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Discussion Starter #1
I just got back into the jeep world. And I picked up a 2012 JKU a few weeks ago. It's a sport model. 6 speed manual.
I found the specs in the Mopar site. It says I have 3.21 gears. I've been reading that these think if I want to go with a 33" tire.
It already has a 32" tire on it. I understand a 33 will be wider but could it make that much of a difference?
I then did some gearing research.
I don't know if this is true. But someone said if you get the towing package from the factory, you have 3.73 gearing.
Well I have the factory receiver and wiring.

Do I have the larger gears?

From what I can tell by my gas mileage I have the lowest gears. I'm getting 17-18 mpg.
It really doesn't make a difference to me since this is my daily driver. It will only leave the pavement a few times a year. I'm just curious how I can find out for sure.
 

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Do you have a jack?

If so you can jack it up, turn a tire one full turn, and count how many times the driveshaft turns. ~3 1/4 times and you have 3.21's, ~3 3/4 times you have 3.73's.
 

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If the online build sheet specs state 3.21, that's what you have. Only way it would differ is if the dealer went in and changed the gears out themselves which is doubtful. Or if it had a previous owner and they did a re-gear on it.
 

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The string method is the easiest way. As above jack up 1 rear tire. Tape/Tie a string to the driveshaft. Spin that 1 tire exactly 2 revolutions. Count the wraps of string around the driveshaft.

3 wraps, 3.07
3.25 wraps, 3.21
3.75 wraps, 3.73
4 wraps plus a bit 4.10.

And Jeep offers 2 different towing packages. Only 1 includes the 3.73 ratios
 

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Discussion Starter #7
Thanks for the info everyone. I typed the vin into that site above and it says 3.21 as well.
I know people say this is no good if you want to go to 33" tires. But the factory tires are 32". It can't be that much of a difference. Can it?
 

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The string method is the easiest way. As above jack up 1 rear tire. Tape/Tie a string to the driveshaft. Spin that 1 tire exactly 2 revolutions. Count the wraps of string around the driveshaft.

3 wraps, 3.07
3.25 wraps, 3.21
3.75 wraps, 3.73
4 wraps plus a bit 4.10.

And Jeep offers 2 different towing packages. Only 1 includes the 3.73 ratios
Yes that is correct it would be one revolution if you have a spool/LSD
 

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If the online build sheet specs state 3.21, that's what you have. Only way it would differ is if the dealer went in and changed the gears out themselves which is doubtful. Or if it had a previous owner and they did a re-gear on it.
Yeah, how many Jeep owners change their gears?? I wouldn't believe the build sheet at this point. Try jacking it and turning a tire as posted earlier...probably the best way to find out what you have.
 

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I have 3.21's with 35's on a 13' Sahara JKU. With Flashpaq 93 mode I feel stock as far as power. I added a hitch and wired in the real 7way tow plug to tow random times never exceeded 2k lbs and it's been fine. Not like you have to move into truck Lane and put hazards on. Sure, I'd like better gears someday when I install a locker but until then I'll just push the gas pedal down more.
 

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Just wrong!!!

The towing package doesn't matter. We have that on ours and it has 3.21 gearing.
When you get the "Max Tow" group package it no longer gets the 3:21's It automatically changes the spec to 3:73's
Watched it with my own eyes when I ordered my 2013 JKU And don't confuse someone bolting on a receiver and calling that a tow package!!!
 

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Thanks for the info everyone. I typed the vin into that site above and it says 3.21 as well.
I know people say this is no good if you want to go to 33" tires. But the factory tires are 32". It can't be that much of a difference. Can it?
Don't let the internet say deter you, put whatever tires you want, deal with gears later, it might not as bad as you think, the stock Saharas are 32's, but they don't measure that, they're more 30-30.5" tops, most 33's are 31.5-32" in reality. The thing with the 6 speed is that you'll really feel the difference in 6th gear, but then again, if you want to wear nice tires, you'll have to regear eventually, might as well start with a tire that you like now, so you won't have to spend more money getting out of the smaller tires in the short term because the big ones look so much better. 35's might be calling.. hint, hint :beerdrinking:
 

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My JK 6-speed manual tranny rig came with 3.21 gears. I put 32" Jeep tires/wheels on it, and I just didn't have enough gearing - I was always stalling the engine when starting off (especially when pulling my little camping trailer). I think I would have been OK with an automatic tranny, but not with the manual.

I had a shop change the gearing to 3.73 (got a decent deal at $800), and it is soooooo much better now.

If I were you I'd do the jack and string thing mentioned above just to make sure the previous owner didn't regear it.
 
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