I have 19 inch Pirellis but went with dedicated wheels in 19 by 8.5 all around.
I think the tire size is 235 35 19. They were about $240 a tire before shipping and tax.
I'll snap some photos later.
I used 10mm spacers on the back to push them out a bit. 8.5 wide on an M3 at the rear is pretty feeble looking.
11 E90 M3
14 F31 328 xdrive