I'm trying to understand the physics of what goes on when brake fade happens at the track. The most plausible explanation I've come up with is that when the pad reaches a certain temperature, the coefficient of friction between the pad and the rotor decreases dramatically, thereby lessening the effectiveness of the brakes.

I assume that the difference between the pads has to do with how hot they can get before their coefficient of friction goes down the tubes. Can anyone confirm this?
-Cor.

 

You are correct

Their coefficent at cold temperatures is a huge facor as well. The higher cold bite pads tend to fade easier. Ther best resistant pads to heat are track pads, that are boprdeline abusive when used in street driving - they are never warmed to their operating temperatures.

Alex

 

I find that my brakes won't fade for the most part. The only time they creep up on you, which is enough to justify a brake upgrade, is if I am being relentless on a downhill canyon road. After about 5 minutes on such a road, I'll realize, the car isn't really slowing down anymore, and that adds to the thrill even more, kinda.

 

Does "cold bite" mean the grippage a pad has at low temperatures? If so, what do you mean by "higher"? Higher priced, or higher quality?

The reason I'm asking is because I'm taking Sasha to driving school in Nashville this weekend, and while I've already replaced my brake fluid with super blue, I'm using stock pads. Phil recommended Greenstuff, but I want to try the stock pads first. Greenstuff is rated as working as high as 550F, but do they work just as well when cold? This is my street car. Any idea what's the highest temperature the stock pads are rated for?

 

He means that most street pads are designed to provide more bite at colder temperatures - driving on the street, your brakes never get hot enough to fully warm up a set of race pads which makes them less effective. They also have more time to cool and you aren't braking as severely. Because most street pads retain more heat and/or have different compounds that take less heat to make maximum friction, they have higher initial bite at colder temps...

FWIW, I autocross competitively and have only experienced fade once, braking extremely hard from 80 to 30 for a tight corner - and that was on the 4th run. Running 4 runs, back-to-back, 1.4 mile 'autocross course' (basically a time trial road course, though) with little time for the brakes to cool and time sitting that allowed heat soak before the next run. This is running times that are close to or better than the stock and modified (but not super-modified) E36 M3's, E36 328, and E46 325 and 330s.

IMHO, the stock brakes are more than fine for most driving schools and DE's - take your car out with the stock brakes and learn the limitations, and then decide if you need to upgrade. While the Green Stuff are fine for street driving, IMHO they retain too much heat for autocrossing and DE's or track days and fade even worse than the stock setup - because they don't dust much, the Green Stuff pads retain more heat, and while they have a higher operating temperature than stock, it's not MUCH more than stock.

For your first driving school or DE, I doubt that it's something you'll need to worry about - in fact, unless you become a track junkie or a hardcore autocrosser (like me), the stock setup will be JUST FINE with the Super Blue fluid. You did the right thing flushing the stock fluid... just go out and have fun!

And, JMHO, but from what I have seen the Ferodo 2500's perform much better for autocrossing and DE's with the stock rotors than the Green Stuff, although they are more harsh than the stock pads on the rotors and will squeal a bit on the street. YMMV!
FWIW, even as a competitive autocrosser that runs 9 events a year and participates in a couple DE's, I don't plan on upgrading my pads and rotors anytime soon, although they may have to be replaced before too long due to excess wear... When they do, I am kicking around upgrading to Powerslot rotors and Ferodo 2500's, but only then!

 

Agree with scobib, you ought not worry about it for your first DE event.

I do lots of track days and so far have been most pleased with the Ferodo DS2500s. I have Super Blue, stainless lines, and have used various rotors. I have recently decided, since there is contradictory info on the benefits of slots/holes/dimples, to stick with OE or OE sized plain rotors from Brembo. They go fast anyway when you do a lot of track days, why should I spend almost twice as much for the fancy stuff when there is no clear benefit. My next step is ducting, as my brakes can get pretty darn hot at some tracks.

 

My .02.

There are really two types of 'brake fade'.

There is PAD fade and there is also FLUID fade.

Pad fade is most common and is a result of pads simply being taxed above their operational temp range. Some pads are good at upper temps (and bad at low) but most stock street pads "give up" at or near 500*F. At this point you can push all you want but the pad won't bite and may well be breaking down. You will usually however have a firm pedal. At least for a while.

Next comes Fluid fade. This is most often the result of the above pad fade being run into the ground. But it can happen too where you have a pad very capable of operating at higher temps such as 1000*F but the fluid won't take the heat being transfered to the caliper and reaches boiling point. This sisutation will result in a soft or mushy pedal.

With this in mind, you now better understand the value of the BBK. (big brake kit) The primary benefit is to extend those operation conditions and buy some head room to work in. The larger and or thicker rotor helps keep the heat from saturating the caliper body as quickly, the pads are designed to both endure the temps and insulate the caliper, and lastly the caliper will often aide in heat disapation via its alum construction rather than trap it as iron does. Hence the reason kits may not require high temp fluids.

 

Thanks everyone, I really appreciate the excellent views on the matter. From what I see, the major advantage Greenstuff will give me is less brake dust; given how much I plan on really pushing the car, it's really not worth it - especially since the stock pads are covered by warantee and Greenstuff is more than I care to spend on a disposable part. Perhaps, if real driving suits me, I might one day need them, but not yet. Gotta get a baseline first, as you say.
-Cor.

 

I would not advise tracking greenstuff. I have had glazing scenarios from the likes.

Alex

 

For autocross and street use- EBC greenstuff is OK
For track then EBC redstuff, Ferrodo DS2500 or Mintex M1144 will work better.

 

is when you stomp on those binders and the pedal hits the floor and you find yourself saying "oh s**t"

 

Another component of brake fade is caused by gasses being released by extremely hot brake pads (and even rotors). Gas pressure buildup between the rotor and pad face can cause the pad to literally 'float' on the rotor much like the way the puck floats on an air hockey table. This is where slotted and/or drilled rotors come into play. The slots/holes leave a way for the trapped gasses to be purged from between the surfaces and increasing the brake effectiveness.

 

We have found that slotted rotors work best with street pads where glazing can be a problem. The slots tend to clean the glaze. Most of the "hard core" racers using my big brake kit have opted for plain rotors because the race type pads don't glaze and the slotted rotors just wear the pads faster. Some of the race only pads have slots of their own cut into the pads to relieve the gasses.