B7 rear brake bias ?

[laraa at sympatico.ca]

Henry, 

Your comment about rear brake bias is truer than you think... 

In the old days, a mechanical proportioning valve was present on many cars
to ease the pressure at the rear for the obvious reason. It was often driven
via a suspension arm and would prevent rear brake pressure if the rear of
the car was higher than the front as in a strong braking event. 

On recent cars with ABS/ESP, it's the ABS/ESP module that proportion brake
bias via the release valves in the ABS block. No more proportioning valve.
So, in fact, there is often full braking power to the rear wheels (in
proportion to the volume of front and rear calipers respective pistons)
until there is some slippage at the rear wheels. As a rule of thumb, and if
my memory is right, the ABS/ESP module will release pressure to the rear
wheels if they are 20% slower than the front. You won't feel it at the pedal
since the ABS pump doesn't work in this scenario, only the internal valves.
So, if you brake moderately, the rear wheels are indeed braking more than
before, hence more wear.

Side benefit, or maybe more of a drawback, if you pull the ABS fuse or
deactivate the ABS module, lock-up of the rear wheels is a lot more likely.
On a car like your Quattro though, this is  mitigated by the AWD system that
links all the wheels together via the center differential.

Well folks, that's it for tonight Technical tidbits. Feel free to correct me
if I'm wrong. 

Louis-Alain


-----Message d'origine-----

Didn't need to replace rear pads on my GTI or 200q in 15
years or so...this car only has 70k on it, must be some good rear brake
bias!

Thanks,
Henry Harper