VAP

really sucks to be you guys on this one! ;-)

egp320i

I have OEM calipers because I can't afford to go with a big brake kit upgrade and so far the OEM girlings are working well enough for me. You on the other hand have many upgrades on your car whether you bought them or made them yourself. I just figure if anybody you would be more inclined to go with the popular 933 porsche brembo's or wilwoods, alcon or something of the nature it would be you.
sure, if I had the extra cash laying around I would like to venture into more stopping power but that will have to be some other day.

VAP

and that just because you choose a caliper that is OEM on some car is not necessarily a bad thing, let alone a step backwards or even horizontal enhancement. An S4 OEM rear caliper with 12.1" cross-drilled/slotted rotor thats ventilated is as much of an upgrade on the rears as 996TT or 993TT is on the fronts. Actually if piston diameters, brake pad surface area, new rotor thickness and diameter sizes combined with leverage increases are measured then added up its a more radical and HIGHER percentage increase of stopping power over the stock rear brakes than the front 996TT conversion is over the stock front brakes! This is NOT a step backwards! Why use a larger caliper then have to manually dial it down hydraulically to 30% of its designed working pressure/effectiveness? Essentially rendering it a virtual single piston caliper capacity wrapped in the additional "dead" weight of a 2 piston caliper!?! Counter-intuitive.

The 00-02 B5/S4 caliper was designed and used on an Audi S-car weighing 800+ pounds more than my car. Its a lighter caliper that is capable of cooling faster and dissipating heat quicker than the stock cast iron caliper that came on my car. It has a 5mm larger piston than my stock caliper which allows for almost 16 sq mm more surface area than my stock rear pistons. It uses a rear pad that is over 25% larger than a stock 90 pad. It accepts a rotor thats over twice as thick as stock and is ventilated for cooler, less fade performance than the solid/non-ventilated 90Q rotor. It uses a larger diameter lighter weight rotor that is cross-drilled slotted and a true-floating configuration. By moving the caliper outward from the axle center-line on the larger rotor more leverage is attained, ie; even more stopping power via greater leverage... just like a cheater bar for loosening nuts/bolts.

Now lets compare it to a Porsche caliper. If I used one I would have to dial in, via a brake proportioning valve, less rear brake bias in order to maintain proper (+ or -) 65/35 front/rear balance. This means installing a proportioning valve as there is NO WAY the ABS could compensate for Porsche rear calipers! I would only be getting the same approximate rear braking performance I'll get now with the S4 calipers. More brakes on the rear would absolutely out-pace the ABS's ability to keep up and work with the system without some mechanical means of reducing their bias. Without some provision for manual adjustment to move some of that stopping power forward, away from the rear calipers, I would lock the rear brakes solid before the front brakes even began to slow me down. You have to remember that the front of the car weighs 2,100lbs while the rear only weighs 1,000lbs. BAD idea!

Then there's the e-brake. No Porsche set-up can retain/use the stock e-brake system that came on the car as-is. That would require a separate spot caliper mounted on the rotor or an inline hydraulic check valve and slave cylinder on the rear calipers hydraulic lines.

Given all this there is really no reason for Porsche or any other OEM or aftermarket brake system to be used on the rear when there's zero-to-negligible benefit. Doing so would only force me to reduce their stopping power via some measure of reduced hydraulic pressure being sent to them any time the brakes were applied.

Beyond that there's nothing innately or intrinsically wrong with OEM rear calipers from Audi for an S-car. They are reliable, work forever and do the job on a car weighing over 25% more than my car. They stop better, cool faster and with the even larger rotors I've chosen the benefit is even greater than the stock S4 set-up.

Nothing wrong with an OEM setup as long as its designed properly or in this case over-engineered for the car its being fitted to. This will be a HUGE leap forward in braking effectiveness for my car. There is no benefit whatever associated with going to a Porsche, Alcon or other rear brake setup on my car considering I'd have to back down their braking effectiveness via a hydraulic proportioning valve to at/near where this brake setup will put me anyway right outta the box while also retaining stock e-brakes.

Now would I like to have a rear Porsche setup? Bet yer ***! But will I gain anything from it as far as enhanced braking or decreased lap times? Absolutely not. The rear brakes just dont play that big a role in stopping the car. All I'd gain with a Porsche or other rear setup is bragging rights with a dramatically reduced caliper hydraulic pressure to make sure the rear brakes dont over-power the fronts. Thats it, nothing more besides increased weight with Porsche rear rotors/calipers. Its just not worth it for the driving I do even on-track.

Think what you will but this is anything but "a step backwards."

|skolnick

Where did you get the hats for your front rotors?

repeater

Aren't the stock 90 and UrS rear calipers the same?

If I'm correct you're saying the B5 aluminum caliper bolts right up and accepts the e-brake fine on the 90, just rotor sizing needs to change?

VAP

you can buy the "real deal" GT2 rotors from WorldPac (even come in Porsche logo boxes) for a smidge over $120 each. You can get them minus the Porsche hats for less but they were out of stock on hatless ones when I ordered.

VAP

and weighing over 3,800lbs. While I can't remember specifics I'm almost certain that the UrS rears would have at least a 40, 42mm or larger rear caliper. I never upgraded the rears on my UrS4 as the 996TT fronts were so incredible. I used cross-drilled rear Zimmerman rotors, shoe'd em in Pagid Orange rear and Blues on front and installed SS lines.

Sorry I cant be more specific but I just dont remember tho I've got a strong hunch the B4/90Q is a smaller caliper.