Cross Drilled
 

I put on some Zimmerman crossdrilled rotors about 10 months ago on my 98 boxster. When the time comes for me to change my pads, do I have to shave the rotors? I'm sure I do, but I asked my mechanic, and he said that crossdrilled cannot be shaved. "they have to be replaced," he said.


But I'm curious on the Boxster S owners with the stock crossdrilled rotors. How would those rotors be regularily maintained?

Well I've heard that the factory boxter S cross drilled rotor and brake wear fast BUT if your rotors are aftermarket and your brake pads arent porsche pads then you might not have to replace the rotors every time you change the pads, if the brakes are made witha more less abbrasive compound like organic type then your rotors should last alittle longer.

Hi,

Crossed-drilled rotors on a boxster are about 99.% asthetic, maybe 1% of them which are tracked regularly actually need them to off-gas the pads.

But, their strength is compromised by the drillings, so they cannot be turned or machined because this would further compromise them. If the lathe didn't cause them to crack between the drillings (and this is why most machine shops will refuse the work), they would most likely crack shortly thereafter.

Unfortunately, if you wanna look cool, you got to pay the price...

Happy Motoring!... Jim'99

I may be mistaken.. but I've always heard that cross-drilling was all about weight. Is that not a factor in the decision for cross drilling?

Sorry about the thread-jack.. but I thought this a good a place as any to ask.

Berj

Hi,

Certainly when you take away material as when drilling the rotors, you are removing Mass (weight), but you'll remove maybe 10%, any more and the integrity of the rotor is lost, not to mention that the loss of Mass also impedes the heat transfer, which is really all braking is - the conversion of inertia (stored energy) and mechanical energy into heat energy which is then vented to atmosphere and removed from the system. Motive force (the car's energy) is reduced to a point below that of the Resistive Force ( rolling resistance, and aerodynamic drag) acting on the car, and the car slows or stops.

But, the reason for cross-drilled rotors is that when a brake pad is pressed hard against a rotor, a plasma builds from the pad material which is burned away and lives between the pad and the rotor. This plasma reduces the pad-to-rotor contact and consequently reduces braking efficiency.

By drilling holes in the rotor, you provide an escape for this plasma (many refer to this as Gas, but it really isn't) and assure better rotor-to-pad contact and more efficient braking.

But, for a street application, you simply don't work the brakes hard enough that it makes any difference. The brakes cool between applications and you're hauling down from 30MPH, not 130MPH, so not nearly as much plasma is produced in the first place. Hope this helps...

Happy Motoring!... Jim'99

Well whaddaya know.. I learn something new every day. Thanks for the explanation.

Berj

I always thought that cross-drilled rotors were simply about increasing the rotors' surface for better heat convection (i.e. cooling). More holes produce more surface for the heat to radiate from. That and the spoiled aerodynamics (turbulence, ventilation) from the holes translates into faster cooling of the rotors. Looks like the plasma explanation is a more scientific way of saying the same thing.

I was not aware that they cannot be shaven just like standard rotors, though. Something to keep in mind.

Z.

Hi,

Again, this is an advantage to drilling the rotors, but ventilating the rotor is primarily for cooling. Some disks are slotted to aid in removing the plasma created too...

Happy Motoring!... Jim'99