Bagged stepside wheel question
 

I have a 70 stepside that is bagged. I have a 18x8 wheel on it now but am upgrading to a 20x8.5. Question is what backspace or offset do I need to run to fit inside the fenderwells with no modifications. Have stock width rear end with drum brakes

Re: Bagged stepside wheel question
 

70 was a crossover year. Some of the early trucks may have the narrower rear axle, so take that into consideration.

My 69 with a 71 rear axle has 17x9 zero offset rims (5" back space). It mounts 275 55 17. It gets you a thumb widths clearance on either side of the tire. My leaf spring truck is flipped so dropped 7" effectively in rear.