Stock tires are 225/45-17 and 245/40-17 right? I dunno what the max you can fit under there is but 245/40-18 and 265/35-18 wouldn't be so bad. Expensive as fawk though.

I wouldn't put 18's on that car anyway though. I'd go to wider 17's but once again I have no clue what sort of a tire fits under the thing.

Theoretically if you went one step lower in profile F/R that'd put ya at 245/40-17 and 275/35-17 which is exactly what most tuners put on FDs so that'd probably be alright balance as well.