[rjs53]

A lot of people on this site are running 20x10 rear and 20x9 in front. The rears easy to find. Put jack stand under axle, pull the wheel put a straight edge on the drum and measure from face of drum to outer wheel well lip and to frame. Remember 3/4” is about the least amount of clearance you want from rubbing.
This will help with backspace, don’t forget section width of tire also