actually, I ran 25 in the rears with eibach springs and they were just fine. When I put the taller nismo suspension on, they stuck out too much so I went down to 15s, but they still didn't rub
25mm spacer and eibachs:
25mm spacer and nismo suspension:
anything smaller than 25 and you will have to use the spacers that require longer studs. the factory studs are slightly longer than 20mm so the studs stick out past the spacer when the bolt on kind is used.