You can check here to see how your tire/wheel combinations compare:
http://www.rimsntires.com/specs.jsp
Error is "approximate"! This calculator used to be "FREE" and it could be used rather effectively to determine chassis/body clearances for various tire/wheel fitments.
I'd be interested in the percentage comparison of the calculator vs. your GPS. I don't know that they've compensated for "rolling radius" or just use advertised diameters.