biggest widest wheel and tire combo for 96 gt

[Unit 5302]

Well even with a 245/45 tire the stock 7.5" wheels are at the maximum safety limits. That's about 32.6mm per inch of tire. Given the fact it would be much harder to do that on a 315/35 series tire, and even a 9.5" wheel would be narrower in ratio than the 245 on a 7.5" rim, you'd be in deep noogie.

A 315/35 tire would be approximately 315mm wide, and have a sidewall height of less than 4.5". At 315mm that would be 12.5". Fitting a 12.5" wide tire on a 9" rim with only 4.5" of sidewall is impossible.

Hehe, if you can follow what I'm saying then points for you, it's late, and I'm babbling.