is it possible to change the rolling radius of a car without any problems? I have 17 inch wheels with 235/40/17 on my E36 BMW and they seem pretty weedy compared to my friends saab's wheels (also 17 inch, but larger profile and thus total diameter)when measured seemed about an inch more in total diameter. I would like to either fit more rubber on, like say 235 50 17, or keep about the same profile and go to 18's. Is any of this possible? Thanks, Luke (uk)