Right nowI have 255/35/18 S03's on the rear (18" RacingHart CR's) but since I've had these on they rub I had the rear fenders shaved a bit which helped, but not completely. I don't know what size the rears were before (trying to find some old documents that might say) but they never had the same problem. I'm guessing that they were a bit smaller. Anyways, what I am trying to figure out is what the next tire size down would be that would fit. Unfortunetly, I don't have the offsets.

 

This, and the fact you don't say anything about rim width, may be your greatest set-back.
A 255 in the proper aspect ratio, on the proper offset and width of rim, will not rub on a non-lowered car (which you also failed to mention if yours is the case).

 

Sorry for the lack of information. The car is lowered on Eibach's. The part that was shaved was the fiberglass from the Veilside fender flares. They can shave the actual fender and make it perfect, but I'm just trying to see how the new price of tires would compare. I think the width is 9.5.

 

Let's say you have the correct offset of +65mm for the rear. A 9.0" rim (like a Volk) that is meant for this car can easily run a 255 tire without problems on a non-lowered car. Even a lowered car might still be OK. However, on a 9.5" rim of an unkown offset, could be an issue as you have seen. You most likely had 245s or maybe even 235s before when there was no problem.

 

You can run the 245/35R18 no problem. You may also want to look at running more negative camber before you switch the tires.