Hello, everyone. I have recently acquired a 2015 JKU Sahara, with the 6-speed manual transmission, and am loving it so far ... I have missed driving a manual! Other than a few cosmetic/functional interior mods, I haven't really done anything to it yet. Looking ahead, I would like to replace the stock bumpers and running boards, and probably a lift to fit 35" tires. I have read plenty of articles about re-gearing when these things are done, but they have all focused on the automatic transmission. Forgive my ignorance, but is this the same case with a manual transmission? What gear ratio should I be looking at? Thanks for the responses, ahead of time.

 

Yes, regearing axles on a jeep with a manual is just the same. I think you don't hear about it as much cuz 1) there are so many fewer manuals on the road, and 2) being overgeared with a manual is not as aggravating as it is with an auto since you can pick the gear you want. In an auto there's a lot of gear searching being done and it can drive you bonkers. Generally, the proper gear set for a manual is 1 higher (lower numerically) than what the same jeep with an auto would be using. You can check out the gear charts for the 3.6L engine. Those charts use the actual tire measurement (ground to hub x2) for those calculations. Most 35" tires are going to measure closer to 34". The rest will really be more about how you use the jeep and what kind of landscape you have there in PA. Some of us lean on the more aggressive side of gearing, others want more of a factory feel. Usually your choice will come down to 2 gearsets that will work and you just gotta pick which way to lean for your own use.

 

I have both a 2007 Wrangler X (later years would be called a Sport) with the 3.8L motor and a 2020 Gladiator Rubicon with the 3.6L. Both have manual transmissions and both are running 35" tires. I regeared the Wrangler to 4.88s and it helps some. But it is heavy and still very much a pig for Interstate driving. The Gladiator came with 4.10s and I have zero inclination to regear it. That rig is much lighter than the Wrangler, but the 3.6L motor provides plenty of oomph (apologies for getting so technical) for all my driving needs, including getting over Colorado Interstate mountain passes . One difference, however, is the transmission in the JL/JTs compared to the JKs: Fifth and sixth are almost useless gears because they are ridiculously tall. The engine is so quiet that I can find myself doing 70 MPH for the past 15 miles in fourth gear without realizing it. However, in 4WD-low for overlanding, something at which the Rubi transfer case rather sucks (it's geared for rock crawling, not the faster speeds of overland travel), those tall fifth and sixth gears are just fine. Anyway, my advice to you would be to hold off on regearing and see how you like the vehicle performance once you're done with the mods that add weight. And if you're rock crawler, you might prefer the lower gearing in 4WD-low, but if you're more into something like overlanding, might be fine without regearing.

 

My son is in the same boat as the OP. His 2016 JKUR with 4.10 gears/6 speed manual is slightly lacking since he installed 35" tires. Right now his budget limits changing gears but he is going to go 4.88 when the bank account allows it.

 

Hi. New on this forum but not new to the sport.

I have a 2014 with 35x10.5 street tires (skinny), and I use Q78-16 bias-plies off-road, which are an actual, measured 36”. 6-speed manual, 3.6. Mine was originally a Willys, so 3.73 diffs. It no longer has any of that, as I replaced the t-case, both axles, etc. because I have used it a lot in Utah, California, Colorado for rock crawling. I went to 4.56. It is perfect for the street tires and perfect for off-roading on the big bias-plies. But on-road on the 36s the Jeep feels noticeably sluggish to me, and then peppy again when I go back to the street tires. This is all on a 2-door with lightweight bumpers and skid plates — I focused on weight savings where I could in my build. If I had everything the same as it is but with a 4-door and heavy bumpers and skids, I think 4.88 would be the ticket.

Hope that helps. I am delighted with 4.56 with the build I have — add 600+ pounds to the rig and I think I’d want shorter diff gears.

One other thing: In my personal Book of Rules, it’s never worth regearing your diffs for less than a 2-step jump. If it’s close enough to only need one jump, it’s probably fine (assuming money and hassle mean anything to you.) So if you have 3.73s, I wouldn’t go to 4.10. If 4.10 is the best choice, 3.73 is close enough to me to not bother with the cost and hassle. Ditto my 4.56 set-up; if I started running 37s on the street I wouldn’t bother regearing to 4.88; I’d either live with the 4.56 as “close enough but maybe not perfectly optimal”, or I’d decide that 5.13 was what I needed and that would be enough jump to make it worthwhile (because if 5.13 would be a good setup, then 4.56 is going to feel pretty crappy.)

Cheers!