275 is the widest i've seen ppl get under a fox without a minitub or modified fenders. To get a 275 in you'll most likely need to remove the quad shocks and possibly adjust the tailpipes inward. When I had 275/50/15s on my 88 lx, they rubbed the tailpipes and quadshocks.
If you're willing to run dumps and remove the quads; 285's and *some* 295's will get on the back. 275 is definitely the max I'd recommend though and that will require HEAVY rolling of the fender lip in the rear.
255 is really the max for the front and work well all around too.