control loops, the thing we can easily detect is relative change -- not absolute change. That is, if something changes 10%, we can detect it much more easily than we can something that changes only 1%, irrespective of what the absolute quantities are.
Or to put it in a hypothetical ABS scenario: if a wheel slows down 5mph too much in 200 milliseconds (I'm just making these numbers up; I have no idea what ABS thresholds typically are...), I can more easily detect the aberration at low speeds than at high speeds. At, say, 25 mph, that 5 mph of extra slowing gives me a signal of 20% (5 / 25). But at, say, 100 mph, that same slowing gives me a signal of only 5% (5 / 100). So the incipient wheel lockup is much easier to detect at low speeds than at high, and I can therefore be more aggressive with my ABS tuning.
Anyway, the above is just a thought, based on general control systems -- Racer_X, as you're the one with the direct ABS experience, please feel free to comment!
Cheers again, and good night!

_Modified by Ceilidh at 3:13 AM 2-11-2005_


_Modified by Ceilidh at 9:32 AM 2-11-2005_


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## LSinLV (Nov 25, 2001)

*Re: some random physics (Ceilidh)*

^^^ He's from Cambidge....you know what's there....
Ouch!!...my head hurts!!
Honestly, thansk Ceilidh, very interesting and logical summation of braking physics, and the math behind them. Goodness, I haven't messed with this stuff since college!
Larry
Keep em coming guys, as I'm not sure if I am going to mount my BBK...even though I got it sooo cheap, it's insane!!!


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## phatvw (Aug 29, 2001)

*Re: some random physics (Ceilidh)*


_Quote, originally posted by *Ceilidh* »_
P.S. -- I almost forgot! Phat, are you reading along? I've been thinking about your report that the ABS seems much more reluctant to invoke at high speeds than it is at low, and that (for various unreported reasons) you're fairly sure that this isn't a fade-type effect having to do with hotter brakes when braking from higher speeds; if that observation still holds, here's another possible reason:
Although the above arguments imply that the *absolute* rate of acceleration might be fairly constant at high speeds and low (assuming no fade, aero effects, etc.), the *relative* rate is pretty different! That is, if we're slowing down at a rate of (to pick numbers straight out of a hat) 20 mph/ second, then when we're braking from 120 mph, we're slowing down 17% in one second (20 mph / 120 mph) -- but in braking from 30 mph, in one second we'll have slowed 67% ! (20 mph / 30 mph). This difference should have an effect on the ABS control algorithms.
Racer_X seems to have much more experience with ABS electronics, so he can comment on whether the following applies (my experience is with robotics control systems, and not with ABS, but the same general principles often apply), but in many control loops, the thing we can easily detect is relative change -- not absolute change. That is, if something changes 10%, we can detect it much more easily than we can something that changes only 1%, irrespective of what the absolute quantities are.
Or to put it in a hypothetical ABS scenario: if a wheel slows down 5mph too much in 200 milliseconds (I'm just making these numbers up; I have no idea what ABS thresholds typically are...), I can more easily detect the aberration at low speeds than at high speeds. At, say, 25 mph, that 5 mph of extra slowing gives me a signal of 20% (5 / 25). But at, say, 100 mph, that same slowing gives me a signal of only 5% (5 / 100). So the incipient wheel lockup is much easier to detect at low speeds than at high, and I can therefore be more aggressive with my ABS tuning.
Anyway, the above is just a thought, based on general control systems -- Racer_X, as you're the one with the direct ABS experience, please feel free to comment!
Cheers again, and good night!

_Modified by Ceilidh at 3:13 AM 2-11-2005_

You better believe I'm reading along... I must admit, reading your daily post is a guilty pleasure of mine








I understand what you're saying about the relative rate a deceleration - the deltas are a higher percentage of the absolute amount at lower speeds for a given deceleration. (I think this could lead into a precision vs accuracy discussion, but that's for a different thread). So while all this might be true, I still feel that it is simply harder to reach the limit of adhesion of the tires with the same brake torque when the tires are spinning faster. So ABS doesn't even have a chance to kick in.
I did some experiments today. Traveling at roughly 20mph with lots of wide open space, I yanked the hand brake as hard as I could. Instantly, I heard the rear tires skid. I did the same thing at 40mph, and I could not get the rear tires to skid immediately... it took a few seconds before I heard anything even though I could feel the car slowing down. I tried this a few times to make sure my arm wasn't getting tired. It is definitely more difficult to get the tires to skid at 40mph.
Whether it is something to do with the properties of the rubber-road interface at speed, the friction of the brake pad at speed, or a nuance in the momentum/kinetic energy/torque relationships we've been discussing, I am not certain. I hope we can figure it out here


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## Racer_X (Jul 14, 2002)

*Re: some random physics (Ceilidh)*

I don't have a lot of time this morning. But I'm 99% sure that ABS controllers do set the threshhold for "lock" as a percentage. I'll send some emails to my friends and acquaintances with more ABS experience than I have, but I'm almost certain that the threshhold is a percentage. 
There are very good reasons for this based on the way the contact patch slips along the ground, and the way that more force is generated as the slippage increases, up to a certain threshhold. Above that threshhold, the tire starts sliding and grip forces fall off quickly. This works in lateral forces and is expressed as slip angle when dealing with lateral loads. But it also affects forces that are linear with the centerline of the wheel (acceleration and braking) and is usually expressed as a percentage of slip. Most street tires generate maximum braking force (and maximum thrust for acceleration) at a slip of about 10 to 15 percent. 
If Provessor Ceilidh wants to speculate, this all has to do with the fact that the tread of the tire changes speed as it passes through the contact patch. Since the road is going by at a constant speed, there will be some slippage within parts of the contact patch, even at a constant speed with no torque force applied to the wheel in either direction.


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## Ceilidh (Jan 7, 2004)

*Re: some random physics (phatvw)*


_Quote, originally posted by *Racer_X* »_
I don't have a lot of time this morning....









Nor do I! I promised myself I'd get straight to work today, but sometimes this Vortex thing is too additive!


_Quote, originally posted by *phatvw* »_
I did some experiments today. Traveling at roughly 20mph with lots of wide open space, I yanked the hand brake as hard as I could. Instantly, I heard the rear tires skid. I did the same thing at 40mph, and I could not get the rear tires to skid immediately... it took a few seconds before I heard anything even though I could feel the car slowing down. I tried this a few times to make sure my arm wasn't getting tired. It is definitely more difficult to get the tires to skid at 40mph.
Whether it is something to do with the properties of the rubber-road interface at speed, the friction of the brake pad at speed, or a nuance in the momentum/kinetic energy/torque relationships we've been discussing, I am not certain. I hope we can figure it out here









Phat, that's one of the great things about you -- you always come up with great experiments that provide some hard data points! (sort of like what Peter does -- only of course Peter's in an entirely different league from the rest of us(!); keep a watch for his damper thread over this next month -- he's been up to some new neat things....)
Anyway, neat experiment, had me head-scratching for a bit ("Oh no! Where did I go wrong??"), but as usual Prof. Racer_X has chimed in with the key to the puzzle! :

_Quote, originally posted by *Racer_X* »_ ......the way the contact patch slips along the ground, and the way that more force is generated as the slippage increases, up to a certain threshhold. Above that threshhold, the tire starts sliding and grip forces fall off quickly. This works in lateral forces and is expressed as slip angle when dealing with lateral loads. But it also affects forces that are linear with the centerline of the wheel (acceleration and braking) and is usually expressed as a percentage of slip. Most street tires generate maximum braking force (and maximum thrust for acceleration) at a slip of about 10 to 15 percent......
......this all has to do with the fact that the tread of the tire changes speed as it passes through the contact patch. Since the road is going by at a constant speed, there will be some slippage within parts of the contact patch, even at a constant speed with no torque force applied to the wheel in either direction. 

(Once again, fascinating info, and explained more clearly and concisely than I could ever hope to!)
Anyway, Phat, when you're locking up your rear wheel from 20 mph by yanking on the handbrake, you're decelerating it over some non-zero length of time (let's just call it t_20). t_20 has a non-zero duration because the deceleration rate isn't infinite: that rate depends upon your arm strength







, the wheel moment of inertia (as discussed above), and the longitudinal force exerted by the road on the tire contact patch. The stronger your arm, the faster the deceleration; the greater the moment of inertia and/or contact patch force, the slower the deceleration.
When I first read your experiment, I was stymied: if last evening's argument were to hold (i.e., that braking force has no direct dependence on velocity), then why should the wheel not lock at 40 mph? If it takes t_20 seconds to lock from 20 mph, it seemed that it should take only t_40 seconds to lock from 40 mph -- and since you described t_20 as being really, really short ("...Instantly, I heard the rear wheels skid..."), then seemingly t_40 should appear almost instantaneous, too. But instead, there was no instantaneous lockup.  So how could this be? Data is data, and was there any way to fit this data point in with the earlier argument about force & velocity? So I was stymied.
And then Racer_X's morning post came in, and when we combine it with your "instantly" observation, we have what appears to be a plausible mechanism (or at least it seems plausible to me -- please decide for yourself whether you want to buy it!).
We'll start by looking at Racer_X's info more closely:

_Quote »_ .......the way the contact patch slips along the ground, and the way that more force is generated as the slippage increases, up to a certain threshhold. Above that threshhold, the tire starts sliding and grip forces fall off quickly. 
.....this all has to do with the fact that the tread of the tire changes speed as it passes through the contact patch. Since the road is going by at a constant speed, there will be some slippage within parts of the contact patch, even at a constant speed with no torque force applied to the wheel in either direction. 

There are a number of things embedded in here, and Racer_X's main thrust is on something a little different, but the part immediately germane to us can be brought out as follows: for the tire to exert braking force, the tire carcass has to distort. (If you want a rather extreme visual image, imagine a cube of green Jello sitting on a plate. Stick an index card on top of the cube (so the top of the Jello is stuck to the card, and the bottom is stuck to the plate), and then push the card in a horizontal direction. Initially the Jello hardly resists (because it's, after all, Jello!), and you can easily push the card; but as the Jello cube starts to distort and lean over, it'll begin to noticeably resist the motion. That in effect is what the entire tire carcass (plus tread blocks, etc.) has to do in order to build up braking force.....) Now, this distortion takes time to develop; it's pretty quick, but it's not instantaneous.
During the time it takes for the carcass to fully distort, the tire contact patch is not applying full force, and the handbrake is mostly contending with the rotational inertia of the wheel. Wheel deceleration can therefore be very rapid (for that brief instant of time, the brake is not decelerating the car; it's only decelerating the wheel). If your initial speed is low enough, and if the wheel deceleration is rapid enough, you can lock up the wheel before the carcass fully distorts (i.e., before the tire contact forces fully build up). If so, you put the tire into the locked-wheel sliding mode where grip is relatively low....

_Quote, originally posted by *Racer_X* »_
....Above that threshhold, the tire starts sliding and grip forces fall off quickly. 

....and you wind up with the familiar handbrake sensation of hearing the wheels skid without feeling a staggering amount of deceleration (a really unpleasant sensation, by the way, when you're using the emergency brake because the primary brakes on your '68 Dodge Dart(!!) have failed...).
So if the above mechanism were to describe your wheel lock at 20 mph, what might be happening at 40 mph? Let's do that case stepwise:
1) Even leaving aside tire forces, it will take you longer to decelerate the wheel (simply because you're applying a constant handbrake force and therefore a constant deceleration, and you're starting from a higher velocity). So if we ignore the tire forces entirely, the time to lock up the wheel would be t_40 = 2 * t_20.
2) But it's worse than that. Every instant of time that goes by before wheel-lock is time spent building up the tire distortion & tire force. So while the 20 mph brakes might have had the luxury of contending only against wheel inertia, the 40 mph brakes increasingly have to overcome the tire traction force -- i.e., the 20 mph brakes only had to slow down the wheel; the 40 mph brakes have to slow down the entire car. As a result, the wheel deceleration is no longer constant, and in fact it becomes lesser and lesser the more the tire distorts. As a result, t_40 becomes considerably longer than simply t_20.
3) The upshot is that if you're going fast enough, you can't lock the handbrake fast enough to prevent the tire forces from building up to their maximum. And if the tire forces are great enough, the wheel won't lock: instead, they'll maintain non-sliding traction against the ground, and car will simply decelerate without lockup.
4) This argument won't work at the extremes: if you're Herculean in strength, you'll be able to lock up the wheel regardless; and if you (or your handbrake) are pathetically weak, the wheel won't lock up at all. But at least on theoretical grounds, there's an inbetween zone where you should be able to lock up the rear wheel at lower speeds, but not at higher velocities...and it's possible that with you, in your car with your brakes and tires, that 20mph - 40 mph is the transition zone.

.
Guys, a couple of things:
A) The first is that I've just destroyed another big block of time having fun instead of working







, and I need to make myself stop -- hence I'm going to not look at this forum for at least a few days, only to save myself from myself. So please don't be offended if I don't comment on or reply to anything!
B) The other thing is an invitation: Racer_X, you might already be aware of this, but there's a fellow on the Suspension Forum named (Peter) "pyce" who's doing some very interesting experiments with dampers (Phat, could you possibly post the link to the damper thread? I can't find it....). As you have a wealth of experience and a keen & articulate insight, it'd be great to have your input as the experiments progress. If you have time, could you please check in on that thread from time to time, and chime in with any thoughts that strike you? No worries if you've no time -- but it'd be helpful to hear your perspectives!
Have a great day (and week, actually) everyone!!
- C


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## M this 1! (May 17, 2000)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

I REALLY wish i was done with my brake data. it'd be SO good for this discussion. most of what has been said is quite accurate. a set of big brakes does not always shorten the cars stopping distance. you need a WELL thought out kit. my 14" kit is 5lbs lighter than my 12" TT brakes it came with. the rotor is the same weight, but does send it further out. one important thing about changing to a huge front set up is: TIRES. with just the 14" Stasis kit, my car stopped worse than when i had their 13" temporary kit on. biggest reason was the poor balance of the massive fronts and normal 10" rears. the car would over cook the front tires as the rears were basically in the air. i finally got the 12" rears from them and the car is INSANELY balanced and eye bulging. i only have 2 runs to compare, but will have all variables when the testing is done.
Best stock run, stock front pads GTI 11.3" rotors, 10" rear with Pagid Blue. = 128ft! pretty good for a 3300lbs car
Best run with same rear Pagid pads but 12" aluminum hatted Stasis rotors Porterfied race pads, 14" Stasis set up, stickier tires
= 115ft.
i'll be doing:
1.stock front set up
2. 14" front, stock rears
3. street pads in 14"/12" set up
all on same tires. 
truth is, a beautiful brake set up like the Stasis WILL reduce stopping distance but the reason to buy them is really to rid fade, gain pedal feel, and look bad ass.


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## Byron N. (Oct 20, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (M this 1!)*

The Stassis kit uses a similar version of Alcon caliper that I have used in the past. I talked about a 97 Audi in my earlier post with them. The front and rear combo your running is very similar to what the Audi A4 had, those brakes are what got me interested in big brakes. I don't think there is a finer street caliper than the Alcon. I would love to see your stopping distances when your done. If possible try to get some 100-0 m.p.h. distances, thats were they really shine. I regret selling my B-type Alcons. Money well spent.


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## idunno (May 9, 2001)

*Re: some random physics (Racer_X)*


_Quote, originally posted by *Racer_X* »_
If someone is trying to pass you under braking, the the latest, hardest braker is going to come out in front, but often at a cost of reduced speed through the middle of that turn you are braking for. In a racing situation, *that doesn't matter* much because the slower car is in front and there's no way for the car with more potential speed to get around. But from a pure lap time perspective, braking too late can hurt your times, too. 


I was with you on this one, until you said "that doesn't matter".....but I
was thinking about motorcycle racing....where you *can* actually pass. 
Defintely right about slowing the "middle" speed. http://****************.com/smile/emthup.gif


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## 90quattrocoupe (Feb 7, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (idunno)*

Stock brakes don't fade

Bull.
I had a 240Z, and downhill on a winding road, I faded the brakes so bad, the whole front end of the car shook when you applied the brakes. This was with upgrades pads and fluid. Ate Blue. The fade went away when I upgraded to vented rotor and slightly larger calipers.
I have a 914 and I faded the brakes the same way, but without the shaking. Upgraded to BMW caliper with pads and fluid and still faded the brakes. Upgraded to 911 calipers and vented rotors and fade went away.
I faded my coupe. Upgraded rotors, pads and fluid and they still faded a little. Upgraded to 996 calipers, 323 rotors, and vented rotors in the rear. I have yet to fade them, and that is just running street pads.
I believe most of your are right, when it comes to braking distances of stock vs. aftermarket brake setups. But that changes, as the number of hard braking instances go up.
But when it comes to fad, you can't beat a bigger, vented vs. vented, or vented vs. solid, rotors and larger calipers. The bigger brakes will keep braking whereas the stock, even with upgrade pads and fluid, will fade.
These are just a couple of examples of upgraded brakes on some of the cars I have owned over the last 40 years.
I made all these brake comparisons with the only change being the brakes. Cars still weighed the same, same wheels, same tires, etc. 


_Modified by 90quattrocoupe at 12:55 PM 2/15/2005_


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## VWGolfA4 (Apr 5, 2000)

*Re: Another proof why BIGGER brakes are NOT always best! (90quattrocoupe)*

This is all very interesting but I will admit some of this is over my head. Im really enjoying this. Please try and keep this informative and not a pissin match. Im debating the option of upgrading my 11.3s on my GTI 1.8T MkIV with better fluid, pads and rotors or getting the TT Setup with upgraded fluid, pads and rotors...


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## Banditt007 (Oct 23, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (VWGolfA4)*

on the street there is no way you are fading stock brakes with good fluid and good pads. I purposely tried to fade my brakes out, to see where the limit was. THis was with stock fluid (not even that fresh either) ferrodo ds2500 pads upfront, redbox in the rear, and 225wide falken azenis. i did countless (20 or more) full force stops back to back from 80-100mph to zero, the brakes did not fade. I would have go on more, except myself as well as my passanger, if one more stop was made, were going to puke. After this many stops after 1 minute of driving normally the brakes were still glowing deep orange......... Even if your brakes fade there should be no shaking when applying the brakes, and if there was that probably ment you were getting uneven pad deposits on your rotors due to the pads working out of their designated temp range. Unless on a road course, or on the street w/ a car with alot more power than stock(so there is less time for the brakes to cool before your back up to high speed where you are going to slow again), you are not fading the brakes out IMO. I'm not talking woopie lets throw some mintex redbox on the front, or i got the best pads ever my hawk HPS's never fail, i'm talking carbotech panther +/ferrodo ds2500 region of pads and good fluid. In my experience, its not going to happen. I drive like a nutcase on the street and the ferrodo ds2500 pads handled anything i threw at them, infact they are pretty much overkill for the street.


_Modified by Banditt007 at 6:05 PM 2-15-2005_


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## alexb75 (Dec 29, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (90quattrocoupe)*


_Quote, originally posted by *90quattrocoupe* »_Stock brakes don't fade

Bull.
I had a 240Z, and downhill on a winding road, I faded the brakes so bad, the whole front end of the car shook when you applied the brakes. This was with upgrades pads and fluid. Ate Blue. The fade went away when I upgraded to vented rotor and slightly larger calipers.
I have a 914 and I faded the brakes the same way, but without the shaking. Upgraded to BMW caliper with pads and fluid and still faded the brakes. Upgraded to 911 calipers and vented rotors and fade went away.
I faded my coupe. Upgraded rotors, pads and fluid and they still faded a little. Upgraded to 996 calipers, 323 rotors, and vented rotors in the rear. I have yet to fade them, and that is just running street pads.
I believe most of your are right, when it comes to braking distances of stock vs. aftermarket brake setups. But that changes, as the number of hard braking instances go up.
But when it comes to fad, you can't beat a bigger, vented vs. vented, or vented vs. solid, rotors and larger calipers. The bigger brakes will keep braking whereas the stock, even with upgrade pads and fluid, will fade.
These are just a couple of examples of upgraded brakes on some of the cars I have owned over the last 40 years.
I made all these brake comparisons with the only change being the brakes. Cars still weighed the same, same wheels, same tires, etc. 

_Modified by 90quattrocoupe at 12:55 PM 2/15/2005_

Every car is different. It could be that some of those cars were too heavy for stock rotors. We are talking mostly MK4 here and the experience is that on the street there's absolutely no way you could fade stock rotor-size if you have good fluid (not just fresh) and good pads. It actually is pretty good in most racings that I have done too, so street is just a cake walk.


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## jhayesvw (Oct 3, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

i dont have the patience to read this whole thread. i read page one and it was blah blah blah. 
i have a 1995 golf sport. it had a 2.0 in it. the 10.1" brakes were adequate. i upgraded the pads to hawk hps with good brembo rotors and stopping was great. 
then i swapped in a vr6. immediately the brakes sucked. yes the fluid was bled. i can swap an engine, so i surely can bleed brakes. 
i got some new G60 11" calipers, carriers, and hawk hps pads. bam. braking is back.
bigger is better to a point. 
as for the Mugen car. i watch every one of those "sports car revolution" shows. 
what you guys may have missed is that the Acura RSX comes with dual piston calipers stock. they brake very very well but fade after a bit. 
Also, as stated earlier, the first test of the stock brakes was done in the dry, the Stoptech test was done in the winter in the wet with snow falling. 
apples and oranges.


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## Racer_X (Jul 14, 2002)

*Re: some random physics (phatvw)*

I'm drawn back to this thread like a moth to a flame. 
I left some unfinished, unanswered questions last time I posted. 

_Quote, originally posted by *phatvw* »_<snip>
I did some experiments today. Traveling at roughly 20mph with lots of wide open space, I yanked the hand brake as hard as I could. Instantly, I heard the rear tires skid. I did the same thing at 40mph, and I could not get the rear tires to skid immediately... it took a few seconds before I heard anything even though I could feel the car slowing down. I tried this a few times to make sure my arm wasn't getting tired. It is definitely more difficult to get the tires to skid at 40mph.
A lot of this is due to suspension design and operation rather than the brakes. 
VW uses a full trailing arm rear suspension. The rear brakes (the only brakes the handbrake operates) cause some interesting things to happen with this type of suspension. The most important (and somewhat non-intuitive) thing is that brake force applied at the rear wheel transfers weight *onto the rear wheels*. The brake torque is applied to the trailing arms and tries to rotate the trailing arms in the same direction as the turning wheels. This pulls downward on the points where the trailing arms and "beam" attaches to the chassis/body. This downward pull puts more weight on the rear suspension, pulling the body down against the rear springs and pushing the wheels back toward the ground. The car squats and there's actually more of the weight of the car on the rear wheels than there would be without the rear brakes applied. 
Moving twice as fast means that the weight will transfer rearward twice as quickly, and unless you pull the parking brake handle twice as fast, the added weight will give the rear tires more grip and it will be harder to lock the rear wheels. 
I also want to go back to this:

_Quote, originally posted by *Racer_X* »_the tread of the tire changes speed as it passes through the contact patch.

And go in a slightly different direction than Ceilidh did. Ceilidh covered part of what is happening, but not quite all of the things that are going on around the contact patch of the tire. 
First, let's look at a tire rotating at a constant speed. The tread has a pretty simple shape. It's a cylinder, but with a flat spot at the bottome where it contacts the flat ground. There are two important dimensions to consider. One is the radius of the cylindrical part. You could measure this from the front most edge to the rear most edge. Let's call this the tread radius for this discussion. The other important measurement is the distance from the road surface to the centerline of the axle. This is often called the rolling radius and it's slightly shorter than the tread radius. The difference between the rolling radius and the tread radius varies depending on load and tire pressure, but there is always a difference. 
Now, the wheel turns at a constant rate, and a constant angular velocity. And the entire tread, *except for the contact patch* travels at a constant linear speed that can be calculated from the tread radius and the angular velocity of the wheel. 
The contact patch is where things get a little wierd. As the rubber deforms slightly to follow the flat surface of the road, the distance from the tread to the centerline of the axle gets slightly shorter. As that distance shortens, the tread slows down, because it's still traveling at a constant angular velocity (the wheel is turning at the same constant rate), but the radius is decreasing. At the point where the tread is closest to the axle centerline, directly below the axle centerline, it is moving at it's slowest rate and begins accelerating again to "catch up" to the speed at the tread radius. But the point where it's at the rolling radius is also where the most pressure is being applied to the road, and that's the actual road speed that you are traveling. 
Increasing the load on the wheel (from added weight or from weight that transfers forward from braking or backward from acceleration) will increase the size of the contact patch, and decrease the rolling radius. This increases the speed differential between the center of the contact patch and the outer parts of the tread. 
Ceilidh is right about the "jello" like quality of the tire rubber, and the carcas of the tire. It's really complicated, and I don't even understand exactly how to calculate how much flex and "give" there is. The short story is that when you start putting major torque into the flexible tire carcass and rubber of the tread, the wheel can rotate slower than the distance covered and the tread surface will still maintain an adhesive contact with the road (with the carcass distorting and the rubber stretching to stay fixed relative to the road as it passes through the contact patch sector). So the wheel might travel forward 12 inches, but the angle that the wheel turns might only work out to 10-11 inches of rotation at the rolling radius. 
The more torque you apply, the greater the distortion and stretching. But at some point, you run out of elasticity. At that point, one of two things happens. On street tires, it's always the rubber that loses grip on the road surface. On a really soft race compound slick, the rubber itself can sheer within the tread and the tire can "blister." Blistering happens when the tread surface stays fixed with the road, but the sheering and break-away occurs within the rubber of the tread . 
Another important thing is that the stretch and distortion is fairly constant regardless of speed, so the difference in speed between the road speed and the angular speed of the wheel is a percentage, not an absolute speed. 
This is why ABS threshholds are a percentage, not an absolute speed, and why tires generate maximum thrust (braking or accelerating) at a certain percentage of "slip". 
BTW, I did talk to a friend who used to write code for ABS controllers, and he verified that the threshholds are always a percentage, and generally they are higher than 20-25 percent to allow the tires to generate maximum grip without engaging the ABS. The actual slip percentage might be one of the "trimming" parameters in some systems. This would allow the engineers to select the most appropriate values for this based on the performance charateristics of the tires most likely to be used on the vehicle.


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## phatvw (Aug 29, 2001)

*Re: some random physics (Racer_X)*

Once again Racer, you've taken this thread to a whole new level! Thank you, this is very interesting stuff!


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## Dicardo (Dec 14, 2003)

*Re: some random physics (phatvw)*

Can you explain to me why you even bother considering the tire radius outside of the contact patch? The vehicle weights this portion of the tire down, and unless their is a change in the forces applied to this point (accelleration, deceleration) this value would be a constant? and the only viable distance to the centerline to consider.


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## Racer_X (Jul 14, 2002)

*Re: some random physics (Dicardo)*


_Quote, originally posted by *Dicardo* »_Can you explain to me why you even bother considering the tire radius outside of the contact patch? 
Because it's easy to wrap a tape around the tire while it's loose, off the car and just divide by 2*pi to get the tread radius. Measuring the rolling radius is more difficult. You have to apply a load equal to whatever car it will be mounted on, and the pressure has to be set to whatever will be used when it's installed. 

_Quote, originally posted by *Dicardo* »_The vehicle weights this portion of the tire down, and unless their is a change in the forces applied to this point (accelleration, deceleration) this value would be a constant?
Actually, it varies with a number of different factors. Any change in load will change it as well. That can be changes in "static" load (passenger gets in or gets out, luggage put in trunk), or dynamic load shifts from one (or more) tire(s) to other tire(s) (weight transfer from acceleration, braking, or cornering). But load isn't the only variable, inflation pressure changes will also change rolling radius, and temperature changes will change the tire pressure. So driving a few miles on the freeway will change the rolling radius slightly (because the tire gets hot and the pressure goes up).

_Quote, originally posted by *Dicardo* »_and the only viable distance to the centerline to consider.
The rolling radius is certainly the most important factor when you start talking about vehicle dynamics. But difficulty in measuring rolling radius, plus the fact that rolling radius changes dynamically with load, temperature, pressure, etc. make it much more difficult to pin down with precision.


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## Redwolf18t (Jan 16, 2005)

*Re: some random physics (Racer_X)*

Wow, what a post. i have learned alot about breaks just by reading this post alone. I'm a newbee to the dub world and moding in general. I currently need to change my rear pads & rotors to pass my states inspection so I thought hell if I have to spend the money why not upgrade to a bigger breaking system. I'm glad I read this post and a few others first before making my decision or worst purchasing a kit. Seems as though I was following a popular misconception. All I can say is thanks to guys like yourselves who share their knowledge & experience to help make folks like me lives a little easier, a little less frustrating. So no big break upgrade for me, I've done the research and I'm going with HPS pads and Brembo rotors all the way around http://****************.com/smile/emthup.gif


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## Jason_Reuben (Jan 15, 2005)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*

It's just like dcomiskey said. Bigger brakes dont help you stop better. The tires you have on your car is the the biggest way to get a smaller braking distance. Though there is a place for bigger brakes. the problem is most people go to the biggest size that will fit. The only thing that brakes do is convert motion energy into heat. So if you get bigger brakes you have a larger heat sink to disapate the heat. But you can also just get cross drilled or slotted to do the same. It does not really come down to people getting better brakes it is mostly about looks. So what if people with hondas want to go slower, as long as I'm not behind them i dont care how much dumb stuff they do.


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## NOVAdub (Jul 28, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (Jason_Reuben)*


_Quote, originally posted by *Jason_Reuben* »_ So if you get bigger brakes you have a larger heat sink to disapate the heat. But you can also just get cross drilled or slotted to do the same. 
Slotted and cross drilled rotors have less surface area and therefore dissipate less heat. For most people driving on the street they only have one purpose, aesthetics.


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (NOVAdub)*


_Quote, originally posted by *NOVAdub* »_Slotted and cross drilled rotors have less surface area and therefore dissipate less heat. For most people driving on the street they only have one purpose, aesthetics. 

Actually drilled/slotted have more overall surface area which, if properly designed, means more efficient cooling. However, the actual friction surface area is smaller and less mass equals less heat capacity. Its a trade-off.
But yeah aesthetics is probably the main thing... especially on fancy-looking cars like Porsche and AMG.


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## NOVAdub (Jul 28, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*

Ooops thats what I meant to say.


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## ck_1.8T (Sep 5, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_
...
But yeah aesthetics is probably the main thing... especially on fancy-looking cars like Porsche and AMG.

Well ...! http://****************.com/smile/emthdown.gif Are you saying that R&D departments of companies like Porsche and AMG, that are known to invest a great deal in braking systems, are simply using multi-pot calipers and large drilled rotors for aesthetic reasons...???















If they do so, they should then probably ask for advice from some vortexers to share their "deep" knowledge on how to develop better effective braking systems...







http://****************.com/smile/emthdown.gif


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (ck_1.8T)*


_Quote, originally posted by *ck_1.8T* »_Well ...! http://****************.com/smile/emthdown.gif Are you saying that R&D departments of companies like Porsche and AMG, that are known to invest a great deal in braking systems, are simply using multi-pot calipers and large drilled rotors for aesthetic reasons...???
















If they do so, they should then probably ask for advice from some vortexers to share their "deep" knowledge on how to develop better effective braking systems...







http://****************.com/smile/emthdown.gif










Sorry I guess I was baiting a bit with the Porsche/AMG comment. But thats ok, I'm glad to explain my position.
If the R&D departments at Porsche and AMG had their way, then the street cars those companies sell would be quite a bit different. Marketing always gets the final say. For street cars, form is just as important as function. For someone that is paying $50,000+, don't you think they would prefer the matching red, shiny calipers? Don't you think they would prefer cool-looking cross-drilled brake rotors? Why do you think 90% of those folks buy those cars? Its a status symbol and it looks pretty. I bet fewer than 1 in 10 Porsches in the U.S. have even been close to a race track, lol.
Bottom line is that those multi-piston calipers do have advantages and disadvantages as we have discussed earlier in this thread (and other threads). One of the advantages is that they look cool. For a street car there is certainly no advantage to having cross-drilled rotors, they are just for looks.
Just because Porsche and AMG place well at LeMans, doesn't mean all their production cars are pinnacles of technology. There are always engineering trade offs, especially when the marketing department gets in the mix










_Modified by phatvw at 11:40 PM 2-23-2005_


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## drew2fast (Jul 27, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

Did they install larger rotors at all four corners? If so, then the loss was greater then what they measured on the dyno.


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## Racer_X (Jul 14, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_Sorry I guess I was baiting a bit with the Porsche/AMG comment. But thats ok, I'm glad to explain my position.
If the R&D departments at Porsche and AMG had their way, then the street cars those companies sell would be quite a bit different. 
<snip>

There's a little more to it than that. Factory sponsored motorsports enters into the picture, too.
Some racing series have rules that limit cars to stock brakes. Even more common is a limitation to stock rotors or stock rotor sizes. So, if Porsche, AMG/Mercedes or Audi want to do well in one of those race series, they have to put bigger brakes on the street versions of their cars in order to have them available to the factory backed race teams in some series. So, in some cases, the big brakes are a "homologation special" to get the big brakes allowed in certain racing series. 
And then, once they have the parts engineered and on the shelf, the marketing department can use them on other "high end" and "special edition" models, partially because customers will pay a premium for "big brakes," and partially to spread the R&D costs across a larger sales base. 
For a VAG example, Audi TT's got 12.3" front brakes and larger rear brakes to homolgate those brakes for certain racing series where Audi has factory sponsored or factory supported teams. They are probably somewhat useful on the Autobahn as well. The US market 20th AE GTI and the 337 got the same brakes because 1) they were available and an easy fit and 2) marketing recognized an opportunity for greater profits, and 3) it was also a good opportunity to spread the engineering costs for those bigger brakes over a larger sales base. 


_Modified by Racer_X at 8:29 AM 2-24-2005_


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## Banditt007 (Oct 23, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Racer_X)*


_Quote, originally posted by *Racer_X* »_
The US market 20th AE GTI and the R32 got the same brakes because

The R32 does not have the same brakes as the 20th AE. It uses a two piston caliper, and is 13.1" i believe. Perhaps you ment the 337? AFAIK the tt brakes come on the new GLI/TT/337/20AE http://****************.com/smile/emthup.gif


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## Racer_X (Jul 14, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (Banditt007)*

You're right. I meant 337, not R32.


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## g60_corrado_91 (Oct 25, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*


_Quote, originally posted by *dcomiskey* »_Also, why did these dumbasses install a cat-back on a NA car? That does nothing other than add the fart sound.









You answered your own question


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## ck_1.8T (Sep 5, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_
Sorry I guess I was baiting a bit with the Porsche/AMG comment. But thats ok, I'm glad to explain my position.
If the R&D departments at Porsche and AMG had their way, then the street cars those companies sell would be quite a bit different. Marketing always gets the final say. For street cars, form is just as important as function. For someone that is paying $50,000+, don't you think they would prefer the matching red, shiny calipers? Don't you think they would prefer cool-looking cross-drilled brake rotors? Why do you think 90% of those folks buy those cars? Its a status symbol and it looks pretty. I bet fewer than 1 in 10 Porsches in the U.S. have even been close to a race track, lol.
Bottom line is that those multi-piston calipers do have advantages and disadvantages as we have discussed earlier in this thread (and other threads). One of the advantages is that they look cool. For a street car there is certainly no advantage to having cross-drilled rotors, they are just for looks.
Just because Porsche and AMG place well at LeMans, doesn't mean all their production cars are pinnacles of technology. There are always engineering trade offs, especially when the marketing department gets in the mix









_Modified by phatvw at 11:40 PM 2-23-2005_

I agree with many of your statements, about people paying 50.000+ to by Porsches and Mercs AMGs, but the bottom line in this discussion is whether these "shiny" multi-pot caliper brake systems are effective...??? The answer is that they are pretty much effective, and stopping distances between 32-36m from 100-0 Km/h aren't ever seen by everyday cars bearing conventional brake systems ...







In Europe the STi Imprezas (265hp) and Mitsubishi Evos (VII, VIII) wear front 4-pot Brembo calipers and 328mm rotors... If you'd driven one of these you would absolutely agree that these are real rally replicas ...







http://****************.com/smile/emthup.gif They are not bought by people for looks since compared to other Q cars, these latter 2 models are ugly cars, but for effective braking they need something more effective than single pot "mini" calipers with the least rotor size and an effective pad with SS lines and fluid ...








Let's not make it such simplistic ...


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (ck_1.8T)*


_Quote, originally posted by *ck_1.8T* »_I agree with many of your statements, about people paying 50.000+ to by Porsches and Mercs AMGs, but the bottom line in this discussion is whether these "shiny" multi-pot caliper brake systems are effective...??? The answer is that they are pretty much effective, and stopping distances between 32-36m from 100-0 Km/h aren't ever seen by everyday cars bearing conventional brake systems ...







In Europe the STi Imprezas (265hp) and Mitsubishi Evos (VII, VIII) wear front 4-pot Brembo calipers and 328mm rotors... If you'd driven one of these you would absolutely agree that these are real rally replicas ...







http://****************.com/smile/emthup.gif They are not bought by people for looks since compared to other Q cars, these latter 2 models are ugly cars, but for effective braking they need something more effective than single pot "mini" calipers with the least rotor size and an effective pad with SS lines and fluid ...








Let's not make it such simplistic ...









I agree about the STI/Evo cars. Those are an entirely different class of car. Extremely ugly by conventional wisdom, but a truly race-inspired design. The brakes on those cars are amazing, but then the tires are quite a bit stickier than other cars out there. Its all about the package. If you put crappy all-season tires on, then you'd be in no better shape than with the base model Impreza RS brakes


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## Dicardo (Dec 14, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*

Well, in another week my Brembo Gran Tourismo kit will be installed w/ 337 rears, so I'll let you know my opinion of the dollar spent. After having much advice, science and opinion thrown about here, I am looking forward to seeing how my butt dyno reads the new brakes.


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (Dicardo)*

Hi Brake Dorks,
I installed Brembo 2-Piece Gran Turismos on my Jetta and If I had known how much of an improvment they give, I would have done them a long time before.
My car has a full suspension upgrade, coilovers, wheels, tires, and swaybars. Forget the power losses due to the inertia the heavy stock brakes give, the benefits of the much improved brake performance makes up for the negligable power losses and reduces unsprung weight by about 15 pounds per corner (front), race teams go to extremes to reduce unsprung weight, and you wont believe the weight savings until you see for yourself! Track times increased by seconds!!!!!!!
Not to mention those power gains from the rotational inertia are only when the car's wheels are spinning, otherwise the light brakes improve acceleration.










_Modified by vespam5 at 5:08 AM 3-8-2005_


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## Racer_X (Jul 14, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*


_Quote, originally posted by *vespam5* »_Hi Brake Dorks,
Always good to start your post by insulting everyone. 

_Quote, originally posted by *vespam5* »_Not to mention those power gains from the rotational inertia are only when the car's wheels are spinning, otherwise the light brakes improve acceleration.
Enquiring minds want to know how your car accelerates when the wheels are stopped. 
BTW, your tires don't fit either, and there's no way you could give a reasonable judgement of handling characteristics with those wheels/tires.


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## rpaller (Jan 5, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (Racer_X)*

Not to mention that the current ride height (in the picture) is detrimental to the handling characteristics of the MKIV suspesnion geometry. Unless it is dialed it back up so the control arms are closer to stock relationship with the ground. (See the suspension tech forum for details on why lower isn't necessarily better)


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (Racer_X)*


_Quote, originally posted by *Racer_X* »_Always good to start your post by insulting everyone. 
Enquiring minds want to know how your car accelerates when the wheels are stopped. 
BTW, your tires don't fit either, and there's no way you could give a reasonable judgement of handling characteristics with those wheels/tires. 

Don't cry, dorks are cool, I know, I'm one. 
Acce;eration (noun):1 : the act or process of accelerating : the state of being accelerated 
2 : change of velocity; also : the rate of this change . 
As you can see, acceleration is a change in velocity, when my wheels are stopped, my velocity is zero, when i release the clutch to take off, I am accelerating because i am changing my speed. Get it brake dork? Lighter rotors require less energy to speed up and slow down, similar to a lightweight flywheel on a tuned engine. Since the brake rotor is part of the drivetrain, it being lighter helps accelerate faster. since there is less to move.
BTW, my wheels are 18x8 OZ's about 17 lbs/ea and yes the falken 225/40-18's that I bought for the front are a much narrower profile than my previous AVS Sports which i wore out. It doesn't really matter because I run race Kosei wheels with falken Azenis tires for the autocross.
Lastly, I can give a reasonable judgement of handling because i know how my car handled before i had the Brembos, and after. I race my car at local autocross events, as well as locally in the hills( http://****************.com/smile/emthdown.gif bad idea), and the gains are very noticable, and the brakes inspire confidence.


_Modified by vespam5 at 7:18 PM 3-8-2005_


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (rpaller)*


_Quote, originally posted by *rpaller* »_Not to mention that the current ride height (in the picture) is detrimental to the handling characteristics of the MKIV suspesnion geometry. Unless it is dialed it back up so the control arms are closer to stock relationship with the ground. (See the suspension tech forum for details on why lower isn't necessarily better)

You my friend are right, not to mention the stock a-arm use cushy rubber bushings, I am working on some that ride on pivot balls (super harsh ride on the street). We were doing a bit of testing with stock a-arms, and under full brake, with Brembos, the front wheels almost touch the back of the wheel arches!!!


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*

Whoa. If you are on the vwvortex and you think "dork" is an insult, then you're just way too sensitive. Lighten up guys!
And vespam5 is making sense. If you shave 5 pounds per corner on calipers, then yeah, your acceleration may very well be better even with a slightly increased rotor moment of inertia.
What was the rule of thumb? 2 pounds of static weight ~= 1 pound of rotating weight?
It is likely that a more economical brake upgrade would have achieved similar results, but vespam5 is satisfied with his purchase and is getting results on the racetrack. That deserves some respect becuase it is a whole lot better than some of the posers who spend lots of money on fancy parts but never go to the track.


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## rpaller (Jan 5, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*


_Quote, originally posted by *vespam5* »_We were doing a bit of testing with stock a-arms, and under full brake, with Brembos, the front wheels almost touch the back of the wheel arches!!! 








I am trying to picture how this can happen in my head. Could we get into details of how this happened?


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (rpaller)*


_Quote, originally posted by *rpaller* »_







I am trying to picture how this can happen in my head. Could we get into details of how this happened?

It's a little hard to picture, but you see the picture above? Under hard braking, the wheels comes about an inch to an inch and a half closer to back of the wheelwell. Does that clear it up?, I think it's mainly because of the soft rubber bushings that the a-arm mount on.


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_Whoa. If you are on the vwvortex and you think "dork" is an insult, then you're just way too sensitive. Lighten up guys!
And vespam5 is making sense. If you shave 5 pounds per corner on calipers, then yeah, your acceleration may very well be better even with a slightly increased rotor moment of inertia.
What was the rule of thumb? 2 pounds of static weight ~= 1 pound of rotating weight?
It is likely that a more economical brake upgrade would have achieved similar results, but vespam5 is satisfied with his purchase and is getting results on the racetrack. That deserves some respect becuase it is a whole lot better than some of the posers who spend lots of money on fancy parts but never go to the track.

Well said


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## rpaller (Jan 5, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*


_Quote, originally posted by *vespam5* »_It's a little hard to picture, but you see the picture above? Under hard braking, the wheels comes about an inch to an inch and a half closer to back of the wheelwell. Does that clear it up?, I think it's mainly because of the soft rubber bushings that the a-arm mount on.

I can visualize the location of the wheel, what I was trying to grasp was the overall system and the stresses being applied by the braking forces to cause the wheel to drag so much as to flex the control arms in a lateral direction.


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (rpaller)*


_Quote, originally posted by *rpaller* »_
I can visualize the location of the wheel, what I was trying to grasp was the overall system and the stresses being applied by the braking forces to cause the wheel to drag so much as to flex the control arms in a lateral direction. 

I think you know what I'm saying, you may be able to see it in any MK 4 under hard braking.
When you brake, the wheels and tires stop, but the car wants to keep going, and you can see it exaggerated with heavy braking power.


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## mark420v (Dec 22, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (rpaller)*


_Quote, originally posted by *rpaller* »_I can visualize the location of the wheel, what I was trying to grasp was the overall system and the stresses being applied by the braking forces to cause the wheel to drag so much as to flex the control arms in a lateral direction. 

i dont think he's talking about the actual a-arms deforming, but more the bushings compressing or something. ecs sells poly a-arm bushings, but im not too sure if they'd be worth the money and effort. maybe in conjunction with TT lca's?


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (mark420v)*


_Quote, originally posted by *mark420v* »_
i dont think he's talking about the actual a-arms deforming, but more the bushings compressing or something. ecs sells poly a-arm bushings, but im not too sure if they'd be worth the money and effort. maybe in conjunction with TT lca's?

Exactly, not the a arm, but the a arm bushings.


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## rpaller (Jan 5, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*

If the arms were deforming you would have bigger problems. It makes sense to me now. Thanks.


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## Girlsound (Apr 27, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*


_Quote, originally posted by *vespam5* »_You my friend are right, not to mention the stock a-arm use cushy rubber bushings, I am working on some that ride on pivot balls (super harsh ride on the street). We were doing a bit of testing with stock a-arms, and under full brake, with Brembos, the front wheels almost touch the back of the wheel arches!!! 

Shine can supply sherical bearings for the front lower control arms. 
http://srsvw.com/parts/partdetail.asp?pid=144


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## M this 1! (May 17, 2000)

*Re: Another proof why BIGGER brakes are NOT always best! (Girlsound)*

i can't believe this is still going on! there sure is alot of exaggerating as well. 
your wheel comes NO where near the back of the fender! i run track rubber and they can't generate enough grip to do that. i know you're loving your stuff, but keep it alittle in the accurate world.


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## alaskagreenjetta (Sep 26, 2002)

*Re: Another proof why BIGGER brakes are NOT always best! (M this 1!)*

I just wanted to add my .02 because I have noticed a huge difference in braking after I swiched over, and I am awaiting for 40" SS in the rear right now. Anyways, I swiched over to ECS stage 2 with Hawk Pads and SS lines, (one snapped so I bought them from a local race shop who had them custom made) and I have ECS cross drilled slotted in the rear, with Hawk HPS pads also. Like I said above I had the 3 piece line 2 rubber and one hard line removed and replaced it with 40" of SS line, BTW if anyone didn't know about the banjo bolts in the rear, they are 12mm not 10mm like the front. So there are some country roads near me usually only used for farm traffic, so it's pretty safe, I brought the car up to about 70ish and worked the pads to warm them up, on the way back brought it up to 100 and got on the brakes, solid smooth braking all the way down. NO ABS, no tire squall, and I have Nokians WR's that are very hard. I find that alot more comforting than worrying about ABS, kicking it, I actully had it kick off once, which was scary in 3 inches of snow. I just wanted to share this with you guys who think that stock brakes are just fine, I just have the satisfaction of knowing I have brakes that will keep me safe. I am moving up to 13" rotors this summer for looks only.


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## mark420v (Dec 22, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (Girlsound)*


_Quote, originally posted by *Girlsound* »_
Shine can supply sherical bearings for the front lower control arms. 
http://srsvw.com/parts/partdetail.asp?pid=144

how would these fare on the streets? would rough roads hurt these or are they pretty durable?


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## vespam5 (Apr 15, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (M this 1!)*


_Quote, originally posted by *M this 1!* »_i can't believe this is still going on! there sure is alot of exaggerating as well. 
your wheel comes NO where near the back of the fender! i run track rubber and they can't generate enough grip to do that. i know you're loving your stuff, but keep it alittle in the accurate world. 

It comes pretty close. Come an look!


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## M this 1! (May 17, 2000)

*Re: Another proof why BIGGER brakes are NOT always best! (vespam5)*

alright!


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## Dicardo (Dec 14, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (M this 1!)*

This post is getting old, but I finally installed Brembo's Gran Tourismo BBK w/ 2 piece floating, drilled rotor in conjuction with 20th AE rear calipers & rotors.
According to the Gtek instrument braking G's went from .5g w/ stock brakes to .94g w/ brake upgrade. The car feels lighter to steer and stops feel harder. I'm looking forward to really working the brakes once they have 1,000 miles on them.
At first blush I would say definitely worth the money. Ideally I could run them against a stock set-up w/ ugraded pads & fluids.


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (Dicardo)*


_Quote, originally posted by *Dicardo* »_This post is getting old, but I finally installed Brembo's Gran Tourismo BBK w/ 2 piece floating, drilled rotor in conjuction with 20th AE rear calipers & rotors.
According to the Gtek instrument braking G's went from .5g w/ stock brakes to .94g w/ brake upgrade. The car feels lighter to steer and stops feel harder. I'm looking forward to really working the brakes once they have 1,000 miles on them.
At first blush I would say definitely worth the money. Ideally I could run them against a stock set-up w/ ugraded pads & fluids.

Hmm sounds odd that there would be such a difference in g forces just by changing the brakes. Was ABS activating in both cases? Were the tires exactly the same with the same tread depth/same road etc? Were both measurments peak g force or an average of some sort? How did the stopping distances fare?


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## Dicardo (Dec 14, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*

LOL! I thought the same thing about the stopping forces. So, the main difference was temperature, as the first run was done during the day, and the comparison run that night. Tires & rims were obviously identical and the runs were done by the same individual.
ABS was activated in both runs. As for stopping distance itself I don't know. Any ideas on how to test run for distance?


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (Dicardo)*


_Quote, originally posted by *Dicardo* »_LOL! I thought the same thing about the stopping forces. So, the main difference was temperature, as the first run was done during the day, and the comparison run that night. Tires & rims were obviously identical and the runs were done by the same individual.
ABS was activated in both runs. As for stopping distance itself I don't know. Any ideas on how to test run for distance?

The g-tech device has a computer and an accelerometer... thats really all you need. Can your g-tech do 0-60 times? If so, it should be able to do braking distances too. The only info the computer needs is:
- speed of car just before depressing brake pedal
- brake force g's (this shouldn't be a peak number, but a running average since the g-force changes over the duration of the stop expecially with ABS activation)
- duration of deceleration event until full stop

Check this out for more info:
http://www.gtechproforums.com/forums/


_Modified by phatvw at 7:10 PM 4-26-2005_


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## Dicardo (Dec 14, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*

The g-tech belongs to the mechanic that installed my brakes, so I'll pick the device up from him, and see what I can do.
On a seperate note, anyone in Ventura County looking for an exceptional mechanic get a hold of Darrin @ Paradise Automotive Electronics in Thousand Oaks. He has installed my gauges & brakes and will do all other custom work on my car. He has fabricated brackets that were needed for clean installs, and gone above and beyond ensuring that each detail was paid attention to. On the floating rotors, he checked the torque for each bolt, found some were loose and then backed out each bolt, and torqued them, stripped my rear calipers and painted them to match the Brembo's, painted the rotor hats, etc. and although I didn't ask for that to be done, he only charged me for a fraction of the time he invested in the car. I can't say enough good things about the guy. You have to be willing to leave your car for 4 days for an install that would take most shops 1 or 2, but the results are far and above what I have seen anywhere else. He is a full service shop, that does everything from rebuilds (mostly classic customs) to metalwork and fabrication (brackets, exhausts, etc) He is NOT a metalshop but has done a great job welding and making the small things which sets his work apart. Sorry for the rant...the guy is just that good.


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## Racer_X (Jul 14, 2002)

I'm glad you're happy with the brake upgrade. I'm very skeptical about the "before" numbers. The stock brakes should be capable of at least 0.85g to 0.9g (depending on tires, maybe a little more with great tires) and shouldn't fade on a single 60mph to zero stop. To get only 0.5g, you either a frail old lady pushing the pedal or something was very wrong with the stock brakes. 
0.94g under braking is an indication of good brakes and great tires. What are you running for tires? 


_Modified by Racer_X at 7:32 AM 4-28-2005_


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## Dicardo (Dec 14, 2003)

*Re: (Racer_X)*

Yeah, the original number vs. the new seems like an incredible gulf. The stop was generated from 60 3x for each "run". The fading of the stock brakes impacted the results.
The tires are 225/40 Pirelli PZero Nero M&S. I was running Toyo Proxis 235/40 before, and they did not seem to grip as well (based on handling NOT braking). The Pirelli are much more predictable to drive on. 
I tried a panic stop @ 80, and could hear the tires squeeling as the ABS kicked off and on. The brake modulation is more my style than stock as the brakes are basically "instant on". Now, for balance, I am comparing a completely stock set-up, to the BBK set-up. Very, very different, and not a true comparison as the pad and fluid capabilities differ.


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## Geordie (Jun 22, 2001)

*Re: (Dicardo)*

Well, the reason I changed everything was that I found the overall effect of crap stock tires and stock brakes of therefore unmeasureable performance to be lacking. Basically I nearly stuffed the car into the back of some jerk who stopped at a merge, looked left, set off again then stopped again even though there was nothing coming. I'd like to have pulled him out through the window. The BAS activated but the deceleration was poor. Quite possibly this was mostly the fault of the stock tires.
I have a thing for OZ and figured that if I was blowing a load of cash on new wheels I'd rather have the PL type with the stainless lip. Actually I tried to get F1s and Chrono Evolutions but they'd just gone off the market. Sadly the 17" Classe PLs didn't make it to the US so I chose 18s with some trepidation which I think was appropriate. If I had it to do again... can't say. I haven't seen anything I'd really like more.
Tire choice was for northern California conditions. No snow, no ice, occasionally a lot of standing water and six bone dry hot months. 
Kevlar ceramic pads all round. I intended to drive relatively fast down some very steep roads on occasions. Anyone who's taken the northern entrance to Yosemite, Old Priest Grade Road ring any bells. 
The stock discs were lost in the 18" wheels, the 12'3s still leave lots of space.
So what's the overall effect? In normal use the brakes bite much harder, pedal pressures are significantly reduced. I can brake way harder than anyone wants to experience in normal driving. After losing a few thousand feet in a few minutes the brakes weren't smoking and didn't suffer any nasty after effects. The smoke was pouring from the wheels on the Taurus in front of me. Last summer I faded the pads on the same hill under similar circumstances.
For the fade resistance I can't really say if the pads or discs made the difference. More metal will certainly heat up less but the pads are also rated for very high temperatures.
For the braking effect, probably mostly the pads, but the increased radius of the disc increases its velocity past the pads and thus increases the friction and that's also a square law effect. The increased diameter also increases the braking torque for the same friction force, so we're probably looking at more like a cube law effect. 
Probably the limiting factor in normal use is the tires. Linear and lateral grip is hugely increased. 
Now about this power thing. The car still goes just as well as the 325Ci we also car pool in. The stock brakes on that, which I changed on Sunday, are vented all round and seem to be a good deal bigger at the back. He runs the same tires though on 17" rims. Anyway, I didn't notice any loss of power. Then again with the F1s I can actually accelerate hard, wet or dry, without much chance of provoking the traction control. 
Since I've had this setup I haven't hit the ABS and we've had a few panic stops due to things like people pulling into the car pool lane on I880 without looking.
So my experience is that there's no down side in terms of driving, but the braking is hugely improved in all circumstances. I can't say whether discs, pads or tires made the real difference in any particular case, but I'm not changing back to find out.
One more thing on power, measuring power by observed acceleration is all very well, but it doesn't measure the way I usually consume power. Most of my power is used defeating drag, and that's something rolling roads don't measure. Mostly acceleration is something I do twice a day, once in Oakland and once in San Jose.


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## rivethead (Nov 27, 2004)

*Re: (Racer_X)*

I am usually not a participant other than to ask questions. I thought that I would throw my 2 cents in. Everything I have read from Racer_x is almost always right on the money. Some people may not agree but that is their choice - I thought that I might give a little support to his points - and ask a question. 
When moving up in rotor size does your braking threshold prior to lockup improve? I would think that you would not end up with quite the spike just before lockup? Thanks
From Baer Brakes website on drilled and slotted rotors:
"Although crossdrilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs."
From Stoptech on Bigger Front Brakes and Rear Brake Bias
Well, let's look at why we upgraded the front brakes in the first place. Contrary to popular belief, the real reason sports- and racing cars use big brakes is to deal with heat. Period. There has been a bunch of stuff published which will disclaim this, but when you look at the braking system from a design standpoint, making them 'bigger' doesn't fundamentally do anything for stopping distance. It's all about the heat. So, you upgraded the front brakes because of thermal concerns but as a hidden surprise got a shift in brake bias. As a band-aid to this condition, you now spend thousands more on a rear brake upgrade because the front system was not sized correctly in the first place.


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## Dicardo (Dec 14, 2003)

*Re: (rivethead)*

The following is my opinion, and should not be construed as fact.
The BBK is easier to modulate (keep in mind both front & rear were modified 13.1"F/10.1"R). Because the brakes feel is "instant on" there is a broader window where your brake pedal input is able to be felt actuating the brakes. Therefore, since the braking force comes on earlier in the stopping cycle, I am able to control the braking more easily. In other words, I'm not modulating the brakes @ their thresh-hold, but rather in their initial travel. And because they cool more quickly, and simply operate at lower temperatures (relative to what the stock brake temperature would be under the same conditions), they behave more consistently.
Also, the steering feels lighter and any loss of power as a result of the larger rotor, I haven't noticed. Just the benefit to steering feel compensates for 1/2 the value of the kit.


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## 130_R (May 24, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (Racer_X)*


_Quote, originally posted by *Racer_X* »_Still, if you want maximum performance, you want the *smallest* brakes that you can use that won't fade in your driving situation(s) and the *smallest* (or almost smallest) wheels that clear those brakes. 

This is not always true either, you want the best compromise between size and rotating mass in a braking system. 
If 9 inch and 11 inch rotor have the same mass, swept area,and are using the same caliper; is smaller really better?


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (130_R)*


_Quote, originally posted by *130_R* »_This is not always true either, you want the best compromise between size and rotating mass in a braking system. 
If 9 inch and 11 inch rotor have the same mass, swept area,and are using the same caliper; is smaller really better?

Yes, the 9" rotor is better because it has a lower moment of inertia. That means it is easier to get it spinning and stop it spinning even though it has the same mass as the 11" rotor.
You have to assume that the 9" rotor meets thermal capacity requirements and the overall brake torque requirements are met by clamping force and coefficient of friction. Forget about the 11" providing more brake torque - its a small difference compared to properly chosen brake pads.
Don't understand _moment of inertia_? Think figure skaters and look it up on google.



_Modified by phatvw at 7:58 PM 5-2-2005_


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## 130_R (May 24, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_
Yes, the 9" rotor is better because it has a lower moment of inertia. That means it is easier to get it spinning and stop it spinning even though it has the same mass as the 11" rotor.
You have to assume that the 9" rotor meets thermal capacity requirements and the overall brake torque requirements are met by clamping force and coefficient of friction. Forget about the 11" providing more brake torque - its a small difference compared to properly chosen brake pads.
Don't understand _moment of inertia_? Think figure skaters and look it up on google.


Moment of inertia is a big time thing man, do you have any calculations showing the intertia difference between a 9" and 11" rotor that weigh 11 lbs. each?


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (130_R)*


_Quote, originally posted by *130_R* »_Moment of inertia is a big time thing man, do you have any calculations showing the intertia difference between a 9" and 11" rotor that weigh 11 lbs. each? 

If you model the brake rotor as a solid cylinder of uniform mass distribution, then the formula is
1/2*M*R^2
where M=mass (lets assume the 11 lbs for simplicity)
R^2 = radius squared (lets work in feet for simplicity 9" diameter = 0.375 feet, 11" diameter = 0.458 feet)
So for a 9" rotor, the moment is:
1/2*11*0.375^2=0.77 lbs-feet^2
For an 11" rotor the moment is:
1/2*11*0.458^2=1.15 lbs-feet^2

So when you go from a 9" to an 11" diameter, as a percentage, the moment of inertia changes by a whole lot!!!!! 0.77->1.15 is about a 50% increase. Now the actual rotor isn't solid, and isn't uniform mass, so these aren't exactly correct, but this gives you a ballpark idea.



_Modified by phatvw at 11:18 AM 5-5-2005_


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## Lamothe (Jun 6, 2005)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

think about it dude
hold a 10 pound weight and try to a regulr type bicepe curl were your lifting are pivoting at your elbow, now do the same thing with a 10 pound weight except use your shoulder with a locked elbow. it creates more leverage. same idea (roughly i guess) as with having a larger rotor


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## Krazee (Jan 26, 2003)

ok, I understand everything about moment of inertia, and how yes, it would take more effort to spin something larger, thus more power. This is why drag racers actually down size brakes. They want less drag when accelerating.
But given that, the 11" brakes would be better under constant braking as the increased surface area means it can handle more heat, since it can disperse more of it, since it has greater surface area. If you increase the surface area, you can then increase the pad swept area. Now the pad is larger, increased at the same rate as the rotor. So actual braking would be better.
Yes, you sacrifice accelerating, probably some handling with the larger rotor, but braking performance is also increased.
Which leads me to my next question. Since one wants more surface area to increase heat capacity and in turn heat dissipation, then why do race cars have drilled rotors? Honestly? _"To allow them to cool faster."_ But again, you want more surface area. And then the same for slots. _"To allow gases between pad and rotor to escape, thus a cleaner surface area."_ Again, surface is reduced, though not as much.
Im puzzled, honestly. Drilled and slotted definitely looks cool, but there has to be a viable (physics related) reason why race cars, BMW, Ferrari and Porsche (to name a few) drill their rotors.


_Modified by KrazeeKorrado13 at 12:30 PM 7-6-2005_


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## Stewz-GTI (Feb 16, 1999)

*Re: (KrazeeKorrado13)*


_Quote, originally posted by *KrazeeKorrado13* »_
Im puzzled, honestly. Drilled and slotted definitely looks cool, but there has to be a viable (physics related) reason why race cars, BMW, Ferrari and Porsche (to name a few) drill their rotors.

_Modified by KrazeeKorrado13 at 12:30 PM 7-6-2005_


Lets not go there







this has been discussed to death.


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## NYC20AE (Jul 2, 2003)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*


_Quote, originally posted by *alexb75* »_
Yes it is!
It just bugs me that people come here and try to go bigger and BIGGER and *BIGGER* and they don't believe that it's not really doing anything for them and if someone who knows tells them (like for a long time Racer_x) they just say, "so why XYZ did it!"
Oh well, if there are not people like that, many companies would be out of business









We have been bred to think that bigger is always better. Back in the day it was carburetors, and now it's big brakes and big tires. I remember my brother bought a 79 Camaro with an 850 Double Pumper on a 305ci small block!







I'd continue with the story if I thought there was anyone here who might know what an 850 Double Pumper is....







I'm Old.


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## Krazee (Jan 26, 2003)

*Re: (Stewz-GTI)*


_Quote, originally posted by *Stewz-GTI* »_Lets not go there







this has been discussed to death.

Well, I stand corrected. Audi R8s do not have drilled OR slotted rotors.
And there is one BMW 3 series with what looks like Stasis rotors and their little 1/2 moon etchings. But no drilling.


















_Modified by KrazeeKorrado13 at 11:55 PM 7-7-2005_


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## RPTOFNDR (Jan 15, 2003)

Cross Drilling allows for rotor expansion when brought up to above operating temps.The metal will expand,the holes will allow the metal to expand. But NOT allow the rotor to warp.
Slotted provides an escape median for rotor/pad gassing.


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## Krazee (Jan 26, 2003)

Yes, we know the theory behind drilled rotors.
But then race cars would run them.


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## osbornsm (May 7, 2004)

*Re: (KrazeeKorrado13)*

OKAY, since there's so many "experts" around here. I have a BIG problem with my brakes.
*Problem:*
Motul 600 fluid is boiling
*Car Specs:*
Carbotech P+ pads
Mobul 600 Fluid
Stainless Lines
Brake Ducting
R-Compound tires
17x8 Superleggera
What can be done about my fluid ??


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## phatvw (Aug 29, 2001)

*Re: (osbornsm)*


_Quote, originally posted by *osbornsm* »_OKAY, since there's so many "experts" around here. I have a BIG problem with my brakes.
*Problem:*
Motul 600 fluid is boiling
*Car Specs:*
Carbotech P+ pads
Mobul 600 Fluid
Stainless Lines
Brake Ducting
R-Compound tires
17x8 Superleggera
What can be done about my fluid ??


So there is too much heat being generated.
You need one or more of the following:
bigger rotors and wheels to increase the heat capacity
weight reduction to reduce the amount of energy being converted to heat. (Lets assume that your speeds will remain the same for now.)
some type of material which is better at dissipating heat than iron for the rotors
same better material for the calipers


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## osbornsm (May 7, 2004)

*Re: (phatvw)*


_Quote, originally posted by *phatvw* »_So there is too much heat being generated.

You got that right !!

_Quote, originally posted by *phatvw* »_You need one or more of the following:
bigger rotors and wheels to increase the heat capacity
weight reduction to reduce the amount of energy being converted to heat. (Lets assume that your speeds will remain the same for now.)
some type of material which is better at dissipating heat than iron for the rotors
same better material for the calipers

- Bigger wheels = more heat capacity







Doesn't that add more rotating mass and worsen the problem at hand?
- What options for rotor material are available? Never knew i had options.
- And yea, only way i'm getting better calipers is the Stoptech / Alcon BBK. Don't have the coin for that right now.


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## phatvw (Aug 29, 2001)

*Re: (osbornsm)*


_Quote, originally posted by *osbornsm* »_You got that right !!
- Bigger wheels = more heat capacity







Doesn't that add more rotating mass and worsen the problem at hand?
- What options for rotor material are available? Never knew i had options.
- And yea, only way i'm getting better calipers is the Stoptech / Alcon BBK. Don't have the coin for that right now.

Bigger rotors generally require bigger wheels. If you get expensive lightweight wheels, you can keep your moment of inertia close to its current state. This is costly, however.
For rotor material, you can look to some of the F1 and Le Mans technology. I think they use some kind of ceramic material and some special brake pads. You do have options, its just going to cost you!
I would first look to a larger 2-piece rotor with better internal vane design and then optimize your ducting solution for that particular rotor.

Oh there is also a technology where you have two rotors, two caliper, and 4 brake pads on each wheel... Can't remember the company that makes that setup. It wasn't popular becuase of the weight... but the heat gets distributed better.


_Modified by phatvw at 1:10 PM 7-10-2005_


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## osbornsm (May 7, 2004)

*Re: (phatvw)*

Thanks Phat ! ANybody else got any ideas out there ?
- - - - - - - - - - - - - - - - - - - - - - - - 
Problem:
Motul 600 fluid is boiling
Car Specs:
Carbotech P+ pads
Mobul 600 Fluid
Stainless Lines
Brake Ducting
R-Compound tires
17x8 Superleggera
What can be done about my fluid ??
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 



_Modified by osbornsm at 5:25 PM 7-10-2005_


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## NOVAdub (Jul 28, 2003)

*Re: (osbornsm)*

I think phatvw abotu covered it. If you dont have th coin for a brake upgrade you can rule out exotic materials. They are $$$$$$. Does ECS have 2 pc rotors for the R yet? That would be a good place to start, and you could always get even higher temp brake fluid like castrol SRF. Its not cheap though, last time I checked it was $80/liter, but it boils at 600deg.


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## osbornsm (May 7, 2004)

*Re: (NOVAdub)*


_Quote, originally posted by *NOVAdub* »_...you could always get even higher temp brake fluid like castrol SRF. Its not cheap though, last time I checked it was $80/liter, but it boils at 600deg.

ECS has 2 piece for the R32. That's prolly the best bet right now. And castrol SRF has the SAME dry boiling point as the MOTUL 600 that i use right now. So no real advantage there.


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## phatvw (Aug 29, 2001)

*Re: (osbornsm)*

BTW these are the exotic materials I was talking about:
http://forums.vwvortex.com/zerothread?id=2082776


----------



## genxguy (May 26, 2002)

*Re: (osbornsm)*

Ah, if you're boiling Motul 600, that's some pretty heavy-duty braking there... I've braked repeatedly from up to 120 in my car on the track and never had the fluid boil on me. Can you tell us a bit more about the conditions under which you have this happen?


----------



## osbornsm (May 7, 2004)

*Re: (genxguy)*

Usually 110 > 40 ish is the max speed i will scrub off before any turn.
Tracks are gingerman and Joliet Autobahn. About 1.5 - 2 miles long and approx 8 braking zones per course.
It seems not to matter which track or if i have long or short braking zones. The rotor simply can not dissapate the heat fast enough. (_see vehicle specs above_)


----------



## genxguy (May 26, 2002)

*Re: (osbornsm)*

I see. And exactly what kind of pedal feel are you experiencing, and when during the braking are you seeing this? Are you sure that it's boiling fluid and not some other brake component that's failing?
I'm not saying you don't know what you're talking about, it's just been that from my experience it's very very hard to get Motul 600 to boil. Not only me, but ppl I know who club race use it as well, and they never had boiling issues.
When was the last time you flushed your brake fluid? Motul 600 should be changed every 2-3 track events OR every year, whichever is sooner. It's very hydroscopic, so it doesn't have a long shelf life either. If you're using old 600, whether on the shelf or in the car, that could result in boiling the fluid.


_Modified by genxguy at 9:56 AM 7-19-2005_


----------



## osbornsm (May 7, 2004)

*Re: (genxguy)*


_Quote, originally posted by *genxguy* »_And exactly what kind of pedal feel are you experiencing? Are you sure that it's boiling fluid and not some other brake component that's failing?

Pedal feel is close to oem until I run a 20min session. Then they're way worse. They still stop fine, just require approx 2in more of pedal travel to accomplish the same effect.
The only other cause for brake trouble that I see would be the tapering of the pad under track conditions. Pad height varies 1-2 mm between leading / trailing edge. Stupid oem calipers









_Quote, originally posted by *genxguy* »_When was the last time you flushed your brake fluid? If you're using old 600, whether on the shelf or in the car, that could result in boiling the fluid.

I bleed my fluid before and after every event. Sometimes i bleed them between run groups at the track !! And even if the Motul is at it's "wet" point, that is still 420 F. Should that not be enough for most applications??


----------



## phatvw (Aug 29, 2001)

*Re: (osbornsm)*

When you bleed at the track do you actually see bubbles come out?
Also, have you considered upgrading the caliper guide bushings to Tyrolsport's brass replacements? They even out the pad wear and improve pedal feel a little bit. I think he might still be working on the R32 bushings but you should call him and maybe you can be a beta tester








http://www.tyrolsport.com



_Modified by phatvw at 5:08 PM 7-20-2005_


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## genxguy (May 26, 2002)

From your description, it sounds like your pads are overheating, not your fluid. Have you tried changing your P+ to track pads? Motul 600 really should not boil under the circumstances you're talking about.


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## osbornsm (May 7, 2004)

*Re: (phatvw)*


_Quote, originally posted by *phatvw* »_When you bleed at the track do you actually see bubbles come out?
 
Sometimes, it's hard to tell. When you're in a big ol hurry.

_Quote, originally posted by *phatvw* »_Also, have you considered upgrading the caliper guide bushings to Tyrolsport's brass replacements?
 
Ha ha... i am a beta tester. See review here
*And Josh.... *wouldn't a overheated pad keep the pedal pressure the same? Why would it require more pressure for same result?
- Why don't you think Motul would boil under these conditions?
- I thought P+ were track pads?
- Sean


----------



## phatvw (Aug 29, 2001)

*Re: (osbornsm)*


_Quote, originally posted by *osbornsm* »_ 
Ha ha... i am a beta tester. See review here



Dude!!!!!!!! You are _THE_ R32 guy on here aren't you!!!
So I take it you're not getting all the advertised benefits of the tyrol kit? Or is the tapered wear from before you swapped bushings?
Hawk HP+ is most definitely not a top-end track pad. It is advertised as a track/street pad. I believe Ferodo DS2500 has similar friction levels and even better fade resistance so you might try those. Or maybe step up to a true track/race only pad like DS3000.
http://forums.vwvortex.com/zerothread?id=1740420
When the pads begin to fade, the coefficient of friction goes down, so to get the same amount of brake torque, you need to apply more pressure aka press the pedal harder. When the fluid fades, the pedal gets mushy, and you may have to press the pedal in further, but don't have to press as hard as when the pads fade.


_Modified by phatvw at 11:35 PM 7-20-2005_


----------



## reflexgti (Dec 19, 2000)

*Re: (phatvw)*

I think osbornsm is using the P+... as in Carbotech Panther+ which is indeed a track pad. I consider the P+ to be much better than the DS2500 and half way to the DS3000.
Steve


----------



## genxguy (May 26, 2002)

*Re: (osbornsm)*


_Quote, originally posted by *osbornsm* »_ *And Josh.... *wouldn't a overheated pad keep the pedal pressure the same? Why would it require more pressure for same result?
- Why don't you think Motul would boil under these conditions?
- I thought P+ were track pads?
- Sean

Josh?? Who's Josh??








So you have the caliper kit from Tyrolsport; you change brake fluid, or at least bleed, for each event; and you have steel-braided lines. That would leave either the rotors or pads as the culprit.
I just re-checked the Carbotech website. They do list P+ as 'beginner-novice lapping day and HPDE pads'. But your car is 3400lbs without the driver, so you should take that into account. Lap after lap, as you gain more speed and skill, you could be overwhelming those 'light track usage' pads. Here's another person that seems to be experiencing similar issues with the P+: http://forums.vwvortex.com/zerothread?id=2095397 
You said your pedal feel stays close to OEM, but you just have to push down farther. If it felt mushy, then I'd say fluid. But if it stays same, just the amount of push changes, then that to me sounds like pads. phatvw said above, when the pad overheats the cof goes down, and you need more pressure i.e. more pedal travel to get the same braking.
Another reason I don't think it's the fluid is because Motul 600 is used by several ppl I know whose cars are about the same or heavier than our cars. They are instructors and club racers, much faster than you or I, I bet. When properly flushed and changed, Motul 600 never boiled for them. Like you said, the boiling point numbers on the fluid should be more than sufficient for HPDE use.
FWIW, I personally use Cobalt Spec VR which according to specs is comparable to Carbotech XP. A friend of mine who tracks a Civic (2300lbs) was recommended Spec B by Cobalt, which is closer to P+ specs. I'm just extrapolating here, but given these, and other facts, I would think your 3400lb car would be better matched to a higher-spec pad.
edit: One of those club racers I was talking about is also a vendor for Carbotech. I'll ask him about this.


_Modified by genxguy at 10:01 AM 7-21-2005_


----------



## osbornsm (May 7, 2004)

*Re: (genxguy)*

Whoops sorry bout the josh thing... was doing 2 posts at once there









_Quote, originally posted by *genxguy* »_That would leave either the rotors or pads as the culprit, you could be overwhelming those 'light track usage' pads. 

Yea, trying the XP9 front and P+ rear for next time I think. That should just about do it I hope!

_Quote, originally posted by *genxguy* »_If it felt mushy, then I'd say fluid. But if it stays same, just the amount of push changes, then that to me sounds like pads. phatvw said above, when the pad overheats the cof goes down, and you need more pressure i.e. more pedal travel to get the same braking.

But the pedal does feel mushy, but i think it's mostly because of the taper on the pads. So it's difficult to diagnose other problems when you can't get a "clean" feeling pedal to start with. So i'm diagnosing as best as possible for now. I think it's cooking pads and the taper mostly. Never had "foot to the floor" squishy.
I hope the problem is not just ALL from pad taper. That's f'ed up.
Where did you get specs to compare Cobalt to Carbotech pads?
Look forward to your Carbotech feedback, thanx !


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## genxguy (May 26, 2002)

The specs for Cobalt and Carbotech pads are in the link that phatvw posted above. Cobalt doesn't have R32 pads, but I'm sure Carbotech can supply you with some. Look for 'magnetic1' on either Audiworld or Vortex, he's the vendor I was talking about.


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## tatge (Sep 20, 2001)

*Re: (genxguy)*

I was thinking about the 4 piston Boxter Calipers with the 12.3" ECS floating rotors to replace my TT upgraded brakes until I read this thread. now I don't know what to do.
http://forums.vwvortex.com/zerothread?id=2106604
I want to be able to use 16" wheels, that's why I like the Boxter setup.


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## NOVAdub (Jul 28, 2003)

*Re: (tatge)*

From reading your other post is sounds like you might need some new fluid. WHen was the last time it was flushed? What type of fluid are you using? Did you try bleeding the brakes?


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## Stewz-GTI (Feb 16, 1999)

*Re: (tatge)*


_Quote, originally posted by *tatge* »_I was thinking about the 4 piston Boxter Calipers with the 12.3" ECS floating rotors to replace my TT upgraded brakes until I read this thread. now I don't know what to do.
http://forums.vwvortex.com/zerothread?id=2106604
I want to be able to use 16" wheels, that's why I like the Boxter setup.

I posted about your issue in your other post, but to the comment of confusion on the "bigger" issue take into consideration that a lot of people have different opinions and experiences. 
Some that have posted in here may have no experience just an opinion on what they heard. 

Take a minute to figure out what _you_ want out of your brakes... 
I would think an Auto-x guy would want something that was really light for good steering response as you are always ontop of the wheel.
You need to reach operating tempature from go, you don't get warm up laps.
You need high bite, with a quick release as you are always on and off the pedal to settle for a tight turn.
Take those points and match them up to a kit or make your own. 
Hope that helps, else try this ->







and re-read the whole thread.


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## ea187 (Apr 23, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

we both live in vancouver, i'll take you for a ride in my car and you can tell me if the bigger brakes don't do anything. they are night and day over stock


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (ea187)*


_Quote, originally posted by *ea187* »_we both live in vancouver, i'll take you for a ride in my car and you can tell me if the bigger brakes don't do anything. they are night and day over stock









But so are better brake pads and sticky tires. And guess whats cheaper...


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## ea187 (Apr 23, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_
But so are better brake pads and sticky tires. And guess whats cheaper...










yes and now add that with bigger brakes and figure what it's like


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (ea187)*


_Quote, originally posted by *ea187* »_
yes and now add that with bigger brakes and figure what it's like

Yeah we've already gone through this in the other thread how the brake rotor size doesn't really affect the actual brake torque output that much - at least compared to the pad coefficient of friction: http://forums.vwvortex.com/zerothread?id=2068629 (Check out ECS's own chart and my calculations for oem brakes with better pads near the bottom!)
The main benefit to bigger rotors is heat capacity and the ability to run lower-temperature pads catered to the pedal feel you want. Also, those big multi-piston calipers just give you pedal feel - very few of the kits out there actually give you much more clamping force than what the oem system already has. I have tried several setups on different cars, and while the big rotors and big calipers feel very nice, and have great feedback, they don't have the best bang-to-buck.


_Modified by phatvw at 1:33 AM 7-26-2005_


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## osbornsm (May 7, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*


_Quote, originally posted by *phatvw* »_I have tried several setups on different cars, and while the big rotors and big calipers feel very nice, and have great feedback, they don't have the best bang-to-buck.

Well, when your pads are being tapered like mad it looks like a viable solution don't ya think ?


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## Stewz-GTI (Feb 16, 1999)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

*Would everyone kindly read the following article from Grassroots Magazine and then return to this post. *
http://www.teamscr.com/grmbrakes.html


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (Stewz-GTI)*

Great article!
http://****************.com/smile/emthup.gif


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## clyde (Aug 31, 1999)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

Quote: "they said it is because of the rotational mass of the bigger brakes"
Probably meant the mass of the larger disks. Much of the mass is the heavier calipers, which don't rotate…


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## Jezztor (Nov 9, 2002)

The most important quote on TeamscR relating quite aptly to STOPTECH brakes:

_Quote, originally posted by *teamscr.com/bigbrakekits.html* »_
Unlike the "if it works on brand P, it must work on your car" approach, at STOPTECH all brake upgrade kits are designed with the characteristics of the original braking system taken into account to minimize these differences. This is the reason that when you order a STOPTECH big rotor upgrade kit the new caliper bores may actually be smaller than the units you are replacing to "balance the equation." This is just one way in which our engineers attempt to retain the original system’s P-T and P-V integrity. Sure, it's not one-size-fits-all, but neither is your car or your driving style. Why should you expect any less from your brake upgrade?


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## turbizznatch (Apr 16, 2004)

*Re: (Racer_X)*

You are the bomb diggitty. College physics all over again. I love this thread.


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## Jezztor (Nov 9, 2002)

If anyone is interested in more physics, please read this thread on calculations I did:
http://forums.vwvortex.com/zerothread?id=2536336
Thanks


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## Rdoppie (Dec 9, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (Stewz-GTI)*


_Quote, originally posted by *Stewz-GTI* »_*Would everyone kindly read the following article from Grassroots Magazine and then return to this post. *
http://www.teamscr.com/grmbrakes.html


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## lookin4avw (Apr 28, 2004)

*Re: Another proof why BIGGER brakes are NOT always best! (Rdoppie)*

I'm not sure if this was mentioned earlier but in the 'Big Brake Math' section of this faq you can see actual results which prove just how tiny the loss of power is. It's a good read and I think before anyone takes this hear say for truth you should look at the physics behind whats really happening.


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (lookin4avw)*


_Quote, originally posted by *lookin4avw* »_I'm not sure if this was mentioned earlier but in the 'Big Brake Math' section of this faq you can see actual results which prove just how tiny the loss of power is. It's a good read and I think before anyone takes this hear say for truth you should look at the physics behind whats really happening.

Of course the losses are calculated for real-world street tests where the car has orders of magniture more kinetic energy than the rotors/wheels.
If you are measuring engine power on a dyno, then only the drivetrain is rotating and rotors and wheels will have a much more significant impact on the engine dyno results


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## IJM (Jul 30, 2001)

*Re: (osbornsm)*


_Quote, originally posted by *osbornsm* »_
Pedal feel is close to oem until I run a 20min session. Then they're way worse. They still stop fine, just require approx 2in more of pedal travel to accomplish the same effect.

I had the EXACT same problem when running DS2500 up front at the track. I switched to Carbotech XP10, but it still gets mushy with lots of travel. I wonder if it has something to do with VW master cylinder design.


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## crapomaticvr6 (Aug 19, 2007)

*Re: Another proof why BIGGER brakes are NOT always best! (alexb75)*

my view is this.
with only basic bolt ons and regualr street driving your stock brake sizes are more than sufficient you just need better pads and rotors and those awesome 50 hp red calipers







at this point big brakes are more for show imho. Now when it comes to real racing not back alley street racing but real brake demanding track racing then I can see big brakes along with other brake mods. ( lines fluids ect..ect ) being more realistic as a true upgrade. As far as a loss in hp well b/c of the numerous different combinations of pad rotor tire wheel size wheight ..on and on and on combos that stuff honestly goes over my head. So I cannot give an educated or compitent answer on this....But I do now that if nothing else youll look cool with big ass rotors and red calipers that say brembo on them










_Modified by crapomaticvr6 at 7:17 PM 8-31-2007_


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## BXVW (Aug 23, 2005)

*Re: Another proof why BIGGER brakes are NOT always best! (dcomiskey)*

cat back exhaust doesnt do anything on n/a cars? why do they sell so many of them like that? what should be done to get power from a vr6 exhaust


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## phatvw (Aug 29, 2001)

*Re: Another proof why BIGGER brakes are NOT always best! (BXVW)*


_Quote, originally posted by *BXVW* »_cat back exhaust doesnt do anything on n/a cars? why do they sell so many of them like that? what should be done to get power from a vr6 exhaust

Wrong forum. This is about brakes.


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## Kit_L (Jun 10, 2009)

*Re: Another proof why BIGGER brakes are NOT always best! (phatvw)*

This thread has some of the worst information i've ever had the misfortune to read through, i'm no guru but there are some utterly false statements in this thread.
There are entire books published on the subject, so i'm not even going to try explain concepts here.
Really rough overview:
Basically, braking has be set up to be proportional to the car/bike/truck..etc intended purpose, one of the most important parts of the design process is the expected average operational temperature. Fundamentally, different brake pad compounds provide different amounts of friction, at different temperatures, much like tyres for instance.
It is right to say the most important part of a brake set up is the pad choice, then brake fluid/hoses on a fast road set up.
On a race car heat dissipation to prevent fade, premature wear/warping the discs is of huge importance also the clamping pressure of the callipers has to be progressive, predictable for pedal feel to set up the pedal box hydraulics, also it needs to be greater to make use of racing compound tyres.
This is achieved by having bigger discs and larger callipers with a greater pad surface area.
To the point of the thread, bigger brakes are not necesserily better, it just depends on their application.
On the street... imho it is most dependant on actual weight of the car and the style of driving











_Modified by Kit_L at 11:57 AM 10-3-2009_


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## Hedgehodge (Nov 7, 2008)

I'm glad I found this thread before I bought a BBK  I wont lie though, they do look very nice but then again so would any rotor thats not rusty and shiny painted calipers. 

Annoying though that I have a set of 15 winter tires and 17 summer. And wtf does less tire cost more different compounds my ass, still the same rating.

Seeing as how I have different sizes I probably want to stay with something that fits in 15's anyways; would it just be a good ideas to buy new:



New Stock size fronts (drilled or sloted also don't matter right?) or should I just get the 337 stock ones
New pads for front and rear (give me an awesome brand that doesnt sound like ****/dirty/nice stopping power) If I have to pick one I rather just have dirty brakes if they stop and dont scream.
Upgrade rear rotors to 10.1 (will this still fit 15) http://www.germanautoparts.com/Volkswagen/Golf/Brake/74/16 ate rotors, I like anti corrosion 
Should I get better brake fluid than the OEM can from VW?


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## VW-Pssst (Jun 10, 2007)

Hedgehodge said:


> I'm glad I found this thread before I bought a BBK  I wont lie though, they do look very nice but then again so would any rotor thats not rusty and shiny painted calipers.
> 
> Annoying though that I have a set of 15 winter tires and 17 summer. And wtf does less tire cost more different compounds my ass, still the same rating.
> 
> ...


as stated multiple times this thread has many misleading statements...

My biggest observation with my BBK is at higher speeds. When going 70+ mph and slamming the brakes, the car freaking stops, Even 100+ and slamming the brakes your cars gonna stop. and fast! bigger rotation of the rotor and bigger pads and 4 pistons to stop is a huge increase of clamping power over your stock brakes. Its common sense on why it stops faster...

The brake fluid differences is temperature, so yes you can change it if you'd like but the DOT ratings are how much heat they can handle...

But yes I dont get how the less tire is more expensive >_< And having to change wheel sizes for winter does suck. But I do love my porsche 4piston brakes and 12.3" rotors. Much more of an improvement over stock. And gotta love the big Red calipers that read porsche nice and pretty


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## GTijoejoe (Oct 6, 2001)

VW-Pssst said:


> as stated multiple times this thread has many misleading statements...
> 
> My biggest observation with my BBK is at higher speeds. When going 70+ mph and slamming the brakes, the car freaking stops, Even 100+ and slamming the brakes your cars gonna stop. and fast! bigger rotation of the rotor and bigger pads and 4 pistons to stop is a huge increase of clamping power over your stock brakes. Its common sense on why it stops faster...
> 
> ...



Keep in mind, only because you have more pistons or larger pads doesn't mean you have more clamping power. You need to compare the overall area of the pistons and pad height. BBK's normally reduce the piston area because of the increase in effectiveness from the larger brake disk (effective radius dimension). BBK's are trying to balance brake gain by giving you a larger disk and stiffer sometimes lighter caliper in return.
This of course will not always balance out because of the increased rotational inertia, so you need to understand the physics of what you’re doing before you weigh the advantages etc.

*If you want it in a nut shell with 100% factual information here it is:*
In any brake setup you are always limited between the frictional forces between the ground and tire interface. Every single OEM brake setup will be able to lock your tires ~1g stop, putting a different brake setup on your vehicle will not do anything other than provide more brake torque. That increased brake torque will do nothing if your tires are already locked, its useless. 

So by upgrading your tires you can increase the available friction (given by the constant weight of your vehicle, we are neglecting down force etc. to keep concepts simple) and the increased brake torque from your brake system will allow for an increased decel 1.0+g. Now this is the general concept to understand brake torque and the threshold of locking tires. (now for some of you racers that already know that some % slip is actually good for the best frictional mu... we are going to ignore all that for now  )

On to increasing your brake torque:
There are a various of ways to do this as many of you know, we are only going to entertain the corner brake system, no pedal/booster/master cylinder speak here, these generally only change effort by the driver.
To increase brake gain (torque) increasing your piston area will give higher clamp loads, increasing your effective radius (disk diameter) will give you higher moment arm for torque calculation Friction Force X moment arm = Torque. 
... and by increasing your pad's frictional mu characteristics will give you higher friction forces. Friction force = Clamp force x mu

Now to put things into perspective:
In general, the only reason to increase your disk size is to compensate for heat energy. The increased energy comes from weight and speed, kinetic energy = 1/2*mass*velocity^2
Larger disks have increased rotational inertia, so limiting how large of a disk or mass you need is best by design. If you aren’t increasing your Vmax or doing multiple high g stops consecutively than most likely you don’t need larger disks.

What does heat do to your friction?
Friction characteristics changes with temperature, there is no such thing as single mu value for a pad. For street pads they are stable at low temperatures, giving good friction characteristics which often will dwindle off and decrease as temp increases. Race pads have high friction values but also need ample temperature to achieve those ranges, meaning, low temp conditions, race pads may have much lower mu values than street pads, which is exactly why race pads are not recommended for street applications…. You may go through that first stop sign or if on the free way that sudden stop may not be so sudden as the mu value is very low.

These temperatures for street vs race pads are in certain ranges, so depending on your application you want to stay within the temp range, this even changes from track to track etc… or auto-x. Many times people feel they need race pads for auto-x, but truth is, you still are not in the temperature range to justify race pads, your Vmax decels are very low compared to 150mph track speeds, and at the beginning of an Auto-x there is no warm up period (generally)

So IMO, if you want to start brake modifications.
1st: change your tires 
2nd : change your pads, if you are dealing with fad and glazing, try yet another pad
Many OEM pads are NAO (non-asbestos organic), going up the chain…than low metallic, semi-metallic, than ceramics to deal with heat are the logical steps. Keep in mind metallics tend to dust, anything that has a high mu will eat your disk, this will also cause rusting and deposits on wheels.
3rd: Need increase brake torque, change your caliper’s piston area
4th: You need heat management, look in to brake ducting or increase your disk size, thickness vs diameter

This is a basic understanding, should help you understand why it is possible to increase stopping distance and decrease HP from the OP’s findings. Brake system’s are all about optimization, there are always trade offs, no perfect system exists. If you have other questions about things not discussed, just ask :thumbup:

Remember, brake performance and feeling are to different things which commonly get mixed up. Some is objective the other subjective, you can measure both, only one will prove which is better.


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## evol_mk3 (Dec 27, 2001)

Couldn't some bigger brakes just be crap?

Why would companies like Audi, Porsche, Lambo, etc., put big brakes on their cars... Or why do race cars put bigger brakes on? To go slower, really?

So, if I took my stock VR and did a brake test against a new Porsche, my VW should win? Or if I put smaller brakes on the Porsche it will brake faster????


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## GTijoejoe (Oct 6, 2001)

evol_mk3 said:


> Couldn't some bigger brakes just be crap?
> 
> Why would companies like Audi, Porsche, Lambo, etc., put big brakes on their cars... Or why do race cars put bigger brakes on? To go slower, really?
> 
> So, if I took my stock VR and did a brake test against a new Porsche, my VW should win? Or if I put smaller brakes on the Porsche it will brake faster????


The top speed and/or the weight of those vehicles is the factor... when you are taking in kinetic energy and squaring the velocity, it has a extreme impact from say a 115mph to 150+mph.
Lambo's for example are not very light, as well have top speeds 180+mph... why do you think motorcycles can have such drastic brake zones? Do they have huge brakes comparable to your car? of course not, its because they weight less than 500lbs.

Also I should add, the duty of the intended vehicle... a porsche/lambo/supercar category is intended for track duty, so instead of one high G stop, it is designed to take several back to back, significantly increasing the energy loading on the brake system.
Braking peformance has everything to do with energy transfer :thumbup:

In the category of race, many race car depending on class actually have very small brakes. Its in the benefit of pure race to become the lightest, smallest, highest cooling effectiveness as possible... big brakes are heavy. Every see the size of the wheel on alot of cars? There is only so big of a disk you can fit into a 15" wheel. Classes which state no use of carbon, than you have no choice but to use a huge mega 14-16" rotor for heat capacity....

Hope that helps your understanding


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## frskniam (Nov 7, 2006)

evol_mk3 said:


> Couldn't some bigger brakes just be crap?
> 
> Why would companies like Audi, Porsche, Lambo, etc., put big brakes on their cars... Or why do race cars put bigger brakes on? To go slower, really?
> 
> So, if I took my stock VR and did a brake test against a new Porsche, my VW should win? Or if I put smaller brakes on the Porsche it will brake faster????


I would also like to add that they do it because big brakes look pretty. Just like if you are after performance, you get as light of wheels as possible, so too with brakes... And in the end you have to make compromises somewhere.


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## Hedgehodge (Nov 7, 2008)

I was just curious if my car should go from what its at to the bigger rear rotors since I'm going to change them anyways. The aniv. edition ones. I just had the rear calipers replaced and rather not replace them just yet. 

Maybe upgrade my rears to 10" and leave the front ones the same size and then upgrade the rear calipers with that tyrol kit and I should be gtg with better pads and bleeding of the brakes? At the moment I only have aprchip/exhaust/TIP/17"summer/15"winter and a few other things but still stock turbo. Even if I went stage 3 turbo it would be a good idea for me to stick with this too?

Thanks for the response, learned a lot just it all still confuses me 

v/r
Semi Sober Hedgehodge


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## GTijoejoe (Oct 6, 2001)

that should probably be discussed in another thread, most likely for your driving stock disk size and bushing kit should suit what you need for the time being:thumbup:

Generally, you understand the specs of what you have compared to what you want to change too, disk size, caliper size etc... than you can understand if you're changing the brake gain effecting the bias.


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## caraddict1 (Sep 30, 2011)

I am new to this forum with a B6 Passat VR6 4MO. My last car was an B7 Audi S4 Avant which destroyed by a tree falling on it. It was equipped with the ECS Tuning BB kit from the Porsche Cayenne, cross-drilled and slotted, with 6 piston calipers. Since its just a migration from 1 car to the other, cost will be minimal. I need info on:

1. Will these brakes fit on the Passat? Are there any reasons I SHOULDN'T transfer the brakes from one car to the other?

2. If it is feasible, can someone suggest a source for an adapter bracket and whatever else I would need to make the Porsche brake setup work on the Passat?

Thanks for your input!


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## night_OWL (Nov 15, 2011)

^ Similar situation, looking at replacing stock 12.3" rotors and single piston calipers on TT with 11" rotors and 4 piston calipers (either Brembo or Wilwood) from a VR6... Any installation issues I could come across? Are there any benefits to having the 4 pistions instead of the single?


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## GTijoejoe (Oct 6, 2001)

caraddict1 said:


> I am new to this forum with a B6 Passat VR6 4MO. My last car was an B7 Audi S4 Avant which destroyed by a tree falling on it. It was equipped with the ECS Tuning BB kit from the Porsche Cayenne, cross-drilled and slotted, with 6 piston calipers. Since its just a migration from 1 car to the other, cost will be minimal. I need info on:
> 
> 1. Will these brakes fit on the Passat? Are there any reasons I SHOULDN'T transfer the brakes from one car to the other?
> 
> ...


Please make a specific thread for your question, has nothing to do with this specific thread.
Just to give you something, yes you can transfer the brake kit from your Audi, the passat and Audi will be very similar.


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## HYDE16 (Aug 20, 2010)

Even after I upgraded the pads and brake fluid they stock brakes still sucked, ended up going with the Forge Motorsport Front Brake Kit and SS lines on my 2011 GTI. Looking forward to getting out for the next HPDE event to test this kit out.

*-HYDE16 Reviews Forge Motorsport Front Brake Kit (MK5 & MK6 330mm Kit)-*


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## VWShamwow (Mar 27, 2013)

Hey I'm almost positive that hands down the biggest effect on stopping distance is the amount of alcohol consumed. I mean i don't drink and drive and my stopping distance is phenomenal!!!


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## evol_mk3 (Dec 27, 2001)

I'm still trying to make sense of this thread.... 

So, I had a mk2 8v GTI. The brakes sucked, so I put on some G60 brakes (bigger). Stopped 100 times better. 

Now if you have a mk3 GTI that ways say 2800 lbs and a Porsche that weighs in around 3000 lbs... How can Porsche bigger brakes not be better for a mk3 to stop faster? Are all these "big Brake" companies (AP, Brembo, Powerstop, BAER) are all just ripping us off??? Selling stuff that doesn't work?? 

If bigger brakes aren't better, than why does Porsche have big brakes? Why do the mk5 Jetta TDI cup cars have bigger racing brakes?


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## GTijoejoe (Oct 6, 2001)

evol_mk3 said:


> I'm still trying to make sense of this thread....
> 
> So, I had a mk2 8v GTI. The brakes sucked, so I put on some G60 brakes (bigger). Stopped 100 times better.
> 
> ...


 Why am I the guy who keeps posting answers in this thread? :laugh: 

Let me clear up your confusion with as little technical jargin as possible. 

When you state, "stop faster" you mean in less time (seconds) and/or distance (feet)? 
Given vehicles with equal weight this will directly correlate to the amount of deceleration the vehicle can exhibit, if comparing apples to apples. 

The main physical factor that reflects the amount a vehicle can decel is the frictional relation ship between the tires and the ground, the _grip _of the vehicle. 
(of course we will through out any aero decel contributions, so no parachuets or reverse thrusters here) 
So, because changing your brakes will not change the grip of the vehicle, the largest brake kit in the world inherently will not increase your decel, or reduce your stopping time/distance. 

The main contribution of a big brakes is to deal with Heat... heat heat heat heat heat from kinetic engergy, because you either stop at very very high speeds, or 300 times in 1hr like racecars. :thumbup: 

There are also other advantages that were already discribed in previous posts above :beer:


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## [email protected] (Apr 18, 2013)

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## VAGaddict (Feb 16, 2002)

Such a gathering of opinions and experience. Im a new R32 owner. Ive been reading lots about braking. Because I have two pairs of TTRS calipers. Im trying to find a way to use them. Looks like I should just stick to the stock equipment and change hoses and fluid. Im not trying to win races. Just trying to have more fun. It would be nice to see some Momoblock calipers when I walk up.


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