I work for a reputable tunning shop in San Diego C.A. know as Group 5 Motorsport. We are known in are area as wheel and tire fitment experts. We offer real fender modifying with the most high tech industry tools available. I have a cooper S and after discussing the car and trying a few different options with people from the likes of Racing Hart, Yokohama, and Brembo I came up with maximum fitment of 18 x 7.5 w/ 225-35-18 with this package some minor fender trimming is needed but it will clear 100% no rubbing even on H&R springs. I can get you the exact off set if you need it let me know.
kevin@group5motorsport.com