What gears do I want?

To much info, just kidding. A lot of good info for me to think about.

Rubicon88, that's a lot of info to think over and it makes sense. If I spend the $800 and go to 4.56 and I'm still not happy with it at least it'll be better. Then I can can go from there if I feel I need more.


Steel City 06, I grew up just outside of Pittsburgh so I know the terrain. Curious what tires and gears you're running? What you said sounds good but I could never talk myself into trying 5.13 without trying something in between. 5.13 just seem like such a huge step.

I'm currently running factory 4.10 gears on 35s but plan to gear to 4.88. Keep in mind I have the 6 speed manual which has a much less aggressive OD than the 42RLE.

The OD on the NSG370 is 0.84. On the 42RLE it is 0.69. So the equivalent of 4.88 gears on the NSG370 would be 5.89 on the 42RLE, which can only be installed on Rubicon models.

If you adapt that to 32" tires, that would actually come out to about 5.38 gears, which are also only available for Rubicon models. So 5.13 for you is actually going to be less aggressive than the 4.88 I want for mine.

To give you a different comparison, a factory 6-speed Rubicon turns 2890 RPM at 75 mph. A 42RLE TJ with 32s and 5.13 gears would turn 2880 RPM at 70 mph, or almost the same as the factory 6-speed Rubicon. (And you've ever had a chance to drive a factory 6-speed Rubicon you'll know it performs very well on steep hills.)
 
  • Like
Reactions: Michelobe
I'm sorry to dig up an old thread with my first post but I've been reading up on gearing and I feel the specific use of for my Jeep is not covered in what I could find.

I bought my Jeep with a 42RLE, Dana 30/Dana 44, 3.73. I've been driving around on Mastercraft 33x12.5 MTs that came with the Jeep. It's slow but I manage fine for the moment but I feel that it's asking a lot from the driveline.

I intend to go upto 35s and look at regearing at that point. The Jeep is a daily driver and will see little offroad use. Where I live, it is likely to be light trails and mud. No rocks to crwal on.

Since wheel speed is a concern with mud and for mostly city driving, I'm considering 4.56 or 4.88.

What do you reckon is the best way to go for my particular application?
 
I'm sorry to dig up an old thread with my first post but I've been reading up on gearing and I feel the specific use of for my Jeep is not covered in what I could find.

I bought my Jeep with a 42RLE, Dana 30/Dana 44, 3.73. I've been driving around on Mastercraft 33x12.5 MTs that came with the Jeep. It's slow but I manage fine for the moment but I feel that it's asking a lot from the driveline.

I intend to go upto 35s and look at regearing at that point. The Jeep is a daily driver and will see little offroad use. Where I live, it is likely to be light trails and mud. No rocks to crwal on.

Since wheel speed is a concern with mud and for mostly city driving, I'm considering 4.56 or 4.88.

What do you reckon is the best way to go for my particular application?
I would go with 5.13 regardless in your position. 5.38 would be better but there is no 5.38 available for the TJ Dana 30. 5.13s will perform well on the road (5.38 would be better) and well off-road as well with 35s.

In 4th gear in 4Low, you will have no issue getting the wheel spin you need in the mud with 5.13 gears. And if you do, 1st in 4Hi should have plenty of torque to start the spin with 5.13 gears. Given you have the NP231 transfer case in lieu of the NP241, that combination will work well in the mud.

With your rear Dana 44, you should be fine with stock shafts, though an upgrade to chromoly shafts may not be a bad idea especially if you get into the habit of flooring it through mud, sand, or rocks.

If you do go mudding, I would recommend chromoly big u-joint shafts like Revolution’s 1350 series in the front (RCV CV shafts are another great option) as the front shafts can easily be destroyed if a spinning wheel suddenly gains traction. I would dare say this is one of the cases in which mudding is harder on components than rock crawling, so I highly recommend this upgrade. It can be done at any time, as the shafts are compatible with any 27 spline locker, stock or aftermarket.

If you think you may end up going off-road in the future, I would also recommend looking into limited slip or locking differentials front and rear, especially in the rear. While these do add significant cost, they will add impressive capability to your jeep in the mud, sand, and/or rocks.

The two differentials I would look at are the Eaton Truetrac and the Eaton E-locker.

The Truetrac is a gear driven limited-slip. I recommend searching YouTube for a video on how it works. Essentially if it detects wheel slippage, it locks the two wheels together to spin both of them at the same speed until traction is regained. It has a limit as to how much torque it can transfer, usually 4-5x the torque on the loose wheel. It’s a great option for driving fast on trails or powering through mud and sand, but no so much for rock crawling. If a wheel is spinning freely in the air, the other wheel will get no tor

The Eaton Elocker has an electric solenoid that powers a dog clutch to lock the two wheels together. So if you think you might get stuck, simply flip a switch and the wheels are locked at the same speed until you turn off that switch. Works very well in deep sand and mud, and especially when rock crawling. It does require user input, unlike the Truetrac. Unlike the Truetrac, it can apply 100% of the available torque to either wheel, so it will work if you have a wheel gaming in the air.

Both of those differentials will behave like stock on the road. The limited slip also gives a small advantage on snow and ice covered roads, though with a few extra handling quirks.

The 3rd option to look into would be a ratcheting differential like the Eaton Detroit Locker. It is an automatic locker that fully locks the differential when one wheel moves faster than the other. Essentially it allows wheels to spin faster, but not slower, than the central carrier. This works very well in sand, deep mud, and well on the rocks, but has some significant handling quirks on the road that can be learned.

Any of those options will give you a massive advantage in the mud and on the trails over the stock open differentials.
 
5.13 is a good gear for a 30" tire. 😉

42rle/30”/5.13=2973rpm @ 75mph
42rle/32”/5.13=2788rpm @ 75mph
42rle/34"/5.13=2624rpm @ 75mph
 
Thanks for the input everyone. The recommended guy in my area for doing gears has closed his shop. He was tired of working 80 hrs a week. I guess it's time to find someone else and get 4.88s (damn that sounds steep) and maybe look at lockers.
I live in the Mills River area, JZM Auto and Tire in Etowah does a lot of work on Jeeps including regearing. I have not personally used them for anything other than patching a tire so i cannot speak to the quality of work they do, but they might be an option.
 
  • Like
Reactions: Michelobe
I would go with 5.13 regardless in your position. 5.38 would be better but there is no 5.38 available for the TJ Dana 30. 5.13s will perform well on the road (5.38 would be better) and well off-road as well with 35s.

In 4th gear in 4Low, you will have no issue getting the wheel spin you need in the mud with 5.13 gears. And if you do, 1st in 4Hi should have plenty of torque to start the spin with 5.13 gears. Given you have the NP231 transfer case in lieu of the NP241, that combination will work well in the mud.

With your rear Dana 44, you should be fine with stock shafts, though an upgrade to chromoly shafts may not be a bad idea especially if you get into the habit of flooring it through mud, sand, or rocks.

If you do go mudding, I would recommend chromoly big u-joint shafts like Revolution’s 1350 series in the front (RCV CV shafts are another great option) as the front shafts can easily be destroyed if a spinning wheel suddenly gains traction. I would dare say this is one of the cases in which mudding is harder on components than rock crawling, so I highly recommend this upgrade. It can be done at any time, as the shafts are compatible with any 27 spline locker, stock or aftermarket.

If you think you may end up going off-road in the future, I would also recommend looking into limited slip or locking differentials front and rear, especially in the rear. While these do add significant cost, they will add impressive capability to your jeep in the mud, sand, and/or rocks.

The two differentials I would look at are the Eaton Truetrac and the Eaton E-locker.

The Truetrac is a gear driven limited-slip. I recommend searching YouTube for a video on how it works. Essentially if it detects wheel slippage, it locks the two wheels together to spin both of them at the same speed until traction is regained. It has a limit as to how much torque it can transfer, usually 4-5x the torque on the loose wheel. It’s a great option for driving fast on trails or powering through mud and sand, but no so much for rock crawling. If a wheel is spinning freely in the air, the other wheel will get no tor

The Eaton Elocker has an electric solenoid that powers a dog clutch to lock the two wheels together. So if you think you might get stuck, simply flip a switch and the wheels are locked at the same speed until you turn off that switch. Works very well in deep sand and mud, and especially when rock crawling. It does require user input, unlike the Truetrac. Unlike the Truetrac, it can apply 100% of the available torque to either wheel, so it will work if you have a wheel gaming in the air.

Both of those differentials will behave like stock on the road. The limited slip also gives a small advantage on snow and ice covered roads, though with a few extra handling quirks.

The 3rd option to look into would be a ratcheting differential like the Eaton Detroit Locker. It is an automatic locker that fully locks the differential when one wheel moves faster than the other. Essentially it allows wheels to spin faster, but not slower, than the central carrier. This works very well in sand, deep mud, and well on the rocks, but has some significant handling quirks on the road that can be learned.

Any of those options will give you a massive advantage in the mud and on the trails over the stock open differentials.
Wow, thank for all the info covering a lot of areas that I will have to address to properly build my Jeep.

I'm from Sri Lanka and access to heavy duty Jeep parts is very difficult and I will have to import components myself. With a very weak currency and heavy import duties, it is also double the cost of the parts themselves usually. We are also Right Hand Drive making some front axle related components like trac bars and steering components hard to find.

I'm planning to hold onto this Jeep and build it gradually. I really want to sit on 35s. First I'm planning to upgrade the tie rod and drag link along with HD ball joints which. Then to get Metalcloak arched fenders and get the 35s under the jeep and regear at that point. I will then look at replacing the 1 inch suspension and 2 inch body lift that the PO put on with hopefully a 4 inch Savvy short arm kit and Fox shocks. Axle shafts will be next. I'm gentle with the Jeep for the most part so I hope the stock shafts will hold for a while.

back to gears, wouldn't 5.13s wind up the revs too high for daily driving? I understand that it will be desirable in a dig offroad. But would you still say it is the right ratio for a Jeep that spends 90% or more time on the road?

Many thanks for your input
 
Great thread. Once we receive his application the Forum Regearing Committee will review it as well as these posts and respond within 30 days.

Be sure we receive the application and $15 fee by the 15th for the August meeting. No late applications will be added to the following months agenda, please apply early, we are covered up already.

The highlighted categories must be filled out, especially the financial section to prove you have the means to finish the build.

Remember you have to regear within 45 days or reapply, and you have to start over if you change tire sizes.

Thanks, and please don’t gripe at me about the rules, I just work here.
 
  • Haha
  • Like
Reactions: JMT and L0jik
Wow, thank for all the info covering a lot of areas that I will have to address to properly build my Jeep.

I'm from Sri Lanka and access to heavy duty Jeep parts is very difficult and I will have to import components myself. With a very weak currency and heavy import duties, it is also double the cost of the parts themselves usually. We are also Right Hand Drive making some front axle related components like trac bars and steering components hard to find.

I'm planning to hold onto this Jeep and build it gradually. I really want to sit on 35s. First I'm planning to upgrade the tie rod and drag link along with HD ball joints which. Then to get Metalcloak arched fenders and get the 35s under the jeep and regear at that point. I will then look at replacing the 1 inch suspension and 2 inch body lift that the PO put on with hopefully a 4 inch Savvy short arm kit and Fox shocks. Axle shafts will be next. I'm gentle with the Jeep for the most part so I hope the stock shafts will hold for a while.

back to gears, wouldn't 5.13s wind up the revs too high for daily driving? I understand that it will be desirable in a dig offroad. But would you still say it is the right ratio for a Jeep that spends 90% or more time on the road?

Many thanks for your input
Your transmission (42RLE) requires a deep axle ratio because of the transmissions gearing, the first gear on your transmission is like second gear on a manual, so you need more torque to get moving. Also, because of how deep your 4th gear is, you need deeper gearing to keep the RPM's higher at freeway speeds. Higher RPMs = more power. I just installed 5.13 gears in my buddies 2004 LJ and he couldn't be happier, he has enough power and torque to accelerate in 4th gear even at 75 mph. Even if your not offroading your jeep, the ratio should still be 5.13 because it makes it easier to drive. And because its less strain on the engine, and you stay in the power band, you will get very good fuel economy.
 
  • Like
Reactions: JMT
....

back to gears, wouldn't 5.13s wind up the revs too high for daily driving? I understand that it will be desirable in a dig offroad. But would you still say it is the right ratio for a Jeep that spends 90% or more time on the road?
...
Post #24 tells you what you need to know
 
Wow, thank for all the info covering a lot of areas that I will have to address to properly build my Jeep.

I'm from Sri Lanka and access to heavy duty Jeep parts is very difficult and I will have to import components myself. With a very weak currency and heavy import duties, it is also double the cost of the parts themselves usually. We are also Right Hand Drive making some front axle related components like trac bars and steering components hard to find.

I'm planning to hold onto this Jeep and build it gradually. I really want to sit on 35s. First I'm planning to upgrade the tie rod and drag link along with HD ball joints which. Then to get Metalcloak arched fenders and get the 35s under the jeep and regear at that point. I will then look at replacing the 1 inch suspension and 2 inch body lift that the PO put on with hopefully a 4 inch Savvy short arm kit and Fox shocks. Axle shafts will be next. I'm gentle with the Jeep for the most part so I hope the stock shafts will hold for a while.

back to gears, wouldn't 5.13s wind up the revs too high for daily driving? I understand that it will be desirable in a dig offroad. But would you still say it is the right ratio for a Jeep that spends 90% or more time on the road?

Many thanks for your input
5.13 gears are intended for the road, and also happen to be good off-road. The 42RLE has a much taller OD than all other TJ transmissions, meaning at highway speeds the engine turns much more slowly than it would in a 5/6 speed manual or 3-speed auto TJ.

That tall OD works wonders for fuel economy in most vehicles, as the power demand at highway speeds is generally pretty low.

However, the TJ has the aerodynamics of a brick, and with large tires has a high rolling resistance. Thus the power demand at freeway speeds is much higher, and the engine needs to provide more power.

Engine instantaneous power is proportional to the instantaneous torque times the revolutions per minute. So to increase power you either increase torque (by opening the throttle more) or RPM (downshifting or unlocking the torque converter).

As such, the TJ ends up unlocking the torque converter or frequently downshifting to maintain speed, far more so than most cars.

By regearing to 5.13, you are getting closer to the optimal RPMs in OD necessary to sustain highway speeds. As such, the car will downshift less often, and unlock the torque converter much less often. When the torque converter is unlocked, a significant percentage of the engine’s power is lost as heat in the transmission, reducing fuel economy. When the torque converter is locked, it has roughly the same efficiency as a manual transmission. So generally by gearing in a way to reduce the amount of time the torque converter spends unlocked, you increase transmission efficiency.

As for engine efficiency, this vastly depends on the load demanded by the engine. An engine is most thermodynamically efficient when at WOT at the peak torque RPM (about 3500 RPM). Below that power demand, the peak efficiency at reduced power scales roughly linearly (a bit more complex, but I won’t go into it too deep) with RPM and ideal demanded torque (throttle position). Since the power demand (at a given highway speed) as a proportion of engine capacity of a TJ is higher than say a Ford Mustang, the ideal RPM for cruising at highway speeds is significantly higher.

Finally, the deeper gearing will help protect the engine and transmission and potentially give them longer service lives. When the torque converter is unlocked, all that heat has to go somewhere. Generally what happens is the transmission significantly heats up, resulting in lower life, and higher odds of failure. In the engine, the lower combustion temperatures lower the temperature of the cylinder walls, helping to reduce engine temperatures. Additionally, in both the engine and the transmission, the water pump/cooler pump spins faster, resulting in a more stable engine temperature and cooler transmission temperature.

As RPMs increase, there is some additional energy loss. Not only do dry friction losses scale linearly with rotational speed, viscous frictional losses scale exponentially with speed. At low to mid RPMs, these losses are counteracted by the things I mentioned above. But at higher RPMs, the exponential losses tend to dominate. Once you pass the peak torque RPM (3500 for a TJ), you will not see any additional efficiency benefits by increasing RPM, and you will see losses instead. At lower power demands that threshold is lower, but it scales with power demand as a proportion of engine capacity.

That said, you still get more power at higher RPMs than peak torque, up to the peak horsepower RPM (4600). It just comes at an ever increasing cost as RPMs rise. So climbing a hill or passing someone, it is generally fine to run the engine up to redline before passing , but for economic reasons (as well as wear and tear), it is not reasonable to indefinitely run at or near redline.
 
  • Like
Reactions: HornedToad
Thanks everyone! That seems to comprehensively cover the question I had. 5.13 is the ratio to go for with 35s and 42RLE!
Only because you have a Dana 30 front and 5.13 is as low as you can go. 5.89 would but nice.
 
  • Like
Reactions: Steel City 06
Looking at the Currie High Pinion 44 with 5.13 and the Currie High Pinon 60 with 5.13 gears. Should only set me back about $10 grandish with ARB Lockers. It is on the list of upgrades but man....Axles cost more than the Jeep when I bought it. Then again, it woudl solve all my problems at the same time. I'm sure it with create new ones....You know #jeeplife.
 
Looking at the Currie High Pinion 44 with 5.13 and the Currie High Pinon 60 with 5.13 gears. Should only set me back about $10 grandish with ARB Lockers. It is on the list of upgrades but man....Axles cost more than the Jeep when I bought it. Then again, it woudl solve all my problems at the same time. I'm sure it with create new ones....You know #jeeplife.
Good suggestion. Spend $10k.
 
  • Like
Reactions: pc1p
We all do when we start. Then we resort to a life of crime to keep it going.
:ROFLMAO: I can see that as the next course of action. Then again, I don't have any other vices than this. So most of my money goes into the Jeep and Wheeling. As for the Axle upgrade, It's a wish list thing. I could easily do it but Most likely will wheel what I got until they fail me. So for locked front and back with a Dana 30 and a Ford 8.8 swap running 488 gears have been pretty good to me.
 
Only because you have a Dana 30 front and 5.13 is as low as you can go. 5.89 would but nice.
I've been looking at a few sites to find a set of 5.13s and the deepest gears for the Dana 30 everyone seems to carry is 4.88. Am I missing something or is 4.88 the deepest gear I can run?
 
I've been looking at a few sites to find a set of 5.13s and the deepest gears for the Dana 30 everyone seems to carry is 4.88. Am I missing something or is 4.88 the deepest gear I can run?
4.88s may be the deepest you can find but the deepest you can run in the Dana 30 are 5.13s
 
  • Like
Reactions: jjvw and DrDmoney