SEGT99

I am running 33s on my 2dr Automatic JK with the 3.73s. Right now around town I run with the overdrive off because it constantly shifts in and out of final gear. (When its time for new tires I am going to go to 35s and flat fenders.)

I am trying to figure out if regearing would help my shifting problem and if it would improve or hurt my gas mileage. Also I am not sure what gear ratio would be best to go with considering I plan to go to 35s in the future.

Thanks for your guys help. This forum has helped me out plenty of times!!!

MOPWR2U

Regearing the differentials should help your gas mileage with an auto trans JK. You will stay in top gear more of the time. Fewer downshifts means less gas burned. On my 2010 JK I got 12 mpg with the stock 4.10 gears and 35" tires. When I changed to 5.38 gears with the same 35" tires fuel mileage went up to 16 mpg. As for which gear ratio to change to, depends on how much money you want to save on fuel. An auto trans JK with 35" tires will get better gas mileage with 5.38 gears than it will with 5.13s, and an auto trans JK with 5.13s will get better gas mileage than it will with 4.88s, and so on. These auto trans JKs are geared WAY TOO HIGH in top gear in stock form.

RCJeeper

Wish I could say the same. Went from 4.10 to 5.13 and lost 1-2 mpg. Painful

Pluke the 2

I don't think so.

Dronac

So if I have 33'' tires and an auto, should I go for 4.88? 3.73's are enough for me offroad with 4 Lo, so I'm regearing for road performance only.

SEGT99

I know the highway milage would go down because the rpm's would be higher just wondering if my keep would get better around town. Its a daily driver.

ethang1977

I can't believe no one has posted "The Chart" yet. lol

nthinuf

Curious about this.

Your mpg with 4.10's and 35's is 1-2 mpg higher than with 5.13's and 35's ???

Or...

You mpg's with 4.10s and 'stock' tires is 1-2 mpg higher than with 5.13's and 35's?

Also, in that long list of mods I do not see a Programmer. Does your computer still think you have 4.10s and 32" tires? If so, how the hell can you compare the mileage between the two sets??

nthinuf

Think again. Instead of constantly 'lugging' the engine and downshifting all the time (which raises the rpm considerably), you are driving in the rpm range that the JK's engine likes to run in. This means that you will not be downshifting nearly as much, which, overall, raises your mpg's. (counter-intuitive, but there is a lot of data supporting this...)

As mentioned above, there is a great RPM chart in the Drivetrain FAQ's, stickied at the top of this modified area. Measure your tires (measured, not mfg's specs) then plug the numbers in. Opinions may vary, but the 2300-2700 range is a good place for auto's to be.

Crasher

At 2000 miles, I put on 34" MTRs and the mpg went from 19+ to 18. Then when I regeared from 410s to 513s, it went to 16.5. (I'm a nut for getting good mpg on anything) I was disappointed. With more miles, the mpg begain to improve. By 7500 miles it was up to 18 driving 62 mph. At 9000 miles, I replaced the MTRs with 35" KM2s and the mpg jumped 10% to 19.6 @ 62 mph. Performance is noticably better.

On the current tank of gas, I have 210 miles. 160 highway miles & 50 city miles and it is showing 18.4 mpg. Stop & go driving and wind is a mpg killer.

The gear change made a big improvement in drivability. It's better than stock now.