Just purchased a used 2011 Platinum Supercrew 4x4 with ecoboost engine. The original tires are 275/55/20 Pirelli Scorpions. I ran two sets of michelin At/2's on my last truck and loved them. Michelin doesnt make that tire size in an AT/2. They do make a 275/60/20. It appears to be an inch taller tire. What is that going to do for my speedometer and or gas mileage?

 

Your speedometer/odometer will be off slightly. Of course this will throw off your milage calculations. I doubt your mileage will be affected more than one mpg.

 

Most speedometer's read 1 to 2mph faster then what your actually going. Going from the same size 275x55x20 Pirelli's on my truck to 275x60x20 Toyo's put the mph reading right on the money according to my GPS. I figure I lost about 1 mpg with the Toyo's vs the Pirelli's due to the increased rolling resistance on the tread of the all terrain Toyo's. I'm still getting up to 20mpg hwy with a 4x4 Screw so that's not bad as far as I'm concerned!

 

Everyone should have this linked...

http://www.miata.net/garage/tirecalc.html

 

(new tire size/old tire size) X indicated speed = actual speed

(31.9/33.0) X 65 = 62.833 or 3.33% different derived from "100 - ((62.833/65) X 100)"