Matt,

The general rule of thumb is that you stay within +/- 3% of the OEM wheel & tire rolling diameter when installing aftermarket wheels & tires. This means that your front aftermarket wheel & tire should be within 3% +/- difference from what the front OEM wheel & tires is. Then the rear aftermarket wheel and tire should be within 3% +/i of the rear OEM wheel & tire.

The front rolling diameter has nothing to do with the rear rolling diameter and there's no need to compare the difference between the two.

For you and your buddies that are looking into aftermarket wheels I'd be glad to help you out and set you up with what's needed.