Not sure if it matters to some but I dont like carying 2 spares when the wheels ya have fit snug. So another thing to consider is the offset / backspacing you will have in the front. Set yer desired wheels in the back and make allowances for that same offset/backspace in your rearend measurements for a single spare option. Unless of course yer running big / little then, I'm full of it. But we all know I ride a sled w/4 matching 15x7's not a hotrod, not yet anyway!