I think you are confusing them with the front wheels. 4.75" backspacing is about the max you can go on the front before it hits the ball joint. For the rear, I've got 10.5" rims with 6.85" backspacing and need 3/8" spacers to get about 1/4" clearance to the leaf spring. That is basically a net backspace of 6.5". I would think a wheel with 5.5" backspacing would work with a little over an inch clearance to the leaf spring. Watch the tire width and the quarter lip clearance when getting too low of backspacing.5.5 backspacing will rub the leaf spring. Mine are 4.5 backspacing, with a 275/50R15 on them, and are maybe 1/2" from the spring.