qfrog Ti20

My sedan needs new pads because I'm changing the brake system yet again. My setup from '08 didn't set the world on fire but it did effectively overheat my front pads/rotors on a regular basis, even at just 1 bar of boost... it took longer but they were still pulsing after a track event and I allow my brakes to cool down by driving the car after being on track. I thnink I did 2 or 3 pairs of front rotors like that both OE BDE and ATE brands. My ducts kinda helped a lil bit too... but the setup is still inadequately cooled IMO. So I've revised my front brakes completely (new rotor/caliper setup). If my calculations are close to accuracy then when my new front brakes go on I will still have a bit more rear bias than I need. Something like Front: 63.32% Rear: 36.68%


Brake system specs out like this

Front:
320x30
36/40mm 4 piston
Pad height 60mm (996 C2)

Rear:
300x22
43mm 1 piston
Pad height 40mm (B5 S4)

I was thinking it might make some sense to run a .62 up front like a DS3000 or a Hawk equivalent along with a .35 or so rear. I've run stock B5 S4 pads in the rear and they didn't leave horrible deposits so maybe I can get away with a stock type pad in the rear. I currently have DS2500 rears but if the calculation is correct they are simply overkill in terms of coefficient of friction (temp range is acceptable).

I called and spoke with somebody at Hawk and he was unable to provide technical info on products, even comparative info. The suggestion I was given was DTC70/DTC60 probably has a bit more rear bite than I want.

?1 Am I off base or am I approaching this in a reasonable way?

?2 Are there any pads with a low (<.4) coefficient of friction but with decent operating range (100-1000*F) available for the rear of a B5 S4?

? Should I just yank out the B5 S4 rear calipers and try to fit some TT225 or VW GLI 38mm rears with DS2500 pads.

The calculated stock B5 A4 quattro setup with DS2500 pads would have been like
F 75.25%
R 24.75%

The setup I ran this past year with DS2500 pads would be something like
F 63.32%
R 36.68%

With my new fronts configuration and current rear configuration if I run a .62 up front and .35 in the rear I would have something like.

F 75.41%
R 24.59%

Setup from '08 with 312mm front w/boxster and 300mm rears w/ B5 S4 calculates as.

F 61.90%
R 38.10%

Thanks in advance.

I was working with the calculator linked below.<ul><li><a href="http://www.jakelatham.com/radical/info/brake_calculators.shtml">http://www.jakelatham.com/radical/info/brake_calculators.shtml</a</li></ul>

ryoung

You're right; you will have too much rear bias with the same pads front and rear. Ideally you should be aiming for something like a 2.4:1 brake bias (71% front); and if you're overheating the front pads, the Ferodo DS3000 is a good choice.

With my Brake Bias Calculator, I get ...

a) 1.69:1 (63% front) with the same pads front and rear

b) 2.10:1 (68% front) with the DS3000 front and DS2500 rear

c) 2.33:1 (70% front) with the DS3000 front and Pagid RS4-2-1 rear

d) 3.00:1 (75% front) with the DS3000 front and OE rear

e) 2.44:1 (71% front) with the DS2500 front and OE rear

On track, c) looks like the best choice, e) the best on the street. The Pagid RS4-2-1 is really a high performance street pad, but it should be OK on track in the rear with the proper brake bias.

I guess my only question is are you sure you're overheating only the front pads when you run the DS2500 front and rear? With the 1.69:1, a heavy rear bias, it looks like you'd overheat the rear first and only the front after the rear has faded away.

BTW: With my Brake Bias Calculator, the <b>bold</b> fields are calculated automatically. Enter any identical system pressure front and rear, 1000 psi for both would be reasonable.<ul><li><a href="http://pws.prserv.net/usinet.Young/BrakeBiasCalculator.html">Brake Bias Calculator</a></li></ul>

qfrog Ti20

I've read some of your posts in the past about brakes on the S8 (ABS/master cyl etc/ pedal travel). Usually good stuff, so I appreciate the help.

I think the DS3000 is what I'll end up with for front pads. I may try the stock Audi rear pads with the DS3000 up front. When I ran my sedan at NJMP Thunderbolt, Watkins Glen and Shenandoah with DS2500 fronts and OE rears they didn't leave deposits. Boost settings varied from 1.0-1.3 bar. I was reaching ~120mph at times.

My front rotors/pads were getting very hot and the problem with the 312x25mm rotor from the A8 is that they have an 8mm cooling channel. When the narrow cooling channel is added to the fact that Boxster pads are ~55mm tall on a disc with a 65mm surface, the heat is concentrated in one area, I can only imagine that the narrow pad may have caused uneven expansion.