Originally Posted by Bbenavitz
It is interesting all these sources tell you it is nothing more than a build up or deposit of pad material, but if you have your rotors turned to true them the lathe operator will show you the metal being removed to bring the run out down to acceptable levels. It is definately not pad material being removed, because if it was your rotor thickness would not be sustantially reduced they way it is to get a true rotor. Since I first started seriously tracking cars in 1989 using stock rotors and race pads I have found that every car since then (Mazda RX2 race car, Acura Integra R, C5 Corvette, Mitsubishi Evo 8, C6 Z06, and now the M3) all will produce a warped rotor after 4 to 6 one day track events, assuming you are pushing hard enough to get a lot of heat into the braking system. In my opinion rotors are consumable items when tracking your M3 just like the pads, brake fluid, and tires are.
Funny... I did not warp one rotor in 6 years of driving schools and 10+ years of racing (and instructing) and I had terrible technique for a number of years -- way too late and way too hard -- great way to build up heat. Add in that for many years the car was a two driver car and you have the recipe for warped rotors. All brakes were stock but the pads were not, they were always race pads. Started with PF90s, used Hawk HT-14 and HT10s, PF01s, and now since I'm retired I run PF06's. PF08's will go on the car next. For the street I use PFC Z-rated pads so there is no need for bedding between the different pads as I swap them. Plug and play. No. I don't work for PFC nor do I have a financial interest in anyone who sells PFC pads (wish I did).
Stock pads on the track will produce pad deposits as I found out at the Salzburgring in 2002 with a new M3. Switched to Hawk pads since I had three more tracks to run (A-1 ring, both tracks at the Nurburgring) and no problems. Those in the group that didn't switch rotors, including some uber fast racers (National champion w/years of ring experience is one example) did have pad deposits even when being careful.
A great way to remove stock pad deposits is to put on a set of aggressive race pads and do some street driving with them. That'll machine a bit off the rotors in no time!
OP: Get some good track pads for your DE events and enjoy your car.