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If the drive train on our 2013's is the same in the Sport, what is the difference in having these gears?

Does the 4.10 run at a higher RPM on the highway than the 3.21's? I am at 2100 at 70 MPH.

Do you run differently in the 3.73 or 4.10?

Seems the 4.10's would be about 2500.........?
 

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I had an 82 Toyota pickup that I run 4.10 gears in... It is deff not made to run on the high way bc your top speed is only going to be around 55 mph... They will put a lot more torque to the rear tires....3.73 on the the other hand is made for the highway and is pretty good on fuel... I have 4.56 in my jeep but for the best on road/ off road gears I would recommend 4.88 ....


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Yes the 4.10 will turn more RPMS..


the ratio is 4.10 drive shaft turns to 1 revolution of the rear wheels.. or 3.73 drive shaft turns to 1 rear wheel revolution or 3.21 drive shaft turns to 1 rear wheel revolutions..
 

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You'll likely get better mileage with a 3.21. I usually use my 4.10 '12 JKUR as a DD - it reads around 17 on the freeway, my '12 3.21 JKU is a bit lighter, but reads 19-20. Both are running the same size Duratracs and speedo corrected. yes, the speedo is just over 2K with the 3.21s.
 

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The #1 reason to change gears is to offset the resistance found when increasing tire size. When you go to 35" tires, your workload on the Jeep increases tremendously. The higher gears become necessary to restore performance, and in some cases recover lost fuel economy.
 

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I have 4.10s and get around 17 to 18 mpg on highway AND surface streets. It runs about 2700 rpm at 70 mph. (Kinda sucks but ain't too bad) where it becomes amazing is offroad and uphill. I was behind my buddy and his are 3.21s . Every incline we hit his speed dropped DRAMATICALLY while I could have easily passed him and increased speed... I would definitely recommend if ur going to be off road alot... First gear and four low this thing walks over anything ... Not to mention when I flip the lockers on hehe
 

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i have 35's on 4.10's 2007 JKU 4D & get pretty big top end speed when i want it. hovers around 2krmp @ 70 (70 actual, not spedo, check with gps & add 1mph for latency). i'd imagine if i had smaller tires my top end speed would really suck due to high rpm. my advice, if you're going with 4.10 slap some 35's on there.
 

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DRoberts said:
i have 35's on 4.10's 2007 JKU 4D & get pretty big top end speed when i want it. hovers around 2krmp @ 70 (70 actual, not spedo, check with gps & add 1mph for latency). i'd imagine if i had smaller tires my top end speed would really suck due to high rpm. my advice, if you're going with 4.10 slap some 35's on there.
Good to know for when mine arrive... Was worried about re gearing
 

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I have a '12 JK Sport with 3.21's running 285/70-17 Nitto Terra Grapplers (they measure 31.75" under the Jeep).

I just had them installed last week. The JK definitely feels more sluggish from a stop but it not too terribly bad.

I made a trip today from Pascagoula, MS to Cocoa Beach, FL - at 75 MPH I was turning 2,000 RPM in 6th gear. I kept the cruise control locked on for most of the trip and the Jeep was able to maintain speed with no issues. I only had to downshift once, when I had to slow to about 45-50 going up a hill. Slipped down to 5th until I got the speed up to 65 and no other issue.

I am not sure how my mileage is going to turn out, but I am monitoring and will compare to my trip here last month when I was running stock 225/75-16's.

I believe 4.10's may be too steep for my set-up and 3.73's may get me back to stock like feel.
 

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I have 4.10s and get around 17 to 18 mpg on highway AND surface streets. It runs about 2700 rpm at 70 mph. (Kinda sucks but ain't too bad) where it becomes amazing is offroad and uphill. I was behind my buddy and his are 3.21s . Every incline we hit his speed dropped DRAMATICALLY while I could have easily passed him and increased speed... I would definitely recommend if ur going to be off road alot....hehe
Getting ready to order 2013 Sahara and was thinking 3.21 was the way to go for mpg as wife will use 90% as a mall crawler, BUT we also live at the bottom of a fairly steep hill and have to go up 2 or 3 times a day to get anywhere.

Are you saying the 3.73 option would offer better torque in getting up the hills or not that much difference compared to 3.21? I'm more about performance than mpg. Thanks.
 

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Getting ready to order 2013 Sahara and was thinking 3.21 was the way to go for mpg as wife will use 90% as a mall crawler, BUT we also live at the bottom of a fairly steep hill and have to go up 2 or 3 times a day to get anywhere.

Are you saying the 3.73 option would offer better torque in getting up the hills or not that much difference compared to 3.21? I'm more about performance than mpg. Thanks.
you answered your own question. 3.73's will out perform 3.21's all things being equal. That said I live in NW Montana where nothing is flat and I love my 3.21's but I don't have 35" tires either.
 

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The worst part of 3.21 gears is when you do regear you have to buy new carriers for the diffs. No need if you are 3.73 going to 4.56 or other.
 

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Just test drove a 2013 3.21 and then a 3.73, both with factory wheels and tires. I felt a world of difference. The 3.21 was sluggish and slow, especially at the lower speeds. The 3.73 felt good and responsive. I'm ordering in the next couple of days and will definately go with the 3.73.\
 

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If the drive train on our 2013's is the same in the Sport, what is the difference in having these gears?

Does the 4.10 run at a higher RPM on the highway than the 3.21's? I am at 2100 at 70 MPH.

Do you run differently in the 3.73 or 4.10?

Seems the 4.10's would be about 2500.........?
The difference in engine rpm's with different axle ratios is easy to figure. It's an exact mathematical difference. Example:

4.10 axle ratio compared to a 3.21 ratio

4.10 divided by 3.21 = 1.277. That means a 4.10 axle ratio will turn 27.7% more engine rpm's at any given vehicle speed.

or

3.21 divided by 4.10 = .7829. That means a 3.21 axle ratio will turn 78.29% fewer engine rpm's at any given vehicle speed

In your example above at 2100 rpm's with a 3.21 ratio, you would be running about 2682 rpm's with a 4.10 ratio.

Mabar
 

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I have 4.10s and get around 17 to 18 mpg on highway AND surface streets. It runs about 2700 rpm at 70 mph. (Kinda sucks but ain't too bad) where it becomes amazing is offroad and uphill. I was behind my buddy and his are 3.21s . Every incline we hit his speed dropped DRAMATICALLY while I could have easily passed him and increased speed... I would definitely recommend if ur going to be off road alot... First gear and four low this thing walks over anything ... Not to mention when I flip the lockers on hehe
This. I Traded in my 3.21 jku for a Rubi and I love the 4.10s.
 

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....3.21 divided by 4.10 = .7829. That means a 3.21 axle ratio will turn 78.29% fewer engine rpm's at any given vehicle speed ...
Minor correction - 3.21 axle ratio will turn 21.71% fewer engine rpm's at any given vehicle speed. Or 78.29% of the RPMs of a 4.10 axle. :thumb:
 
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