# Phatvw Brake FAQ



## phatvw (Aug 29, 2001)

Article #1 - All about rotors









- picture courtesy http://www.racingbrake.com
- note that this is not actually a racing brake rotor, just a generic picture used on their website
- note how the slot goes all the way to the edge - poor design?
Heat capacity
# Heat capacity, in the context of rotors, is the amount of energy that can be
absorbed by the rotor before the temperature gets high enough to cause brake
fade. The mass of the rotor is proportional to the heat capacity. Therefore, a
lighter rotor will not allow as much energy to be absorbed as a heavy rotor.
Solid vs Vented
# Vented rotors are hollow with internal vanes. This increases the surface area of
the rotor and allows air to cool the rotor mass more effectively. A 10 pound vented
rotor will cool much quicker than a 10 pound solid rotor. In many cases, a vented
rotor can weigh less than a solid rotor and still provide more effective braking
because of the cooling effects alone.
Where does the air go?
# For solid rotors, all the air travels over the surface of the rotor - the same
surface as the brake pads.
# For vented rotors, a considerable amount of air flows through the interior.
Because the rotor is spinning so fast, it creates a vacuum and air is sucked into the
center of the rotor and forced out through the edges via centrifugal force (yes like a
centrifuge, not centripetal you grade 8 science teachers!) The air follows the pattern
of the internal vanes.
Curved vs straight vanes
# The vanes inside vented rotors provide structural integrity to the rotor as well as
the channels for air cooling. There are several different styles of vanes.
# Straight vanes are the most common because they are easy to manufacture.
# Curved vanes are common in higher performance cars as they promote better
cooling than straight vanes.
# There are several manufactures with more exotic vane patterns who claim their
vanes are the best. You may judge for yourself. For examples see http://www.racingbrake.com
Drilled (perforated) rotors
# A common misconception is that the purpose of drilled rotors is to promote
cooling. This couldn't be further from the truth. The real purpose is to reduce
weight and in older cars, to allow the pads to "off-gas." Modern brake pads
don't off-gas so this is no longer a concern. Many motorcycles have huge rotors
which contribute to good brake modulation/feel, but usually all the heat capacity
isn't needed. So to save weight and enhance appearance, holes are drilled.
# Many high performance cars like Porsche and AMG come with drilled rotors
from the factory. For these cars, the drilling is mainly about the looks. So are the
brightly colored calipers and huge, heavy wheels. When folks do serious high-
performance driving on a racetrack, they usually swap to regular plain rotors.
# Drilled rotors generally wear out brake pads faster and produce more
brake dust as a result.
# Drilled rotors have a shorter service-life than plain rotors and tend to develop
stress fissures/cracks over their lifetime. Plain rotors also develop stress fissures,
but the fissures are often more severe on drilled rotors.
Basic requirements for high-quality drilled rotors:
# Holes should be cast, then smoothed. If drilled, then the entire rotor should be
heat-treated to relieve internal stresses in the metal lattice structure. Many drilled
rotors are not heat treated and don't last.
# The edge of the hole itself can be machined to have a chamfer or angled/curved
surface leading from the rotor face to the inside of the hole - in theory this will
reduce pad wear. But after any significant machining, the rotor should be heat
treated again - thus increasing cost. Does the cost of the rotor outweigh the cost
of the pads?
# All holes should be located at a different radius (distance) from the edge
of the rotor. Think about how the pad runs over the entire surface of the rotor. If
more than one hole is at the same radius, then certain areas of the brake pad will
run over more holes than other areas. This causes uneven brake pad wear and
may unevenly heat the rotor during use (hot spots).
# Advanced: For folks that have studied calculus, you might recognize that even
with holes spaced out properly, the pads will STILL wear unevenly because some
areas of the pad will go over the MIDDLE of the hole, while some will go over the
edge of the hole. I don't know how to solve that one...
# Vented: Holes should be located in the center of each vent passage between the
vanes - not drilled through a vane and not drilled right next to a vane. In the
center. This will maximize any and all cooling/dust-venting effects of the holes and
preserve the structural integrity of the rotor.
# Vented: Each vent passage should have the same number of holes - otherwise
you are putting more stress on the vent passage with more holes. Better to
keep things simple and have even stress all around the rotor. No 3 holes - then 4
holes - then 3 holes nonsense.
# In certain cases, the brake pad must be machined down to an appropriate size
to strictly meet the above requirements - so treat the brake rotor and pad
together as a system.
Slotted rotors
# Slotted rotors are great for shedding water and mud off the rotor surface in
Rally racing or wet-weather racing. For street driving they may marginally
improve initial brake "bite". Some brake systems use a rain sensor to detect wet
conditions and "pre-dry" rotors in anticipation of a stop by engaging the brakes
ever so slightly. Arguably, this is a more intelligent way to combat the problem.
# Slotted rotors act as a self-cleaning mechanism where brake dust and other
debris are wiped clean from the pads
# Slotted rotors accelerate pad wear and produce more dust just like drilled
rotors. They also add noise and vibration.
Basic requirements for a high-quality slotted rotors
# Any advanced machining like slotting or chamfering the edges of slots should be
followed by heat-treatment to relieve the internal stresses in the metal.
# Slots should extend beyond the edge of the pad for maximum benefit.
# The brake pad should not be able to cover the whole slot.
If the pad did cover the whole slot, then the slot effectively becomes useless for
that instant because no gases/dust can escape. Keep it simple: make the slot
longer than the brake pad, so the gases and dust always have a place to go.
# Slots should not extend all the way to the edge of the rotor either the inner or
outer edge. Otherwise structural integrity is compromised.
# Just like for drilled rotors, each section of the brake pad should run over the
same amount of slotted-area - otherwise you get uneven pad wear and hot-spots.
# In certain cases, the brake pad must be machined down to an appropriate size
to strictly meet the above requirements - so treat the brake rotor and pad
together.
Slotted + Drilled
# Purely for looks
# Almost all have some design flaw - i.e. they don't meet the requirements
above. The failed requirement is usually hole placement. The designers pay so
much attention to how the slots are going to look that they ignore everything else.
It is not impossible to get these right, but it is very difficult.
# Try to find a racing team that uses these rotors and wins!
Two-piece rotors
# Lower weight, but still good heat capacity compared to one piece
# Better cooling due to open center section - more air can get sucked into the
middle of the rotor
# Allows separate heat expansion of center section vs rotor ring - helps protect
wheels/hubs/wheel bearings from crazy temperatures and potentially reduces
warping of the wheels, hubs, and the rotors themselves.
# User-serviceable two piece rotors with a re-usable center "hat" and a bolt-on
rotor "ring" generally increase costs and require more maintenance than single
piece rotors, so they are a poor choice for street cars. For racing, they are great!
# Non-user serviceable two piece rotors such as the "radial-pin" design on the
2004 VW R32 are a great compromise. You get most of the benefits of a modular
two-piece design at a fraction of the cost.
# Good Stoptech article: http://www.stoptech.com/tech_i...shtml
Which mounting direction? Left or right?
# The direction only matters if the internal vanes of the rotor are curved as the
curves will affect the airflow through the middle of the rotor. The direction of the
slots or drilled holes on the surface of the rotor does not matter at all. For curved-
vane rotors, the rotor will be marked "L" or "R". If you don't see those markings,
mount it whatever way looks best
Plain rotors
# Plain rotors are the best choice for 99.9% of applications. Still not convinced?
Even Tirerack says plain rotors are best: http://www.tirerack.com/brakes...id=87
Name brand vs no-name rotors
# Why pay double the money for a Brembo rotor vs Autozone or no-name? You
guessed it there is little benefit. Spend your money on brake pads instead.
# Exceptions: if you must get drilled or slotted rotors, you're far better off with a
name-brand rotor that comes cast with holes from the factory rather than some
guy who drills Chinese-sourced rotors at the back of the shop.
# There are quality control differences between companies and every
manufactured product has a manufacturing tolerance. But finding real data on
different brands is very difficult. When real data is unavailable should you
automatically trust innuendo from the big players? Does made in USA or made in
Germany autmatically make it a better product?
Cryogenic/frozen rotors
# There is no independent proof that these rotors last longer or stop better than
regular rotors. Materials science will tell you that any changes to the metal lattice
structure due to cryogenic cooling, will likely be nullified the first time the rotors are
heated up to operating temperatures. Its possible that pads might last a little
longer if temperatures don't get too high but its surely not worth the extra cost.
Save your money and get long-lasting pads instead.
Exotic rotors (carbon, carbon-ceramic, carbon-Kevlar, etc.)
# Some really expensive cars come with a $10,000 option for exotic brake
materials. These brakes are excellent for racetrack conditions since they are very
lightweight but can withstand extreme temperatures without brake fade. This
provides a competitive advantage for racing.
# For the street, it doesn't help a lot for stopping. The reduce unsprung weight can
improve ride comfort and handling a little bit, but most folks wouldn't even notice.
So you can safely chuckle at all those Porsche guys opt for the $10,000 ceramic
brakes and don't take their cars to the racetrack.
# Some of these companies claim these brake systems will last well over 100,000
miles for day-to-day use. When was the last time you saw an exotic with 100,000
miles on it?
Anti-corrosion/rust coatings: zinc/cadmium/electroplating/etc.
# Some rotors come with a protective coat of zinc or cadmium which prevents
rust. Only the areas of the rotor which don't contact the brake pad will be protected
through the life of the rotor. Protecting the internal vane structure and center
section is a great idea! BUT, once the brake pad touches the "swept" area of the
rotor they will scrape off the coating. You cannot prevent rust on the "swept" area
of the rotor since they are mode from cast-iron.
# For racing you absolutely do NOT want the swept area covered with any
coatings. During race use, the coating can melt off in molten chunks and stick
to your wheels. Or worse - it could melt and "fill-in" the little stress fissures on a
rotor so when you do tech inspection the rotor might look OK, but its got serious
structural problems. So if you have coated/plated rotors and are going racing,
have the rotors "turned" or machined to get rid of the coating before using them.
Warped rotors
# See Stoptech article http://www.stoptech.com/tech_i...shtml
Other articles/knowledge
http://www.stoptech.com/tech_i...shtml
Disclaimer
# I have no affiliation with any brake companies.
# I am neither a materials engineer nor an automotive engineer.
# All the info here can be gleaned from materials engineering textbooks,
braking websites, racing discussion forums, etc. I recognize that the article lacks
references which is a major downfall, so take anything in this article with a
grain of salt. I will work on improving the research over time. Please add any data
you have


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (phatvw)*

*Article #2 - all about pads*


_Modified by phatvw at 6:03 PM 9-2-2007_


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (phatvw)*

This article is great!
http://www.scottbarton.net/UpgradingBrakes.html


_Modified by phatvw at 4:55 PM 3-19-2008_


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (phatvw)*

*Article #4*


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (phatvw)*

*Article #5*


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## Banditt007 (Oct 23, 2002)

*Re: Phatvw Brake FAQ (phatvw)*

nice work


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## a2gtinut (Dec 2, 1999)

*Re: Phatvw Brake FAQ (Banditt007)*

very nice but..
"*Name brand vs no-name rotors
Why pay double the money for a Brembo rotor vs Autozone or no-name? You
guessed it there is pretty much no benefit. Its all the same stuff. Spend your money
on brake pads instead.
Exceptions: if you must get drilled or slotted rotors, you're far better off with a
name-brand rotor that comes cast with holes from the factory rather than some guy
who drills Chinese-sourced rotors at the back of the shop*."
There is a big difference in materials used by cheap "made in China" brakes and ATE or Brembo parts.


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (a2gtinut)*


_Quote, originally posted by *a2gtinut* »_very nice but..

There is a big difference in materials used by cheap "made in China" brakes and ATE or Brembo parts.


Thats what I always thought too... but I was never able to find any proof. And when there is no proof, I consider any marketing by the big players to be FUD (fear-uncertainty-doubt) 
I'll change the article when I see a real test from grassroots motorsports or something showing that no-name plain rotors fail to meet OEM spec.


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## a2gtinut (Dec 2, 1999)

*Re: Phatvw Brake FAQ (phatvw)*

you have point.
Once made a mistake and bought cheap rotors for my moms old car instead of spending $$ at the GM dealer.
they were bad, really bad. Even with quality pads they would "warp" every 10k miles of normal city driving.


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## Dan GSR (Dec 10, 2004)

*Re: Phatvw Brake FAQ (phatvw)*

http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif 
i try to tell ppl, but they just dont want to listen
o well, let them piss away their money


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (a2gtinut)*


_Quote, originally posted by *a2gtinut* »_you have point.
Once made a mistake and bought cheap rotors for my moms old car instead of spending $$ at the GM dealer.
they were bad, really bad. Even with quality pads they would "warp" every 10k miles of normal city driving. 

I'm sure if you scour the Internet you can find similar annecdotes about Brembo, Zimmerman, Stoptech, ATE, pretty much any brake brand. Its impossible to get every single set of rotors and wheel hubs made 100% on spec. There is always manufacturer tolerance and when you have a stack of 5 parts all on the edge of tolerance, you can easily get vibration etc.



_Modified by phatvw at 12:41 PM 2-4-2008_


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## sdoow (Feb 4, 2008)

*Re: Phatvw Brake FAQ (phatvw)*

This is RacingBrake and we just noticed this thread. The first posting is only a typical picture used to describe various designs of the brake disc available in our complete article: "Type of cooling vanes for ventilated rotors".
*This is not our rotor* which was considered by 'Phatvw' as a poor design. If you want to learn the unbiased evaluation and the latest technology on brake engineering accumulated through the past decade please visit our website for complete details:
http://www.racingbrake.com
Our authorized VW and Audi brake products are represented by AP Tuning with the following contact information:
AP Tuning (VW / Audi)
30 South 5th Avenue
Lebanon, PA 17042
717-272-0916
[email protected]
http://www.aptuning.com

_Quote, originally posted by *phatvw* »_*Article #1 - All about rotors*









- picture courtesy http://www.racingbrake.com
- note how the slot goes all the way to the edge - poor design


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## phatvw (Aug 29, 2001)

*Re: Phatvw Brake FAQ (sdoow)*

RacingBrake, thanks so much for the post. I had meant to send you guys an email about that pic because it doesn't look like the other great rotors you sell! I have updated the caption to reflect that it is not a racing brake product.


_Modified by phatvw at 8:32 AM 2-4-2008_


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## AAPL (Apr 5, 2004)

*Re: Phatvw Brake FAQ (phatvw)*

Yea that garbage pic cannot be RacingBrake stuff. They make the most high end products my buddy here in cali swears by RB stuff because of the bulletproof reliability. 3 track seasons on the same rotors! Brembo what? http://****************.com/smile/emthup.gif


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