Gear Ratio Question

[Sean B]

I’m looking for opinions on what ratio to go with. We have a LJ Rubicon with NSG 370, 6 speed. It is on 35s. I was leaning toward 5.13 but considering 4.88. Looking for feedback on people with the same combination. Jeep is mainly my wife’s, summer vehicle, not crazy off-road use but also not a ton of highway either.

 

[Mudflat]

You will probably get all kinds of opinions on this one, but I would go with 4.88 gears with 35” tires. I’ve got the same transmission, but I’m on 33” tires. I’ve got 4.56 gears & I think it’s just perfect (for me). It seems like 4.88 gears with your 35” tires would be close to that.

 

[machoheadgames]

I would go with 4.88 if I knew the 6 speed was staying long term. However, if there was a chance I was going to end up swapping it out for the AX15, I’d go with 5.13 just in case. Considering how unpredictable the 6 speed can be as it ages, I’d probably err on the 5.13 side of things. It’s only an extra 150 or so rpm on the highway anyways.

 

[JMT]

I agree. 4.88. I had the 6-speed before a transmission swap and 4.56 with 33’s was perfect. When I went to 35’s the 4.56 was not enough, but 4.88 would have been perfect.

 

[Sean B]

I agree. 4.88. I had the 6-speed before a transmission swap and 4.56 with 33’s was perfect. When I went to 35’s the 4.56 was not enough, but 4.88 would have been perfect.

Thanks guys, I initially thought 5.13 but then doing some reading was looking more at 4.88. We actually like the 6 speed and would like to stay with it. I saw a new set of 4.88 revolution gears in the classifieds and it got me thinking.

 

[JMT]

Thanks guys, I initially thought 5.13 but then doing some reading was looking more at 4.88. We actually like the 6 speed and would like to stay with it. I saw a new set of 4.88 revolution gears in the classifieds and it got me thinking.

Jump on it. FWIW I’m also pro 513.

 

[Sean B]

Jump on it. FWIW I’m also pro 513.

I’m just torn between the 2 ratios, either one would be much improved over the 4.10 in it though

 

[JMT]

I’m just torn between the 2 ratios, either one would be much improved over the 4.10 in it though

Well, you’ve got a 4:1 transfer case. That helps your crawl ratio if that’s important to you. You’re already going to be pretty deep (87:1 with 4.88’s and 94:1 with 5.13’s). The LJ is bigger and heavier than a TJ, but I don’t see that as an issue. It’s your call, and the ratios for this transmission get debated all the time on here, so it’s going to be a toss up. For your uses I think either will be fine, but I’d lean toward 4.88.

 

[Harold&Cat]

The lower you go with the gears the faster the driveshafts turn therefore discovering/creating more vibrations .
I went from 3.73 to 4.88 and have found different sources of vibrations . The worst was my front driveshaft , it was worn out and I didn't even know it .

 

[Ashim]

I have 5.13's with my TJ Rubicon auto on 35's. I'd say 4.88 would be fine for the manual. My opinion though is to get rid of the OEM rear locker when you regear. Go ARB or E-locker.

 

[Sean B]

I have 5.13's with my TJ Rubicon auto on 35's. I'd say 4.88 would be fine for the manual. My opinion though is to get rid of the OEM rear locker when you regear. Go ARB or E-locker.

Thanks, sounds like 4.88 is the way to go, along with upgrading the rear locker.

 

[ChadH]

FWIW - grimjeeper can help you with understand gearing/tire size choices with real world speed/rpm changes. I was debating keeping my 3.73's or swapping to 4.10's on my TJ with 31" tires. The site helped me make a decision - opted for 4.10's, and it is fairly accurate. Considering I did not account for weight applied to the tire, RPMs/speed is not off by much. Sounds like you have a good plan but maybe worth exploring for fun.

http://www.grimmjeeper.com/gears.html

 

[Sean B]

FWIW - grimjeeper can help you with understand gearing/tire size choices with real world speed/rpm changes. I was debating keeping my 3.73's or swapping to 4.10's on my TJ with 31" tires. The site helped me make a decision - opted for 4.10's, and it is fairly accurate. Considering I did not account for weight applied to the tire, RPMs/speed is not off by much. Sounds like you have a good plan but maybe worth exploring for fun.

http://www.grimmjeeper.com/gears.html

Sounds good, thanks for the info!