Baystate Jeepers

Looking to re-gear my JKU for better performance/daily driving capability. I'm thinking 4.56 or 4.88s. What are you running and are you happy with your setup?

My JKU currently has 37" ridge grapplers on 20" wheels. I requested the build sheet from Jeep and was disappointed to see it came with the 3.21s, not that any other factory option would have made a difference with the 37s.

I daily drive it and do some moderate trails and a lot of oversand driving here on the cape.

I'm still running stock from the factory on my JKU Sport, which would be unlocked 3.21s. I'm on 35"s at the moment, my only modifications so far have been a programmer to adjust the shift points and spedo to the proper wheel size. I'm looking into 4.88's, (I Actually have a 4.88 gear set for a Dana 30 I won in a contest) but want to swap the front axle to at least a 44 first. My plans are 37's or 40's eventually, so don't want to trust in the 30 without trusses and/or sleeves.

4.88 with a D30 or 5.13 if it’s a Rubicon. 4.56 isn’t enough for 37’s, 5.13 is too weak in a D30 unless you don’t wheel.

It changes depending on auto/manual and if pre-2012 or 2012+

Check this site:
http://www.wanderingtrail.com/Mechanical/gearratio.html

That should get you closer to your answer.

I'm running 4.88s on 35s on mine 3.6 auto. great performance coming from 3.21s. Between those 2 I'd do 4.88s

Hello Adam,

My Manual 6sp JK had 4.88s and I was very happy with that. To give you an idea my manual JK on 37" Nittos was around 2550 rpm at 70 mph. Automatic has a slightly different OD ratio. Auto is .83 vs .0797 on the manual. The auto will run about 100 RPM higher at 70 mph than the manual.

Fantastic feedback, thank you all! After reading your responses, I think I'll go with the 4.88's.

You'll be happy with 4.88s but don't go any lower. 5.13s would be even better with serious wheeling, but you said you daily your rig so I wouldn't recommend going that high. I run 4.88s on my 2-door JK 6-speed with 37s. Drives great on the highway on the way out to our runs.

I ran 35s with stock 3:21s. It eventually cost me a transmission. I upgraded my stock Rubicon gears to 4:56 and am pretty happy with the performance.

The Rubicon transfer case is 4x1 , yours is not ! Your low range is something like 2.73 x1 Means they can get away with 4.56s in low range cause it multiplys by 4 times , you will need 88s cause you at 2.73 x1 . If you look at a tire Vs. gear ratio chart , its color coded to show you stock gearing and tire size . Then look up what you did to it by goin 37s. It will so you the best gear for the combination. Usually we go a little higher rpm than stock to help off road. A Dana 30 front axle has issues with strength and size of the ring gear. 5.13s put so many teeth on the ring gear they end up being to thin and the pinion having less teeth , they become so weak . Thats why everyone will recommend 4.88s over what you need 5.13s. Find a wrecked Rubicon axle ? Aftermarket axle ? FjR68