[Biturbos4] Stock Brake Upgrade
AudiBiTurbo at aol.com
AudiBiTurbo at aol.com
Wed Nov 24 00:47:45 EST 2004
In a message dated 11/23/2004 5:29:29 PM Eastern Standard Time,
mbenno at yahoo.com writes:
Mark thanks for the objective feedback. I have some additional question on
this thermal capacity issue...
...Thermal capacity of the system, which takes into account car
aerodynamics, cooling, mass of the rotor, vane design, etc.
I thought the weak thermal link in the system was the OEM rotor and that
going to just about any other aftermarket rotor dealt with common warping.
...Rotor warping can be caused in various ways. The most common is getting
an overly hot rotor and pad stopped and keeping your foot on the brake (at a
stop light, for example). Of course, this same scenario can lead to "pad
dispersion" (the pad material imbedding into the surface of the rotor, causing
hard spots). To most people, the resulting pulsation is "warping." In severe
cases, you can see an outline of the pad on the rotor surface.
I don't understand how the caliper has poor thermal capacity, does it have
something to do with the pad size vs. piston size?
...The calipers in the S4's case only limit the system's thermal capacity by
limiting the rotor size. A larger (wider as well as diameter) rotor can
flow more air, have more mass, etc. The piston size versus pad size versus
master cylinder size only has to do with bias and feel.
Also, would a OEM sized floating rotor (eg ECS tuning) deal with the thermal
issue as well. My understanding is that composite rotors have better
venting. Plus the dual material prevents warping common in the stock rotors.
...dual material (rotor hat typically being aluminum and the rotor typically
being a nodular iron, if I remember my materials course) has nothing to do
with venting. It's all in design. The reason for 2 pc. rotors is that you
can make the hat out of a lighter material, and move that mass into the rotor
face area, making the webs stronger. In general, 2 pc. rotors weigh less, but
have more inertia, so it's not uncommon to see a dyno loss, despite less
dynamic weight for the suspension. The 2 pc. design allows the rotor to float
(think "side to side") which makes the braking more even on both the inner and
outer surface. Basically, this means no warping from an uneven heating
issue, but they could still warp if you take a hot rotor/pad and keep the pad in
contact as it cools (say, at a stop light). As an interesting aside, in
testing, one of the reasons Stoptech flowed 20% more air than the same sized
Porsche GT-2 rotor is in the vane design and the face that the hats are
directional and optimized for airflow. They patented directional hats here in the USA.
Then brake bias comes into play. But since you didn't ask about it, I won't
type any more. But I will mention that weight, spring rate, and master
cylinder sizing all come into play when choosing the proper piston bore size and
ratio. Although the caliper bodies are the same before machining, an S4
caliper isn't the same as a 2.8/3.0 caliper, nor are either the same as a 1.8T
The point is that it's an entire system. There's no such thing as a magic
rotor, but there are things which aren't expensive and will improve brake
efficiency. Slotted or 2 pc. rotors, proper pad composition for your driving
conditions, and maximizing airflow are all important. Hanging some hoses under
the car and aiming them at the hub will help at speed.
Good luck, and I hope I've helped clear up some mystery and give you some
ideas to ponder.
_AudiBiTurbo at aol.com_ (mailto:AudiBiTurbo at aol.com)
More information about the Biturbos4