i have a 2013 f150 xlt with the 5.0 - i had the leveling kit put on the front [ 2 in. i think ] i recently got new 285 65 r18`s -WRANGLERS with kevlar - really good tires paid 1300 $$ at FORD - why am i getting 13 m.p.g.- oh yea i have the super crew and it`s a 4x4

 

Did you recal the speedo for the larger tires?
What axle gear ratio?
How many miles have you gone since the tire change?
What has your driving been? In town?, Highway? Mixed?
At what speed?

 

no i didn`t recal - and the tires are a week old - no hwy. driving it`s basically around town but i got better than this just didn`t think it would be this bad

 

It'll do better on the highway and that will bring up the overall average, but in town it takes a certain amount of energy to move that mass around and those larger tires have decreased the final drive ratio which means the engine has to work harder. What does it have 3.55 gears? Consider going to 4.10.

 

how much $$$ would it cost to go to 4:10 gears

 

You will have to check some local shops for install rates but figure on $500 in parts and at least that to have them installed.

 

thanks - sounds doable

 

Look at the specs on the new tires. They are likely in the 32+ height range whereas the stock 18 inch tires coming on the vehicle are around 30 inches tall. This will change the speedometer readings accordingly. I changed tires shortly after purchase of my 2011. My odometer was off by about 1/10 per mile initially. It's dead on now. This is based on mileage checks locations on fwy as well as my gps. I lost about 2 mpg as shown on the odometer and hand calculations. When I add fuel now it's almost dead in to the gage where before the gauge as off by easily as much as a half gallon of fuel.
I think Ford put an undersized tire on relative to the speedo gears. Thus the change in actual fuel consumption.
Just my thoughts

 

Go online to the manufacturers spec on the rolling diameter of the stock tires compared to the tires u have now.
then do some math and figure out how far out the speedo is.
truck computer is trying to comput the fuel economy based on the stock tire size.
with larger tires your traveling farther than the speedo says and it shows with a decrease in computer readout of fuel economy

 

Larger tires almost always drop your fuel economy, too. Hell, changing from highway tires to a semi aggressive all terrain tire (wider, not taller) lost me 2 mpg when I had my 5.4... More grip = more rolling resistance.

First step is getting your speedo calibrated, otherwise your numbers are wrong to begin with.

 

Larger tires change your mileage automatically. This changes the revolutions per mile. This will determine mileage numbers. Most of us with standard OEM tires when hand calculating find that our mileage is off from what the gauge on your dash tells you by 5-10%. Going up a small amount in overall diameter will result in your mileage to be more accurate to the gauge as well as hand calculations.
If you look at OEM tire diameters you find they are close to 32 inches. I put 33.5 diameter tires in my truck. Using the highway mileage markers in test zones, as well as my GPS I was able to determine that my actual mileage was now more accurate to the odometer. I also noted that my MPG was different by about 1/2-1 mpg. This had nothing to do with the rolling load or resistance but instead the revolutions per mile. This is I. Part why the tire MFG includes this data when you look at tire specs. Of course you will see bigger changes in mileage should you go to a significantly larger tires -say from a 32 to a 35 inch tire.
Just some thoughts to ponder. Your mileage may vary.

 

Anyone ever get pulled over for putting on those fake bullet holes on your trucks pulled over by the police?

 

So you went from a tire that was 32" tall and 9" wide to a tire that is 35" tall and 12.5" wide and raised it from stock height to 6" higher. Your mileage went down on the highway because you are now at box truck height and have increased rolling resistance by a large factor. I'll equate it to trying to walk in a hurricane with an umbrella wide open, it takes a huge amount of energy to do that.

 

May be a little hard to read these calculations, but you really didn't make any great changes, as far as tire sizes. Even a 2" level isn't much. You could figure your mileage as usual, but add 1.6% to miles, since that's how much further you're actually going per mile now. What was your previous mileage?
BTW, I'm assuming you had 275/65/18 on as OEM, you only gained .52" in diameter, not much at all.

Diameter inches (mm) 32.07 (814.7) 32.59 (827.7) 0.51 (13) 1.6% Width inches (mm) 10.83 (275) 11.22 (285) 0.39 (10) 3.6% Circum. inches (mm) 100.77 (2559.46) 102.37 (2600.3) 1.61 (40.84) 1.6% Sidewall Height inches (mm) 7.04 (178.75) 7.29 (185.25) 0.26 (6.5) 3.6% Revolutions per mile (km) 628.78 (390.71) 618.91 (384.57) -9.88 (-6.14) -1.6%

On Edit, just discovered how olde this thread was, I beg forgiveness.