What size spare???

Hey all. My question is, what size spare to use? I have 205-60/15 on the front. 225-60/15 rear. The rear end is a 8 1/4 SG. I would think if I have a flat on the rear I need a tire the same diameter, right? But a 225 will rub on the front fender when I make a turn. So instead of trial-n-error, does anyone know the best choice to start with? Thanks.

If it matters wheels on car are 15x7 cop wheels, spare wheel is 15x6 steel factory. both with factory backspacing. Thanks