Fuel Economy Seems Really Bad?

That is the biggest part of your poor mileage.

 

310 miles, tank took 17.85 gallons, approx 17.5mpg this time around.
All stock. but my speedo is calibrated for 16's and I am running 17's.
I use the mid grade gas.
100 miles highway, no traffic. 210 miles backroads during traffic.

 

285/75-16 BFG K/O man sized enough for you?

Ran them at 65psi, 40,000 miles and the treadwear measured with a gauge was perfectly even all the way across.
If anything, the "little 2WD tires that are wider and with a lower profile are more sensitive to overinflation.

Yes, it's about contact patch... and at 10psi over the factory door sticker, only 5psi over the sidewall, the contact patch is still solid.
And when going to a different tire, the door sticker goes out the window. The door sticker is assuming you are running the stock tires. Go to a heavier load range tire, and the proper inflation increases.

The only advantages to lower inflation is a smoother ride, and better flotation for mud and sand.

Hypermilers routinely run their tires to 50-55psi and suffer no ill effects.
I don't advocate running that high, but I have no qualms about going to, or 5psi over, the sidewall pressure.

The sidewall pressure is NOT the pressure limit.
The sidewall says "Max Load XXXX at XX PSI Cold"
That means that the tire is rated to carry XXXX when inflated to XX.
A lower inflation reduces that load capacity. Raising the inflation does not increase it above that, but it is not unsafe to reasonably exceed that pressure.


You talk about only getting 12mpg... your tire pressure just might be part of that.

 

Load Range E can go significantly higher.

Go by ride comfort. Approach the sidewall pressure, when it starts to ride like a covered wagon, back off 5 psi and you've got a good compromise between ride, handling, MPG, and tire life.

 

Are you factoring in the change in tire diameter to your calculations? You shouldn't be getting any different mpg from that small of a size increase. I went from stock BFG Rugged Trails in 265/70/16 to GY Duratracs in 285/75/16 and didn't notice any measurable change in mpg, once I factored in the 8% tire circumference difference.

 

I average 22.3 with 35psi on stock 18 inch wheels with Michelin LTX M/S tires. That feels good coming from a Hemi Jeep and a v10 f250 lol

 

You are correct - my fuel economy isn't as bad as I originally thought. I'm glad for that.

However, the tire pressure definitely improved the economy by about 0.5mpg. I'm going to bump the pressure to 45 next week and see what effect it has. I'm sure there's a point of diminishing returns, but I'm curious where that is...