I got the revs per mile from discount tire's tire size calculator which seems to be wrong for my tire (since the size isn't always exactly as stated). Hankook actually claims that it is not 631 revs per mile but actually 651 which actually puts my milage closer to only .5 off instead of 1. That's by my math which is actually more dissapointing because it means i'm only getting 15.6 in the city. Could be worse I suppose. My moms Yukon only gets 13 in the city and it has normal tires.

How did you figure your's out?