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Gears for 37's and auto

TxJeepers

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Ran 5.13s for nearly 3 years on my '19 3.6/auto/37's. It was a beast in 4lo. Great on the road though it seemed top end wasn't the best. Currently have a '22 3.6/auto/37's with the factory XR 4.56. It is OK but not great. Better than 4.10s but no where near as good as the 5.13s. All that said, if I were to regear and I am not, I would go 4.88s. I think that might be the sweet spot between wheeling and highway.
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jhackathorne

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I have not seen anyone mention this or bring it up, but what role will the weight play in this equation? Obviously diameter changes, but the weight on various tires fluctuates rather drastically.
 

kah.mun.rah

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I have not seen anyone mention this or bring it up, but what role will the weight play in this equation? Obviously diameter changes, but the weight on various tires fluctuates rather drastically.
Absolutely. Weight of the tire/wheel combo, tire tread type, tire psi, weight of the mods, engine type, transmission type, type of terrain, and even elevation are all small factors that when combined make a difference in the equation. Because of that the spectrum of “what works best” can be pretty broad. What some are calling a “sweet spot” is probably the midpoint/average of the spectrum.
 

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J0E

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You can run 4:10 with 37s, not a happy drive, 4:56 will improve the performance and 488 the happy camper.
JLR 2.0T auto, 37's and stock gears. Yes, lower gears will improve 0-60 on the strip, but who cares. My rig is not a daily driver but wheeled hard every weekend. I can climb 38 degrees in M1 at just over 1,100 RPM. Stock I could idle up.

A typical torque converter will have a torque multiplication ratio in the area of 2.5:1. The main point to remember is that all properly functioning torque converters do indeed multiply torque doing initial acceleration.

Why anyone would wheel in a stick is beyond me. I smell burning clutch every weekend. I take the same line, stop where the clutch guys were smoking and laugh, then take off.

Biggest advantage of clutch is when you roll over and leave rig for a few days. Once you roll it back over you don't need to add engine oil to the transmission.

I know you don't want a calculator, buy my bt39.com/GearWheelSpeed makes it easy to compare. For example, my stock JLR gears with 37's is lower than a stock non-Ruby with stock tires.

I'm very happy with 4.88
My bt39.com/GearWheelSpeed agrees with you:

Jeep Wrangler JL Gears for 37's and auto 1668064207743


The 8 speed auto allows you to over or under gear with minimal consequences. The 1st gear is so low compared to any auto ever offered in a Jeep it's almost comical. A jk with an auto would require 5.13 gears just to match a stock JL Rubicons 1st gear drive ratio. The double Overdrive does the opposite on the top end. A JK with 4 10's would have the same freeway rpm as a JL with 4.88's. In our 2019 we drove, wheeled, and roadtripped for 37k miles on 37's and stock 4.10s and never felt a need for more gearing. When we went to 38's, I decided to regear. My jump in head first personality got the best of me and we went all the way to 5.38's. Way too low period. It was in 8th gear all the time. At freeway speed it felt like it needed to shift but there was nowhere to go. Destroyed fuel economy, somehow was slower 0-60, and just didn't cruise on the freeway as well. I could see 4.88's but absolutely no lower. With the new XR, I won't even consider regearing from the 4.56's.
Exactly
I’ve been contemplating gear changes as well. Sounds like everyone is saying for a 2.0 auto on 37s they recommend 4.88.

I tow a 3,000 lb camper so I figured 5.13 may be a better move. Thoughts?
Why, so you can tow in 8th gear? I tow my 2,200 camper with my JLR fine, although the fastest I've gone is 60 MPH, and that was over the speed limit. That was uphill. With the turbo it pulls fine at 10,000 ft.

You’re paying extra when it’s down hill with a tail wind where I’d be spinning 500 less rpms under minimal load conditions. Having run both over geared and under geared for 10’s of thousands of miles I’d much rather have the ability when the opportunity arises to spin 2200 rpm’s instead of 2700. If I prefer the throttle response, I can put it in 7th and have the same drive ratio you do in 8th. Drafting a big rig, flat roads, down hill with a tail wind, etc are all reasons we have 2 overdrives in the first place. Gearing so low that you cruise in 8th at any speed above 50mph (where I was at with 5.38’s and 38’s) just feels like I’m leaving a lot on the table. The trans has 8 gears, why spend hours at a time never seeing anything but 8th. My driving habits didn’t change and we lost between 2-4mpg vs the same 38’s on 4.10‘s. The decreased fuel efficiency was across the board from daily driving around town to 1,000+ mile road trips. Gone are the CJ days where we had to gear so low for trail use that we couldn’t keep up with the highway traffic for sure, but I don’t see any gain from gearing too low and am much happier towards the other end of the recommended gearing for tire size.
Exactly again, but I do wish the JL had a 10 speed like the Bronco.

Ran 5.13s for nearly 3 years on my '19 3.6/auto/37's. It was a beast in 4lo. Great on the road though it seemed top end wasn't the best. Currently have a '22 3.6/auto/37's with the factory XR 4.56. It is OK but not great. Better than 4.10s but no where near as good as the 5.13s. All that said, if I were to regear and I am not, I would go 4.88s. I think that might be the sweet spot between wheeling and highway.
With a 2.0T, auto, and Ruby 4:1 xfer case, what advantage do lower gears offer offroad? I can climb vertical in M1 at 1,200 RPM.

I have not seen anyone mention this or bring it up, but what role will the weight play in this equation? Obviously diameter changes, but the weight on various tires fluctuates rather drastically.
The mass of the vehicle is what matters, the increase in rotational inertia from a larger diameter tire is insignificant compared to the inertia of vehicle.

I have a 37/4.88 setup presently
It works very well for highway driving, utilizing all 8 gears. I have off-roaded all over the country and been very happy. I use it a lot for a daily driver when travelling and it works well.
If it were more of a dedicated off-road vehicle I would have gone with 5:13
I'm 100% offroad on 37's, 38's soon with stock gears.

Lower gears might make sense for high speed, but I don't see a reason off road.
 
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Caymanedge

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I have a 37/4.88 setup presently
It works very well for highway driving, utilizing all 8 gears. I have off-roaded all over the country and been very happy. I use it a lot for a daily driver when travelling and it works well.
If it were more of a dedicated off-road vehicle I would have gone with 5:13
 

StingrayMRB

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I have a 3.6 but I did a prolonged drive with two different 2.0s (2+ hours) - one with 37s and no re-gearing and one with 39s and 4.88s. My humble opinion is the 2.0 will tolerate being OEM longer because of the boost but you don’t need as short of a gear for that engine. If I had a 2.0 with 37s, I would’ve done 4.88s to preserve gas mileage and not use as small of a pinion.
Companies like Yukon will give the best advice on what gearing. DIfferent models of Jeep salso have different requirements. From what they told me, the 2.0 with the auto requires taller gears with 37s than the 3.6L 6 speed Manual does. I have the manual JLUR and Yukon recommends 4.88 gears to put me back closer to stock (shceduled for next week). The JK will have different requirements. Whether you get better gas mileage depends on where you drive. In Florida with wide open roads, with no traffic, and where you can keep your speed up, Ok maybe you'll get slightly better mileage. If you have any kind of up hills or a lot of traffic, such as in Atlanta, you will have to gear down more often for the hills and pull otu more with the stop and go traffic. Gearing down always means revving the engine higher and therefore you get worse gas mileage. 5.32s I believe was the number they recommended to get a JL back to stock with the 2.0 and the 8 speed auto.

As far as engine power differences there is only a very slight different in total output. A few small upgrades like air filters and exhaust easily puts the 3.6 over 300P. There is a bolt on supercharger kit will make it equal to the Hemi for $7000. Goes back to the old statement, there is no replacement for displacement.
 

Zandcwhite

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Companies like Yukon will give the best advice on what gearing. DIfferent models of Jeep salso have different requirements. From what they told me, the 2.0 with the auto requires taller gears with 37s than the 3.6L 6 speed Manual does. I have the manual JLUR and Yukon recommends 4.88 gears to put me back closer to stock (shceduled for next week). The JK will have different requirements. Whether you get better gas mileage depends on where you drive. In Florida with wide open roads, with no traffic, and where you can keep your speed up, Ok maybe you'll get slightly better mileage. If you have any kind of up hills or a lot of traffic, such as in Atlanta, you will have to gear down more often for the hills and pull otu more with the stop and go traffic. Gearing down always means revving the engine higher and therefore you get worse gas mileage. 5.32s I believe was the number they recommended to get a JL back to stock with the 2.0 and the 8 speed auto.

As far as engine power differences there is only a very slight different in total output. A few small upgrades like air filters and exhaust easily puts the 3.6 over 300P. There is a bolt on supercharger kit will make it equal to the Hemi for $7000. Goes back to the old statement, there is no replacement for displacement.
If they recommend deeper gears for the 2.0t they've clearly never driven both, although you did say taller gears initially which would be Numerically lower. In my experience, the manual could use more gearing. For 37's and the manual I'd go 5.13s, 3.6L and the auto I'd go 4.88s, and 2.0t I'd go 4.56's.
 

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StingrayMRB

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If they recommend deeper gears for the 2.0t they've clearly never driven both, although you did say taller gears initially which would be Numerically lower. In my experience, the manual could use more gearing. For 37's and the manual I'd go 5.13s, 3.6L and the auto I'd go 4.88s, and 2.0t I'd go 4.56's.
A slip of the pen, so to speak but my logic is still valid with the rev's. Mine has the 3.6, manual, and stock 4:10's. My gas mileage sucks. I live in Atlanta and I'm from N.E. Tennessee where I owned a couple of CJ's previously. I know how I struggle with my JLUR, in Atlanta, having to constantly change gears. I bought it this way so my point of reference is manuals that were geared properly and how much better they drove. If I have to be doing 90 to use 6th gear on the highway, that is a problem. 1 problem being my Toyo MT's aren't rated for those speeds for extended periods of time. It puts more strain on my clutch because first gear is too high and so I have to rev and slip to pull out. Reverse doesn't work as well either since it is a higher gear than first is 3.x vs 5.x. Now add my tools, on-board air, hi-lift jack, winches, under body skids,....etc and I've added a lot of weight which exacerbates the issue. Which goes back to my other point, it depends on where someone lives, drives, and how the rig is outfitted as to what works best for a particular situation.

I can't say what Yukon engineers drive but seeing as how they make the gearing that a large number of us buy, they probably know better as to what would make the vehicle drive as close to stock as possible. Nothing against my local big name offroad store but they keep giving me JK specs for my JL so I take what they say with a grain of salt sometimes. I'm not a gearing expert but did work as a mechanic and ran a fab shop for many years where I changed gears for off-road only vehicles, before doing what I do now. I understand it's a math and physics problem and everyone's needs are different. This is my daily driver so I want something close to stock because it will give the best balance of mileage and performance for all of my uses.

The 4:1 T-Case makes offroading OK but still not the true low range I can get with the right gears. Mathematically the number doesn't change but the effectiveness of the number changes with tire size.
 

Zandcwhite

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A slip of the pen, so to speak but my logic is still valid with the rev's. Mine has the 3.6, manual, and stock 4:10's. My gas mileage sucks. I live in Atlanta and I'm from N.E. Tennessee where I owned a couple of CJ's previously. I know how I struggle with my JLUR, in Atlanta, having to constantly change gears. I bought it this way so my point of reference is manuals that were geared properly and how much better they drove. If I have to be doing 90 to use 6th gear on the highway, that is a problem. 1 problem being my Toyo MT's aren't rated for those speeds for extended periods of time. It puts more strain on my clutch because first gear is too high and so I have to rev and slip to pull out. Reverse doesn't work as well either since it is a higher gear than first is 3.x vs 5.x. Now add my tools, on-board air, hi-lift jack, winches, under body skids,....etc and I've added a lot of weight which exacerbates the issue. Which goes back to my other point, it depends on where someone lives, drives, and how the rig is outfitted as to what works best for a particular situation.

I can't say what Yukon engineers drive but seeing as how they make the gearing that a large number of us buy, they probably know better as to what would make the vehicle drive as close to stock as possible. Nothing against my local big name offroad store but they keep giving me JK specs for my JL so I take what they say with a grain of salt sometimes. I'm not a gearing expert but did work as a mechanic and ran a fab shop for many years where I changed gears for off-road only vehicles, before doing what I do now. I understand it's a math and physics problem and everyone's needs are different. This is my daily driver so I want something close to stock because it will give the best balance of mileage and performance for all of my uses.

The 4:1 T-Case makes offroading OK but still not the true low range I can get with the right gears. Mathematically the number doesn't change but the effectiveness of the number changes with tire size.
I'm not telling anyone how they should gear, just my experience. Comparing to "proper" gearing in a CJ can be misleading in either direction. Depending on the year they had between a 3.05 and a 4.03 1st gear and a 1-1 top gear. For a cj to have a similar 1st gear ratio in HI range to a stock JL rubicon it would need 6.89 gears. To have a similar top gear ratio it would need 2.95 gears. Crawl ratio gets even wilder with the 4-1. The CJ would need 10.1 axle gears to match stock JL crawl ratios. The massive gear spread of both the manual and the auto in the JL allows you to effectively run just about any gearing you want. We have double the power of those old CJs and way more gearing options. That huge gear spread is the reason you'll get guys running 5.13s and 35's while others are more than happy on 4.10s and 37's. I preferred 4.10s to 5.38's with the auto and the 2.0t on the same tires, and somehow it was a half second quicker 0-60 with the 4.10s. Reversing in HI range was the only place I'd say the Jeep was better with the 5.38's, but LO range is an option and I spend way more time at freeway speed than I do reversing in deep sand/mud/snow where I'd want deeper reverse gearing in HI range. Toyo mts are Q rated, good for 99mph all day by the way (as are most MTs and on 2k+ mile road trips I can confirm they will roll 90mph for 10+ hours at 25psi).
 

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OP, I'd suggest driving it with 37s on stock gears before deciding to upgrade. I just installed heavy 37s on KMC beadlocks (~110lb per corner) and was fully prepared for it to be a dog, but honestly the stock 4.10s felt alright with the little 2.0T. Still hit 8th gear on highway at 65+, even saw it on occasion at 55ish on secondary roads. I'm at a much lower elevation than you (~500ft lol), but the turbo should experience less issues at elevation than the 3.6 in regards to power.

My Jeep's mainly for wheeling and so keeping that robustness in the ring and pinion with the 4.10s is something I'm happy for. IMO, the 2.0 + 8 speed doesn't need to be geared all that deeply to feel alright, given my recent experience. Granted, I drive it like it's a Jeep and not a sports car.
 

J0E

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OP, I'd suggest driving it with 37s on stock gears before deciding to upgrade. I just installed heavy 37s on KMC beadlocks (~110lb per corner) and was fully prepared for it to be a dog, but honestly the stock 4.10s felt alright with the little 2.0T. Still hit 8th gear on highway at 65+, even saw it on occasion at 55ish on secondary roads. I'm at a much lower elevation than you (~500ft lol), but the turbo should experience less issues at elevation than the 3.6 in regards to power.
I agree. I'm on 38x13.5R17 Nittos on Raceline beadlocks with stock gears.

>I just installed heavy 37s on KMC beadlocks (~110lb per corner)

It's not the 110lb per corner that reduces peformance, it's the 1,200 lbs per corner (weight of the vehicle). Taller tires = higher gears so that reduces acceleration, but the rotational inertia of the wheels/tires doesn't measurably.

My Jeep's mainly for wheeling and so keeping that robustness in the ring and pinion with the 4.10s is something I'm happy for. IMO, the 2.0 + 8 speed doesn't need to be geared all that deeply to feel alright, given my recent experience. Granted, I drive it like it's a Jeep and not a sports car.
I wouldn't regear if offered for free for that reason.

All the haters that say on 37's you must regear, I just recovered a fully dead TJ 4.5 miles with 20° pitch common. It's was 82° outside and the hottest the AT got in M1 was 215° - when I got greedy and used M2, it quickly climbed to 226°, so I slowed down and returned to M1. The AT must have a really efficient cooling system.
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