what fits

I have a set of 255/60r15 tires under my 73 dart swinger. The rear rims are a set of 15x7 steelies with a 3.5 backspacing I believe. The car has an 8 3/4 and the tires fit absolutely perfectly without any modifications to the car! There is lots of clearance everywhere so its never rubbed.

The car used to have an 7 1/4, and with that rear end the perfect rim was a 15x8 with 4.5 backspacing.