Gears for 37" tires

[GrayGoose]

so I went to 5:13's and am happy to report that I LOVE IT! The performance is so much better - even will roast the tires now and no issue holding 8th gear at highway speeds. Only regret is not swapping the gears sooner.

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[WK2JT]

so I went to 5:13's and am happy to report that I LOVE IT! The performance is so much better - even will roast the tires now and no issue holding 8th gear at highway speeds. Only regret is not swapping the gears sooner.

I go in Wednesday for my 5.13 swap... can't wait.

 

[GrayGoose]

I go in Wednesday for my 5.13 swap... can't wait.

Do tell - how does it perform?

 

[WK2JT]

Do tell - how does it perform?

Haven’t gotten to drive much after the break-in... long story. So far it’s great. However, I haven’t towed with it or had it in the mountains yet. 8th gear around 45 now and approximately 2,400 RPM at 75 MPH. But it feels so much stronger throughout the rev range and not struggling now.

At lower speed around town, what this thing really needs is a trans tune to hold gears longer. The efficiency police have this thing up shifting and lugging 1,200-1,500 RPM. I’m going to call Livernois and see what their trans tune does and if they sell it separately.

 

[Harold0819]

I'm planning on a regear on my JTR. I have 37s and stock Rubi 4.10s. Bouncing between 4.88s and 5.13s. I want towing capacity and cruising ability back. I live in the northeast so our highways and roads have alot of hills so it hunts for gears at times, especially on the highway. I was a little leary of 5.13s due to the significantly smaller pinion. But I know plenty of people who did 5.13s in JKs with 44s with no issue....definitely no bueno for a dana 30. I also may at some point go a bit larger, 38s or 40s and 5.13s would be better. You guys with 5.13s any issues?

 

[TRAILJT]

Hello, I have 4.88s on mine with 37" tires. 4.88 is the Best ratio for 37s. Stock gearing had my transmission confused as to which gear it needed. I personally would not go with a lower ratio. The lower you go the more apt you are to break teeth on your ring and pinion unless you go to a larger diff. When you use lower gears, you lower the service factor of the diff. If you do the calculation 4.88s are just a fraction lower than stock gears with stock tires. Hope this helps.

 

[stickshifter]

And I am of the opinion that 4.10 gears are the best if you have a Rubicon. Even if I didn’t have a Rubicon I wouldn’t go any lower that 4.30 on 37s.

And maybe that’s fine in Tennessee or Pennsylvania - but don’t presume that what works for you at sea level works everywhere. There are a lot of folk on here who live in the Rockies and face very different conditions. I live at 8,500 feet and commute down a steep winding canyon to 5,500 feet. The road is next to a creek and the moisture creates black ice in winter. It also snows a lot. I’ll wager I have different ideas than some folk about what engines are “powerful” what constitutes “tight steering”, and what tires are “good winter tires”. Everyone drives in different conditions and has different needs/wants, and people also have different expectations of their vehicles. It’s all good when we remember that what works for us is related to our own environment and to our own expectations. Peace.

 

[WK2JT]

And maybe that’s fine in Tennessee or Pennsylvania - but don’t presume that what works for you at sea level works everywhere. There are a lot of folk on here who live in the Rockies and face very different conditions. I live at 8,500 feet and commute down a steep winding canyon to 5,500 feet. The road is next to a creek and the moisture creates black ice in winter. It also snows a lot. I’ll wager I have different ideas than some folk about what engines are “powerful” what constitutes “tight steering”, and what tires are “good winter tires”. Everyone drives in different conditions and has different needs/wants, and people also have different expectations of their vehicles. It’s all good when we remember that what works for us is related to our own environment and to our own expectations. Peace.

Agreed... I think 4.88 would probably be great for most, but going over the Eisenhower/Johnson pass in CO, I almost wish I went 5.38 instead of 5.13, especially when pull a trailer.

 

[Harold0819]

I ended up up with 5.13s. After speaking with people from many vendors, both retailers and manufacturers they all agreed that 5.13s are the way to go. I'm currently running 37s but will likely go up in size a bit as well but also want towing ability. Just got my gears, installation kits, and one piece RCV axles shafts so I can also delete my FAD. Having my local Jeep dealer do my install. They are very mod friendly and the manager told me they will honor any warranty issue in my Rubicon axles minus the ring and pinion. Will let you know how it is after my install.

 

[davetha]

I ended up up with 5.13s. After speaking with people from many vendors, both retailers and manufacturers they all agreed that 5.13s are the way to go. I'm currently running 37s but will likely go up in size a bit as well but also want towing ability. Just got my gears, installation kits, and one piece RCV axles shafts so I can also delete my FAD. Having my local Jeep dealer do my install. They are very mod friendly and the manager told me they will honor any warranty issue in my Rubicon axles minus the ring and pinion. Will let you know how it is after my install.

That's awesome they'll warranty everything. The one piece RCVs is actually one thing I regret. If you swap your front driveshaft and set your castor to spec you may experience some driveline vibrations.

It'll all depend on your lift height, driveshaft, etc..

 

[Harold0819]

That's awesome they'll warranty everything. The one piece RCVs is actually one thing I regret. If you swap your front driveshaft and set your castor to spec you may experience some driveline vibrations.

It'll all depend on your lift height, driveshaft, etc..

I'm running RockKrawler's 3" lift and have a stock driveshaft. I don't anticipate any vibration issues but if I do I'll swap out the driveshaft for an Adam's shaft. My JKU has a 5.5" kit with Adam's front and rear driveshafs and no vibrations. Hopefully won't be an issues. Not a big fan of the FAD system. Flashback nightmares of the 80s and vacuum failures on my Comanche.

 

[FLUndertaker]

Well, after a few weeks with the 5.13s in, I'm very pleased with the outcome. There was never any real concern for low speed driving due to the 8sp gearing, but it makes a huge difference above 50 mph or so. Additionally, my mpg has gone up about 2mpg so far and the more miles I put on it, it keeps climbing due to averaging on the speedo. I'll ignore the input from others who have gone up in tire size without regearing and trying to claim their Jeeps don't need it since they, apparently, have magical unicorn jeeps that defy the basic laws of physics. For the rest of us commoners, regearing will put your engine/trans back in the correct RPM range to account for the larger tires and will in essence, "re-center the fulcrum". Keep in mind that attempting a direct RPM conversion for gearing won't be adequate since you have added considerable unsprung weight, rolling resistance, and increased wind resistance. I got the Yukon gears from Northridge for less than $900 including master install kits, and install near me was 1K for both axles.

Any issues with lose of passing ability at highway speed as some have reported?

 

[davetha]

Any issues with lose of passing ability at highway speed as some have reported?

Why would you loose passing ability going to 5.13? Comparatively it's only slightly higher than running stock tires and 4.10, and with the 8 speed you could theoretically hit much MUCH higher than highway speeds before red lining in 8th gear.

 

[WK2JT]

Any issues with lose of passing ability at highway speed as some have reported?

My experience with 5.13’s and 37’s has been quite the opposite. I believe it was a particular banned site the mentioned kickdown to 5th was lost. However, that is speed/RPM dependent and I have not lost that running 65-70. I suppose the RPM range might be too high for that to occur if you’re running 80, but I rarely run the rig that fast and not sure why I’d be kicking down at 80. 5.13’s have certainly made the driving experience more pleasurable. I want to eventually go 5.38’s with the 37’s.

 

[Ole Cowboy]

I ran 4:88's and put 80k miles on that Jeep, MUCH of it Hwy on trips to Ca, Nv, Moab, Rubicon, Death Valley Baja you name it....That said it was a TJ and Bulletproof 6. That is down-low for both HP/Torque, you get nearly 80% of your torque just off idle and time that engine gets North of 3000 rpm is gasping for air. BUT the V6 does not eve come alive until you get beyond 3000 rpm. Were it my build I would go 5:13 -5:36 cogs because the V6 don't get happy until it goes upstairs in the rpm band. Down side is mpg, but if you bought for mpg you may have bought the wrong thing. Let me add, if you plan on running the serious big boy pants trails 4+ level I would reach deep and go 5:36...WHY? Slow rolling does not provide a lot of RPM's and you need make them thru the gears.

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