Tire size and gas mileage

If we get about 17mpg with stock tires, how much lower will 35" and 37" get?

 

I don't know what the numbers will be, but from my experience with my previous truck, keep in mind: going from OEM size to say a 35, the circumference is about 7% more, so with every rotation of the wheel, you actually go 7% farther than with the OEM wheel. So when you calculate your MPG, whether it is hand calculated of the truck's computer, you can actually add 7% to it.
In other words when you go to bigger tires, it will look like a big drop in MPG, but if you make the correction, it is not really that bad.

 

So for those who have 37" tires, bed racks, roof racks, rtt, skids and sliders, they are probably going to get like 10mpg or less? Geeesh!

 

315/70/17" Bridgestone Revo3 inflated to 35 psi
I did a test mostly on the highway, traffic verry light, at no more than 70 miles per hours. Two people, a dog and about 200 lbs of gear and luggage. Hwy 17 in NY State is a good mix of up and down hill most of them at less than 1000' altitude.
I got 22.167 MPG ,measured at the pump, on a 315 miles trip. No, I did not take in consideration that the 315 tire has almost 6% bigger circumference.
I am pretty sure that I lost something after I installed the bigger tires but I see more of a difference when I drive more agresive vs when I don't use the leaded food.

 

Are steel skids significantly heavier than aluminum skids?

 

My stock platinum averaged 21.6 mpg’s for the first 1700 miles. After putting on 305/70r17 (34x12) Ridge Grapplers weighing 68 lbs I was averaging 18.1 mpg’s after 1800 miles (not factoring difference in tire size). I’m now running 285/75r17 Toyo AT3’s (34x11.3) which are a C load and weigh 59 lbs. I don’t have enough miles on them yet to get an accurate mpg number.

 

37’s and lift, 12.5mpg. Jb4 and hammer down.

 

I don't understand how a raptor with 60 more hp on 37s can get 16 combined. Same size motor and similar truck, though I'd guess raptor is heavier. 10 speeds on both and Toyota runs the watered down oil.
Perhaps it's just Toyota being their traditional conservative self and prioritizing longevity. Time will tell