DUDE454

Im runnin a about a 68# tire now but its only a 31. I found some 35's that only weigh 48lbs and are 2 inches thinner. My question is sence they are skinnyer and weigh less, how much would my MPG drop going up to the 35?

GMTURBO

Tough to know. You'll require more gas pedal to get moving but your cruising RPM will be lower.

96_xj

still will effect.

it is not the weight (rotational mass has little effect)

it is the revolutions per mile of the tire.

your tire will still spin less revs per mile due to its circumference which will move your power band at all speeds.

so you are still going to lose MPG and lots of it.

96_xj

to correct it you want to regear and that will put you in the "stock" power band

also think about it.

your 31 weighs it weight

now compare it to the 35 which has alot more rubber but yet... it weights less???? i would not want to run it on the trail. I can only imagine how thin it is

rob93

I dont understand, the 35s are 2 inches narrower? What kind of 31s and 35s are these?

FloydXJ

The weight of the tire and wheel does effect MPG, I believe. When I was looking around, I found some "studies" on it, mostly for faster vehicle applications. They found that there was a slightly noticeable increase in city MPG and a very slight increase in MPG for highway. While the rotational momentum is higher on the highway, it still doesn't appear to save any energy.
A heavier combo will make the most difference in acceleration and deceleration.
But overall, you should have an increase in MPG, but don't be suprised if it is practically unnoticeable. I have heard of people switching to alloy wheels from steel and being able to spin the tires easier and acclerate harder on the road. But again this is not a first hand account for me.

DUDE454

The 31's ive got are 31x11.50 and are bias ply, they weigh a ton! The 35's i found are only 10 inches wide and theyd be mostly for mud

Paddletrucker

More will affect the efficiency of the tire than simply size and weight. Those things will undoubtedly have an effect, though.

The other factor is called "rolling resistance"

I don't know if it's even considered on tires for light vehicles, but in tractor/trailers, we buy tires with rolling resistance in mind. The stiffness of the sidewall, the depth of tread, the softness or hardness of the rubber, the tread design, and I'm sure other things all contribute to rolling resistance. Heavy truck tires are assigned a rolling resistance score. The lower the value, the more efficient the tire.

I used to run recapped rear tires and trailer tires. I had really good luck with them. Never blew one out and they usually lasted between 325,000 and 400,000 miles on my tractor and sometimes even longer on trailers. That's pretty good for those things.

I learned about rolling resistance in tires and began running some numbers and decided to experiment. I bought some Michelin tires with a very good rolling resistance rating, but they cost a LOT more than the re-capped tires I had been running, and they didn't last as long. With all things being equal on my loads, though, I saved so much in fuel, that I paid for the extra tire cost and buying them more often and had quite a bit left over. Over a three year period, I made a LOT more money buying tires with better rolling resistance than tires that simply lasted longer.

The last time I bought tires, Michelin raised their prices drastically, so I'm trying out a fuel efficiency tire from Bridgestone, and so far, I really like them, too. I'll save big time on the increased fuel economy they're giving me.

The tires we run on 4WD's are pretty soft and have a tread pattern that I would imagine does not at all contribute to fuel mileage. I would imagine that the softer side walls, the deeper and more open tread, and the overall design of the tire will contribute more to the efficiency of the tire than the weight and size.

This will give you an idea of what I'm talking about, or you can simply Google up all kinds of info on rolling resistance to see if there's any low rolling resistance tire that would work for what you do with your Jeep.

http://en.wikipedia.org/wiki/Low-rol...sistance_tires