I am running 285/75-17 which have a section height of around 33.8. My X came with the 24s package and has 3.73 gear ratio. When I am running highway speeds, I either have to drop it down out of overdrive or loose about 10 MPH on hills. Obviously I need to regear, but can I scoot by just locking out overdrive when running on the interstate or hilly highways? I don't rock climb so I don't need a super low crawling gear. Anything I would gain in an automatic with regearing versus locking out overdrive?

 

I have a manual but fwiw I would regear, and seriously consider a Tranny cooler.
The auto tranny's in the JK are ok in stock form but it doesn't seen to take much to start overloading the tranny's capability without re gearing, and or a tranny cooler.
Bigger tires, heavier bumpers, lights, recovery gear..etc=a lot more weight and stress on the drive line and re gearing will be the best way to take a lot of load off the tranny.
Adding a cooler will definitely help keeps temps in line and will be less expensive then re-gearing but not as effective at reducing stress, just keeping temps cooler which in turn increases Tranny life.
In the mean time I would lose a little mpg and keep O.D. off as much as you can.
Ultimately thought Re gearing will give you your best bang for the buck in both acceleration and Trans piece of mind and allow your Trans to use od the way it should, take the added stress off of the drive line, it will have more pep when you step on it, and you may get better mpg then you are now with od off.

 

I would like to know too i have a 09 jk x auto want to run 315/75r16 which are like 34 in duratrack but i don't want to regear all i do is drive around town and go to work. Just beside up hill problems would that be it?

 

I had a 2008 with 3.73 and an auto trans. The 35's slowed it down greatly. But for local driving and small highway commutes it was ok!

 

If you haven't already, get a tuner, it will help to some degree. I had a jku 3.73 with about 33s and it was a dog on the highway. I bought a superchips tuner and saw a good improvement. Still woould be better to regear IMO, but try the tuner first, yoiu may be ok with just that.

 

I'd go with some 4.88 gears when you get the chance. Gas mileage, acceleration, & trannie life will be greatly improved.

 

If you hate the performance, regear.
If you can deal with it, don't. Just hit the OD Off button when you get in don't worry about it.




There are some good rpm charts in the drivetrain section of the faq's (stickied to the top of this modified area). Use actual 'measured' tire heights. Not sidewall height. Not mfg's spec. Measured! For OD Off rpm's, divide the od on rpm by .69 (for 07-11 autos, not sure what the od ratio is for '12's).

 

Im having the same issue, auto trans and 33 MT tires. I have to pull a 1500 lbs trailer across the country and the Jeep stuggles uphill already w/o the extra weight. Does anyone know the approx cost to regear the JK ? Once regeared do you then have to get a tuner to readjust speed, trans shift points etc ?

 

It varies drastically by location and by shop. Anywhere from $650 to $2500 or so, that is new gears for both axles, all labor and out the door. Start checking your local shops to see what the costs are in 'your' area.


Re-Calibrate for the new tire size. Everything will be off because the computer still thinks you have stock tires.

 

I didn't but mine is an 07 that came stock with 4.10s.