Currently I have on 275/65/18 SL (40lbs) and I’m looking to go to 275/70/18 E (60lbs) on a 2012 5.0 3.75ratio FX4.

I was thinking about going to the second tire size listed. At first I’m thinking that’s not a big difference it should be no difference in performance and I get the extra ~ 1” of clearance (I get a lot of snow) Win win. But then I’m reading some posts on the web about big MPGs drops.

I dont want to take the mpg hit, but I want to confirm I’m reading the proper stuff.

I can go with the same size as the stock tire, but the weight difference is still 20lbs per tire more on the E rated 10 ply tire for the tires I’m looking at. Don’t know if that’s going to affect it any differently.

Specifically I’m looking at the General Grabber ATX. right now I’m running Cooper Discoverer M&S.

Do you think I’d take a huge MPG hit by changing ?

 

My '17 took a big mpg hit when I went from the stock p rated 275/55r20's to E rated275/70r17's. Same diameter and width but a lot heavier. Must have something to do with the rotating mass. I replaced the 275/65r18 factory Goodyears on my '20 with Cooper ATP's of the same size. Only 5# heavier per tire and MPG was not affected.

 

The rolling resistance from a stock tire to a AT tire and then to a Mudd tire will decrease mpgs. Same with going from a lighter P tire to a heavier E tire. So both of them together and it's a double whammy. No to bad but I would expect 1 or 2 mpg lost on average to a maximum lost of 3 mpg.

 

I went from 275/65/18's to 265/70/18's when I replaced my factory tires. It is somewhat of a compromise in size splitting the height exactly. And they are available in a lighter weight P series tire. They are 1/2" taller vs 1" taller for 275/70/18's. They are about 20mm narrower, (that's about 3/4"), you never notice. All things being equal a narrow tire will help fuel mileage. This might be something you want to consider.

When those wore out I went to an E rated 275/70/18 with a more aggressive tread. These are about 15 lbs heavier than either of the 2 previous tires. The fuel mileage did decrease, but it is hard to say exactly how much. I had my front brakes replaced within the same week as having the new tires installed and the brakes were installed incorrectly allowing one side to drag slightly on the rotor. I had about 3 mpg fuel mileage loss which I initially attributed to the tires. But after getting the brake issue corrected my fuel mileage is better. It hasn't been long enough for me to say for sure, but I'm probably less than 2 mpg off. In addition to larger, heavier tires I also went with a more aggressive tread so it isn't really an apples to apples comparison.

There is a lot more to fuel mileage than the tires weight and diameter. The tread pattern and tire width has a huge effect on rolling resistance and if you change more than one thing it is hard to pinpoint what is going on. I also went to a 1" taller E rated tire on my Tacoma years ago. Those tires are also 15 lbs heavier than stock. I did that years ago, long enough to know what is happening, and there was ZERO difference in fuel mileage. I suspect mostly because I stayed with a very similar mild AT tire.

I've never seen any data to back it up, but suspect the trucks axle ratio plays a role. My Tacoma has 3.73 factory gears in it. Changing to a bigger tire effectively changes the ratio on all vehicles. But if the truck is already geared low enough I don't think the loss of power is enough to matter. In some cases it may even help. My Ford has 3.55 gears which are bordering on being too high anyway.

 

Expect to lose ~2 MPG due to the weight + tread pattern

Rotating mass is a big deal. 20 lbs per tire is a big difference, and it negatively effects everything, acceleration, braking, handling, ride quality, mileage

 

I lost some on mine, but gained some back after getting a custom tune, which also corrected my speedo. Mine was an even bigger weight difference. 41 lbs to 69 lbs, thta was going from 275/55/20 on a summer street tire to a 285/55/20 all terrain.