A 215/45/17 has an OD of 24.7 inches, and a 205/55/16 has an OD of 24.9 inches. Thats how I decided I was getting that winter size. As close as I could get to stock tire size for speedometer accuracy, and the 55 series having a larger cushioning sidewall for the winter.
The iPikes look great with studs - are they directional though??