larry0071

You likely see these claims from folks who have no idea how to track actual miles and gallons used, instead they do as you eluded to and make false claim based on the lie-O-meter.

2014 JK, automatic, fairly well loaded with steel armor/bumpers/winch, 4.88 gears and STT-Pro 37x13.5-18 tires and I am pretty consistent at 13.5-14 mpg set at a true 68 MPH. If I move that speed up, the economy goes down. Driving around town and idling at 40 mph to work and back I can get 17-18 mpg. My F-350 diesel hauling a 13,000 trailer gets about the same :-(

Back when it was stock with 3.73 and 32"x10 rubicon/willys tires it would do 21-ish on the interstates and 18-19 around town.

SF_E60

I have to admit I do rely on the Lie-O-meter so maybe my 16.1mpgs on the freeway are false readings :crazy eyes:

Once again I'm running stock bumpers no winch nor tire carrier.

Erok

I adjusted my computer to account for my upgraded tire size, and the lie-o-meter comes pretty damn close to the calculations I run on the side.

I'm driving a manual 2012 JKU with 35" tires and 4.56 gears and that combo feels pretty perfect. I cruise at 80 a lot, and still have oomph if I need to pass someone (our toll roads go up to 85 in places!). I average about 15 mpg.

larry0071

You can get the dash to read pretty close if you play with GPS to monitor speed and keep changing tire size to get your indicated speed within 0-0.5 of the GPS speed using a smartphone application. That will have your dash mpg reading real close, around 1 MPG off (lying to you to make you feel good). But getting that speed nailed in also gets your odometer nailed in real close so that it can be used for measuring. For me with STT Pro tires of the 37x13.5-18 persuasion, I have to use 35.75" diameter to get the speedometer/odometer damn close to perfect. If I chalk them and use the roll out method distance divided by pi, it is way off.

Any ways, getting the actual speed/odometer is a big help to actually getting some data that is meaningful. Then alsways doing a full tank fill up, and saving the slips, resetting the odometer after recording the miles traveled on that amount of just fully replaced fuel, and dividing the total miles recorded by the total gallons required to totally fill the tank that is always totally filled at each fuel stop.... now your getting a database of useful information. Any other way is like throwing darts in the dark. Not very reliable.

SF_E60

I thought re-programing my 35's with the AEV procal would help. I will try diving my total miles with the total gallons next time to see how close it is from what it's reporting now. Thanks for the tip

Smudgeontheglass

I have a 2012 with 4.10 stock gears with 35x12.5r17 Nitto Trail Grapplers and the 6-speed manual. On the highway I get 14-15mpg and putting around in the city I get 15-16mpg. On really windy drives I can't use 6th gear and my fuel economy tanks. The previous owner of the tires had 4.56 and loved it. I will eventually be going to a smaller tire size as the 35s are overkill for my type of wheeling so a gear change is not in my future.

Scvette01

OK.....

Found a guy on Facebook group that has a 2012 JKU Auto , 35s and just had 4.88s installed. Going to meet him and go drive it. I know its not 4.56s, but at least Ill get an idea.

I know at 70, I'm turning 2,250rpms in OD.

Also the local 4wd shop that is well know in the community here in STL, has a special going ... Front and Rear , Full kit for Yukon gear swap, and gear lube replaced again at 500 miles... For $1850 out the door, that a reasonable price?


Ive done rear diffs at work, but only GM and personally its been a loooooong time since Ive done one. Thinking of leaving it up to that shop , since they do about 2-3 JKs a week and have a warranty and all

Ripa777

Yea idiot gauge ... never have done miles/gals.... will try in the way home. But will say there were nasty head winds on the way here.

nthinuf

Some areas you can get regeared for around 1k out the door. East coast and pacific northwest, people have posted quotes of up to 3k. But $1500-1600ish seems to be the norm. Best bet is just to call around to other installers in your area, rather than trying to judge it by what people in other states paid.

If you want to refresh your memory, this is a decent writeup.
https://www.jk-forum.com/forums/jk-w...gearing-82262/

SF_E60

I guess it all depends on your location, Rebel Offroad here in socal charges 1300 which includes a free 500 mile inspection and gear oil.