I had 265 60 15 on mine.. no problem.. 285 60 15 will fit, but for safety, cut the parkbrake cable holder off the side of the trailing arm and reweld it on the top of the arm..that will give you about 3/8 inch clearance to the tire.
I'm running 255-60-15's they look nice and beefy and don't rub on anything, they also don't cause alot of hunting in the front end.
What I mean by that is the wider of a tire you put on the front of a vehicle the more tendancy it has to hunt cracks and differences in road surface and can make the car a pain in the butt to drive even with a good alignment and tight suspension.
Then again I live in Pennsylvania, home of the worlds worst roads.
Oh and try to stick as close to the same tire circumference as the oem tires are so you don't get speedo error. http://www.1010tires.com/TireSizeCalculator.asp?action=submit
heres a link that has a handy tire size comparison calculator.
I agree with ya Raybies on the roads in Pa., I'm only adding my.02 and everyone can do what they please, but I stick with OEM size tires,in the past I did the same thing, put bigger tires on, everything. It always caused me problems. I know it's good for business, but it's more of a cosmetic thing than an improvment. My 96 Ford F-150 4WD has OEM size tires on it and it works beautifully and the brakes last as long as they should. I also ride ATV's regularly(Don't hate me, we have hundreds of miles of abandoned stripmine roads) and that sub-culture always goes to the biggest,badest tires they can find, then wonder why their machines wear out prematurely, I go smaller and the machine performs better and last longer, for my Vette's it's OEM tires..............