TDGTIRE

Hey guys, I changed the tires on my 2012 FX4 eco boost. I took the 275/55R20 Pirelli off and put on 275/60R20 Michelin A/T2. I have 4,000 miles on the truck, have changed the oil and used Mobil 1. I just went from Macon, Ga. to Savannah, Ga. 150 miles, I got 17mpg running 70mph. I took the truck on a short trip when brand new and got a little over 20mpg. Would going up 1 inch in tire diameter cause such a decrease in fuel mileage? If so, can the computer be reprogramed to help this?

TheWhiteBeast

Yes, and yes.

11screw50

Well, an increase in tire size even with the same brand/model tire will reduce mileage some, replacing tires with a larger,heavier tire with a more aggressive tread pattern will reduce it more. I wouldn't expect a 3mpg drop just from that however, there are other variables in play here.

Weather? wind and temperature can both affect mpg
Route? unless you're comparing the same trip, the terrain will be different.
Speed. You mention speed after the new tires but not before. Keep in mind that there is a little more than a 3% difference in actual speed (at the same speedometer reading) with the new tires.

TDGTIRE

Do I carry it back to the Ford dealer to reprogram?

CaSCrew11

I suggest letting the engine break in a bit more. My mileage on my lariat with ecoboost, started getting better mileage around 8k-10k miles.

TDGTIRE

actually the shorter trip was a combination of highway, maybe 40% and the rest was back roads with some stop and go. I would have expected the 17mpg on that trip, opposed to the longer trip that was straight highway.

alabamaredneck

I second that.... took the ecoboost I had some mileage before it settled...

BCMIF150

I would suggest driving it instead!

shortride

iTrader: (1)

Beat me to it.

//V

I was told, and maybe this is not correct, that they can't just program the computer to whatever tire size you choose. And a difference of 1" is not really worth it anyway. It is probably about a 2-3% difference. You can calculate the difference yourself and multiply by whatever percentage it is if you really care that much, but is that really going to change anything? Just drive and enjoy.