A 10 inch rim will work but I think for a 12.50 an 8 inch will be better. You will get a little better rim protection with the 8 than the 10. 3.75 or 4 inch backspacing will work though. I've got the 3" Calmini suspension lift and I'm running the 15X8 black rockcrawlers with 3.75" backspacing and 33X12.50 BFG muds and don't have any rubbing issues except with the fender wich will be cured within a week via a 2" body lift. I know somebody who is running the same setup with the 10" rims and has major rubbing problems even with the 3" body lift on top of the 3" suspension lift.