RE: E30 Brake advice

["Fadeev, Alex" <Alex.Fadeev@xxxxxxxxxxxxxx>]

GGray sez:
> E30 Brakes...
> " gas slotted and drilled rotors don't work..."
> Unfortunately Gas slotted rotors do work. They off gas the 
> pad and keep the pad/rotor in contact instead of running on
> a boundary gas layer created by heavy brake applications 
> or as what most people would describe as, brake fade.

Corrections:
1). Brake fade is not (just?) gas layer between pads and rotor. 
Brakes fade after constant, heavy, repeated use on the track. As brakes get
hot, two bad things happen:
(a). the heat transfers to the brake fluid (through the calipers). Brake
fluid boils. When your floor the brake pedal the air in the fluid is
compressing internally instead of pushing the caliper to squeeze the pads
around the rotor => no brakes.
(b). The brake pads themselves fade as they heat up. 

Problem (b) is addressed by buying brake pads that better withstand hot
temperatures (those typically need to be warmed up and don't work too well
when cold). Problem (a) is partially addressed by using braking fluids with
higher dry boiling points and flushing the system regularly. 

Increasing the size of pads/rotors will _not_ effect heat transfer through
the caliper's piston (brake fluid boiling). Unless brake caliper's piston
diameter is increased (or its metal composition is changed), the piston will
continue to transfer the heat to the brake fluid at the same rate. Larger
pads/rotors will heat proportionally slower, so there will be a bit less
heat to transfer to the brake fluid through the caliper. But if you
regularly boil your brake fluid and flushing it in favor of a fluid with
higher boiling temperatures does not help (and neither do different pads,
airducts to cool the brakes, etc), only then is it time to either stop
resting your foot on the brake pedal or install new calipers/brakes.

Rotors:
It is not that drilled rotors do not work. They do. But IMH experience, not
any better then regular rotors. I also had a bad experience with drilled
rotors cracking on me (from the outer drilled holes to the outside of the
rotor). 

Then again, I may not be rabid enough to 'gas' my rotors/pads enough to see
the benefits. Those who race regularly/professionally, please correct me if
'gassing' is a major issue on the track. It is NOT an issue on an autocross
course!

Disclaimer: I have not had any personal experience with gas slotted rotors.
In theory, they should not suffer from cracking  nor do they give up much
rotor surface. For all I know, they might be great. If nothing else, they
should clear moisture from the rotors faster during that first morning panic
braking. 

> You
> will also see shorter stopping distances by upgrading the
> brakes especially if you do any autocross or track events 
> where the brake system gets heat soaked. 

Corrections:
1). Your chances of experiencing 'brake fade' on an autocross course are
negligible. Don't waste your money on bigger brakes if you autocross - go
with better pads.
2). The stopping distance will never get shorter with bigger brakes. You may
keep it from increasing as your brakes fade, but bigger brakes do _not_
equal shorter stopping distances. All brakes fade. Larger brakes just take
longer to fade.


Hope this saves someone from getting ripped off. 

If you believe I am wrong, please convince me otherwise. I am always open to
arguments. Just please skip the obligatory insults.

thanks for your time,
alex

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Here is another data point from a post to the UUCDigest #449: