E46Fanatics - View Single Post - Cross drilled Rotors?
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Old 07-12-2011, 11:31 PM   #76
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Join Date: Apr 2010
Location: China.
Posts: 136
My Ride: e46 m3
Cross drilled rotors are absolutely derived from a performance background, the pad materials used on the racing cars of around 1950's (I think) were not as developed as the pads we all have access to now, one of the problems was that when operating at high temperatures these pads often exhibited out-gassing, the gasses created from the pads was enough to cause an ever so slight layer of 'boundary lubrication' between the pad and disc, that is, not enough to separate them, but enough to reduce some of the asperities of each part contacting, the holes gave somewhere for these gasses to escape, some of the early pads also had low co-efficient's of friction, the multiple edges gave the brakes a bit more bite, with increased pad wear and dusting.

As for cooling, I am unsure, I would think that would probably have to be looked at on a case by case basis, however I do not think cooling gains from cross drilling would normally be anything special, I have never seem any numbers on this.

Anyway, modern pads are much better in regards to gas production and co-efficient of friction, Cross drilling is more of a cosmetic thing than it used to be, though it's benefits do remain, and yes the hole is a stress raiser, however a good quality floating rotor should still give many miles of trouble free service, like everything it's a trade off, less service life - more performance. I have found the standard floating rotors to be of decent quality, I have had them red hot (literally) on numerous occasions, while they do overheat too quickly, they have decent power before this happens.
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