Re-gearing… please ELI5

[Jeeb]

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!!!

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[word302]

Because of the bigger circumference of the tires, the drivetrain will be spinning slower for each mile than it would stock. You’re thinking “that’s great, less RPM means better gas mileage”. The problem is that the 3.6 is gutless at low RPM. It has trouble making power below 2000. The new gears will bring you back into the optimum power band for your engine. The stock gear ratio is already too high (numerically lower number 3.45:1). Depending where you live and how you drive you’ll want 4.88s or maybe even 5.13s (especially if you think you’ll EVER jump to 37s or if you drive in the mountains or tow). Your thinking is actually backwards. When adding larger tires you get through the gears slower as the larger tire moves further for each revolution of the axle/engine/transmission for each given gear.

 

[Jeeb]

Because of the bigger circumference of the tires, the drivetrain will be spinning slower for each mile than it would stock. You’re thinking “that’s great, less RPM means better gas mileage”. The problem is that the 3.6 is gutless at low RPM. It has trouble making power below 2000. The new gears will bring you back into the optimum power band for your engine. The stock gear ratio is already too high (numerically lower number 3.45:1). Depending where you live and how you drive you’ll want 4.88s or maybe even 5.13s (especially if you think you’ll EVER jump to 37s or if you drive in the mountains or tow). Your thinking is actually backwards. When adding larger tires you get through the gears slower as the larger tire moves further for each revolution of the axle/engine/transmission for each given gear.

That makes total sense now. Thank you so much for educating me on this! I guess that means waiting to save more money for the additional mods.

 

[Traveller128]

We have a '22 Willys JL 2 door also, and regearing for us made the Jeep more usable everywhere. We went with 4.10s because we run 33" tires, but if we'd have decided to do 35's I would have put 4.56 in.

It's flat out easier to drive offroad with usable gearing. 5th gear is our county rd and highway gear (55-65) and 6th is our freeway gear (80MPH here). With the stock 3.45's the trans gear ratios did not match up well at all.

 

[Jeeb]

We have a '22 Willys JL 2 door also, and regearing for us made the Jeep more usable everywhere. We went with 4.10s because we run 33" tires, but if we'd have decided to do 35's I would have put 4.56 in.

It's flat out easier to drive offroad with usable gearing. 5th gear is our county rd and highway gear (55-65) and 6th is our freeway gear (80MPH here). With the stock 3.45's the trans gear ratios did not match up well at all.

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

 

[BuyHold]

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

If you are going to 35s, you may want to consider 4.88s. For what it is worth, i had 4.10s on 35s (6sp manual) and it was passable but not anything I thought was good. I now have 5.13s on 35s and love it (low and slow, very infrequent highway driving, never >70mph). Gearing/tires definitely a matter of taste and use-case.

https://www.jlwranglerforums.com/forum/threads/help-appreciated-anyone-with-a-v6-manual-transmission-with-4-88-gears-and-33”-tires-that-loves-the-combo.118874/

https://www.jlwranglerforums.com/forum/threads/4-56-or-4-88-manual-transmission-jlur-on-35s.115143/

edit: You may find that a lot of Auto Tranny lovers will chime in re: gearing. Since you have a 6sp their input won't be too relevant for you.

 

[Jeeb]

If you are going to 35s, you may want to consider 4.88s. For what it is worth, i had 4.10s on 35s (6sp manual) and it was passable but not anything I thought was good. I now have 5.13s on 35s and love it (low and slow, very infrequent highway driving, never >70mph). Gearing/tires definitely a matter of taste and use-case.

https://www.jlwranglerforums.com/forum/threads/help-appreciated-anyone-with-a-v6-manual-transmission-with-4-88-gears-and-33”-tires-that-loves-the-combo.118874/

https://www.jlwranglerforums.com/forum/threads/4-56-or-4-88-manual-transmission-jlur-on-35s.115143/

edit: You may find that a lot of Auto Tranny will chime in re: gearing. Since you have a 6sp their input won't be too relevant for you.

Great info, thanks! I have some good reading ahead of me! I do a lot of highway driving. Maybe 5.13 is too much?

 

[J.Ferreira]

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!!!

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.

 

[Jeeb]

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)

Whoa. Bookmarked!!!

 

[J.Ferreira]

If you are going to 35s, you may want to consider 4.88s. For what it is worth, i had 4.10s on 35s (6sp manual) and it was passable but not anything I thought was good. I now have 5.13s on 35s and love it (low and slow, very infrequent highway driving, never >70mph). Gearing/tires definitely a matter of taste and use-case.

https://www.jlwranglerforums.com/forum/threads/help-appreciated-anyone-with-a-v6-manual-transmission-with-4-88-gears-and-33”-tires-that-loves-the-combo.118874/

https://www.jlwranglerforums.com/forum/threads/4-56-or-4-88-manual-transmission-jlur-on-35s.115143/

edit: You may find that a lot of Auto Tranny lovers will chime in re: gearing. Since you have a 6sp their input won't be too relevant for you.

This one is important, @Jeeb
Plenty of auto guys don't even bother to regear, cause the auto will just work and shift whenever it feels it needs to. That's far from the case with the manual.

 

[J.Ferreira]

Whoa. Bookmarked!!!

It's super fuckin' neat. I haven't regeared myself yet, but playing with the calculator has taught me I'll probably do 4.88 when I get to putting 35's on her.

 

[6th Floor Mule]

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!!!

This is one of those controversial topics, so “expert” opinions will vary ?.

IMO . . . it really depends on your intended usage, elevation where you live, and tolerance for performance loss. If your Willys is your daily driver and you spend time on the interstate trying to keep up with traffic on hilly terrains, it’s gonna suck. If you live in the mountains and you want to tow, it’s gonna suck and/or may not even be possible.

With that said, it IS “doable” if you spend all of your time in town and you’re willing to accept that your 6 speed has suddenly become a 4 speed (i.e., you’ll seldom use or need 5th or 6th gear). I have a very similar combo, but with a couple extra doors and 66lb “not quite 35 inch” 33.86“ tires. I do plan to re-gear, but it’s a “want” and not a “need“ at this point. I realize the combo is FAR FROM OPTIMAL, but it’s fine for my “around town and light trail” usage. Good luck ?

 

[AlgUSF]

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

I'm in the 4.56 on 35's club as well once my factory A/Ts run down a bit and I'm closer to the end of my powertrain warranty.

 

[Jeeb]

This is one of those controversial topics, so “expert” opinions will vary ?.

IMO . . . it really depends on your intended usage, elevation where you live, and tolerance for performance loss. If your Willys is your daily driver and you spend time on the interstate trying to keep up with traffic on hilly terrains, it’s gonna suck. If you live in the mountains and you want to tow, it’s gonna suck and/or may not even be possible.

With that said, it IS “doable” if you spend all of your time in town and you’re willing to accept that your 6 speed has suddenly become a 4 speed (i.e., you’ll seldom use or need 5th or 6th gear). I have a very similar combo, but with a couple extra doors and 66lb “not quite 35 inch” 33.86“ tires. I do plan to re-gear, but it’s a “want” and not a “need“ at this point. I realize the combo is FAR FROM OPTIMAL, but it’s fine for my “around town and light trail” usage. Good luck ?

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!

 

[J.Ferreira]

This is one of those controversial topics, so “expert” opinions will vary ?.

IMO . . . it really depends on your intended usage, elevation where you live, and tolerance for performance loss. If your Willys is your daily driver and you spend time on the interstate trying to keep up with traffic on hilly terrains, it’s gonna suck. If you live in the mountains and you want to tow, it’s gonna suck and/or may not even be possible.

With that said, it IS “doable” if you spend all of your time in town and you’re willing to accept that your 6 speed has suddenly become a 4 speed (i.e., you’ll seldom use or need 5th or 6th gear). I have a very similar combo, but with a couple extra doors and 66lb “not quite 35 inch” 33.86“ tires. I do plan to re-gear, but it’s a “want” and not a “need“ at this point. I realize the combo is FAR FROM OPTIMAL, but it’s fine for my “around town and light trail” usage. Good luck ?

Isn't that the other way around? With 3.45 in the Willys I don't use 6th gear (it's got no nuts) and 5th is jussstttt enough overdrive to keep pace at 70 through subtle rolling hills in Colorado. 4th for semi steep and 3rd for very steep.
I've driven a manual with 4.56 on flat land and was able to gain speed in 6th that I couldn't with mine, and I've done it in 4.88 in another Jeep. That thing was impressive in the higher gears.



Edit: I misread your comment. You meant it's doable to go larger tires without the regear.
Apologies!

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