I was just wondering if there's a computer update or anything that I can do to help me out on my 2012 EB? I recently put 20" eagle alloy 079 rims with LT285/55/20's on my EB and my gas mileage dropped 2-3 gallons?? This tire size isn't much bigger than the factory 275/65/18's that were on it, adding in that the 20" after market rim might be a bit heavier, but still, I can understand a slight drop in mpg, but not as bad as I'm seeing? I have the 3.73 gears, was averaging about 14-15mpg until I swapped wheels, now I'm at 11-12 around town. Any ideas from the group??

 

Which tires did you get? The Toyo AT2's in that size are about 20lbs each heavier than stock and are about an inch wider. That's a lot of unsprung wieght and more contact patch on the ground. So the extra friction and weight will kill MPG. Don't forget that you are actually registering less mileage on each tank due to the increased size. So your actual drop is probably more like 1-1.5 mpg.

 

Overall diameter isn't what really kills mileage with new tires/wheels. It's the weight difference that gets ya. The factory tires are VERY lightweight to begin with. Something like 30 lbs each.

Any weight you add to the tires/wheels will hurt. If you do the math on the weight difference between the factory setup and what you have now, I bet you'd be shocked.

 

Yep that happens. Same thing with my 2012 fx2 5.0 with 3.55's. I saw a 2-3 mpg drop when I put my harley replica 22's on. I get 13.5-14.5 driving to and from work and 18.5-19 on long highway trips. I was getting 16.5 city and over 20 hwy before.

 

Did you recalibrate the speedometer?

 

I dont know if your asking the OP or me but yes I did. It is still off by about 1/4 inch. Ford has limited their computer to only programing factory tire sizes so mine is set to the stock harley davidson 275/45/22 and I am runnning a 305/40/22 nittos 420s.

 

size + weight.....less mpg....

 

How do you re-calibrate the speedo? Something I can do or Ford has to do?

Also, thanks for all the input. I kind of figured the weight and rim was killing me, just didn't think it would be that bad?? The tires are Nitto Terra Grappler AT's.

 

You can do it with a tuner or have the dealer do it with a reflash.

 

Goto the dealer....but they'll only do it for select sizes.....or go get yourself a sct hand held programmer....

 

I second getting a hand held programmer. SCT would be a good choice as you could then get custom tunes as well.

 

Yeah each pound you added in rotating mass... is equal to 8 lbs of steady weight. so if you added 200 lbs of rotating weight it's like throwing 1600 lbs in your bed and driving around with it. Plus if you changed offsets and your wheels/ tires stick out more they catch air which is drag... that also cuts MPG... you're right with me... I'm getting 12.8 on my 5.4 in town with a little intersate after changing wheels and tires and going to E Rated tires which are much heavier. I also added an AS 2 inch leveling kit and blocks in the back so I lost 3/4 of an inch on my 1.5 inch rake. I didn't notice any change in MPG with that which everyone else says they loose with the level. I did mine at seperate times so I could see which one actually changed MPG and it was all tires n wheels...

 

Also check tire pressure. If you keep them a little harder they roll easier. Try several pressures until you find a balance between MPG and ride quality. Just do not exceed the limits stamped on the tires.