Yellowfin

If anyone knows the answer to this, it's ^this guy^. Although, for 35's I don't know that I'd gear as deep as 5.38s. I'm on 5.13s and 37s and it does fine. Kinda wish I'd gone 5.38s for a little more low-end, but it's much better than stock 4.10s was. If the OP plans on going bigger than 35's in the future, then I'd for sure say 5.38s. Otherwise, I'd go 4.88s, or 5.13s at most.

But then I suppose it also depends on the weight of the rig, too. But that's getting a little more technical.

Matthewd5

2012 3.6 manual 6 speed

4:88 or 3:13 is a coin toss

From what I've read and learned from those gear charts...

4:88 is good for off road and great for highways

5:13 is great for off road and good for off road

If you go off road often and commute short distances I would say 5:13, but if you off road just a few times a year and drive back and forth to that three letter word that starts with j and ends with b, then 4:88 might be more comfortable

I don't drive it every day but I just drove from southern maine to southern Connecticut for thanksgiving and the 5:13's were good, but I definitely topped out around 75-80 with MTR/K's

But I don't do road trips like that every month

The drive to the Catskills and Pennsylvania Penns Woods Jeep Jamborees should be interesting

Matthew

planman

The OP has a pre-2012 automatic Rubicon.

For the 3.8L engine to operate efficiently, produce enough torque, and reduce transmission downshifting, it needs to run at least 2500 rpm at highway speeds.

With 35s at 70 mph, 4.88s would barely turn 2300 rpm. 5.13s would only turn 130 rpm more than 4.88s. 5.38s would turn between 2500 and 2600 rpm.

5.38s will result in better fuel economy for an 07-11 automatic with 35s because the extra couple hundred engine rpm will make almost no difference in cruising fuel economy, but it makes a big enough difference in torque output that it reduces transmission downshifting.

Transmission downshifting hurts fuel economy substantially more than a couple hundred engine rpm.

4.88s with an 07-11 automatic and anything larger than 33s is an extremely poor choice that results in worse performance and worse fuel economy.

planman

Thank you.

The difference between 5.13s and 5.38s for an 07-11 automatic on 37s is 113 engine rpm at 70 mph.

113 rpm would reduce transmission downshifting--improving mpg. When not downshifting, the 113 rpm would not materially reduce mpg.

Matthewd5

Sounds strange but I guess it makes sense, never been into automatics

Matthew

meep97

I have 35s and 3.73 gears and don't mind it all that bad. It's still got enough get up and go for me. Sure I won't win any races but that doesn't bother me. Off road tho, I almost always have to put it in 4lo to do anything. But in 4lo I still have all the power I need off road.

planman

Next time you do a highway drive at 65-70 mph, try it with your overdrive turned off. That will result in about the same engine rpm as 5.38s. Driving between Cody and Billings, your fuel economy will actually be better--especially between Cody and Belfry.

You can regear for about $1300 in Billings. However, with 3.73s, you can just make it a habit of turning off the overdrive.

meep97

Is that both axles for $1300? I'm planning on coming up to Billings on the 7th-8th. Definitely will give it a try and see how I like it.

Yellowfin

If you're paying more than that for both axles, you're getting ripped! Gear sets w/ master install kits can be had for about $550. That's what I paid for my Yukon 5.13s w/ master install kits and Timken bearings.

meep97

Well I live in rip-off central and had 3 different shops tell me it would cost between $1000-$2000 each axle. Only shop I could find less than $1k was at $600 and you buy the parts.