Also hear that star specs run wider...

 

Just a thought. Run your 18's for the street & convert yourself over to the 17" wheel/tire for the track. Tires are a good percentage less expensive & you can run your 40 series.

R-spec 255/40/17 tire & you are golden

 

Yes. +20 offset will rub in the rear for all of your options.

I rubbed on 265/35/18 with +35 offset and -1.5 rear camber on the rear fenders which has +15mm more offset than you. With a 235 wide tire you are in the same boat towards the rear fender as I started. So, you would need to roll just to get a 235 wide to not rub (at the same tire height as 265/35). Your best bet is an agressive roll and the 255/35/18.