I run 15 x 8's with 4.5" backspacing on my Cragar SS wheels on my '69 Road Runner. I run 275 60 15 M & H street tires that have an overall sidewall width of 12.2". There is roughly .750" clearance between the fender and the springs. They never rub. If you are using 10" wheels, the 5.5" backspace should be what you are looking for. Good luck. Tom