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Re-gearing math?

electric_jeep

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Joined
Nov 2, 2020
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16
Location
New York
I’ve been reading the forums and have a specific question I cannot find perspective on. I have a 2006 6MT with the 3.07 axel and 31.5” wheels. I’ve verified these numbers by driving and spot checking.

My setup is not as quick as I’d like.

I am thinking of going to 4.56 gears and 33”s. So question, it seems that I’m in an overall 13.68 ratio in first gear with my current setup. If I upgrade to 4.55 it would calculate to 20.33.

Would I be able to shift into 4Lo (2.72) and use 2nd gear - which ends up being a 21.8 ratio - to test what the “after” feels like? Wouldn’t that give me very similar feel of how I’d accelerate in 1st gear after regearing? Yea I’d be going from 31.5” to 33” but I think that would coincidentally be the difference between the 20.33 and 21.8, give or take.

Anything wrong with my logic?

A0F999E9-27B1-4899-8AE4-B66B8C5C235E.jpeg


PS ignore the stock tire size. PO changed to 31.5” and didn’t regear or change Speedo 😭

PPS I know there’s a question of if 4.56 is the right move and it depends on a couple of things. Gonna hafta split track that convo bc I have an electric motor with different performance characteristics, not the 4cyl or flat 6.
 
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HornedToad

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Aug 12, 2020
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Sacramento
This is my go to gearing calculator:

https://www.marlincrawler.com/java/getspd_calc.html

You can plug in the info for your scenarios there easily. And the short answer is yes, 2nd (with 4.56’s) will feel close to your current 1st (with 3.07’s) but will still be a little faster. Also—yes you can use 2nd gear in 4-low. And yes, 4.56 gears with the 6 speed is a good choice as long as you are committed to never sizing up to 35s. And if you do really technical off-roading you will want to go lower. But for good highway performance I would say 4.56’s and 33s are a good combo.
 
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TexasTJ2004

I love my TJ
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I’ve been reading the forums and have a specific question I cannot find perspective on. I have a 2006 6MT with the 3.07 axel and 31.5” wheels. I’ve verified these numbers by driving and spot checking.

My setup is not as quick as I’d like.

I am thinking of going to 4.56 gears and 33”s. So question, it seems that I’m in an overall 13.68 ratio in first gear with my current setup. If I upgrade to 4.55 it would calculate to 20.33.

Would I be able to shift into 4Lo (2.72) and use 2nd gear - which ends up being a 21.8 ratio - to test what the “after” feels like? Wouldn’t that give me very similar feel of how I’d accelerate in 1st gear after regearing? Yea I’d be going from 31.5” to 33” but I think that would coincidentally be the difference between the 20.33 and 21.8, give or take.

Anything wrong with my logic?

View attachment 351140

PS ignore the stock tire size. PO changed to 31.5” and didn’t regear or change Speedo 😭

PPS I know there’s a question of if 4.56 is the right move and it depends on a couple of things. Gonna hafta split track that convo bc I have an electric motor with different performance characteristics, not the 4cyl or flat 6.

Tell us more about your electric motor conversion.
 
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OP
electric_jeep

electric_jeep

New Member
Joined
Nov 2, 2020
Messages
16
Location
New York
This is my go to gearing calculator:

https://www.marlincrawler.com/java/getspd_calc.html

You can plug in the info for your scenarios there easily. And the short answer is yes, 2nd (with 4.56’s) will feel close to your current 1st (with 3.07’s) but will still be a little faster. Also—yes you can use 2nd gear in 4-low. And yes, 4.56 gears with the 6 speed is a good choice as long as you are committed to never sizing up to 35s. And if you do really technical off-roading you will want to go lower. But for good highway performance I would say 4.56’s and 33s are a good combo.

Thanks for the input. I am not sure I was clear - I want to get an idea of how it might feel NOW before I regear.

If using my current 3.07 gear, 2nd gear, and 4-low (21.8 ratio), would that get me the “seat of pants” feel for what first gear in 2-high would feel like after regearing (4.56 * 4.45 = 20.3 ratio).

I’ve hear people say “I want to know how it might be like to accelerate from a stop after regearing” but haven’t seen anyone suggesting this hack for those with transmissions and transfer cases that happen to Line up ratios like this.
 
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Jerry Bransford

TJ Guru Moderator
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Nov 9, 2015
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Fleming Island Florida
I’ve been reading the forums and have a specific question I cannot find perspective on. I have a 2006 6MT with the 3.07 axel and 31.5” wheels. I’ve verified these numbers by driving and spot checking.

My setup is not as quick as I’d like.

I am thinking of going to 4.56 gears and 33”s. So question, it seems that I’m in an overall 13.68 ratio in first gear with my current setup. If I upgrade to 4.55 it would calculate to 20.33.

Would I be able to shift into 4Lo (2.72) and use 2nd gear - which ends up being a 21.8 ratio - to test what the “after” feels like? Wouldn’t that give me very similar feel of how I’d accelerate in 1st gear after regearing? Yea I’d be going from 31.5” to 33” but I think that would coincidentally be the difference between the 20.33 and 21.8, give or take.

Anything wrong with my logic?

View attachment 351140

PS ignore the stock tire size. PO changed to 31.5” and didn’t regear or change Speedo 😭

PPS I know there’s a question of if 4.56 is the right move and it depends on a couple of things. Gonna hafta split track that convo bc I have an electric motor with different performance characteristics, not the 4cyl or flat 6.
The usual ratios we recommend don't work with an electric motor, I personally wouldn't even know where to begin with that powering your TJ.
 
OP
electric_jeep

electric_jeep

New Member
Joined
Nov 2, 2020
Messages
16
Location
New York
The usual ratios we recommend don't work with an electric motor, I personally wouldn't even know where to begin with that powering your TJ.
Here’s the performance graph for the motor. It’s 176 ft-lbs of torque from 0-3750rpm then declining from there. I know it’s not apples to apples but it’s probably close to the 4 cyl except the torque is fully available at 0rpms so maybe not 🤷‍♂️



853C7531-A61B-4B4D-A8A7-3CAC8D7F608D.jpeg
 

TheBoogieman

Disturbed American
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Location
C-Ville VA
The usual ratios we recommend don't work with an electric motor, I personally wouldn't even know where to begin with that powering your TJ.

I know a guy who has the answers to that and the world's problems. He says they're all solved. :rolleyes:
Biden I did that.jpg

Please delete this @Chris and don't ban me. I couldn't resist.
 

Mudflat

TJ Enthusiast
Joined
Sep 15, 2020
Messages
498
Location
Lumberton, Texas
I don’t think I have an answer to your question, but I’ve attached some “before & after” data from when I changed from 3.07 gears to 4.56 gears. 4.0 liter & 6 speed manual.
By the way, you will need the 39 tooth speedometer drive gear if you go with 33” tires & 4.56 gears.

9C3E84B9-F6A0-4C84-9299-9FB332759D22.png
 
OP
electric_jeep

electric_jeep

New Member
Joined
Nov 2, 2020
Messages
16
Location
New York
I don’t think I have an answer to your question, but I’ve attached some “before & after” data from when I changed from 3.07 gears to 4.56 gears. 4.0 liter & 6 speed manual.
By the way, you will need the 39 tooth speedometer drive gear if you go with 33” tires & 4.56 gears.

View attachment 351228

Thanks for this perspective - very helpful. Especially the speedometer fix. I’m at some point going to need to just roll the dice and regear regardless of the different performance characteristics of the electric motor.

4.56 but I might keep my 31.5” tires until they are done, then go to 33”.

I might go dual motor which will be 350 ft-lbs of torque and 250HP so that would “solve” some problems too.
 
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TRE3TOP

Guest
Thanks for this perspective - very helpful. Especially the speedometer fix. I’m at some point going to need to just roll the dice and regear regardless of the different performance characteristics of the electric motor.

4.56 but I might keep my 31.5” tires until they are done, then go to 33”.

I might go dual motor which will be 350 ft-lbs of torque and 250HP so that would “solve” some problems too.

More power doesn’t solve a gearing issue
 
T

TRE3TOP

Guest
I’d love to learn more. Any articles or knowledge you can drop on me? I’ve been trying to understand this exact concept.

Gearing makes the power available more usable, just adding more power doesn’t really make the power band more functional. Sure you’ll be able to turn the tire better because there is more power available, but you’re still not going to be operating in your optimal power band window.

However with the very minimal information of your electric setup you have provided. It’s going to be hard to accurately give you an answer to what gears will give you the best performance for your situation.

Hope that helps.
 
OP
electric_jeep

electric_jeep

New Member
Joined
Nov 2, 2020
Messages
16
Location
New York
Gearing makes the power available more usable, just adding more power doesn’t really make the power band more functional. Sure you’ll be able to turn the tire better because there is more power available, but you’re still not going to be operating in your optimal power band window.

However with the very minimal information of your electric setup you have provided. It’s going to be hard to accurately give you an answer to what gears will give you the best performance for your situation.

Hope that helps.

The power band is a constant 176 ft-lbs from 0-3750rom, then dropped off after that. Peak HP band is between 3000rpm and 6000rpm. It’s definitely different than an ICE. Does that make sense?
 
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TRE3TOP

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The power band is a constant 176 ft-lbs from 0-3750rom, then dropped off after that. Peak HP band is between 3000rpm and 6000rpm. It’s definitely different than an ICE. Does that make sense?

Yes it does but I don’t know how that’s going to feel compared to the stock engine. I don’t have any electric vehicle experience. Making full torque from 0 should definitely help your case even if it starts to wane at 3750. Horsepower range sounds reasonably similar to stock. I’d probably lean towards the 4.56 like you were thinking if you’re staying in 33s. Again just kinda guessing here.
 

steelhd

TJ Addict
Joined
Jan 1, 2019
Messages
1,199
Location
Eastern WA
Gonna hafta split track that convo bc I have an electric motor with different performance characteristics, not the 4cyl or flat 6.
I went through the EV conversion exercise a year or two ago to decide if that was feasible for how I want to use my Jeep. IIRC the answer was you are looking for a 9 to 1 reduction from the motor to the wheels for the street. I decided that the best way to do that and eliminate a lot of drivetrain loss is by dumping the transmission (auto or manual) and installing a reduction gearbox. I also decided that to really wheel it offroad I would also have to install a divorced Atlas transfer case.
 
OP
electric_jeep

electric_jeep

New Member
Joined
Nov 2, 2020
Messages
16
Location
New York
Yes it does but I don’t know how that’s going to feel compared to the stock engine. I don’t have any electric vehicle experience. Making full torque from 0 should definitely help your case even if it starts to wane at 3750. Horsepower range sounds reasonably similar to stock. I’d probably lean towards the 4.56 like you were thinking if you’re staying in 33s. Again just kinda guessing here.

Yeah I’m guessing too lol. I think I’m gonna hafta just do the gearing and I’ll report back.

That’s why I wanted to run it in 2nd gear at 4-low. Gonna get a new transmission mount and if that fixes this issue I’m currently having with the transmission twisting, then I’ll also run that test and report back!
 

TKFX

Member
Joined
May 6, 2022
Messages
52
Location
La Crescenta, CA
I’ve been reading the forums and have a specific question I cannot find perspective on. I have a 2006 6MT with the 3.07 axel and 31.5” wheels. I’ve verified these numbers by driving and spot checking.

My setup is not as quick as I’d like.

I am thinking of going to 4.56 gears and 33”s. So question, it seems that I’m in an overall 13.68 ratio in first gear with my current setup. If I upgrade to 4.55 it would calculate to 20.33.

Would I be able to shift into 4Lo (2.72) and use 2nd gear - which ends up being a 21.8 ratio - to test what the “after” feels like? Wouldn’t that give me very similar feel of how I’d accelerate in 1st gear after regearing? Yea I’d be going from 31.5” to 33” but I think that would coincidentally be the difference between the 20.33 and 21.8, give or take.

Anything wrong with my logic?

View attachment 351140

PS ignore the stock tire size. PO changed to 31.5” and didn’t regear or change Speedo 😭

PPS I know there’s a question of if 4.56 is the right move and it depends on a couple of things. Gonna hafta split track that convo bc I have an electric motor with different performance characteristics, not the 4cyl or flat 6.

Your logic makes sense.

How do you normally drive with the current setup, I can't imagine you are going through all your 6 gears? The electric motor setup I have dealt with only had a single gear reduction. I take it you currently only use gears 1 and 2? As gear 1 will top out at ~45mph and gear 2 will top out at ~80mph.