Thought of this today after measuring my duratracs... they're measuring quite a bit under what I expected. Figured it would be interesting to see what other tires actually measure (not just what the manufacturer spec says).
Post up the following format:
Goodyear Duratrac
245/75/17 = 31.4
GY website says = 31.7
Actually measure = 30.5 (6 months old, <5k miles, 35 PSI)
(Side Note: this could also be a reason for people reporting variations in MPG. If i programmed my XK for the 31.7" diameter my MPG reading would be about .6 higher than actual because it would think i was traveling further for each rotation)