Back space question
 

What back spacing will I need, is 4" up front ok and 5.5 out back?
I want Center line Qualifirers to my 66 Chevelle in 17's x 8" with 245/40 up front 17 x 9.5" and 285/40 on the back
I am after the deepest dish look I can get, the car also has air shocks on the rear too
Thanks
Sean

The more backset you run the smaller the dish because the wheel rim will move closer to the center of the car.

4" up front 'should' be ok since typical with an 8" rim would be 4.5". So you'll have an extra half inch of dish depth. Of course that pushes it in and a tight turn may cause them to rub. Your rears are 1.5" wider and you added 1.5", so all the extra is going in, making the dish shallower. Of course with a 5" backset you may scrape and have to roll the fender edge. Sounds like 5.5 might be right.