Rubicon Regearing Help

[nomadjay]

Hi! First time posting, and pretty new to the jeep community — but before I start I just want to say thanks to everyone in this forum. Been lurking for almost a year and have learned so much.

I have a 2020 JLU Rubicon 3.6L automatic and trying to decide if I should regear, and if so, which ratio would be best for my situation. I use it primarily for overlanding and essentially live in it for months at a time. In other words, I’m carrying a lot of extra cargo weight (will list some below). I’m running 37” KO2s (which are roughly 35.6”) on the Teraflex Alpine RT2 Outback Overland short arm suspension system. I barely ever see 8th gear unless I’m going downhill for a while on the highway I’ve been thinking of regearing from the stock 4.1. But feel like I’m getting contradictory info on the benefits. Ideally I’d like to gain back some MPGs - especially on the highway as my normal runs can be long highway miles then a few weeks in backcountry, forest roads, or desert, etc. I don’t do any hardcore crawling or wheeling. More just camping and getting out to more remote areas to shoot photos (I work as a photographer). Although I did Hells Revenge recently to learn a bit from an experienced friend and loved it, but doubt I’ll be doing a ton more.

I’ve read a ton of posts and am now just confusing myself more haha so I appreciate any help and tips! Would a regear help me gain back some MPGs on the highway and street? Or would it be more to gain back some lost performance with all the added weight and bigger tires etc? And what gear ratio would you recommend? Also any other tips to help gain back some MPGs would be super appreciated! Thanks in advance!

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[grimmjeeper]

You're not likely to get back a ton of mileage with a regear. Maybe a little bit don't hold your breath.

Best bet for MPG is to keep it at about 65MPH or under. Wind resistance increases as the square of your speed. So going 70MPH, you have 4x the wind resistance of 35MPH.

Smaller tires help aerodynamics. Removing stuff from the outside of the Jeep helps too. But that conflicts with what makes it good for overlanding.

For most people, 4.88 or 5.13 are the best ratios for 37s. For overlanding with a lot of highway miles, 4.88 is probably the better choice. You'll get full use of 8th gear and still have plenty of gear for technical off road trails.

 

[grimmjeeper]

I will add, if you step down to 35s, your mileage will improve and you likely won't need a regear. 4.10s are the bottom end of what I would call acceptable for 35s. You'll get more 8th gear back too. And you can still do a ton of trails without any problem.

 

[ArmyRN]

The factory gears with the XR package and 35" tires (closer to 33") is 4.56 (my 23 Jeep). If you're running 37" tires, I'd get 4.88. You'll get 8th gear back, better acceleration from a stop, less stress on the driveline, and probably better mpg. Gears would be a win-win.

If you're really heavily laden, consider 5.13 gears. Not that much of a jump from 4.88.

To get better mpg from your setup? Go easy on the gas pedal. Go slower. Youre driving a vehicle not designed with aerodynamics in mind.

 

[nomadjay]

You're not likely to get back a ton of mileage with a regear. Maybe a little bit don't hold your breath.

For most people, 4.88 or 5.13 are the best ratios for 37s. For overlanding with a lot of highway miles, 4.88 is probably the better choice. You'll get full use of 8th gear and still have plenty of gear for technical off road trails.

I will add, if you step down to 35s, your mileage will improve and you likely won't need a regear. 4.10s are the bottom end of what I would call acceptable for 35s. You'll get more 8th gear back too. And you can still do a ton of trails without any problem.

You're not likely to get back a ton of mileage with a regear. Maybe a little bit don't hold your breath.

Best bet for MPG is to keep it at about 65MPH or under. Wind resistance increases as the square of your speed. So going 70MPH, you have 4x the wind resistance of 35MPH.

Smaller tires help aerodynamics. Removing stuff from the outside of the Jeep helps too. But that conflicts with what makes it good for overlanding.

For most people, 4.88 or 5.13 are the best ratios for 37s. For overlanding with a lot of highway miles, 4.88 is probably the better choice. You'll get full use of 8th gear and still have plenty of gear for technical off road trails.

Thanks so much for this! So 4.88 would be a good middle ground of gaining back a bit of performance and maybe (if the jeep gods smile upon me) a tiny bit of mpg haha

Side note - Big thanks for making your website. Your article on regearing really helped it all click & make sense when I first started trying to understand the reasons for regearing and what it actually does for the Jeep.

 

[nomadjay]

I will add, if you step down to 35s, your mileage will improve and you likely won't need a regear. 4.10s are the bottom end of what I would call acceptable for 35s. You'll get more 8th gear back too. And you can still do a ton of trails without any problem.

I was actually just about to ask if it would be worth looking at switching to 35s. Would there be any benefit of going 35s with 4.88 as well due to the extra weight I’m carrying?

 

[AcesandEights]

4.11 -> 4.56 is about 10%. There is definitely a difference, but you may not "feel" it. I'd go with 4.56 and change to 33" or 35" tires. It seems 37" tires would be a poor choice for overlanding, and that 33" or 35" will get you just about anywhere you could go but the toughest rock gardens.

Another way of looking at it, you increased the rear gear (the tire) by over 10%. So you're running 10+% taller gearing just by way of the tires. The tires are also heavier. So if you just went back to 33" tires, it'd be like putting in 4.56 gears, roughly. I mean it wouldn't, because you have 4.11, but it would be the same as having 37" tires and 4.56 gearing...back to stock, except you added all the overlanding stuff.

 

[nomadjay]

The factory gears with the XR package and 35" tires (closer to 33") is 4.56 (my 23 Jeep). If you're running 37" tires, I'd get 4.88. You'll get 8th gear back, better acceleration from a stop, less stress on the driveline, and probably better mpg. Gears would be a win-win.

If you're really heavily laden, consider 5.13 gears. Not that much of a jump from 4.88.

To get better mpg from your setup? Go easy on the gas pedal. Go slower. Youre driving a vehicle not designed with aerodynamics in mind.

Thanks for this! Sounds more and more like 4.88 would be the way to go. I tend to drive slow as I’m in no rush to get anywhere and definitely can see the difference in MPG. But those 75-80mph highways out west kill me haha I’m either feeling like I’m about to get run over for going under the speed limit or burning gas.

 

[nomadjay]

4.11 -> 4.56 is about 10%. There is definitely a difference, but you may not "feel" it. I'd go with 4.56 and change to 33" or 35" tires. It seems 37" tires would be a poor choice for overlanding, and that 33" or 35" will get you just about anywhere you could go but the toughest rock gardens.

I definitely agree with the tire size. I originally wanted to do 35s but somehow let myself get talked into 37s Was trying not to buy tires again as my 37s still have a lot of life in them but sounds like in the long run it’ll be much better on the wallet to drop down to 35s.

 

[JT1]

4.10s in 7th are nearly exactly the same ratio as 4.56s in 8th. So if you like how it drives now and it holds 7th most of the time on the highway as its sits, you won't gain anything except access to another gear. MPG should be exactly the same.

 

[kah.mun.rah]

If you have 37s now but there is a chance of going down to 35s in the future, go with 4.88. If you keep 37s and live at high altitude and live where there are a lot of hills, I would consider 5.13.

 

[ArmyRN]

4.10s in 7th are nearly exactly the same ratio as 4.56s in 8th. So if you like how it drives now and it holds 7th most of the time on the highway as its sits, you won't gain anything except access to another gear. MPG should be exactly the same.

Probably true, but with 4.10 you're always starting off from a stop in like second or third gear compared to having 4.88 or 5.13 gears. 4.88 or 5.13 gears makes it easier driving in town, stop and go traffic, and ability to go slower in technical off road situations.

And you'll still have 8th gear for highway driving.

 

[Dirtflirt]

I agree with the advice of going back down to 35" tires, they will be ok with the 4:10 gear setup not perfect but ok. I experienced the loss of 8th gear on the highway with the stock tires at the slightest hill or headwind. I believe that 4:56 would be the sweet spot with 35s but not worth the expense of the regear. I am running on 37s but my jeep is not my daily driver and I trailer it to off-road parks to do some things that most people don't do. The 37s IMHO make it a little spooky and dodgy on the road and the MPG is pathetic. I have not regarded it yet but it is on the radar, out in the trail when you are in 4 low (with a 4:1 transfer case and an 8-speed tranny)it does not matter at all. I believe from reading your post that your main focus is highway driveability. The 35" tires will do everything that you described that you do with your jeep, and you can get out and play on some rocks as well if you choose.

 

[shane h.]

I just put 4.88s in my 2019 JLUR (3.6L with 8sp auto). I'm running 35s and hated the way the Jeep drove on the 4.10s.

The 4.88s are probably too much for 35s. I'd guess they are perfect for the 37s.

As far as gas mileage, you aren't going to get a lot back. My mileage is basically unchanged from 4.10s to 4.88s. But the Jeep drives so much better now. I'll turn about 2300 rpms in 8th running 70mph down the highway. The Jeep no longer seems to be "working" to maintain speed.

 

[nomadjay]

I agree with the advice of going back down to 35" tires, they will be ok with the 4:10 gear setup not perfect but ok. I experienced the loss of 8th gear on the highway with the stock tires at the slightest hill or headwind. I believe that 4:56 would be the sweet spot with 35s but not worth the expense of the regear. I am running on 37s but my jeep is not my daily driver and I trailer it to off-road parks to do some things that most people don't do. The 37s IMHO make it a little spooky and dodgy on the road and the MPG is pathetic. I have not regarded it yet but it is on the radar, out in the trail when you are in 4 low (with a 4:1 transfer case and an 8-speed tranny)it does not matter at all. I believe from reading your post that your main focus is highway driveability. The 35" tires will do everything that you described that you do with your jeep, and you can get out and play on some rocks as well if you choose.

Thanks! It sounds like 35s are going to be the way to go. Going to price tires next week then drive it a bit before deciding on the regear. But now I’m like hmmm, if I’m changing tires maybe I should get new rims haha

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