quattro digest, Vol 1 #4967 - 19 msgs

Larry C. Leung l.leung at juno.com
Sat May 24 10:54:43 EDT 2003

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Boy, rhis is an old thread....

Cross-drilling was developed in order to allow brake pad gasses to escape
the critical
pad to rotor faces during VERY hard braking when the pads actually heat
up enough
to cause out-gassing. The pressure of the boiling of the pad material is
enough to cause
loss of contact between the pad and the rotor. Again, this is only of
issue in EXTREME
braking, such as in racing. Of course, cross drilling has drawbacks as

Loss of rotor pad contact area (less potential braking force EXCEPT in
the cases of
                extreme pad outgassing)

Loss of rotor mass (this ultimately  higher potential brake temps when
the rotors heat up)

Reduction of pad and rotor life (see the first point)

Potential stress risers at the holes, causing the not so uncommon problem
of cracked
rotors in lesser drilled rotors.

BUT, they LOOK cool.

Of GREAT NOTE, Porsche does NOT use drilled rotors on any of their actual
race cars!

SLOTTED rotors were developed later to allow the escape of pad
outgassing. Thus,
they allow the gas to escape out the slots, with notably LESS of the
drawbacks of the
drilled rotors, but they still suffer some of the drawbacks to a degree
with the exception
of rotor cracking.

If your car is only going to see the street, you will unlikely see the
performance advantage
of drilled or slotted rotors (but they LOOK cool!). Even in autocross,
still unlikely to see
an effect. On the TRACK, however, especially with a heavier car, it may
help, and rumor
has it that it has an advantage in the wet, as water gets swept in to the
slots/holes and clears
the rotor faster.....


> To: quattro at audifans.com
> From: tihol_tiholov at sd27.bc.ca
> Subject: Re: better rear brakes
> Date: Fri, 23 May 2003 14:18:46 -0700
> Bret says:
> >"If slots/holes are so good, why is there only one automotive
> >manufacturer who uses them?"(Porsche.)
> Expensive if made well, that's why.  Porsche seldom compromises
> with
> anything and certainly not with brakes, even if it turns to be
> expensive.
> Almost (if not all) all WRC (World Rally Championship) manufacturers
> use
> slotted metal rotors on their group A cars.  This has been going on
> for
> quite awhile.  ( The carbon-based rotors are not slotted, though
> Porsche
> has drilled carbon-based rotors.)
> Greetings,
> Tihol

 From: CL Wong <montesawong at yahoo.com>
> Subject: better rear brakes
> To: AudiFans <quattro at audifans.com>
> Cc: 200q <200q20v at audifans.com>
> >"If slots/holes are so good, why is there only one
> automotive
> >manufacturer who uses them?"(Porsche.)

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