I have an 04 A4 Sline with 18" rims, they have 235/40/18s on them can i fit a 245/40/18?

 

Those rims are only 8.5" wide, so 235 is about as wide as you should go on that rim. You might be able to get a 245 on that rim but you risk that chance of the tire popping off the bead of the rim, in other words, a blowout.

 

Really??? even on a run-flat? shouldn't a wider tire actually seat better? What I was worried about was touching the suspension behind the wheel.

 

you shouldnt go on 245. Actually a saw much better handling in my car when i changed 235 for 225.

 

You can fit it, but I don't see why you would, it looks terrible. Like previously posted, if you are going for a different size, then go 225/40

 

Have you ever tried mounting a tire on a rim before? You would know what im talking about once you tried mounting a 245 on a rim that small.