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Discussion Starter · #1 ·
i have a 2012 jk 6 speed manual with 3.21 gearing. i just bought 15x8 mb tko's and 35/12.5/15 goodyear mt/r's. and will soon have a 2.5" lift. does anyone else have a set up like this and like their 3.21 gearing? from what i read here it looks like a regear is in my future. i don't want to but will if i have to. i am just wondering if there is anyone out there who has this set up and likes it. i am looking forward to all responses.
 

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Discussion Starter · #3 ·
i am sure of that. will it be so bad that i won't wanna drive it till i regear?
 

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35's with the 3.21 will run, it will just run very very slowly. Acceleration will be very poor and will only get worse with multiple passengers and cargo and forget decent mpg. I went 4.88 and I would say its better than stock with the new tires and lift but not exponentially.
 

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i have a 2012 jk 6 speed manual with 3.21 gearing. i just bought 15x8 mb tko's and 35/12.5/15 goodyear mt/r's. and will soon have a 2.5" lift. does anyone else have a set up like this and like their 3.21 gearing? from what i read here it looks like a regear is in my future. i don't want to but will if i have to. i am just wondering if there is anyone out there who has this set up and likes it. i am looking forward to all responses.
I thought you were waiting till the spring time to buy the tires? Right on man!!!
 

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Its all matter of opinion. The shop i go to has done 35's with 3.21 gears in 2012s in a few jeeps and the owners say it isn't bad and the shop says it isn't that bad either when they have driven them. You are just going to have to find out when you get them installed if you can personally handle it or not. Regearing to 4.88 or higher isn't necessary considering 4.10 can handle 35's quite easily.
 

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Ok, missed the manual part somehow. With a manual you aren't really going to be too happy and are going to want to regear.
 

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I got a 2010 with 3.21's, 2.5" lift, and 35's. It's not that bad as everyone makes it out to be. I've been wheeling with 3.21's for the past 2 years and the only thing that sucks is I'll sometimes stall on larger rocks trying to just creep over them. Yes it's not going to have the best pick up and 6th gear will be almost useless but it's really not that bad.
 

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Discussion Starter · #11 ·
great to hear that! i will still be looking to regear but i am kinda hesitant. what kind of mileage are you getting?
 

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Discussion Starter · #12 ·
glad to hear that. do you have a manual also? what kind of gas mileage are you getting?
 

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For a DD it will most likely be unbearable, if not for you then for your wallet. There were a few people who brought 35's and end up selling them to get 33's. My 33's I have on my '12 is a bit sluggish, god only imagine what that additional weight and size for 35's would be like. Plus you have a manual..so a regear will definitely be in your future.
 

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Discussion Starter · #16 ·
hey Elarson. if you had it to do over again would you still go with 4.88 or something else?
 

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I have a pentastar, 35's and 4.10's and I still feel like I need to lower the ratio. I can't imagine running 3.21's.

I would guess it's like your always towing a trailer behind your Jeep.
 

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There's no way I would ever run 35's without regearing if I had 3.21s. You have to compensate for the big change in tire diameter but also you have to compensate for the substantial addition of weight. You'll hate life if you try to drive with 3.21s and 35" tires.

I personally wouldn't go any taller (numerically lower) than 4.10s, that's for sure. If you're going to the trouble of regearing, you shouldn't half-ass it. The 4.10s will be a close match to the factory 3.73 gears with the 255/75R17 stock tires. That wouldn't be a horrible combination if you daily drive your Jeep. If you want/need more power, a set of 4.56 gears would give you that without pushing your RPMs too high on the freeway. I personally wouldn't go any shorter (numerically higer) than 4.88s with 35's on a Jeep that sees regular street use. The manual trans has a pretty deep first gear and not much of an overdrive and getting much shorter that that on gears will push your RPMs too high.

Of course, since you're going to be changing the rear gears over the carrier break (going from 3.73 and lower to 3.92 and higher) you'll really want to consider some kind of locker. There's no extra labor since you're changing gears already and you have to buy a carrier already, why not spend a little more and get a limited slip or locker?
 

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I've been running 3.21s and 35" KM2s on my '12 6-speed since May, which has been about 7,000 miles.

There's definitely a difference... I won't lie. But it's really only noticable in 1st & 6th. It wasn't even as bad as expected off road. Though it's worth mentioning that most people feel the KM2s run small, which could be helping the situation. My 35s measured 33.5" from top to pavement @ 28 psi on the Jeep (and well over 34" on the spare).

6th isn't really an issue... I just don't use it anymore. I run around 2,400 RPM at 75 in 5th, which is fine. I can get on it to pass, don't have to downshift for hills, and it gets around fine on the highway.

1st is a bit more of an issue, but I've compensated by giving a little more gas and getting off the clutch sooner. You just have to adjust, though with the limited clutch feel in the JK it's not always easy.

Through the rest of the gears? No real change. You just stay in 1st longer, and then run the other gears in the power band. If I'm honest, it's a lot like my '05 Unlimited with the 6 speed, where 1st was so low, I started in 2nd a lot anyway.

Regearing would be great... Gaining the 6th gear back, which would result in having closer ratios, would help a little with drivability. And it would definitely be the biggest help when starting from a stop. But once you get going, you essentially are driving a 5 speed and I don't see the big deal for the short-term. I'm saving up for front and rear selectable lockers or TrueTracs to put in when I regear, and have had no issue with pushing back the regear until after i save the extra cash. So the current plan is 4.56s in the spring.

Edit: And I've gotten betwen 16 and 18 mpg calculated in mixed driving.
 

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zx6r said:
hey Elarson. if you had it to do over again would you still go with 4.88 or something else?
As a daily driver and off road toy no the 4.88 fits me perfect. It accelerates on the road better than stock and is a decent performer on fuel. More towards off roading yes I would have gone further than 4.88.
 
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