Cross Drilled Rotors

["Steve D'Gerolamo" <steved3@xxxxxxx>]

Gas slotted rotors actually *decrease* the ability of the rotor to 
withstand heat. This happens because you're removing some metal -- 
metal that would otherwise work as a heat sink. That's why gas-slotted 
rotors don't tend to warp as much as cross-drilled rotors (which have 
had more metal removed).
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			The problem with most cross drilled rotors is that the drilling disturbs
the integrity of the casting and the holes are often too big or
non-chamfered.  These holes act like a cheese grater causing accelerated
pad wear.  In addition, because of the size & location of the holes, cracks
will often develop between the outer holes and the outer circumference of
the rotor....these cracks will eventually split the rotor, not a good thing
when you're trying to stop from triple digit speeds on the track.  Simply
drilling a rotor will not greatly improve cooling....the rotor must have
the proper cooling vanes to effectively capture the air and force it
through the holes.  This forced air travelling over and through the rotor
takes heat with it and keeps the temperatures down.

Porsche, and now supposedly Brembo, have cross cast rotors where the holes
(4mm instead of 8mm) are actually cast in the rotor upon manufacture.  With
dual internal vanes, cross cast cooling and stainless steel alloy
construction, Porsche's rotors are top's in the industry.  If BMW ever
adopted this technology, there would be no need to consider big brake
upgrades for track applications.   SD
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Steve D'Gerolamo - The Ultimate Garage
201-262-0412 / steved3@domain.elided / http://www.ultimategarage.com

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