My wife is moving up to 18" for her Summers on her 2011 WRX and has a spare set up tires I can use. I know I'll be over by about 2% on diameter (3% if they were new), but I'm mainly concerned with width. It may make sense and be cheaper to just jump on fender rolling now if that's what's needed, but I'm obviously worried about making contact inside the wheel well too. For suspension I have 9kg springs up front and 7kg in the rear so I'm going to have less travel as well.