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St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13
The widest wheels you are going to be able to fit under a C6, without fender or body modification is going to be a 10" front and 11" rear. With the wide body kit (ala Z06) you can go up to a 10.5 or 11" front and 13" rear.
I have fit up to a 305 front tire and 345 (still waiting on 355's) in the back under a Z06.