Questions on gear swap 2018 Jeep JL

Dalvarado55

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Newbie with gear change questions. I have a 2018 JL with the anti slip rear Dana 44 3.45 gears. Looking to jump to 315 70 17 tires and would like to upgrade the gears. What’s the best gear ratio for those tires? I have the 2.0l turbo engine. Also if I upgrade the gears does that mess with the anti slip in the rear axel? Any input will help.

thanks,
Dave





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GerJL

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Newbie with gear change questions. I have a 2018 JL with the anti slip rear Dana 44 3.45 gears. Looking to jump to 315 70 17 tires and would like to upgrade the gears. What’s the best gear ratio for those tires? I have the 2.0l turbo engine. Also if I upgrade the gears does that mess with the anti slip in the rear axel? Any input will help.

thanks,
Dave

Here is my take on it. Assuming you have the stock 245-75/17 with a 3.45 gear ratio.

If you go to

https://tiresize.com/calculator/

you will see your tires are 31.5 inches. A 315-70/17 measures 34.4 inches.

An equivalent gear ratio for that size tire would be

34.4 divided by 31.5 times 3.45 = 3.76 ratio. That theoretically would provide an equivalent gear ratio to what you have now. So with the available gear sets you could go slightly under to 3.73 or over to 4.10 like the Rubicon. However taking into consideration the 315s will be heavier I would err on the side of caution and go to 4.10.

That said, take into consideration the Rubicon with a 4.10 ratio has 285-70/17 stock or 32.7 inch tires. If I owned a Rubicon and was going to 315s from the stock 285s the ratio would be

34.4 divided by 32.7 times 4.10 = 4.31 ratio. So as a Rubi owner I would probably move up to 4.56 or 4.88.

I only point out the Rubi numbers because in regearing your sport, I would actually consider going to a 4.56 or 4.88 myself. As I mentioned those 315s will be heavier, so the extra gearing will help and also give you some room to grow if you want a truer 35 tire or even 37s.

Now for the LSD. In reading a lot of posts on this forum, there seems to be two issues that pop up more than others. One is steering and the other is a knock/failure of LSDs in the Dana 44s. Considering your vehicle is two years old and no problems, you may have been lucky. Who knows if adding 35s will bring a problem to light. Plus those LSDs wear out and need to periodically be maintained. If it was my Jeep and I was going to drop the money to regear, I would consider putting in a better option like a Detroit Truetrac or selectable locker while the diff is apart depending on what your use case is.

Hopefully that all makes sense. I am going through this exercise myself right now determining if I want a sport and upgrade or start with a Rubi.

Link to the thread on LSD issues (currently about 77 pages long)

https://www.jlwranglerforums.com/forum/threads/knock-in-rear-with-dana-44.16921/
 
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Therby

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I have the same set up, sport with 44 rear and lsd etc. But i have the 3.6 and manual trans

i went with 4.56 ratio on 315/70r17 and i think its perfect.

As said before, I think the only lower gear is 4.10 then up to 4.56.
Ever plan of doing more than 35s?
 
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Dalvarado55

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Thanks for the information. Right now I don’t have plans for 35’s. Any issues with the LSD?
 

Therby

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Thanks for the information. Right now I don’t have plans for 35’s. Any issues with the LSD?
nope, if you read on here people say it sucks and wears out quickly but mine hasn’t had too many issues and works well still
 

Headbarcode

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Thanks for the information. Right now I don’t have plans for 35’s. Any issues with the LSD?
The 315/70-17's you mentioned in your original post are actually the metric version of 35's. They just run slightly smaller, but still get lumped into the same size category.

I suggest doing the tires for now, and see how it feels. Having the 2.0/8-speed auto combo is the best for handling larger tires. As long as you reprogram for the new tire size, you may find no need to regear.

I have a 2.0/8-speed Rubi and jumped from the 32.7" factory tires to 38x13.50's. Still have the factory 4.10's and reprogrammed the speedo with the Tazer, so my speedo would be correct and the transmission would have correct info to properly place its shift points. It drives great and I'm not sure at this time if I would ever bother regearing.
 
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Dalvarado55

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Wow!!! That’s really helpful information. And would save me a lot of money too! Did you see a significant drop in your MPG? I’ll probably do the tires then and see if I have to re gear based on your info. Thanks so much
 

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