Sean F

Interesting. I do go quite a ways in between hard braking zones at the Glen. There are really only two real hard braking zones for my car and another two that get a brief full application. I'll give it a try blocking the inlets and see what happens.

gbaker

...like a local oval tracker who experienced a rotor explosion that sent a chunk up into the engine compartment, where it jammed the throttle linkage wide open. Talk about a deviation from plan.

Veloce Raptor

**** like that won't buff out.

Sharptt

I agree. Either too much cooling or uneven cooling. It may seem counterintuitive but sometimes you need to let the rotors get and stay hotter. Look how cherry red the ALMS and Rolex car rotors are when they run in the dark. I would start by blocking off the brake ducts.

Veloce Raptor

Yup. And the Glen--where it is usually cool, especially in the mornings, and where lighter/lower HP cars don't really use hard braking in many places to keep heat in the system--is one of the worst places for this.

ngoldrich

FWIW...
on my old 944 Turbo E-stock race car I got 14 races (PCA, SCCA, NASA) in one season out of a set of rotors...

btw - I ran PFC pads on that car and OE rotors...

Norm

chrisp

At the Glen I drag the brakes quite a bit on the out laps. With my Hawks when rotor/pad temps are too low I lose braking because the pad is below it's temp range. This is how I know if I need to block off brake ducting. Maybe the PFC's don't do this and you run them too cool too often.

Veloce Raptor

Chris is right. You will see a lot of racers to a couple of light left foot brake taps before the brake zone for T1, before the Bus Stop, before the Toe, to make sure they have brakes (!) and no pad knock-back, and to put a little temp into the brakes. Watch Leh Keen's video from the Glen, posted here in the past, as an example.

Same thing at Road Atlanta, IMO, in cooler weather.

Gary R.

No brake ducting on my car(s), no problems yet and I use OEM rotors. I've worn rotors out (takes quite a while even with PF97s), never cracked any in two years..

TD in DC

Interesting info. I cracked the rotors on my 944, which really surprised me because I barely need to use the brakes on the thing, and it has great cooling. Now I can see why the less I use them, the worse I may be making the situation for rotor cracking.

Sean F

No kidding, I never would have thought to use less cooling.

RickBetterley

So, my long and slow braking is actually an advantage? Finally I can feel good about myself.

Larry Herman

IMHO it most likely has to do with the combination of the immediate rotor surface temperature and the overall amount of brake cooling. A differential in temperature with the metal itself will cause cracking due to the differing amount of expansion.

When I raced my old Carrera, I ran Ferodo Asbestos Free pads, and thought it didn't stop the best (read higher entry speeds ) they never faded and I ran for 9 years on the same set of rotors. No BS. I did have a cool-brake kit on it.

When I changed to PF97s in 1998, I started to experience all kinds of problems. Yes I had a good deal better braking performance, but it came at the expense of the occasional softening and pulsating pedal, fried caliper seals every other event, and cracked rotors every third season. The PF pads were just generating too much friction for the system to handle. I feel that the smaller pads, when forced to brake at the limit of the sticky R tires, will produce some really high localized temperatures at the face of the rotor, as opposed to bigger brakes, which will spread a lower temperature across a larger area. Maybe that's why they are failing so quickly.

Noel

Very interesting. I too had never considered this. Two weekends ago while at the Glen, when off the track and back in the paddock my rotor temps were only 200F and the caliper temps were only 180F, which I thought was really low. I have a similar setup to 1957 356 except that I have the wider Carrera capilers and rotors. I guess I need to check my rotors, as they are about three seasons old.

dave1200

can you post a pic? Id like to see them.