When I bought it, it had 265/70/16s on factory wheels. About 7-8 mph off by GPS.
Swapped to 265/70/16s on wider aftermarket mags. About 7-8 mph off by GPS.
Swapped to 265/75/16s on factory wheels. About 7-8 mph off by GPS.
That's what I'm going by. Internet calculators are great & all, but the real world experience w/ this particular scenario shows otherwise.