C5driver

The stock rims on my non-existant 535 Sport are 18x8 fronts and 18x9 rears. The rims I'm looking at are 18x8.5 fronts and 18x9.5 rears. I'm going to be mounting the stock tires on the new rims.

What, if any difference, will there be in the appearance of how the tire sits in the rim? Will the quarter inch difference per side cause the sidewall to curve in significantly, or will it still be squared?