For show purposes, I have 14X7 Thrusters with Redlines front and back on a 68 Nova, Baldwin Motion re-creation that puts out about 550hp. For casual street use, I'd like to put on some Rallys and bigger tires. Do you think, in an after market rally style wheel, a 15X8 with 5" backspace and a 255/60/15 tire will work in the back without modifying anything? How about 15X7 with a 4" backspace and a 225/60/15 tire in the front. Will that combination rub anywhere, anytime?

If you can fit 14"x7" wheels on your car then brake clearance isn't an issue. That size wheel and back spacing sounds like it will work but is pushing the limits in my opinion. A more conservative tire size might give better performance as nothing you run on the street is going to hold the motor anyway.

Big Dave

The 15x8 with 5" backspace may work. The trouble area will be the lower shock mount area. The 15x7 wheels will hold the 255/60R15 just fine. The tires on my Nova (pic in sig) are 245/60R15 front and 255/60R15 rear all on 15x7 wheels with 4" backspace. On the rear there is about 3/4" between the wheel rim and the shock.

Looks good on your car! Tire suggestion for general all around street?

Thanks Bob.
I like the BFG Radial TA . Second choice would be some Goodyear Eagles. They have a muscle car look, but maybe that is because they were the trie of choice many years ago.