Congrats on your purchase. The M3 is much wider in the rear so your biggest concern is whether your car has enough clearance to accommodate the M3 offset without rubbing. Search the 3 series threads. I seem to recall 2007 E90 owners saying that there was enough clearance in the rear of the E90. I am not sure if that applies to the E91 though. I think the front should fit without much issue.
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