sundevil

So did some research by finding out what my JK's 6th gear ratio is. My desired road trip speed in 6th and I found my actual mounted tire size.
Apparently the newer "same" transmission of the newer jeeps after 2009 have a different ratio for their 6th. These calculations are for mine with the older version with the shorter gear.
Which one would be better for my intended application as a DD. 4.56 or 4.88 as a manual 2007 JK on 35's.

Important Details
Drive Highway A lot so typical cruising speed is 75 mph.

Thanks

Ajkaz

I would go 4.56 because of your HWY driving. My 07 on 37's with the same tranny is perfect with 4.88s, but RPMs were too high with 35's before the tire upgrade. If you plan on moving up in tire size or have a very heavy rig I would consider the 4.88.

Canvas

4.56 are good for a pavement princess but if you plan on wheeling I would go up to the 4.88 and call it a day. The 4.88's will give you the desired power needed when wheeling and rock crawling.

I have 5.13's with 35's and the manual and I am pushing about 3000 rpm's on the highway doing 70. I commute 40 miles one way. And yes it is my DD.

sundevil

Thanks for the input Canvas! what type of mpg are you seeing with that? I commute and going 70 going to work and then I plan for road trips 75. I have my lockers ready to be installed just need to finalize my gear selection.

Canvas

I get about 14 around town and on the highway. Jeep's are not the most aerodynamic vehicles out there.

I am hoping to get a little better MPG with 37's

Ajkaz

Good point on power during wheeling and crawling. I have the Rubi xfer case and it makes all the difference in the world, I guess I take it for granted sometimes.

sundevil

Thanks Ajkaz! What type of mpgs were you seeing with the 4.88 combo and 35s @75? The only think I have left to add would be a winch up front!

Ajkaz

I lived in Peoria and took the 101 down to the 10 to Tempe for work. I would average 18-19 Hwy @ 70 & 15-16 around town w. AC on.

jsukey

This:

Cats&Jeeps

I like the 5.38's with duratrac 315/70r17 (34's) with the automatic/3.8L. live in Mich pretty flat, but spend time driving out west with my DD, mpg is important (averaging 15mpg) but so is a little more power in the Mountains/foothills. I also pull a small trailer with rooftop tent.

I typically run rpms cruising around 2200-2500 at 55-70mph.

If you look at the 3.8/original manual with the .84 od and 4.10 rubicon you'll see similar rpms from the factory at 55-70 for which I setup my gearing. Maximizing HP and Torque cures of the anemic 3.8.

I originally followed the charts but was disappointed with the results imo it just becomes personal preference and intended goals. I like driving the jk without having to downshift for every little bump in the road. I can pull up small grades in OD without downshift. Good luck