Originally Posted by Clownhunter69

I can't say about the 4.56 gears but my '07 JKU, 6 Speed with 4.88's on 35's does great on the Autobahn over here in Germany. I can run 100mph at right around 2900-3000 RPMs in 6th gear. I had kept the 3.21's in the axles for a long time because I was worried about the high speed mileage and revs. Once I geared down, I actually got better gas mileage and got my 6th gear back. I'm sure either the 4.56s or 4.88's will be fine. Like a previous poster said, it's just a couple hundred RPM's at 70 mph. I chose 4.88's based off of talking with Dave at Northridge, based off of my driving style and off road needs, and it has turned out a perfect balance of off and on road performance.

Originally Posted by planman

With a 6 speed, 4.56 gears with most 35s (measure about 33.5" mounted with the weight of the JK on the ground) will run about 190 rpm less at 70 mph than 4.88s.

For anyone who lives at higher elevations, has a heavy 4 door, tows, runs heavy tires (i.e. Toyo), etc., 4.56s would be a foolish choice to save 190 rpm at 70 mph. The reason why is that with the JK engine, you need the higher rpms for more power, and at the same time, 190 rpm really isn't going to make that much of a difference in fuel economy or drivetrain longevity.

Since the OP lives at a low elevation without rolling hills, he could get away with 4.56s, but he will regret it if he ever decides to go with 37s, adds hundreds of lbs of upgrades, or moves to a higher elevation.

It is kind of funny to read posts from guys expressing gear ratio choice as something speculative or some emotional type of unknown guessing game. Please don't take this personally. I used to feel the same until I learned differently. I made the colossal mistake of installing 4.56s on my 04 TJ automatic (same 42RLE as the JK) to run 33s because I was fearfull of high rpms on the freeway in Montana. Had I understood the math and power curves of the TJ engine and the gear ratios of the automatic, I would have done 4.88s for 33s, or even done 5.13s with a D44 front axle to run 35s some day.

It isn't nebulous. At 70 mph with 35s, on a 6 speed, 4.88s will run about 190 rpm higher than 4.56s. That's it. If you spend all your time at 80 mph, then good fuel economy isn't in the realm of possibility anyway.

Originally Posted by pawj112

2900-3000 rpm at 100mph???? Holy cow. I have been told at around 70 mph 4.88 and 35's you are sitting around 3k.

So confused. Thinking about just doing 4.88. My biggest fear is regretting 4.56 after eventually adding bumpers, tire carriers etc. Etc.

Just don't want to get 12mpg on the highway.