From what I have seen and experience 17x9 all the way around although 17x8 in the front is better. Max size front tire without major modification is ideally 245/45/17's but I am running 255/40/17's on a 9" wide wheel without any problems. As for the rear generally a 275 wide tire is as big as you can go, although some do squeeze in bigger rubber, but that extra rubber has to be outside the fender normally if you want to go bigger that 275.
__________________ 1988 Mustang GT - 331, hand ported Twisted Wedge heads, TFS Stage 2 cam, R-Series intake, 1 3/4 long tubes, dual 3" exhaust, tko 600, Zex 100 shot, ect.
357 rwhp/ 361 rwtq on motor
428 rwhp/ 484 rwtq on 100 shot
12.48 @ 111 mph on motor (2200ft + elevation)
11.7 @ 120 mph on 100 shot (2200ft + elevation) | 
1991 Mustang LX, Widest Rims And Tires? 
