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W8MM said:
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Fanch said:Ever driven a BMW on the track Eclou?



Now, now, Fanch, you're being a little bit naughty with your jokes

The one thing that prompted me out of driving a BWM at the track was my sense that BMW product engineers didn't build in as much brake heat capacity as I felt to be enough. No matter which model of BMW I tried (including M3, M5, etc.), the brakes would go off after a few laps of spirited track driving. The Porsche drivers then on the track with me never seemed to have any discernible issues with their brakes.

While it is axiomatic that tire friction limits ultimate deceleration levels, the BTU capacity of the brake system is a possible weak link regarding track driving, too.

One can exceed the thermal capacity of ones tires by driving with too much slip angle and constant sliding through entire turns. Every tire compound has an optimum temperature range for which grip is at a maximum. Too cold and too hot are both bad for grip. Over-driving ones tires makes them less grippy in braking as well as cornering. Lots of racers have "cooked" their tires from over-exuberance and then pay a penalty later in a race.

Now we come to brakes. A big deal with me is have enough manageable instantaneous brake torque at each wheel to firmly establish tire friction as the limiting factor. BMW brake designs don't seem to have enough long-term heat capacity to provide this essential retarding torque, lap after lap. They just can't seem to eject enough heat energy, thus gradually get way too hot to function correctly.

Once the heat capacity issue is addressed (as Porsche has), then it's down to feel and "friendly" behavior. I prefer a brake pedal feel that doesn't have much movement associated with increasing pedal pressure. This feature makes it easier for my large, clumsy feet to traverse between the brake and the throttle without unwanted drama.

I also am enamoured of consistent pedal pressure for a given rate of braking deceleration. There's nothing worse (in my mind) than a car control that acts differently every lap. If the pedal feel required for success in each corner is consistent, then my driving confidence can translate into more nearly perfect execution.

For all of the above reasons (and more), I prefer PCCB brakes to traditional cast-iron Porsche brakes. One may regard my opinions as subjective, without properly instrumented data. However, I like to think that I have a sound engineering basis for forming my opinions.



Coming from an engineer and an accomplished track driver, this sounds to me (albeit a layman) as a great explanation .