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Old 10-02-2012, 10:15 AM   #1
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is 3.21 gear that bad?!

I have a jk 2dr 2012 mountain edition automatic and I was disappointed that my rig have a 3.21 ratio!! The question is I already installed TF 3" and 35" MT tires, is 35" to much on the gear and eventually gonna break down!? Or I don't know!

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Old 10-02-2012, 10:22 AM   #2
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I have a jk 2dr 2012 mountain edition automatic and I was disappointed that my rig have a 3.21 ratio!! The question is I already installed TF 3" and 35" MT tires, is 35" to much on the gear and eventually gonna break down!? Or I don't know!
No your jeep is not going to break down. Your gear ratio and tranny will not be damaged by the 35s however your wallet will and the 3" lift is probably gonna need a new front DS.

The auto in the 3.6 is better than the 3.8 but your gears paired with that size tire pretty much null that advantage out. If you want to restore some of the power and mpg loss your experiencing, then look into re gearing soon.

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Old 10-02-2012, 10:27 AM   #3
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Old 10-02-2012, 10:28 AM   #4
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I have a jk 2dr 2012 mountain edition automatic and I was disappointed that my rig have a 3.21 ratio!! The question is I already installed TF 3" and 35" MT tires, is 35" to much on the gear and eventually gonna break down!? Or I don't know!
Are you in the United States?
I ask because the Mountain Edition wasn't sold in the US with the 2012's...so I'm not sure which engine and tranny you have. Your avy looks like it is Dozer, which is a 2012 color...so I'm just not sure.
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Old 10-02-2012, 10:45 AM   #5
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I'm from Kuwait and plz what do mean by new DS?
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Old 10-02-2012, 10:47 AM   #6
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Old 10-02-2012, 10:48 AM   #7
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Dude, you'll be fine. You're not going to be doing serious off roading, are you? I have the 3.21's and have zero complaints.
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Old 10-02-2012, 10:50 AM   #8
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Old 10-02-2012, 10:50 AM   #9
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Actually I'm 90% on road
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Old 10-02-2012, 10:51 AM   #10
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dude, you'll be fine. You're not going to be doing serious off roading, are you? I have the 3.21's and have zero complaints.

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Old 10-02-2012, 12:24 PM   #11
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It has been fine for me around town and even some of the hillier highways with the stock 32s, I just downshift if I need more torque. It just feels weird to accelerate up to highway speed (70mph) and only turn 4,000rpm in third gear. It would be even weirder at 3,700rpm with 35s.
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Old 10-02-2012, 01:41 PM   #12
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Drive a properly geared Jeep then return back to yours. You'll understand then.
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Old 10-02-2012, 01:44 PM   #13
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It has been fine for me around town and even some of the hillier highways with the stock 32s, I just downshift if I need more torque. It just feels weird to accelerate up to highway speed (70mph) and only turn 4,000rpm in third gear. It would be even weirder at 3,700rpm with 35s.
3rd gear?
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Old 10-02-2012, 02:43 PM   #14
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Old 10-02-2012, 03:12 PM   #15
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drive a properly geared jeep then return back to yours. You'll understand then.
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Old 10-02-2012, 09:41 PM   #16
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3rd gear?
Yep. I think redline in 3rd gear is around 110. Theoretical top speed is 200+ in 6th, although it is probably drag limited to 100.
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Old 10-02-2012, 10:57 PM   #17
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Dude, you'll be fine. You're not going to be doing serious off roading, are you? I have the 3.21's and have zero complaints.
This coming from someone posting on Percocet...
is your Jeep lifted/have 35s POP?
The Jeep won't break with 3.21s but it won't get you anywhere fast and might break your wallet from mashing on the gas pedal. There are just certain spots in the power band that suck the torque out of the Pentastar like a vampire at a blood bank. Seasonal pun intended.
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Old 10-03-2012, 11:29 AM   #18
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all, true jeepherz, and yet will outperform a 3.8 engine with 3.73 ratio.
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Old 10-03-2012, 11:45 AM   #19
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Drive a properly geared Jeep then return back to yours. You'll understand then.
Don't do it! Do not drive one and have to go back to the 3.21, it will suck. I can't believe the difference from my 3.21 to my 4.10's. It's unreal.
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Old 10-03-2012, 12:12 PM   #20
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Don't do it! Do not drive one and have to go back to the 3.21, it will suck. I can't believe the difference from my 3.21 to my 4.10's. It's unreal.
Did you re-gear then Sueby? Or did you trade-in? Are you an automatic? If so- can you share some real world specifics on RPM/gearing? I am between 4.10s and 4.56s- whenever I win the lottery. I've seen the charts- but frankly they're just a piece of paper. Most concerned with 35-45 MPH range and what gear you're in at that speed (assuming a flat road/normal dirivng conditions). And appoximate RPMS at 70.
Thanks!
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Old 10-03-2012, 12:18 PM   #21
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for now im gonna stick with the stock gear 3.21! until i save some cash then re-gear mowahahahaha to 4.56!!
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Old 10-03-2012, 12:27 PM   #22
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Did you re-gear then Sueby? Or did you trade-in? Are you an automatic? If so- can you share some real world specifics on RPM/gearing? I am between 4.10s and 4.56s- whenever I win the lottery. I've seen the charts- but frankly they're just a piece of paper. Most concerned with 35-45 MPH range and what gear you're in at that speed (assuming a flat road/normal dirivng conditions). And appoximate RPMS at 70.
Thanks!
I traded the sport for a rubi so I'm not gonna be much help to you. I chose the lazy way to regear.
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Old 10-03-2012, 12:43 PM   #23
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I finally found a shop to lift my 2012 auto. I'm going with a 4" Skyjacker and Procomp 35's. I have 3.21's and live in Florida. I have fingers crossed that the Pentastar will do the job without re-gearing!!
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Old 10-03-2012, 12:56 PM   #24
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This coming from someone posting on Percocet...
is your Jeep lifted/have 35s POP?
The Jeep won't break with 3.21s but it won't get you anywhere fast and might break your wallet from mashing on the gas pedal. There are just certain spots in the power band that suck the torque out of the Pentastar like a vampire at a blood bank. Seasonal pun intended.

Won't get you anywhere fast? Who's going fast, it's a Jeep. ANd it's save you money in gas. Won't matter in 4-lo, and with the new engine.

Also, most people run roads 90% of the time if not more, so no real advantage there, either. It's not like people are road racing in these things and passing every chance they get.
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Old 10-03-2012, 02:16 PM   #25
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Sigh. I was trying to be brief (and light-hearted) since the OPs question pertained primarily to if 3.21s & 35s would do damage. Which it won't-as was mentioned in posts prior to mine.
I don't drag race my Jeep. Most have noticed there is a difference in overall performance (and I don't mean speed) of the engine and tranny with 3.21s and 35s. Ie: the 3rd to 4th shift now occurs in my Jeep at 1200 RPMS. Many manual owners say they lose 6th gear completely. Just because I lament the performance change doesn't mean I want to speed- I just want the engine and tranny to perform in the same manner it did when I test drove it. (vs. with 34s.) I
I would like to add that some people don't notice or care so its not all bad and of course its all a matter of opinion.
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Old 10-03-2012, 02:19 PM   #26
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I traded the sport for a rubi so I'm not gonna be much help to you. I chose the lazy way to regear.
That's what I thought. Trader! (literally).
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Old 10-03-2012, 08:45 PM   #27
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Drive a properly geared Jeep then return back to yours. You'll understand then.
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'properly geared' is a matter of opinion and situation.
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Old 10-04-2012, 06:00 AM   #28
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2012-Auto w/3:21`s...was worried as hell when I installed 33 Duratracs. Noticed very, I mean very minimal power loss...how bad will it be with 35's...I do not think it should be bad at all...I lost 2 mpg's though...oh, I am far an expert or do I have the knowledge the others have. This is just my observations...
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Old 10-04-2012, 07:18 AM   #29
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I have the 3:21 as well with stock 17 Sport S wheels. Was wondering how 18" stock would perform? I am mostly on pavement.
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Old 10-04-2012, 07:32 AM   #30
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I have a '12 Sport with an auto. I lifted 2.5"s and went to 33" Duratracs. I noticed it lost a bit of its jump on road. I ended up re-gearing to 4:10's and installed an Auburn LSD at the same time. Thought about lockers, but I'm mainly driving slippery New England roads with the occasional light trail ride in the summer. It feels perfect with the 33's and 4:10's. plenty of giddy up down low and it doesn't kill me on the hwy either. I average 16.5-18 MPG. I'm thinking 4:56's might be ideal for an auto with 35"s. just my opinion. Good luck either way

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