Nice new sig by the way Daspes

Most of the more popular off-road tires here are "e" rated.

You can run any thing you want and only notice a slight difference in ride quality ,we had some 225/75 GY ATS's on the KJ with a C rating and went to a 245/75 MTR E rated and the ride was not much worse if any ,when properly inflated
as far as a loss in mpg 90% of the loss comes from bigger OD and not weight
even 15# per tire is a drop in a bucket when you think about it ,75# that is what a 10 year old kid
I mean come one does riding a 10 year old around in the KJ cost you that much more fuel?

um ,yeah, ok
You can run any thing you want and only notice a slight difference in ride quality ,we had some 225/75 GY ATS's on the KJ with a C rating and went to a 245/75 MTR E rated and the ride was not much worse if any ,when properly inflated
as far as a loss in mpg 90% of the loss comes from bigger OD and not weight

To clear up a misconception. There is a huge difference between sprung and unsprung weight. To the engine it takes 4x the energy to move driveline components (heavier flywheel, driveshaft, rims, tires, etc...) than anything that is riding above the suspension. in you example of 15# per tire it is equivalent of cary around a 375 pound child (4x15=90x4=360=15 for the spare=375). It will not be huge hit on MPG but if you are trying to conserve where you can it will be there.

Most of your true off-road tires will be "e."

My Trxus M/T's are e-rated. But, like yours, they are not on a KJ so my tires or yours really do not matter, huh? No one gives a crap (again) what you run on your TJ or what you do with it.

check your calculator
4 X 15 = 60 not 90
and I have never seen such rubbish
I can tell you this I can roll a 200+ # tire from the front of a truck with a 20K # rated front axle
just as easy as I can roll a 50# tire from a KJ
It is the tire OD
if it were not then you would see NO drop in mpg between a 33" tall tire and a 30" tall tire if they weighed the same
and well that is not true

If you install a heavy tire and wheel assembly, expect to see the miles per gallon of any vehicle plummet. The last thing you want is to have a customer in your face because you didn’t explain about the potential loss in performance and fuel mileage before you installed the new plus-sized parts. The easiest way to explain this is to think of the tire and wheel as a gyroscope. It takes a great deal of energy to spin it and stop it. Also, the more mass that it has, the harder it is to change its direction, like making a sudden lane change to avoid an accident. Until now, we associated this issue primarily with performance vehicles. However, hybrids are sensitive to these same types of changes.

Every pound of rotating weight is equal to 4-9 pounds of in car weight. For example, if you have a wheel that weighs 2 lbs. more then your competitors x 4 wheels, your car believes it has an extra 70+ pounds in the seat. It also critically affects your unsprung weight.

With less weight acting upon the suspension [unsprung weight] your suspension can do its job more efficiently. Its quicker to react so thing will not only get more comfortable , but it will also handle better. It does matter sometimes where the weight is being lost on the car as this can change the balance of the car. Look into a few things when trying to better your suspension through weight.

The final factor of this, everything is being used less....even the engine. So you get more reliability , better gas mileage , more performance & less wear and tear. It all equals pluses and remember most vehicle manufacturers now adays are always playing the weight battle.

First let's look at the weight factor. Without taking a cutting torch to your vehicle, or drilling lightening holes in the body and chassis, you can reduce the weight. There are two types of weight to consider - sprung and un-sprung weight. Sprung weight is exactly what it sounds like - the weight born by the vehicle's suspension. That includes the body, chassis, motor, interior, and trunk (or bed in a pickup). Reductions in this type of weight are not easy to come by; but if you are the "pack rat" type that carries everything you might possibly ever need in your vehicle, then taking a close look at all of that dead weight you are carrying around and taking steps to reduce it will help some. Also, the old adage that a clean car runs better has some basis in truth - not from any gains in aerodynamics of a clean body, but in less weight of the junk you are hauling around. Cleaning the chassis, motor and undercarriage with a pressure washer periodically will also help. Built up mud, tar and road grime on the undercarriage, motor and chassis add much more weight to the car than the little bit of dirt you wash off the body. However, even relatively large weight reductions in sprung weight will not give you the gas savings that a small reduction in un-sprung weight will.

Un-sprung weight includes the weight of the axles, wheels and tires. There isn't much you can do about the axle weights, but the wheels and tires are a different matter. If you are using oversized, extra-wide tires and wheels, then you are paying a price for them in reduced gas mileage. In this area, a relatively small weight reduction can produce significant gains in gas mileage. After market custom wheels are not necessarily bad. Many of them are made of lighter materials than factory wheels and adding a set of custom wheels can be an advantage as long as they are lighter and not much wider than factory stock wheels. Tires, too, should be of the same size as factory stock, or at most one size larger, and no wider than 70 series. Not only will reductions in un-sprung weight give you increased gas mileage, but you should notice a performance improvement as well.

So if weight doesn't matter and only OD does, why did I gain nearly 2 MPG when going from a heavier 245/75 to a lighter 265/75? I stick with my real world knowledge learned from the track that unsprung weight matters, my real world experience with my KJ and what R&D has proven.