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Oscar Indy

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Okay. I'm a numbers and jeep nerd.
I really liked my JK on 37s 4.56 gears and manual trans.
I wanted to see what gears in the JT I would need to emulate that setup. Turns out it's probably pretty close to the factory 4.10s and might not need to be regeared at all. My crawl ratio will be SLIGHTLY higher at 77:1 in JTR when it was 81:1 in the JKR.
On road, it will be pretty close to the same I basically get an extra gear between 4th and 5th (perfect place for it) and an extra overdrive gear. (Nice cause at 80 I would turn more RPMs than I liked in the manual. In the pictures below the left side is my old JKR (37s, 4.56, Manual) Right side is my incoming JTR (37s,4.10,Auto)
JK VS JT Gearing 1.PNG

JK VS JT Gearing 2.PNG

JK VS JT Gearing 3.PNG

JK VS JT Gearing 4.PNG

http://www.grimmjeeper.com/gears.html
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BrandRezake

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Okay. I'm a numbers and jeep nerd.
I really liked my JK on 37s 4.56 gears and manual trans.
I wanted to see what gears in the JT I would need to emulate that setup. Turns out it's probably pretty close to the factory 4.10s and might not need to be regeared at all. My crawl ratio will be SLIGHTLY higher at 77:1 in JTR when it was 81:1 in the JKR.
On road, it will be pretty close to the same I basically get an extra gear between 4th and 5th (perfect place for it) and an extra overdrive gear. (Nice cause at 80 I would turn more RPMs than I liked in the manual. In the pictures below the left side is my old JKR (37s, 4.56, Manual) Right side is my incoming JTR (37s,4.10,Auto)
JK VS JT Gearing 1.PNG

JK VS JT Gearing 2.PNG

JK VS JT Gearing 3.PNG

JK VS JT Gearing 4.PNG

http://www.grimmjeeper.com/gears.html
I had 4:56 gears in my JKU with 35s and I remember thinking I could have gone with just 4:10s. Offroading and slow climbing was pretty damn sweet though!
 
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Oscar Indy

Oscar Indy

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I had 4:56 gears in my JKU without 35s and remember thinking I could have gone with 4:10s. Off reading and climbing was pretty damn sweet though
Was that an auto or a manual? I ran the 37s on the 4.10 gears for about a year before regearing to the 4.56. Main reason for that was I wanted the pull power back after building my offroad trailer. I know tons of guys on 4.10 and 35s in the JK and are plenty happy.
 

BrandRezake

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Was that an auto or a manual? I ran the 37s on the 4.10 gears for about a year before regearing to the 4.56. Main reason for that was I wanted the pull power back after building my offroad trailer. I know tons of guys on 4.10 and 35s in the JK and are plenty happy.
Manual. On the Highway the RPMs would be in the 3000's. I liked how fast I could jump off the line and 4wd was amazing. Just the Daily Driving felt that the 4:10's would have been perfect.
 
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Oscar Indy

Oscar Indy

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Manual. On the Highway the RPMs would be in the 3000's. I liked how fast I could jump off the line and 4wd was amazing. Just the Daily Driving felt that the 4:10's would have been perfect.
JK left JT right comparing manual transmissions.


Number of forward gears
1st Gear
4.46 5.13
2nd Gear
2.61 2.63
3rd Gear
1.72 1.53
4th Gear
1.25 1.00
5th Gear
1.00 0.81
6th Gear
0.79 0.72
Reverse
4.06 4.49

That manual..... kinda sucks.
 

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Ole Cowboy

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Okay. I'm a numbers and jeep nerd.
I really liked my JK on 37s 4.56 gears and manual trans.
I wanted to see what gears in the JT I would need to emulate that setup. Turns out it's probably pretty close to the factory 4.10s and might not need to be regeared at all. My crawl ratio will be SLIGHTLY higher at 77:1 in JTR when it was 81:1 in the JKR.
On road, it will be pretty close to the same I basically get an extra gear between 4th and 5th (perfect place for it) and an extra overdrive gear. (Nice cause at 80 I would turn more RPMs than I liked in the manual. In the pictures below the left side is my old JKR (37s, 4.56, Manual) Right side is my incoming JTR (37s,4.10,Auto)



http://www.grimmjeeper.com/gears.html
Excellent and very comprehensive chart.

That said if you just need on data point I use the RCI (Rock Crawling Index):

Rubicon OEM: 1st gear ratio X Transfer case low gear ratio X Rear axle ratio divided by tire height = RCI

Now input your Jeeps data and see how it compare. Objective to have the same RCI as the Jeep Rubicon.

FAQ:

Why Rubicon?

In short Rubicon is a know n performer on off road trails in OEM from. Its also balanced 4:1 (first gear), 4:1 (Low transfer case), 4.10 (axle ratio). NOTE all ratios are in the 4.x this gives a balanced and extremely strong driveline! NOTE this data applies to the Jeep TJ, manual trans, because I know the ratios off the top of my head.

Do I need to use the Rubicon, I don't run trails I run in the sand?

No you don't, use any set ratios you want based upon a know performance. No OEM vehicle will perform on the trails like the Rubicon. Sand is different, possibly the new Jeep Mojave will be a better index for sand.

What does the index (RCI) do for me.

It gives you a know results in a unique environment that you can build to and expect similar results.

What about the Crawl Ratio is that not all I need to know?

NO, because the crawl ratio does not take into account tire size (height) which can have a major impact on you results. Example: Same crawl ratio fro Rubicon 66

Jeeper A has oem tires at 32 inches tall: RCI = 2.1

Jeeped B has 37's = 1.7. Less than 2.1 and your performance is degraded because it takes more effort to turn those 37's

Jeeper C has 37's and 4:88 gears instead of 4:10. RCI 4 x 4 x 4:88 = 2.1 RCI, same as the OEM Jeep Rubicon of Jeeped A above. As a result I would expect a similar results on the trail as Jeeper A

Take away: Building to an index assure similar results of a know value. You pick the index of you Buddys rig its the best wheeling rig you have ever seen. Take his ratios plug into the formula and now a know index metric to measure you efforts by.
 
 



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