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#11: 02-20-2005, 11:08 PM
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Title: Burning Monkey
Location: Seattle, Washington
Car: Turbocharged 2.5i Outback
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Well, I'm late in this, but some points on blank vs. slitted vs. cross-drilled rotors.

For the street, blanks are more than adequete. They simply don't look too cool, which is why there is a large amount of slitted/cross-drilled rotors on street cars.

For the track, slitted rotors make the most sense in terms of circuit performance, especially over longer periods.

Which leads us to cross-drilled. There are two types of cross-drilled - ones that are actually, physically drilled, and ones that are cast with the drill holes in place (Porsche rotors). The cast-hole rotors are fairly sturdy. And expensive. At the track, rotors are like bags of chips while watching the superbowl - expect to replace them regularly. So if you are serious about your track braking, balance your needs vs. replacement costs.

Cross-drilled rotors cracking: All rotors have the possibility of cracking, cross-drilled (non-cast) are simply the most prone to it. Yet you can easily make a cross-drilled rotor last longer without cracking than even a blank rotor. The main failure point for rotors is not on the track itself, but after you leave the track. Most people go 100% (or more, at least for them) on the track up to the last second, pull off, stop the car, set the e-brake and let those expensive rotors cool off rapidly. <crack!> What really does it is the brake pads - the rotors are exposed to air everywhere but the pads, and when you let it cool off from Extra Crispy to Slightly cool with most of the rotor cooling off *much* faster than the section of the rotor under the pads, the difference in temperature will make *any* rotor brittle quickly.

If you want your rotors to last after track racing, either take one or two really slow, easy cool-off laps before you pull off (if you have that choice), or try to slowly roll around somewhere to let the brakes cool off more gradually and evenly.

Porsche owners with those expensive ceramic rotors have had some fairly expensive replacement bills (think half the cost of WRX or more...) after relatively low mileage on those rotors because they do just that - pull in and stop. Even Porsche thought they would know better...


Paul Hansen