One more item on cross-drilled rotors: they crack and chip like all get-out.
The spiffy "cross drilled" rotors that Porsche uses (and aircraft manufactures
for that matter) actually have the holes cast into the blank before machining.
Why? Simple metalurgy. When you drill the hole, you screw up the crystaline
structure of the metal left at the edges of the hole. When you cast it in,
you don't have the problem. So they last a lot long, don't crack as badly
and don't have the same sorts of catastrophic failure modes...
Regular rotors that have been drilled are fine for "real" racing use where
you have a log of the hours accumulated, lots of testing, good records on
expected life, and an agressive program of tossing them when they approach
your anticipated end-of-life point. For guys like most of us, trying to
stretch component life as long as possible, that's not such a good deal.
Stan
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