how wide is the rim? if its 9" wide, dont go any skinnier than a 275. if its a 10" rim, dont go any skinner than a 315. a set of nitto 555r's never hurt anyone. id also try some of the BFG's.
i think im going to go wtih the BFG KDW2s in a 295 since it has 10.5" wide in the back. i thas 285s on it now and they look ok. my old car had 315s on it and they looked good but 315s for an 18" rim are real expensive