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Old 05-07-2012, 11:40 AM   #1
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Gearing question

Dumb question but how do I find out what gearing I have?? I don't know, I'm an idiot! 2011 JKU Sport S, six speed manual transmission, V-6.

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Old 05-07-2012, 11:51 AM   #2
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Found it. 3.21 rear axle ratio. Now what does that mean versus the 4.1?

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Old 05-07-2012, 12:07 PM   #3
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Quote:
Originally Posted by Jervboy
Found it. 3.21 rear axle ratio. Now what does that mean versus the 4.1?
Stock size tires no bigger
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Old 05-07-2012, 12:14 PM   #4
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Found it. 3.21 rear axle ratio. Now what does that mean versus the 4.1?
It means that at the same speed on the same size tires and in the same gear, you'll be spinning ~500 or so less RPMs than somebody with 4.10 gearing.

Because your engine puts out more torque and more horsepower the more RPMs you spin until you hit redline, this means that the jeep with the 4.10 gearing will feel "peppier" at the same speed--it would hold speed better and feel as if it's got more "get up and go" when you push the pedal. It will also be easier on the clutch in that it will lug less when you start.

You can "simulate" the first benefit (higher RPMs at a given speed) by simply waiting until you reach higher RPMs to shift gears (3k+) and not using 6th gear anymore. You can't simulate the second benefit (easier on the clutch).
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Old 05-07-2012, 06:51 PM   #5
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Found it. 3.21 rear axle ratio. Now what does that mean versus the 4.1?
3.21 = Transmission output shaft turn 3.21 revolutions per 1 revolution of rear axle
4.10 = transmission output shaft turns 4.10 revolutions per 1 revolution of axle.
The faster the output shaft turns in relation to the axle; the greater your mechanical advantage. Also, while having greater mechanical advantage, you will also be running your engine closer to its "sweet spot". I.E. higer torque and HP output to rear wheels. So your lower gears( higher numerical value) almost gives you a "double whammy"!
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Old 05-08-2012, 05:24 AM   #6
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All right, that I understand. Why then make the stock gear ratio 3.21 if it seems the better way to do it is a higher ratio?? Fuel economy? I don't really get it? My Jeep is a 6 speed manual, it sounds to me from what I am reading on the forum that the better gear ratios are higher, why then does the manufacturer put a 3.21 ratio in my Wrangler???
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Old 05-08-2012, 05:34 AM   #7
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Originally Posted by Jervboy
All right, that I understand. Why then make the stock gear ratio 3.21 if it seems the better way to do it is a higher ratio?? Fuel economy? I don't really get it? My Jeep is a 6 speed manual, it sounds to me from what I am reading on the forum that the better gear ratios are higher, why then does the manufacturer put a 3.21 ratio in my Wrangler???
Easy answer.... Economy.

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Old 05-08-2012, 05:50 AM   #8
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So better gas mileage then? That I can understand because before I changed my tires, and even after, I think I get excellent gas mileage with my wrangler, consistantly 17-18 MPG all around and upwards of 21 on the highway. I just changed from the stock 255/75/R17 to dura tracs, 285/70/R17 and think I have noticed a slight decrease in the MPG but not much. This gearing thing is bothering me! So it will affect my rig offroad?
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Old 05-08-2012, 07:21 AM   #9
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So better gas mileage then? That I can understand because before I changed my tires, and even after, I think I get excellent gas mileage with my wrangler, consistantly 17-18 MPG all around and upwards of 21 on the highway. I just changed from the stock 255/75/R17 to dura tracs, 285/70/R17 and think I have noticed a slight decrease in the MPG but not much. This gearing thing is bothering me! So it will affect my rig offroad?
Your duratracs are a light tire which helps.

3.21's are not ideal but you will be fine off road. Remember, in 4wd the transfer case reduces the gear ratio too.
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Old 05-08-2012, 08:03 AM   #10
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i have the same gears, if you have the auto it will be fine for the size you are running, when i ruin the the gears, then i will up grade.

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