No the M bumper isnt changing anything as far as room for the tires. I just spent a lot of time looking at diameter and width of tires and the 255s seemed far more likely to work and look right. As I sent to Kabrich...I cant stand stretched tires where there is any wheel poke. No offense to anyone here but that looks so odd to me plus does anyone here really want to expose the wheel further to curb rash... Second is tire diameter, which you dont see as much but a tire too tall for the car, wheel, etc and that looks odd as well. Like my grandpa in the 80s who would want as much tire sidewall as possible for a cushy ride on his Cadillac.
doesnt look right on these cars or really any cars these days. To me, lower profile is always better as long as the wheel/tire fender gap can be reduced by lowering. And assuming you dont have to drive on crappy roads like up in LA where you would bend wheel with too low a profile.