Quick Backspacing Question

Why do you want to put a 225-60-15 on an 8 inch rim? A stock 6 inch rim will suffice for that size tire. Are you looking for the fartcan look? Just remember if you put a tire on a wheel wider than the tire, if you scuff a curb or pothole you ruin the wheel and tires are generally cheaper to buy then wheels. I like a little side wall bulge to protect the rim. I run a 255-60-15 on a 7 inch rim with 4.5 inches of backspacing with no rubbing and no ill handling.