I just got some 265/75-16 Treadwright Guard Dogs on taco wheels on my 87 pickup. I also have a Flip Pac on the same truck. With my old 31s I was getting around 16-17 mpg and now I'm getting 13.5 mpg and topping out around 60 mph on the freeway. I'm on stock gears and I know I need to fix that. I'm curious if this mileage hit is to be expected or if its a bigger problem than incorrect gearing.

 

I find it hard to believe I stumped all of yotatech...

 

I got the 245/75 guard dogs and they weighed in at 59 pounds a piece. Even with 4.56's I still took a hit on mileage. How much did the 265/75's weigh? I just remember it said 59 pounds on my UPS tracking email.

 

I never weighed them but they are some heavy suckers.

 

Well, lessee.... a worn 31 is not a 31 anymore: if the tread started out 1/2" thick and you wore them down to the wear bars, you've shrunk the tires an inch, turning them into 30's.

A 265/75r16 is about 31.5" tall and about 10.5" wide. How wide were your old tires? If they were narrower, the extra width of the new tires is more aerodynamic drag so likely less MPG's.

And as mentioned, a heavier tire will run down mileage too simply because it takes more torque to accelerate the tire.

 

My old tires were 10.5" wide. This is beginning to sound a lot like just a gearing problem...