I'm running 18x8.5's with a 225/40 lowered about the same as you with Tein S-tech's. The rims have a +42mm offset and just ever so lightly stick out from the fender. It's only noticeable if you look directly from the back of the car on either the left or right side.

I know you're looking more for a 235, but I thought I'd give you my input regarding the 8.5" width rim.