# slotted rotors vs vented



## 83rabbGTi (Jun 1, 2001)

*slotted rotors vs cross drilled*

im doing a project in school and i need some sources for this topic... if anyone could put there .02 cents and give a little comparison that would be great mmmkkk

















_Modified by 83rabbGTi at 11:50 AM 2-3-2005_


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## kdiver58 (Jan 25, 2004)

*Re: slotted rotors vs vented (83rabbGTi)*

Vents cool a rotor and slots help stop a gas boundery layer from forming between the pads and the rotor.


_Modified by kdiver58 at 8:45 PM 2-3-2005_


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## Racer_X (Jul 14, 2002)

*Re: slotted rotors vs vented (83rabbGTi)*

Well, I'll try to add a bit to this. Kdiver58 is right, venting and slotting have two different purposes. So here's some info on vented rotors vs. solid rotors and drilled rotors vs. slotted rotors vs. flat surface rotors. 
There are two basic types of rotors used on cars. Solid rotors are used on the rear of VW's and on the front of older, lighter, slower models. The front rotors on most newer VW's are vented rotors.
A solid rotor is a single, solid disc of material. The caliper squeezes on the disc, and heat from the friction builds up on the rotors (and pads). The surface cools as it rotates around through the air where the rotor isn't touching the pads. A vented rotor has two discs separated by some webbing that forms vents through the rotors. Air can flow through these vents and cool the rotor from the inside. It's easier to use pictures than it is to describe.








The first rotor is a solid rotor. The second is a vented rotor. Note the difference on the lower edge in the pictures. 
Vented rotors have nearly twice the surface area exposed to cooling air, so they run cooler and reduce fade. They are also generally a bit heavier because they are generally thicker and have additional weight from the webbing between the rotor "plates". The added mass helps a bit with thermal issues, too. But the big advantage is the addes surface area inside the vents that helps cool the rotor.
That brings us to the comparison between flat surface ("stock") rotors, slotted rotors and drilled rotors. Generally speaking, if you select your brake pads to match your driving situations, stock rotors give the best performance and longest service life. If you push your brakes to the point where the pads overheat and fade, then slots or drilling can help reduce fade by giving the gasses produced by the overheating pads a way to escape. But there are serious disadvantages to slotted or drilled rotors. Both slotted and drilled rotors will wear pads out much quicker than flat surface rotors. Pad wear can be 2 to 5 times faster on slotted or drilled rotors than on stock, flat surface rotors. 
Here's some pics. 








Stock rotor








Slotted rotor








Drilled rotor
Drilling puts a lot of very significant machining stress into the rotor casting, and the unfilled holes are natural stress raisers. Some manufacturers cast the rotors with the holes in the castings, and that avoids some of the machining stress. Another possible way to reduce the machining stress is to give the rotors a stress relief heat treatment after drilling. But no matter what you do about the machining stress, you still have the stress raiser from the open hole. As a result, drilled rotors always have a very short service life before thermal stresses and fatigue start to crack the rotors around the holes. This isn't an issue for racing applications. Racers can change rotors every weekend (or several times during one weekend) as long as the brakes perform better. But for street use, drilled rotors have a very short service life.
Slotting doesn't put as much stress into the rotor as drilling, but the slots are still stress raisers, and there is still a potential for the rotor to crack along the slot. This is made worse if the slot is poorly designed. Slots that run off the edge of the rotor, for example, are much bigger stress raisers than slots that don't go all the way to the edge. Slots also shed water and contamination much better than flat surface rotors (and a little better than drilled rotors). And the slots tend to scrape the surface of the pads, cleaning any foreign contamination or any glazing from the pads. This cleaning action also wears pads even quicker, so slotted rotors are often the worst for pad wear. 
And everything I've said so far about slotting and drilling applies to all slotted or drilled rotors. But there can be additional problems with slotted or drilled rotors from the pattern of the slots or holes. If the pattern is very well engineered, you get the benefits of fade resistance with only the disadvantages I've outlined so far. Most drilled or slotted rotors that are made by brake component manufacturers have well engineered patterns (the brake companies understand the issues with drilling and slotting and know how to do it properly). 
But, there's another class of slotted or drilled rotors (and this includes every rotor I've seen that is both slotted and drilled) that are drilled and/or slotted by third parties. These people (companies) take stock rotors and do their own machining work to drill or machine slots into the rotors. Generally, these "tuner shop" rotors do not have well engineered drilling patterns or slot patterns. Often, the people doing the drilling and slotting just make a pattern that "looks cool". The problem with these rotors is that they can have all kinds of very bad side effects on your brakes. They can wear the pads unevenly, and they can have thermal issues that lead to fatigue and thermal stress problems (cracking, breakage) much sooner than well engineered rotors. They can also make stopping distances significantly longer due to problems with thermal issues and uneven pad wear issues. These rotors range from useless to outright dangerous.


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## j-dub (Oct 22, 2000)

*Re: slotted rotors vs vented (Racer_X)*

Racer_X great information. I have an additional question about brake pads gassing. Is this idea a hold over from when brake pads were made with asbestos(sp?) or do today's pads gas just as much when pushed hard?


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## 83rabbGTi (Jun 1, 2001)

*Re: slotted rotors vs vented (83rabbGTi)*

wtf!!! thats what i meant sorry i wanted a comparison between slotted rotors and cross drilled rotors! but thanks you very much...thats all the info i need


_Modified by 83rabbGTi at 11:54 AM 2-3-2005_


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## lynx8489 (Jul 29, 2002)

*Re: slotted rotors vs vented (83rabbGTi)*

very helpful info racer X thanks again.
i am about to replace my entire brake system with new rotors,hawk ceramic up front and hawk hps in the rear as well as SS lines. 
i was all set to buy the Brembo or ECS tuning slotted rotors for the front and rear until i read this post. 
with the pads and setup described above, should i just get the brembo stock replacement rotors which will save some money and pad life? i really dont care about looks i just want more performance. But if a slotted rotor will perform better and just wear out pads quicker, i am willing to replace the pads more often. 
what do you run on your car?
do you have a good website source for brake parts? 
so far i've found ECS tuning and tirerack have decent prices, got any secrets? 
thanks for your time i am completely new to brake upgrades. 
brandon


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## Racer_X (Jul 14, 2002)

*Re: slotted rotors vs vented (lynx8489)*


_Quote, originally posted by *lynx8489* »_what do you run on your car?
That depends on which car we are talking about. For the "basic transportation" vehicles, I run Hawk HPS pads and rear shoes from Carbotech or Porterfield. I just got another set of Hawk HPS for the Dodge Caravan (freaked out the parts guy). I also have Hawk HPS on the Miata, and the Ford Escort wagon will get them when it needs pads. 
For the race car (1983 Rabbit GTI), I run Ferodo race compounds. I've run DS-2500 on a few tracks that are easier on brakes, and DS-3000 Endurance for the tracks that are harder on brakes and for longer endurance races. The car is really set up for endurance events more than sprints. At the rear, I run some race compound shoes that are no longer available. I'm down to the last set, so I'll be ordering some shoes from Porterfiedl soon (R4 race compound). 
The diesel Jetta gets leftovers from the race car. So I have DS-2500 on very worn vented rotors (at or maybe slightly under minimum thickness) on it. Since the car is incapable of speeds over 90mph, and rarely goes over 75mph, there isn't as much heat load on the rotors as on the GTI's at full speed. 

_Quote, originally posted by *lynx8489* »_do you have a good website source for brake parts? 
so far i've found ECS tuning and tirerack have decent prices, got any secrets? 
Adirondack (http://www.germanautoparts.com) or Potterman (http://www.parts4vws.com) for the VW's, at least for rotors, brake hoses and the like. Though http://www.tirerack.com also has good prices and some good stuff. I've gotten my Hawk pads from them for some of our vehicles, and for some of our friends vehicles as well.
Another good source for Hawk HPS pads is Pep Boys. I hate the place and try to avoid them as much as possible, but they actually carry Hawk HPS and can look up almost any application. I couldn't get anyone to find the right pads for the Dodge Caravan except Pep Boys. The guy thought I was crazy for wanting those pads for a minivan, but he looked them up and they had them in stock. The price was a few dollars more than TireRack.com, but not enough to make up for shipping charges. And TireRack.com didn't have a listing for the Caravan (though they sell the exact same pads for other cars that use the same part).


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## ScooterMac01 (Apr 20, 2003)

*Re: slotted rotors vs vented (Racer_X)*

Would like to add my voice of gratitude to you Racer_X for taking the time to sort out the pros and cons on brake rotors. It is folks like you that mke the Tex a good source of information, not speculation.
Cheers!
Scott


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## TurboZen (Oct 15, 2000)

*Re: slotted rotors vs vented (Racer_X)*

Great information http://****************.com/smile/emthup.gif 
Most people should first upgrade thier pads with stock rotors before anything else. This way brake bias is still static. I've heard of people spending $10,000 on break upgrades and still didn't stop better than stock.
When I decide to change the front pads, I'm going Hawk HPS. Thanks for the info


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## lynx8489 (Jul 29, 2002)

*Re: slotted rotors vs vented (TurboZen)*

thanks again Racer X you make this forum informative, enjoyable and technical, we all appreciate your time.


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