Originally Posted by gthal
245 front and 275 rear is very common. Beyond 275 is doable but tough. Potenza RE-11 in a 275 rear is tons of grip.
Sounds like enough grip. It's interesting because I run 295s on my M3 with no problem. I feel a car like the C63 should be setup for some nice wide tires. Although I will admit 295 on an M3 is overkill. 275 is probably perfect.