Re: Coupe Quattro rotor warpage

[petek@pharmacop.com (Pete Kieselbach)]

Sean wrote:

"... Drilling rotors will only lessen the rotor mass and actually
leads to warpage because it takes less heat to warp less mass."


        I imagine this could become another endless thread, but what the
hell - here's my contribution:

        I disagree about the less mass bit.  Actually I believe that
warping is caused by differential thermal expansion (or more likely,
contraction - more on this later).  The less mass there is, the more
rapidly it will cool (or heat), but as long as there is uniform cooling,
the lower mass rotor should be no more prone to warping than the higher
mass one.

        It's that "uniform" cooling bit that I believe is the culprit here.
If you apply uneven cooling to the rotor, part will cool (thereby
shrinking) faster than the rest, and voila: one warped rotor.  Where does
this non-uniformity come from, you ask?  The best guess I've heard of is:
the brake pads (as in leaving the pressure on the brakes while stopped
after hard braking).

        Any better theories out there?

        By the way, I put drilled rotors on a Scirocco I had awhile back,
but would be hard pressed to say that they made any improvement in braking
performance, though they were loud!  I suspect that new un-drilled rotors
would've worked just as well.  Another tidbit I heard, but can't confirm:
all those holes can hold water and make the brakes slower to dry out after
going through a puddle...

'90 100q (161K, great brakes)
'95 Merc Villager (35K, warped rotor)
'73 Norton 850 Commando Roadster (41K, might stop in time)

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      Peter Kieselbach                       ... the look in his eye
      Pharmacopeia, Inc                     seemed to say to the sky
      101 College Road East                 "how to amuse them today?"
      Princeton, NJ  08540
      (609) 452-3788 (phone)
      (908) 422-0156 (fax)
      petek@pharmacop.com

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