Re-gearing… please ELI5

[6th Floor Mule]

I do take roadtrips and want to be able to make use of all six gears. Seems like 4.88 is the way to go if I lift it and go with 35s.
Appreciate you sharing your insight and knowledge!

Yes, if you want to road-trip and use all 6 gears, the 3.45’s gotta go ?.

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[Mustang5755]

I bought a 2020 Rubicon with 35s and a lift. I had to set the tire size and that's done. But for me it's the opposite, it go through the gears fairly quickly getting to 6/7 gear by around 45 MPH. It's smooth and not a problem but I don't know if that's abnormal and if it is what might be driving that. I have the 2.0L Turbo.

Thanks for any advice.

 

[word302]

I bought a 2020 Rubicon with 35s and a lift. I had to set the tire size and that's done. But for me it's the opposite, it go through the gears fairly quickly getting to 6/7 gear by around 45 MPH. It's smooth and not a problem but I don't know if that's abnormal and if it is what might be driving that. I have the 2.0L Turbo.

Thanks for any advice.

The 2.0 does a better job at low RPM so it handles the larger tires better. You also have a Rubicon so you’re starting with 4.10 gears. Altitude also doesn’t affect the turbo motor nearly as drastically so you have a lot of things working in your favor. While you would still see some benefit from a re gear it would be way down the priority list for me with your setup.

 

[Mustang5755]

The 2.0 does a better job at low RPM so it handles the larger tires better. You also have a Rubicon so you’re starting with 4.10 gears. Altitude also doesn’t affect the turbo motor nearly as drastically so you have a lot of things working in your favor. While you would still see some benefit from a re gear it would be way down the priority list for me with your setup.

Thanks, so should I not be concerned that it gets to 6/7 gear by 45 MPH or would I be more concerned the other way. It is an automatic as you mention and i was told it had a learning mechanism to it that would calibrate itself post me changing tire size but I don't see a ton of change with the gear intervals. Like I said, I'm not sure it's a problem I'm just curious. It drives fairly well but it has 35s and a lift so it's not going to ride like stock.

 

[J.Ferreira]

Thanks, so should I not be concerned that it gets to 6/7 gear by 45 MPH or would I be more concerned the other way. It is an automatic as you mention and i was told it had a learning mechanism to it that would calibrate itself post me changing tire size but I don't see a ton of change with the gear intervals. Like I said, I'm not sure it's a problem I'm just curious. It drives fairly well but it has 35s and a lift so it's not going to ride like stock.

There's only so much learning that is possible, at a certain point physical limitations of the mechanical parts would end up playing a role. But like @word302 said you have a Rubicon, so you already have an advantage of better gearing.
This thread started with a Willys guy with 3.45s which even with an automatic would be pretty unhappy with 35's.

 

[J.Ferreira]

One more day of work.
4 days off.
2 days of work.
5 days off. (3 in Vegas)
Drive 5 miles to new job.

Off to bed. Later y’all.

When I told my bosses today that I’ve decided to still go with the new job. They put on a very good face and were outwardly respectful of my decision…but I could see in my GMs eyes the wheels turning for whatever they’re going to do. ?
I’ve been the primary fuel control builder at work for the last few months and they’ve been dragging their feet teaching the new girl to build.

 

[AVGeek99]

I have a 2021 6MT JLUR. I ran 35s on the stock 4.10s for the first two years. It wasn't a speed demon by any stretch, but it was perfectly acceptable. It had no issues cruising 80 to 85 in 6th on midwestern interstates. Through the rockies on I70 in CO it held speed pretty well in 5th, needed 4th in the steep parts, maybe third for the last 1/2 mile of Loveland pass before the Eisenhower tunnel.

Around home on the county roads around the Twin Cities. I'm ran 6th at 60mph and higher unless I was on a hilly road, and would then drop to 5th. All in all the 4.10s weren't ideal with 35s, but they were perfectly acceptable.

3 weeks ago I had mine lifted and regeared to 4.88s to prepare for 37s in Jan or Feb. So right now I'm running the 4.88s on my 35s. It has very noticeably more power. Enough that I would say 4.88s may be overkill for 35s.

It really depends on where you live and drive, and if you tow on road trips. 5.13s should only be an option if you tow quite a bit. If you live in the mountains 4.88s would probably be very good on 35s. If you live in flatter country 4.56s are probably your best bet if you tow very little or not at all.

I went with 4.88s because I'm going to 37s in Jan or Feb. With 37s 4.88s will get me just a touch shorter/lower than a purely stock Rubi on 33s. Probably very similar considering the added weight. For me, based on what the 4.88s are like with 35s, they'll be perfect with 37s.

 

[grimmjeeper]

Whoa. Bookmarked!!!

If you have a few minutes, you can click on the link at the top that covers why you want to regear.

Basically it's a wordy version of what people here have already said.

 

[Jeeb]

If you have a few minutes, you can click on the link at the top that covers why you want to regear.

Basically it's a wordy version of what people here have already said.

I’ll definitely read up on it all as much as I can. Thanks for the advice!

 

[COJeeper]

Roys gear calculator is a god send.
http://www.grimmjeeper.com/gears.html

1. Aisin D478 for the transmission
2. NP241/NV241/NVG241 for transfer case
3. n/a
4. whatever gear ratio you want to see
5. Tire size you plan on running

Plug those details in and there is a left column and a right column that you can use to do side by side of different comparisons of tire sizes/gears.
It'll give you crawl speeds, RPM at various highway speeds and RPM at each gear vs the speed you're going in that gear.
Give it a whirl!

It can seem a little intimidating at first, but knowing the transmission and transfer case is the first step. (conveniently provided)

EDIT: 4.56:1 if you do a lot of highway driving. 4.88:1 if you do a fair bit of off roading/crawling. 5:13:1 if you're real serious in the crawling/essentially zero highway.

Well, I did something wrong, I think. I will go try it out right now but I don't think my Jeep can go 252 miles per hour on the road....

 

[J.Ferreira]

Well, I did something wrong, I think. I will go try it out right now but I don't think my Jeep can go 252 miles per hour on the road....

?? did you put in the wrong transfer case or gearing or tire size or something
That’s wild

@grimmjeeper
Something happened lol

 

[Old Jeeper]

Hello Jeep Friends!

I hope this is the right place to post this….
H

Hello Jeep Friends!

I hope this is the right place to post this….

I have a 2021 two door 6sp manual JL Willys that Id like to add a 2” Mopar lift and 35” tires to. I get all kinds of mixed responses about the need to re-gear. Some say the difference isn’t that big of a deal while others say I’ll never use 5th and 6th gear again without a regear.

Being completely naive and having major limitations on my mechanical knowledge ?, I assumed the extra weight of the tires and wheels would make the engine work harder leading to higher RPMs making it so that I am in 5th or 6th gear quicker than I am now. Is it actually the opposite of my ignorant assumption?

Can one of the many experts on this forum explain like I’m five, what I should expect with my 6 speed Willys and this setup?

thank you!!!

I have a jeep Rubicon, and when I ordered it, I specified the 488 gears because I put 35s on there as soon as I got it. 36 is just not a real cheap engine. I didn’t like it when it came out. I don’t like it today but it’s what I have so I live with it. The problem with it most people know as it horsepower and torque. Don’t show up until you get way down the street versus the old straight of the TJ. Best engine that ever set a jeep if you’re into Offroad in the rocks.

Regearing is not cheap and you got two axles to contend with. If you got the coin put in a set of 488si I would not recommend going to 513’s unless you plan on going to 37 down the road.

what’s it like running four eights and 35s just call yourself the red light bandit. It really really wakes up that V6 I love it absolutely love it and you can dart in and out of traffic I mean to tell you!

 

[Traveller128]

My Charger, with the stock 2.62 rear gear and the Nag1 trans, showed that it was capable of 231 MPH at 5900 RPM. Not going to happen, but mechanically, that's what the math said.

It's limited to 170 MPH in the ECM now (and will do it) with the 3.06 I installed, but mechanically it now shows 198 MPH at 5900. Much more reasonable.

 

[grimmjeeper]

Well, I did something wrong, I think. I will go try it out right now but I don't think my Jeep can go 252 miles per hour on the road....

That's not uncommon to see. There's no sanity check to say whether the jeep can physically reach that speed in real life. It just does the math and spits out the result. It's up to the user to know that no Jeep is going to hit 200+ MPH without outside help.

 

[AdamG]

Super helpful thanks. What would a ballpark figure be for a shop to do a 4:56 regear?

I paid $2875 all in. Since the LSD clutch packs do wear out, you might want to consider replacing the factory one with something like an Eaton TrueTrac or Nitro Helix while they’re in there, shouldn’t cost any more other than the price of the LSD itself.

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