Brake fade

[C M Smith <cmsmith@domain.elided>]

Classic brake fade on drum brakes was caused by expansion of the drum away 
from the shoes. You eventually ran out of pedal travel due to the drum 
surface moving away from the extreme end of travel of the wheel cylinders. 
That was caused by heat.

Brake fade on disc brakes cannot be caused by this. Boiling of water 
contaminants in brake fluid was and remains a serious cause of fade in disc 
brakes. Also, for a time, brake fluid itself was prone to boil, but 
matching brake fluid specs to your particular application pretty well 
eliminates this cause. This was due to heat.

Outgassing of pad material is, I believe, due to heat.

Brake fade is caused by heat, no matter what the actual mechanical cause is.

Pad wear is a result of the friction removing pad material, not directly a 
result of heat but the friction of course generates heat. Indeed, heat is a 
necessary result of braking or the car won't slow down. Kinetic energy 
needs to be converted into potential energy, and heat is it. The hotter 
your brakes get the better they are working, up to the design limitation 
when the pad material disintegrates. That burning smell is the pad 
disintegrating. The brakes will fade at that point. This is due to heat. 
There are other types of braking technology which are not so dependent upon 
creating and dissipating heat, but none are used on racing cars and 
precious few on street cars (though streetcars were notorious for using re 
generative braking)

While drilled rotors can deal with outgassing, they cannot deal with 
disintegration of the pad material except by cooling it. I agree drilled 
rotors have damn all to do with cooling on a  street car.

Grooved rotors are even dumber. The grooves can have no significant effect 
on heat transfer. Indeed, both drilling and grooving reduce the heat 
absorption capabilities of the rotor due to simple mass reduction, reducing 
the heat holding capacity of the remaining material. Plus, street brakes 
are expected to last a long time. The rotors are designed to wear and be 
replaced. How long do you think those mickey mouse grooves are going to 
last before rotor wear eliminates them?

Plus, the number one problem facing the street driver is keeping his 
performance brakes hot enough to work properly, not cooling them off. Most 
street driving is done with "cold" brakes and the pads are designed 
accordingly. I drive fast, sometimes very fast. I have NEVER overheated 
even stock drum brakes, let alone disc brakes. Driving fast on the street 
involves minimal use of brakes and certainly the kind of repetitive heavy 
braking experienced when doing hot laps is anathema to the quick street driver.

As Fangio was reputed to say: for fast driving use less brakes and more 
accelerator. If you are driving in traffic or even alone on the highway, 
anticipation is the key to successful fast driving. Just about every time 
you use the brakes you are eating into your average speed and extending 
your eta. I pride myself on the minimal use of brakes while on the highway. 
It is a rare highway indeed that requires the kind of high performance 
brakes that race cars benefit from.

Cheers all and let the flames begin.

PS The responses to my heretical pronouncements on Japanese vehicles were 
interesting. Some even tried to pretend that Japanese cars were no more 
reliable than other makes. Well, from the factory door that can be 
conclusively proved to be absolutely false. Japanese built cars are far 
more reliable on average than those of any other maker. Even Japanese cars 
manufactured in other countries tend to be more reliable than the average 
for that country. It's the system they use which others have emulated with 
similar improvements in quality. As the Japanese cars age, I concede that 
reliability depends on how they have been driven and far more important, 
how they have been serviced. It is distinctly possible that Japanese car 
dealers have less experienced mechanics. It can probably be proved that 
owners of Japanese cars in general neglect proper maintenance and the cars 
suffer accordingly in the hands of subsequent owners. I find the quality of 
service for my Alfa and for my SAABs to be of a very high quality. But the 
mechanics and service people get lots of experience fixing them don't they?
Michael Smith
White 1991 164L
Original owner
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