Rebelman

What effect MPG more? Weight or diameter?

BFG has two offerings.

275x65x18 = "32.1 - 57 pounds
275x70x18 = "33.2. -58 pounds

I assume weight has the biggest impact. If so, the 275/70 seems like a no brainier if you like the look of a taller tire?

HacksawMark

The taller tire will get "worse" mpg since the odometer will record less miles traveled for the same distance; about 4.5% less. If you make the math adjustment every time you fill up, you'll have a better idea on the mpg. I would say more than anything for this particular size would be the rolling resistance of the tire.

katoom

Well then I guess if you got that corrected your MPGs would return? NO, actually it's still going to be worse with the taller tires b/c now you've changed your final drive ratio and it's going to require a little more power from the truck to turn the tires. Going from a 65 - 70 is only an inch so unlikely much will be noticed...