I am doing the 5 lug conversion on my 91GT. I wonder if I have to do some modifications on my rear end to make the 17x10.5 wheels to fit in the back. i am planning to go with 285/40R17 tires. thanks.
It depends on the offset/backspacing. You may have to roll the fenders or maby you might have to eleminate the quads or flip and cut the boots. May need to use do a little massaging with a BFH. If your going to go with a 10.5" wheel, why not 315/35R17??? They would fit the wheel a lot better.
run a search and you should have plenty of results on this topic. There are plenty of threads of people wanting to put large, wide wheels on fox's. I just put some (supposedly) 15x10's w/ 6.5 backspacing on mine today w/ some 275/50/15 bfg's and they fit w/o flipping or removing quad shocks and no spacers, but a lot have to either remove the quads or use a spacer. The 17's w/ 285/40's should be around 26". 90+ had wider fenders. You might have to roll your fender lips and use a spacer. Each car is different when it comes down to it.
I run a set of 325(app.12.7")/50/15s by taking 1" off each axle and heating and beating the fender well. You might get by with just heating and beating the fender wells.