07JK 2dr auto 3.21 gear. Do I have to regear to run 33"s? - Jeep Wrangler Forum
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Old 08-02-2012, 04:13 PM   #1
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07JK 2dr auto 3.21 gear. Do I have to regear to run 33"s?

I am a newbie with a bare stock 07 JK auto. I have 3.21 gears and 29" tires 16" wheels. I came across a chart that said I should regear for any tires larger than 29". I can no longer stand the 29"s but I have no money to regear at the moment. Will I do any damage if I run 33"s and no regear?

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Old 08-02-2012, 04:26 PM   #2
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3.21s with an auto? Did it not automatically come with 3.73s in 07?

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Old 08-02-2012, 04:30 PM   #3
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If you have 2007 auto, you have either 3.73s or maybe 4.10s, but definitely not 3.21s.

The easiest way to tell what gears you have is to drive 70 mph and remember your RPMs, and then go back to that chart (make sure it's the chart for the auto transmission, as it's different for the manuals) and use your tire size to see where you fall. You can also contact Chrysler for your build sheet.

That said, you're still undergeared as all pre-2012 autos were. For practical purposes, the biggest downside of being undergeared is your jeep is more of a "dog" than it needs to be, and this will get worse the bigger your tires get.

If you regeared to 5.13s for example, your jeep would actually feel pretty "fast." I doubt you think it feels fast now, and it will feel even slower with bigger tires.

So you can definitely go to 33s without regearing and without damaging anything. It's just your gas mileage will drop and it'll feel like more of a dog.
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Old 08-02-2012, 04:38 PM   #4
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Do you NEED to re-gear? No. Should you? Maybe.

I ran 33’s on 3.73 auto for while and didn’t find it bad. Hell I am now on 35’s a with the same gears and tolerate it. Although suffice to say I am going 5.13’s soon…

At 33” tires and an auto you will want like 4.88 if you plan on never to go any bigger than 33’s. 4.88’s would probably be decent though for 35’s. Seems like the consensus for 35’s, auto trans and 3.8L is 5.13 or 5.38. Choice is yours.

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Old 08-02-2012, 05:04 PM   #5
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Quote:
Originally Posted by oilwell1415 View Post
3.21s with an auto? Did it not automatically come with 3.73s in 07?
No. 3:21 standard
optional 4:10 tow package
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Old 08-02-2012, 05:09 PM   #6
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Quote:
Originally Posted by MTH View Post
If you have 2007 auto, you have either 3.73s or maybe 4.10s, but definitely not 3.21s.


So you can definitely go to 33s without regearing and without damaging anything. It's just your gas mileage will drop and it'll feel like more of a dog.
Thnks for your thoughts. Power at the moment is not an issue for me, so I think I will go 33s until I have the cash to regear.
P.s. i've read 3:73s were not an option on 07 JK(at least not 2dr)
only 3:21(stock) and 4:10(optional towing package)
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Old 08-02-2012, 05:53 PM   #7
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Quote:
Originally Posted by phillybaggett View Post
P.s. i've read 3:73s were not an option on 07 JK(at least not 2dr)
only 3:21(stock) and 4:10(optional towing package)
My understanding is the pre-2012 auto transmission JK never, ever, ever came with 3.21 gears. Only manual transmissions came with 3.21s standard prior to 2012.

This makes sense, because it would be a disaster of underpower for any fool who upgraded to the Sport S with 32" tires. They'd be turning just over 1600 RPMs or at 70 mph, which I don't think would even be enough power to keep them going on a flat highway.

But get going at 70 mph and look at the chart to confirm. Or order your build sheet to really be sure. My prediction remains that you have 3.73s or, if you have either the "off road" or "towing" package, 4.10s.

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