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Old 10-22-2012, 09:24 PM   #1
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35" tires 3.21 gears

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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Old 10-22-2012, 09:34 PM   #2
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Prepare to be blasted with you need 4.88 or more.

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Old 10-22-2012, 09:37 PM   #3
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i am sure of that. will it be so bad that i won't wanna drive it till i regear?
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Old 10-22-2012, 09:38 PM   #4
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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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Old 10-22-2012, 09:39 PM   #5
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Originally Posted by zx6r
i am sure of that. will it be so bad that i won't wanna drive it till i regear?
Depends on the person. My buddy found it unbearable.
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Old 10-22-2012, 09:42 PM   #6
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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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Old 10-22-2012, 09:46 PM   #7
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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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Old 10-22-2012, 09:55 PM   #8
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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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Old 10-22-2012, 10:01 PM   #9
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argh!!!!!#$#%%&&*(*($#$^%**(*(
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Old 10-23-2012, 07:14 AM   #10
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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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Old 10-23-2012, 07:22 AM   #11
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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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Old 10-23-2012, 07:26 AM   #12
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glad to hear that. do you have a manual also? what kind of gas mileage are you getting?
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Old 10-23-2012, 07:53 AM   #13
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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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Old 10-23-2012, 08:19 AM   #14
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Just to give you a feel my 2012 auto JKU with 35's and 4.88 gearing is getting an average of 15.3 highway mpg at an average of 75 mph. City driving is down around 13 or 12.5. And that's with a re-gearing.
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Old 10-23-2012, 08:23 AM   #15
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It's my DD but I don't drive much. I live 3 miles from work so I bike there sometimes when I'm not lazy. I usually get 13-15 mpg so yea that sucks, but like I said it don't bother me that much. I do plan on re-gearing just haven't done it yet.
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Old 10-23-2012, 08:39 AM   #16
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hey Elarson. if you had it to do over again would you still go with 4.88 or something else?
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Old 10-23-2012, 08:53 AM   #17
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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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Old 10-23-2012, 09:47 AM   #18
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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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Old 10-23-2012, 10:11 AM   #19
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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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Old 10-23-2012, 10:12 AM   #20
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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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Old 10-23-2012, 10:22 AM   #21
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thanks for all the replies and keep them coming. i just called my local 4x4 shop and they told me $1500 an axle for a regear. they are the only game in town in my little area but i told them i felt like they were charging way too much. i told them on the forums nobody seems to be paying more than $1500 total. i have a friend who runs a chrysler dodge jeep dealership and they mod a lot of jeeps there and have them for sale on the lot too. he told me to come up and give them a chance so i am headed up in about an hour to see what they can do for me. and he said a decent warranty goes with all the installs so while i am there i will check out what they can do on a lift for me too.
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Old 10-23-2012, 11:15 AM   #22
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My reasonably mod-friendly dealer said they'd prefer me to buy the parts (R&P, rebuild kits) and they'd just charge labor, which they quoted at $800. Not bad, for a total under $1,600 or so for the more expensive 4.56 gears.
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Old 10-23-2012, 02:42 PM   #23
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i have a similar set up

I will say i am pretty impressed with the pentastar. I have 3.21 gears the 6 speed and 315 70 17's with a 2.5in teraflex lift before the 315's with just the lift and 255 70 18 sahara rims i was getting between 22 and 24 mpg i drive rural highway to and from work mostly flat for about 30 miles each way. 1 or 2 small towns i have found that if you put it in 6th gear and hit cruise at say 55-60 and use mid grade fuel it is faily easy to keep the mpg above 22 now i always coast up to stop lights and stop signs and stay out of the gas pretty much. now using the same tactics i have been averaging 19.5 to 20.5 with my 315's also using the bigger tires makes your mpg calculator look lower than what you actually getting as well as you odometer reading. for instance my 315's are 20% larger than stock 225/75/16 so i take my 17.3 avg mpg times that by 20% and it gives me 20.7 that is what im currently getting also you can take your odometer and do the same thing so for 100000 miles on the odometer you have actually traveled 120000 if you use the same tire size for the lif of the vehicle or basically 200 extra miles for evey 100 that the odometer reads while you have them on there
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Old 10-23-2012, 02:49 PM   #24
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In the TJ world its barrable around town but when you hit the highway you might as well be going backwards
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Old 10-23-2012, 03:32 PM   #25
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i went to my friend who is the service manager at a jeep dealership and i think i am getting a fairly decent deal. i am gonna go with the aev 2.5" dual sport xt suspension lift. i will drive it for a few miles anyways with the 3.21 gears. their quote on a regear was in line with what i have been reading on the forum at around $1500. i guess the next question what be what gears? Elarson says 4.88 works great for him and i was leaning towards those too. anyone else have any suggestions or preferences?
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Old 10-23-2012, 04:17 PM   #26
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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.
Excuse my ignorance but why will it be worse in a manual compared to an automatic?
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Old 10-23-2012, 04:57 PM   #27
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i wondered about that too
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Old 10-23-2012, 06:57 PM   #28
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Excuse my ignorance but why will it be worse in a manual compared to an automatic?
Technically there is a difference- why there are two gearing charts by Jeep. I can't seem to find the right one; if someone has a link.....
From a "driving perspective"- in manuals you basically lose 6th gear and first is harder to launch as mentioned. (Seems to be the general consensus; there are those that are ok). With the automatic it tends to downshift at too low an RPM or "lug"- but the tranny still does the work. Put it in drive and go. I have an auto and find it annoying enough to re-gear. (4.10s coming for me). But imagine losing an entire gear and having to give it extra gas just to get out of first. Makes the performance change in the manual much more pronounced.
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Old 10-23-2012, 07:17 PM   #29
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are you running an auto or 6 speed manual? i know i will be regearing just wanna hear why you will be going with 4.10
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Old 10-23-2012, 07:36 PM   #30
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Auto. Personal preference really. If I could find the right chart.....I believe 4.88s run around 2700 RPMs at 70 MPH. Elarson???? I'd like to stay just under 2500 RPMs at that speed. Should have said 4.10s or 4.56s. Same price so unsure right now.
I should mentioned MPG doesn't matter to me; I stopped looking after the lift and 34s.

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