I was wondering how accurate my equation was. I'm thinking it's probably pretty close. When my speedo reads 60, I'm doing 66. 20-21 mpg with 235's isn't too bad then, seeing I do 40 miles of my daily commute going 75-85mph. I would like to get a gps just to be sure, though.

99 Sportage 2Dr, 1.5" body lift, 30x9.50 Cooper M/T's, high lift, CB, custom bumpers, Warn manual hubs, Tom Tom GPS, snorkel.
99 Jeep Cherokee 3" lift, 31" mud terrains