Tire Pressure in Relation to MPG

[Tractor Dan]

Ok. Here is my setup.

97 Ranger
3.0L
2wd
Automatic
2 inch lift
31x10.5x15 firestone destination AT's
8.8 rear end with 4.10 gears

What i'm trying to figure out is this. At one point someone at the tire shop told me to run 55 psi, come to find out that was way too high. Well by tire rating and what Ford suggests. So the tire shop dropped it to 35psi and ever since my mpg has went down. Running 45 to 55 psi i was getting 12 to 14 mpg. Which got me about 150 miles out of a half tank. Now running 35 psi i'm getting like 125 out of a half tank.

Does the higher tire pressure affect mpg? I know it does i'm just not sure how. Also with running the big tires i know that throws off the speedo but does it throw off the odometer? If so how can i figure out how much it's off? I don't think i asked these questions before but if i did forgive me. Anyways hhopefully i can figure this out. My mechanic told me to jump it back up to 45. The max tire PSI is 40.

Dan

 

[Sasquatch_Ryda]

I have 31x10.50R15's on my 97 3.0L 4x4....I run em at 30 psi to get the best wear out of them. Run the pressures too high and you'll wear the centers out of the tires, too low and you'll wear the edges off.

The higher the tire pressure the less rolling resistance = possibly more mpg.

 

[4x4junkie]

Definitely more MPG.

I run the 35x12.50s on my BII all the way to 35 PSI on the street (max on their sidewall).
In my case, the very frequent aired-down use offroad tends to help balance out the treadwear to some extent (especially if the trail is rocky & difficult). Without such use you'd have to keep the wear more even with with a lower (or "correct") pressure.
Maybe a set of tires rated for mileage might work better for you if mileage is important (I know Michelin makes some good tires with this in mind). Such tires are typically AS (all-season) tires rather than ATs though, and have a harder tread compound.

 

[Tractor Dan]

Miles isn't really important to me. I excepted when i put the lift and all terrains on that my mileage was gonna go down. Best i was getting in town before the tires was roughly 17 on a good day. Too many traffic lights in our town. I only noticed the mileage change because of how much i lost over the course of a half tank. I would like to get back to where i was on mpg before they dropped the pressure. I can be happy with that. The sad thing is i put the lift and tires on and have yet to take it and do any off roading or trail riding. No where around my area i don't think. I just do highway and occasionally get into ditches if i gotta help somebody. Gotta say though last winter the old girl shocked me. My neighbor got his Mountaineer stuck in snow, i hooked up to it with a strap and on a sheet of ice pulled it out. So i wanna stick with my all terrains just want the mpg up to where it was before they dropped the pressure down. I'll just have to watch every time i take it in to get the tires rotated that they don't play with the pressure or anything. Also surprisingly for running them at a higher PSI they are wearing fairly even. I'll have to get some pics if i can borrow my friends camera. Mine went to crap on me and my phone sucks.

Dan

 

[gw33gp]

Running high pressure will wear the center of the tires more, long term. If you can live with that, you can get a little better gas mileage. You will also have a slightly rougher ride and handling could degrade a little. Traction under certain conditions will also not be quite as good. You should not run them higher than the maximum indicated on the tire. You may be able to get away with 10% over the maximum but more than that is not good for the tire.

I run 32 to 34 psi on the front with my 31" tires and the rear pressure depends on the load in the rear but can be as high as 45 psi and never below 30 psi. I get around 16 mpg combined city street and freeway driving. The highest I ever got was 18 mpg on the highway.

Larger tires for sure affect the odometer. It has the same percent affect as the speedometer. Going from a 29" tire to a 31" tire will make the odometer about 7% off. If you calculate gas mileage to be 14 mpg without correcting for the larger tire, you are actually getting around 15 mpg.