I'd bet it has more to do with the rolling resistance, mainly from the tread design, than the weight. I'm getting a little less fuel economy from Grabber X3 mud tires than the KO2's I had before. They both weigh about 64lbs, so the difference is all in the rolling resistance.I'm curious how much of a drop in fuel economy others are seeing. I'm thinking of switching from my current Duratracs to these tires but the extra 10lbs per tire makes me wonder how much of a hit I'd take on economy.
But, remember this, without expensive analytic equipment, it is VERY hard to measure a real difference in fuel economy. There are just so many variables, including human variables, that can cause a subconscious difference in the way you drive and also in perception. Even on the same commute route there are thousands of variables that can change without us knowing it.
That's not to discredit the loss of mpg some are noticing. They can be very real. It's just very hard to tell. But there certainly seems to be a pattern developing.
Btw, I like almost everything about this tire and the MT Boss, too. The only drawbacks I see are in the weight, lack of a C load range, and I happen to like white letters, but that's no biggie. And D is better than E for a Wrangler. I think they'll be killer in snow. They have sillica in the tread compound which will add to their winter grip. I absolutely LOVE the side biters, too. And the MT has lots of siping and more biting edges than most MTs, so I'd bet it would be outstanding in snow, as well. That's good because my experience with MT tires is that they leave a lot to be desired in the snow, especially when packed. I haven't tested the Grabber X3's in snow yet. Hopefully that's coming soon.