Rubicon Recommendations for Regear 37”

[Gladiator Overland]

Title says it all curious to hear real world results. Want something still good on the hwy and able to stay in 8th. But also want to make up for the tire size. Notable that I will be applying these recommendations to the Eco Diesel. Trying to get my ducks in a row now getting all my mods for when I order the truck next year.

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[Renegade]

There’s lots of info on here and the JL Forum about 37s and gears, but no one here would have “real world” info pertaining to the diesel yet.

 

[Phljeeper]

Title says it all curious to hear real world results. Want something still good on the hwy and able to stay in 8th. But also want to make up for the tire size. Notable that I will be applying these recommendations to the Eco Diesel. Trying to get my ducks in a row now getting all my mods for when I order the truck next year.

I would suggest driving it on 37s with stock gears before making any decisions on a regear. Depending on where you live, how you use your truck and how much you tow will impact the decision for no regear (keep stock 4.10s) vs what size of regear. And also no one knows about the diesel on the JT yet since it isn’t available. You may want to post on the JL forum as there may be some with the diesel there.

 

[Renegade]

I would suggest driving it on 37s with stock gears before making any decisions on a regear. Depending on where you live, how you use your truck and how much you tow will impact the decision for no regear (keep stock 4.10s) vs what size of regear. And also no one knows about the diesel on the JT yet since it isn’t available. You may want to post on the JL forum as there may be some with the diesel there.

Diesels get 3.73 gears, but yes, I would drive it first to see. The OP’s stated goal of the transmission using 8th gear may be his deciding factor, despite adequate performance without regearing. A lot of people seem to get hung up on that, even when performance is still otherwise acceptable.

 

[Gladiator Overland]

Let me rephrase this as everyone gets hung up on the extra torque of the diesel. What I want to know is what people are doing now even with the current Drive Train. If I can get this information then I can have a baseline here as to what to expect and look for.

My plan is to lift and put wheels and tires on. I can now say that I will definitely need a regear no matter even having the extra torque. I spend most of my time in the mountains and will be spending a good portion in the hwy. I do have a few concerns as I am sure as has been mentioned that the diesel will be undergeared compared to the petrol offerings. That said with regear I will also have to strengthen the drive train to ensure I offset the extra power going to it to prevent damage. This vehicle will be driven a good bit on the hwy getting from one destination to another. IE east coast to west coast As well as the mountains most of its times. Mileage is a huge concern even with an extended fuel tank. Without the regear I could most likely get by due to the extra torque. Yet some as the petrol it will suffer due to the larger rotating mass.I will also check with the JL forums. Thanks.

 

[Sorbs]

No need to regear. 4-Lo for when you need it in the rocks, 2-hi for the freeway on ramps, and 4-hi when you don’t need 4-Lo. I’m at 6,500’ for daily commute on 37s. Offroad + actually works well too.

 

[Alabama Mud Machine]

With the iDrive unit and the Tazer JL Mini to reprogram my shift-points and speedo for my 37's, my Jeep has plenty of power for a V6 with the stock 4.10 gears...Then again, I don't tow anything with it. It's quite impressive actually. That 8-speed auto really makes all the difference. I mean, it's not the same as my 450hp Mustang GT was, but for what it is, it's pretty decent. I would love to see a 5.7 Hemi V8 option. Down the road, I do see a 6.4 SRT Hemi swap in my JTR's future...

I wouldn't mind swapping to 4.88's in the future, just to increase my powerbands throughout the RPM spectrum. Plus, it would probably improve my MPG's a good bit, too. Currently I'm only averaging like 12.5 MPG... But I only have like 500 miles on my Jeep, so it's nowhere near broken-in yet.

 

[Gladiator Overland]

After doing some research I have found that everyone with the diesel JL and 37s are sticking with the stock 3.73 gears. After using the gearing calculator and strangeengineering.com. I found there was only a 200rpm drop from 33” to the 37”. Looks as if unless you are fulltime offroad and need the extra torque or towing alot that you wont need to regear uness going bigger than 37” tires. Here are the results.

 

[Alabama Mud Machine]

Keep in mind that 200 RPM for a diesel is about like 500-600 RPM for a gas-burner. RPMs are RPMs, but the way the engine utilizes them within it’s powerband are totally different, due to the inherent nature of both types of engines.

For example, a 200 RPM drop in a diesel that starts redlining at only 3,500 RPMs, is a much more noticeable power loss, compared to a 200 RPM drop in a gas-burner that redlines at 6,500 RPM.

 

[Brfertig [HACKED ACCOUNT]]

The 31 inch tire on a reg Sport is 3.73 gears is equivalent to 37 inch tires on 4.56 gears.
The 31 inch tire on max tow with 4.10 gears is equivalent to 37 inch tires on 4.88 gears.
The 33 inch tire on Rubicon with 4.10 gears is equivalent to 37 inch tires on 4.56 gears

I have 4.88 gears but Covid has kept me form giving real feedback at this point in my build. I am more of a regear before light bar kind of guy so I have 35 spline shafts, arbs, and 4.88 gears all ready to install when my shop opens back up. I am doing the install but the shop is closed ATM.

Just my .02 cents, good luck on your build.

 

[rdcox23]

4.88s, 35s and the six speed manual here. Couldn't be happier. Drives great and the MPG actually improved if I keep it under 70 MPH. Will eventually be going to 37s, and I'm not worried about power loss at all.

 

[JTPatriot]

Just installed my 3" lift and 37" Milestar Patagonia M/T's this weekend. I live in Kansas, so pretty flat but windy. 15 to 30 mph winds maybe more sometimes less. I have 4.10 and auto. I will be regearing to either 4.88 or 5.13 in the very near future. 75 mph with a head wind 6th gear, sometimes shifting down to 5th. No head wind will see 7th but will drop into 6th with any rise of the road. I am planning on towing my 3500 Lbs camper on occasion and this current condition is not going to work. Even if not towing the constant shifting is annoying. I knew regearing would probably happen but wanted to see how it did with stock setup. Just wanted to add my experience with 37's and 4.10's.

Now the biggest question is 4.88 or 5.13. I know with the camper 5.13 will probably be best but 90% of the time it is my daily driver and back and forth to work 22 miles round trip. So probably 4.88? What do all of you say?

 

[rdcox23]

I'm getting 18+ mpgs with 4:88s and the manual transmission if I keep it under 70 mph.

 

[Texops]

I just picked up my Overland yesterday & am still doing break in, 5.13’s because i pull my 5000# camper. 1900 rpm at 55mph in 8th it ran mostly in 8th but sometimes in 7th. 37” Nitto trail grapplers. I also have a big heavy rear driveshaft 1350 joints Tom Woods.

 

[DesertDog]

Now that there are some diesel Rubicon‘s out there. Any thoughts of 37’s and stock gearing?

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