BIRA - neu S4 brakes

A Little Experience with the neu-S4 HP-2 Brakes

I'm tearing up my brakes on my neu-S4, both on the street and the track. What do you guys offer?

Hey, I heard a rumor that you may be coming out with a 996 TURBO caliper setup for the neu-S4. Is this true? It looks like from your website that you've come out with this kit for some other Audis. If you are, do you have an expected release date?

The neu-S4 (model year 2000 and above) has pretty darn good street brakes stock from the factory. If we had had these type of brakes on the older cars here in the USA (this same design was used on the S8 in Europe) then I doubt there would be the cottage industry there is in Audi brake improvement. Even so, when I got my neu-S4 in 2000, I was asked by the BIRA membership to design an improvement. Seems members were toasting brakes at track events.

The result of that effort was System 2, the 996 Carrera monobloc caliper over the stock 321x30 rotors (which are big rotors, taken in context of what's available.) I tested this successfully on my 1991 200tq and I was quite pleased.

The problem with the stock brakes on the neu-S4 is not the caliper, as the HP-2 caliper is quite capable of producing enough clamping power. The problem is that the stock calipers and pads are powerful enough to overcome the capabilities of the stock rotors quite easily. When I ran the 996 Carrera calipers over the stock rotors on my S4 it made the problems worse; I over-temped and killed the rotors. I was showing rotor temperatures exceeding 1200 degrees, even approaching 1400 degrees, and that's WAY too hot for the material used in the stock rotors. I later designed a bracket to run the 996 twin turbo caliper over our stock rotors on the S4, but I dropped the idea of building it. Doing so would have made the problems even worse.

I re-installed the stock calipers over stock rotors (a new set), and I really didn't notice a difference in braking power (not as good a pedal feel, though, as with the Carrera calipers.) So, the weak link in this design is the rotor. Why this didn't show itself when I was running the same calipers, pads, and rotors on my 200q still mystifies me, but I suspect it was a combination of car weight and airflow in the front end. So, in my opinion, for the street we really have enough braking power bone stock off the showroom. If you want the pedal feel and the looks, the Carrera caliper works great, but you'll kill the stock rotors on the track.

So, what's the solution? For "track use" I'm offering multiple options, mostly based on your budget:

The first level is to upgrade the stock rotors and pads to Coleman multi piece "replirotors" and a high-temperature compound pad. The Coleman rotors are a much better metallurgical design, the air passages are much bigger, and it will flow a lot more cooling air. These rotors will cost about $800 for the pair. For pads I'm open to ideas (and a big fan of Kerr Friction pads from Paul Weston), but the only currently-offered off-the-shelf pads for the HP-2 calipers that I would use on the track are Porterfield R-4. At $400 per set that's quite a chunk of change for just a set of pads, and reasonable alternatives should be cropping up soon. I believe that this combination will overcome all the shortcomings of the stock braking system and will be quite sufficient for both high-performance street and light track use. Unless you just gotta have aftermarket calipers peeking through the wheels, that is...

The next level of performance would be to add the Carrera caliper to the Coleman rotors, what we call System 2 "Plus". This would give you quite a bit better caliper strength and a bit more power, and the pads are available for the Carrera calipers for about $120 (I prefer the Kerr Friction race compound from Paul Weston). An advantage of this option is that since it's all based on stock rotor dimensions you can buy either the rotors or the calipers/brackets first, then "upgrade" to the other component as time/money allows. Once you add the Coleman rotors to the standard System 2, you're looking at about a total of around $1600.

The latest offering is System 6, the new 996 Turbo caliper over the Porsche 322x32 factory drilled rotor rings. This is the same "GT-3" rotor and caliper combo you've seen on the $2800 brake systems from Germany. BIRA will be supplying the bracket and a custom rotor ring hat. This design has a total cost below $2000, depending on component prices and availability, and it clears the stock S4 17" wheels.

Of course, the members are being kept abreast of all these designs and more on our private email list and web pages. You can get a listing of all our publicly-released designs from the "Designs" page on the web site http://www.bira.org

Update, June 2001

As some of you are aware, I drive a 2000 S4. I've made commentary on the stock brakes for this car. Time to "put up or shut up."

So, in the never-ending quest for perfection, I tested some System 2 Coleman rotors on my S4 using the stock calipers. This test happened at an SCCA Car Control Clinic at Lime Rock Park, an event very similar to the Q-Club and BMW Club lapping events. This one was in conjunction with an SCCA Regional 3-hour Enduro for IT cars and the instructors were all SCCA Competition License holders.

I've been trying to get some high-temperature pads for the car to test at the same time, but none were to be found except for Porterfield R4 pads at $400 per set. I'm not going to pay $400 for a set of pads, so I went out there on stock pads to see what I can learn.

There's been a lot of banter regarding the suitability of Coleman rotors for sedan street and track use. We had some initial complaints from replirotor buyers regarding vibration, but after insisting that they be assembled and cut true to begin with, that issue has gone away. I had mine cut after assembly and experienced no vibration on the street after installation.

First session was slower, with every car having a ride-along instructor. I didn't drive too fast but I drove fast enough to get a feel for the brakes; they were holding in there. After about the second session I was let go solo (I'm a former pro-license holder) and I worked on getting some clean speed. I cheated on the "speed limit" (85 mph) a few times to test out the brakes, and initially they worked great. However, I could feel that the harder I pushed the more I was fading the pads. Finally, after about 3 laps I pretty much over-drove the brakes pads: the brake pedal got soft, braking distances increased significantly, and the steering wheel and brake pedal started shaking like an old tractor.

Thinking that I had warped the rotors (to my amazement) I cooled the car down and came in to look it over. I kept my feet off the brakes and pulled in to my area. The brakes, although toasty warm, looked great: there was still a lot of pad area, the rotors were REALLY clean with no grooving, and the aluminum hubs looked fine. I let it all cool down so I could drive it on the street. When I did the pedal felt soft initially and then firmed up (did I boil the fluid?) but I was surprised on my first touch of the brakes that there was no pulsation at all; they brakes weren't warped.

Same thing happened second session: brake fade, vibration, longer braking distances, and my ABS was confused as all hell (I'll explain later). Same result after: pulled off the track and the brakes were not pulsing.

This all brings me to several conclusions:

I think the Coleman replirotors rotors work great on this car. I took at 3600-pound behemoth and to beat up those Coleman rotors, and they held right in. I've done the same thing with the stock rotors the stock rotors warped and grooved severely, tearing up the pads with it. I experienced that also with a buddy's A6t at Summit Point last year (I was running System 2 in my S4 at the time); when he came off the track and drove the car home the vibration never went away and he saw stars all the way to CT. These Coleman replirotors are NOT warping, look as if they were just put in the car, and are up to the task of the heat we're generating with the HP-2 calipers
The stock S4 pads are no where near up to the task. I measured rotor temperatures to 1100 degrees, and the stock pads were literally melting at the rotor surface. The vibration I was feeling was the pad material turning to slag and melting onto the rotor surface. This is the same experience that [a BIRA member] had running stock Boxster pads with System 1 on his A6, and [another member] experienced with stock pads on his UFO-equipped 200q. They both reported bad vibration on the track that went away on the street. In both cases, a race-compound pad at subsequent events eliminated the vibration on the track.
The ABS system on these cars is not made for the track. This car does not have any mechanical brake bias adjustment, it's all controlled by ABS. Therefore, the same line pressure is going to all four corners. When I fade the front brakes and then push harder on the pedal to account for it, I'm locking up the rear brakes and the ABS is kicking in. Unfortunately, I wonder if it's not super-intelligent system (or maybe TOO intelligent); I feel really weird things in the brake pedal and with the balance of the car. I could have sworn that at one point the pedal was pulled away from my foot slightly when I used the brakes to trail-brake. This would likely explain why I had similar weird ABS problems with the System 2 brakes on this car last year.

So, there you are. Maybe some time this year I will attend another lapping session, this time with better pads. Then we'll see how deep I can brake...<grin>

GregA