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"New, front rotors are 28mm. Minimum thickness after machining is 26.6mm. The wear limit is 26.0mm. The reason that turning the rotors isn't typically recommended is that you reduce the amount of metal to act as a heat sink, which is important at the track, to deal with heat. "
Your rotors have the minimum thickness info stamped on the hubs. You may be able to see that without taking the wheels off (unless you're running D90's).
You are totally correct even though that's not what I typed above. Sorry about that. 28mm front and 24mm rear is, indeed, the new thickness not the minimum as I stated above.
26mm front and 22mm rear are the minimum measures.
Your shop that turns the rotors will have the correct data for your car - and will tell you if they think they can be turned or not. Don't waste your time second-guessing the shop with your calipers and such, just take them in and ask them to tell you whether or not they can be turned. My shop said they weren't sure, I said do it anyway and got a little discount because they came out slightly thin, but I just kept them in case I need a convenient temporary spare.
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