So Rubicon NSG370 with 35s the recommendation would still be 4.88s? Does the lower gearing the transfer case come into the decision?
What gear ratio should I install in my Jeep Wrangler TJ / LJ? (and other re-gearing FAQs)
- Thread starter Chris
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So Rubicon NSG370 with 35s the recommendation would still be 4.88s? Does the lower gearing the transfer case come into the decision?
That all depends on your personal preference. Low range is going to be the only difference when it comes to the Rubicon.
I run 4.88 on 31's, no issues at all on hwy and gets 19 mpg. The rec's we would make were based on the vehicles eng/trans combo and what they were doing with it. We would find a combo that would place the engine at an optimal rpm torque wise in top gear at the desired mph. Unless it is a dedicated trail rig, on road will always dominate where the vehicle spends most of its time. Easy vs hardcore wheeling never really entered the picture. That is what low range in the tcase is for.
4.88 and 31’s sounds low to me but I don’t know your exact circumstances. My old CJ with 33’s and 5.13 gears got like 9-mpg. Haven’t check closely but my current 2.4 4-cly with 33’s/4.56 gearing is getting between 16-19mpg which is decent and stays within the RPM powerband. 4.88 and 33’s is a great combination for both off-road and street-ability. I nearly went with that ratio. 4.56 vs 4.88 are very close so it’s splitting hairs. I drive my TJ 90% on road including 100 freeway miles to my wheeling area so 70+ mph with no high RPM droning is important. Yes 4 low is a bit higher than optimal but I can live with it. Might look into a Rubicon T-case to get lower 4- low. Gear selection always involves some sort of compromises
I haven't checked prices lately but another option for low range is a 4 to 1 kit for your 231 t-case ..
So will 4lo be lower/slower with 4.88 gearing? Already feel like a small baby can out crawl my Rubi! Not that that is a bad thing, just curious. This will be the first Jeep I've ever re-geared.
Just to clarify, the difference between the Rubicon t-case (NP241) and the standard t-case (NP231) is the low range gearing and the over all strength of the case. The Rubicon has a stronger case and a low range of 4.0:1, the Non-Rubicon has a low range of 2.72:1, and both have a 1:1 high range output.. The Rubicon already has a lower crawl ratio in "low range" so it will still have a lower crawl ratio then a non-Rubicon. Does that help?
I had a Teralow 4:1 kit installed in my NP231 on a previous SE TJ. Worked great but apparently there where problems and Teraflex no longer offers it for sale. Is there another 4:1 kit being sold today? A Rubicon 241OR is an option but it’s a big heavy expensive beast and can have clearance issues when doing other mods like a belly up T-case skid.
Final crawl ratio is really important when you only have 4 angry squirrels powering your Jeep. Stock my 05 SE had a crawl ratio of around 45:1. Now with 33’s and 4.56 gears I’m around 55:1. Adding a 4:1 T-case would put my crawl ratio at 81:1
If I had went with 4.88 gears my final crawl would only have been 59:1, 5.13 gears would get me 62:1. You can see that lowering your T-case ratio gets you low big time. My prior SE had this setup, 33’s, 4.56 gears, Teralow 4:1. It crawled plenty good
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As far as I know no one else ever did a 4:1 kit for the 231, There are other options but all of them have high dollar signs and varied levels of customization. There have been some discussions within this forum talking about t-case/4:1 options.
https://wranglertjforum.com/threads/teraflex-4-1-transfer-case.4802/
Yes. When you change axel ratios you change your final crawl ratio. As an example assuming you have 31’s, 4.11 gearing and a 4:1 T-case your crawl ratio in 4-low 1st gear is 73:1. Going to 4.88 gearing will lower your crawl to 88:1. If your running or planning to run 33’s or 35 tires then you might consider 4.56 or 4.88. Depends on the type of wheeling your doing. Rock crawling or difficult technical trails you want that low gearing in 4-low. Driving Forrest service roads and easy trails then I wouldn’t go much lower than what your geared now. It sounds like you feel your 4-low crawl ratio is sufficient for how your setup now. But adding bigger tires in the future you may consider lower axel gearing.
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Thanks. Yea, looks like I’m going to start down the 35 rabbit hole. Got plenty of more research to do, and funds to gather. Love to get back on 15in wheels and C rated tires too, just to first hand experience the change.
Crawl ratios have value for comparing various set-ups with manual transmissions, but with automatics the number is largely academic due to slippage in an AT which effectively results in an unlimited crawl ratio. Still, crawl ratios can be fun to compare.
Crawl ratio = transmission low gear ratio X transfer case low range ratio X axle gear ratio
My old CJ-7 with T-5 manual transmission, Dana 300 transfer case and AMC 20 rear axle:
Stock = 4.03 x 2.62 x 3.54 = 37.38
As modified with Ford T-19 manual transmission and 4.56 axles = 6.32 x 2.62 x 4.56 = 75.51
My '06 LJ Rubicon with 42RLE automatic transmission and NV241OR transfer case:
Stock TJ/LJ Rubicon = 2.84 x 4.0 x 4.10 = 46.58
(A non-Rubicon TJ with 42RLE is typically 2.84 x 2.72 x 3.07 = 23.55 or 2.84 x 2.72 x 3.55 = 27.42 or 2.84 x 2.72 x 3.73 = 28.81)
LJ Rubicon with 4.88 axles (as purchased) = 2.84 x 4.0 x 4.88 = 55.44
LJ Rubicon with 5.38 axles = 2.84 x 4.0 x 5.38 = 61.12
LJ Rubicon as currently modified with Rubi-Crawler underdrive and 5.38 axles:
Rubi-Crawler engaged, transfer case in high range, 2.84 x 2.72 x 5.38 = 41.56;
Rubi-Crawler disengaged, transfer case in low range, 2.84 x 4.0 x 5.38 = 61.12;
Rubi-Crawler engaged, transfer case in low range, 2.84 x 2.72 x 4.0 x 5.38 = 166.24
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Crawl ratio = transmission low gear ratio X transfer case low range ratio X axle gear ratio
My old CJ-7 with T-5 manual transmission, Dana 300 transfer case and AMC 20 rear axle:
Stock = 4.03 x 2.62 x 3.54 = 37.38
As modified with Ford T-19 manual transmission and 4.56 axles = 6.32 x 2.62 x 4.56 = 75.51
My '06 LJ Rubicon with 42RLE automatic transmission and NV241OR transfer case:
Stock TJ/LJ Rubicon = 2.84 x 4.0 x 4.10 = 46.58
(A non-Rubicon TJ with 42RLE is typically 2.84 x 2.72 x 3.07 = 23.55 or 2.84 x 2.72 x 3.55 = 27.42 or 2.84 x 2.72 x 3.73 = 28.81)
LJ Rubicon with 4.88 axles (as purchased) = 2.84 x 4.0 x 4.88 = 55.44
LJ Rubicon with 5.38 axles = 2.84 x 4.0 x 5.38 = 61.12
LJ Rubicon as currently modified with Rubi-Crawler underdrive and 5.38 axles:
Rubi-Crawler engaged, transfer case in high range, 2.84 x 2.72 x 5.38 = 41.56;
Rubi-Crawler disengaged, transfer case in low range, 2.84 x 4.0 x 5.38 = 61.12;
Rubi-Crawler engaged, transfer case in low range, 2.84 x 2.72 x 4.0 x 5.38 = 166.24
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Just out of curiosity, being someone who has never experienced off roading with an automatic transmission before, I get that going up has virtually unlimited crawling capability with small regards to gear ratio. My question is, what is the hold back like descending steep grades? Is there a tendency to run away if not using the brakes?
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So if you shift into 1st even with torque converter slip it still holds back with no issues.... Good to know thanks. You never know one day I might go over to the dark side where there are no clutch pedals.
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My 2008 JK Rubicon was an auto. It wheeled surprisingly well despite the naysayers in my Jeep group. As mentioned downhill in 4-low was always controlled, never felt like it was to fast or having to drag the brakes etc. In some ways it was easier than a stick. Example going up a really steep hill, stopping and then restarting. Not having to work 3 pedals with only 2 feet and the resulting pucker when you roll back. You can really concentrate on driving a line instead of working the Jeep controls if that makes sense. It’s almost cheating. That said, a manual trans is still much more enjoyable to me but that’s just a personal preference and tradition talking.
I drove my re-geared TJ on a 220 road trip into the foothills of the Cascade Mts, mostly freeway at 65-72 mph. 70 mph in 6th gear the rpms was 2930 which was a bit higher than I thought it would be but didn’t seem overly buzzy. Lots of hills and long sections of low grades to climb. The 2.4 with 4.56 gears and 33” tires easily pulled 6th gear and overall performance in every category was better than stock which was 28” tires and 3.73 gearing. Very satisfied with this setup. I think 4.88 gearing for my setup would be perfectly acceptable also. Not sure exactly what I’m getting mileage wise with the new setup. I roughly figured 16-19 mpg but I will figure this out with better accuracy. It’s a Jeep so mileage is a secondary consideration but if you can get somewhat decent mileage through proper gearing vs tire size then that’s a good thing
I drove my re-geared TJ on a 220 road trip into the foothills of the Cascade Mts, mostly freeway at 65-72 mph. 70 mph in 6th gear the rpms was 2930 which was a bit higher than I thought it would be but didn’t seem overly buzzy. Lots of hills and long sections of low grades to climb. The 2.4 with 4.56 gears and 33” tires easily pulled 6th gear and overall performance in every category was better than stock which was 28” tires and 3.73 gearing. Very satisfied with this setup. I think 4.88 gearing for my setup would be perfectly acceptable also. Not sure exactly what I’m getting mileage wise with the new setup. I roughly figured 16-19 mpg but I will figure this out with better accuracy. It’s a Jeep so mileage is a secondary consideration but if you can get somewhat decent mileage through proper gearing vs tire size then that’s a good thing
Okay. Did a more in-depth mileage test with my new gearing. My TJ is an SE so 4 cly 2.4 engine, stock 28” tires, 3.73 gears and six speed trans.
I am running 33 x 10.5” tires now and 4.56 gearing. Mileage in 600 miles of combined driving is 19.5 mpg. Where I drive are somewhat hilly roads. I didn’t baby it, just normal driving. Pretty sure that all freeway driving should get me into the 20’s mpg.
So pretty happy with my gear selection. 4.56 and 33’s ends up being slightly lower than stock. Running about 130-ish rpm higher cruising at 70 mph in top gear. Plenty of power on road ( as much as 4 squirrels are capable of anyway) for keeping up with traffic and passing etc. I think if I was doing a higher percentage of wheeling to road I might have gone with 4.88 but for now I’m satisfied that the 4.56 gearing will be more than satisfactory for on road driving. As a side note, have yet to see how she drives off-road in moderately difficult situations. Stock crawl ratio was 45:1. I’m sitting at 55:1 with my current gearing/tires so while lower it isn’t where I’d like it to be but still an improvement over stock.
I am running 33 x 10.5” tires now and 4.56 gearing. Mileage in 600 miles of combined driving is 19.5 mpg. Where I drive are somewhat hilly roads. I didn’t baby it, just normal driving. Pretty sure that all freeway driving should get me into the 20’s mpg.
So pretty happy with my gear selection. 4.56 and 33’s ends up being slightly lower than stock. Running about 130-ish rpm higher cruising at 70 mph in top gear. Plenty of power on road ( as much as 4 squirrels are capable of anyway) for keeping up with traffic and passing etc. I think if I was doing a higher percentage of wheeling to road I might have gone with 4.88 but for now I’m satisfied that the 4.56 gearing will be more than satisfactory for on road driving. As a side note, have yet to see how she drives off-road in moderately difficult situations. Stock crawl ratio was 45:1. I’m sitting at 55:1 with my current gearing/tires so while lower it isn’t where I’d like it to be but still an improvement over stock.
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As for me and my 01 TJ 4.0 NV3550, I will be going to 35" tires and 4.88 gears. I currently run 33" with 3.73 gears. It's awful driving into a slight headwind or up a slight incline on the freeway at 70 mph. Driving it from Arizona to Wisconsin several years ago was brutal on some of the steep hills.
Oldguy
TJ Enthusiast
Oldguy
TJ Enthusiast