How many of you guys run 37s on stock 4.10 gears?

[Minty JL]

on my '23 Mojave I ran it on 37x13.5s until I installed the lift, no rubbing or nothing

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[Jammer]

Its fine till you drive one with gears. I did 5.13s and wondered why I waited to swap them out. Night and day difference.

I was told over 37s on the 3.6 motor on a regular Rubicon JL 513s you will lose some top end 488 is the way to go. But I can't imagine there's that much difference between 410 and 488. I'm at 4:10 right now for 6 years 37 is grapplers I hit 7th and 8th gear all the time RPMs are perfect I mean it works fine that's why I've never done it I can't imagine to be any different I haven't drove it another one like that with 488 I will do 513 my buddies have done and you lose the top in passing gear. I mean I get that it came with 33s and you're going to a 37 but we reprogrammed it with a tazer for 37s and I think that makes a big difference the transmission just right by doing that and that's why you do that but as far as gears I'm still hitting 7th and 8th every time I'm on the highway and the RPMs aren't too high I just don't think they'll be that much of a difference between 4:10 and 488 maybe I could drive one sometime I guess and see with the 488

 

[Jammer]

I couldn’t stand long road trips with the 4:10 gears with 37’s, I was constantly putting the transmission in manual to get the right gear and 8th gear was mostly non existent. I went with 5:13’s and very pleased.
To be fair I had no issues with 37’s and 4:10’s around town it wasn’t an issue.

I was told 513 is too much with 37s you lose that passing gear on top end that's a big difference 488 puts it back to stock I heard 513 is a lot of low end yes but you lose that top end it's like putting a small sprocket on a bike and you take off quick but then a guy with a bigger sprocket passes you on top in

 

[DanW]

I notice that most regrear to at least 4.88, some 5.13, yet AEV seem to set up all their rigs with 4.56’s on 37’s.

When planning my truck I intended to regear with 37’s but a local shop convinced me to stay 4.10 as many do. His take was the 8spd, 4.10 JT handles 37’s well.

I did choose light 37’s. The 37/12.5r17 Load C BFG KO2 is only 65 lbs.

After living for years with 35´s and 4.56 gears in my JL with manual transmission, I´d definitely go to 4.56 with the auto. 4.88´s would be fine, but there´s a point where you get too many rpm on the highway in 8th and autos do better with the same gearing/tire size than manuals. So my JT does as well on 35´s with 4.10´s as my JL does with 4.56´s on 35´s. But 4.88 is not much more than 4.56. I would not want to live with 5.13´s with 35´s. It would be a waste and would really take away the efficiency of the 8th gear ratio on the highway, IMO. Maybe not as much with 37´s, but after living with 4.56 and the manual, no way would I consider going to that ratio.

The guy who did the gears on my JL felt 4.56 for 35´s and 4.88 for 37´s was the sweet spot. That again is with the manual. I think 4.56 would be the sweet spot for 37´s with the auto.

I´d see if someone on the forum lives near you with a gear swap and 37´s and ask to take a ride with them. Or you could ask a good shop that does the swaps if they´d reach out to a happy customer for you to take a ride.

It is really a guessing game. I went through agony deciding between 4.56 and 4.88. I would have hated 4.88 on the highway and I think first gear would have been too short. Fortunately, I guessed correctly. Again, that´s with the manual. The auto is a different animal. I have zero need or desire to go up from 4.10 on 35´s with it.

The other observation I have after the gear change in the JL.....The only place regearing makes a meaningful difference is 1st gear and top gear. Everything else is completely dependent on your driving speeds and style, and in my JL, it made no difference at all outside of 1st and 6th. 1st became a total granny gear (it was fine before the swap) and it made it so that I can pass in 6th on the highway without downshifting and take most hills without losing speed and downshifting. It made 6th gear useable, where as with 4.10´s it was just too tall.

Hope this helps. If it causes more confusion, that´s normal with planning a re-gear. LOL!

 

[DanW]

I was told 513 is too much with 37s you lose that passing gear on top end that's a big difference 488 puts it back to stock I heard 513 is a lot of low end yes but you lose that top end it's like putting a small sprocket on a bike and you take off quick but then a guy with a bigger sprocket passes you on top in

Based on my experience, 4.88 would be a little more aggressive than stock. 4.56 with the auto would be the sweet spot and closest to stock, IMO. That again is with the auto. With the manual, 4.88 with 37´s would be the sweet spot. Autos handle taller axle ratios a little better because of the slushbox vs. the manual with it´s direct-drive.

Auto manufacturers used to give a slightly higher axle ratio to manuals. I think most still do, with the few manuals left out there. I can 100% see that going back and forth from my JL manual 4.56 and JT auto with 4.10 with both on 35´s. And the JT´s 35´s have a couple eighths of an inch greater diameter, too.

But 4.56 and 4.88 are close enough that I don´t think one could go wrong, either way, with the auto and 37´s. I´d go 4.56 if you do lots of highway and/or live in flatter lands. 4.88 if in the mountains or do less highway driving. Just my 2 cents.

And don´t expect it to suddenly feel like a Hemi. Like I said, it mostly helps 1st and top gear. The transmission finds the right gear for the right speed or need with everything in between. No difference at all there.

Funny note....I can imagine that re-gearing was a MUCH bigger deal back with automatics were 3 or 4 speed and manuals were 4 or 5 speed. With so many ratios now, it isn´t as big a deal. When I started driving in the 80´s it was a huge improvement to have a 4 speed over a 3 auto. I had a Pontiac Sunbird with a 3 speed that advertised a locking torque converter to feel like 4. LOL. It worked. It was nice. But wow, three speeds with that little 84hp 1.8 liter. Of course the car weighed nothing, so it was fine for its day. LOL!

My brother had a mid-70´s Chevy short bed 2wd regular cab base pickup with a 3 speed manual on the steering stalk. The old ¨3 on the tree!¨ LOL. I wasn´t old enough to drive it or pay attention, but that just seems so weird to me to shift a manual on the column. But it was normal in those olden days.

 

[Jammer]

I was hitting 8th last night at 80 mph and was at 2200 RPMs with my 37s that's not bad on my 2018 Rubicon with 410s is it ? 2018 JL Rubicon

 

[Zachanadandy]

Still on the stock 4.10s with 37s since the truck had 1100 miles. At 35k now. Still see 8th gear, tows just fine even up hills. Even an overloaded 8200lb trailer was no problem. The idea that a regear is going to be game changing is just false in my experience. Our 2019 jlur we regeared from 4.10s to 5.38s on 38s. It wasn't better at anything. It got into 8th gear a lot more often... like any speed over 40mph. Not bad...if it was a 10 speed. There's no reason to be in the 2nd overdrive with no more shifts by half the legal speed limit or west. Gained 1mpg around town, lost 2-3 on the highway. For our use that's a massive hit as our AZ property is 600 miles from the house. 99% of that is freeway at 80-85mph. Losing a huge chunk of fuel economy under the use where we burn the vast majority of our fuel every year is not good. Being a Rubicon the 4-1 transfer case offered plenty of crawl ratio before the regear. Gears that low made 1st gear almost useless in 4LO outside of the most technical obstacles. And the measured 0-60 didn't improve either. Another guy on the JL forum tested his 0-60 before and after with the dragy and had the same rest. 1/10th quicker 0-60 with the only gain being very slight off the line boost in 1st gear. The entire graphed runs above that were identical. People think they gain power back and the truck is quicker because it's running through the gears quicker. The most under whelmiing mod I've ever spent $3k on in any vehicle. If you want to gain power back you're better off with a tune for less than 1/3rd the cost. If your really want to gain power spend 2x the cost and get a supercharger. Gears offer very little that you can't gain with a simple downshift and the auto does that...automatically.

 

[Gladiatorx2]

I have kept 4.10 gears in both my Rubicon's. I live in East Tennessee with elevation range from 900 to 5000 feet above sea level. There are not many flat spots. 95% of the time I am satisfied with the 4.10 as being adequate and have no complaints . I am averaging a little over 17 mpg in combined city/highway and see 8th gear regularly .

Only on steep grades at low speeds in the mountains of Cherokee NC and the Smokies this combinations seems less than adequate .

I do feel that there is something to gain in performance and drivability but in my cause it doesn't out weigh the cost. I do go off road at least every other week in either TN, NC, or KY and have no complaints with 4.10 gears.

 

[nbennettksu]

My friend [in a JLR] ran 40's on 4.10's for a while before upgrading to 5.38. He was fine but like others mentioned, he wondered why he waited so long. I know the JL is different and a lighter vehicle, this was for reference only.

I have another friend with an eco diesel rubicon running stock gearing on 40's and he's got no plans to change gearing.

 

[Camaroboi13]

I have another friend with an eco diesel rubicon running stock gearing on 40's and he's got no plans to change gearing.

I’m on 3.73s on 37s and love it. Eco diesel. I have no plans on changing gearing either.

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