Kevin:
Finally, your brake question gives me an opportunity to answer a question
for once, rather than just ask (stupid) ones.
I am a track driving instructor for the Porsche Club, BMW Club, etc. As a
group, we spend a lot of time discussing brake equipment issues between
ourselves and with our students. Further, living in Florida and spending a
lot of
track time at Sebring, brake cooling issues are paramount. I drive a '92
Porsche 968 track car (in addition to my TR6).
The prinicipal reason for larger rotors and calipers in a high-performance
application is heat dissipation. Other issues don't come into play to any
significant extent (feel, etc.). If you are trying to run fast laps with
heavy
braking for extended sessions with an air temperature of 95 degrees and a
track temperature much higher, you need to be concerned about boiling the brake
fluid and losing hydraulic pressure to push the caliper pistons.
First, you optimize the brakes you have. That means using fluid with the
highest boiling point (we all use Ate Super Blue), changing it frequently
(every 1 to 3 events, or even during the event if needed), and making sure that
the brakes have adequate cooling built in (remove backing plates, add air
ducting). We also use pads made to perform best when heated to very high
temperatures. My favorites are made by Performance Friction. When cold, I
really
need to press pretty hard on the brakes. When hot, I can pretty much get into
the ABS by using my big toe on the pedal, despite the use of very wide and
sticky Hoosier track tires.
If, despite all the measures listed above, the brakes overheat under heavy
use, it is necessary to install larger calipers and rotors. They will
dissipate heat more effectively and will overheat less. But they are
expensive, and
add significant unsprung weight, which is undesirable.
This all came into play directly for me several years ago. I had a 968
street car that I started to use more and more often at the track. My
independent repair shop came into possession of a factory sport suspension
(M030)
setup, minus the larger brakes, and offered it to me well below cost to get
rid of
it. The guy who had ordered it had totaled his car before it could be
installed. Anyway, I was concerned about installing the racing suspension
without
enlarging my brakes. I did it anyway. Now I have been running the stock
(still pretty impressive) brakes with their built-in cooling ducts and racing
pads for several years in Florida without ever having a fade or overheating
problem and with superb braking. Therefore, there is no rationale at all to
spend $3000 for larger, heavier brakes.
The moral of the story is to have brakes big enough to dissipate enough heat
to meet your needs, but no bigger. Anything else is for show, but not
functional.
Michael
'76 Tahiti blue
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