Quick Backspacing Question

Im running sbp axles with a 1 inch billet aluminum adapter to go to bbp wheels, the 1inch adapter gives me more room to my leafs, im running a 275/60r15 on the rear and have about 3/4" of clearance between my sidewall and leaf and about 3/16" to my quarter lip. If i didnt run them id be limited in rear tire width, still thinking i could squeeze some 295/50r15's on there but wheels arent wide enough lol