I've got 17x8 "Bullit" rims with 5.71 inch backspace, with a 1 inch adapter, so that gives me 4.71 inches backspace. But looking at all my suspension and steering components, I can tell that if I had a 16 inch or 15 inch rim, it would rub against the upper control arm, so you must be right about the 4.25 backspace on a 15x7 rim. So the lesson here I guess is that the maximum backspace you can have depends on the diameter of the rim.
__________________ 66 Coupe - CandyApple Red, 2 barrel 289, C4.
66 Coupe - (father-daughter project). Tangier Orange, 302 with AOD, 17 inch Bullit wheels.
69 F-100 - 351c. Emerald Green Metallic paint. Still "in progress".
68 Barracuda - Rusted out project. 318 in the frame rails for now. Maybe a 360 in the future.
00 Mustang - (son's car) V6, 18 inch Saleen wheels. |