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Old 03-03-2012, 04:40 PM   #31
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Got my new one this morning. Build sheet even had my name on it. 3.73 gears, max tow, SiriusXM. Big difference.
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Old 03-03-2012, 06:03 PM   #32
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looks sweet. wonder if the jeep I am trying to buy tomorrow has 3.21 or 3.73. reading all this is making me sweat just a BIT. never really saw this coming, I'm new to this whole realm of 4x4 and off roaring (whether it be dirt or serious mud). Guess I'll have to see! Good thread though. Sweet ride, congrats.

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Old 03-03-2012, 08:11 PM   #33
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You definitely want to make sure it has what you want. I was fortunate in my situation. Guess it helps to have some loyalty to my dealer.
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Old 03-03-2012, 08:23 PM   #34
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When I was flying down I-35 last Tuesday doin' 77-78mph I was wishing for 3.21's.
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Old 03-29-2012, 07:29 AM   #35
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What is the real mechanical difference between 3.21 and 3.73? What would have to be changed to re-gear from 3.21 to 3.73 ? And can this project be done at home? What specific tools for the job would you need?
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Old 03-29-2012, 08:40 AM   #36
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Originally Posted by Rabuck
What is the real mechanical difference between 3.21 and 3.73? What would have to be changed to re-gear from 3.21 to 3.73 ? And can this project be done at home? What specific tools for the job would you need?
It raises your RPMs for a given speed, which translates to horsepower. There are charts and formulas you can use to determine precisely how much, but, for example, I'd expect going from 3.21 to 3.73 would add about 300 RPM at 70 mph.

Absent a high degree of sophistication and specialized equipment, you can't do it at home. There are quite a few shops that won't even do it.
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Old 03-29-2012, 08:57 AM   #37
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Originally Posted by MTH

It raises your RPMs for a given speed, which translates to horsepower. There are charts and formulas you can use to determine precisely how much, but, for example, I'd expect going from 3.21 to 3.73 would add about 300 RPM at 70 mph.

Absent a high degree of sophistication and specialized equipment, you can't do it at home. There are quite a few shops that won't even do it.
Dang alright thanks, I'm already thinking of re-gearing after towing a 4x8 trailer with lawn mower equipment up hill, after I get my upgraded tires I think 3.73 would be best
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Old 03-29-2012, 09:01 AM   #38
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If your going to be towing and larger tires you may even consider 4.10's.
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Old 03-29-2012, 09:14 AM   #39
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If your going to be towing and larger tires you may even consider 4.10's.
From what I have learned there is a big difference between 3.21 vs3.73 but I there between 3.73 vs 4.10?
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Old 03-29-2012, 09:32 AM   #40
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From what I have learned there is a big difference between 3.21 vs3.73 but I there between 3.73 vs 4.10?
Same kind of thing.

Going from 3.73 to 4.10 would probably add another 200 RPMs or so at 70 mph on top of what the 3.73s would add. So I'd expect going from 3.21 to 4.10, you would see about 500 more RPMs on the highway at the same speed in the same gear. That would translate to somewhere around 20 more horsepower. I'm speaking in very general numbers here, mind you.

And remember 4.10 is still a stock ratio--for 2012s like you have, it comes standard on manual transmission Rubis and is an option for the autos. So those extra 500 RPMs aren't going to be "too much" or anything like that. A stock Rubi driving next to you on the highway would have the same RPMs.

So I agree with Rick. If you're going through the expense of a regear, you want to go to at least 4.10. Maybe even 4.56, though I'd want to hear from someone with a 2012 who's actually done that first. For pre-2012s, the numbers are even more aggressive--4.56 would be the minimum for a regear to be worthwhile, and many folks with autos go to 5.13s and 5.36s. Rick has 4.88s.
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Old 03-29-2012, 09:38 AM   #41
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Okay so I'm either going big or nothing but I'm probably going to stick with my 3.21 and just get 33" tires to stay safe until I eventually get a rubi one day and 35" or 37" 😚
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Old 03-29-2012, 11:03 AM   #42
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Okay so I'm either going big or nothing but I'm probably going to stick with my 3.21 and just get 33" tires to stay safe until I eventually get a rubi one day and 35" or 37" dde1a
I personally think this is the best approach. I have a '12 Auto with 4.10s and turning 2600 rpm at 70 gets old and burns through gas. Limit your tranny to 4th for auto or 5th for manual and you'll have the same effect without the added cost.
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Old 03-29-2012, 02:13 PM   #43
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i also have the 3.21 gears, was supposed to come with 3.73, havn't changed tire size yet, but 3.21 will run 33s without any problem.
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Old 03-29-2012, 03:27 PM   #44
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I personally think this is the best approach. I have a '12 Auto with 4.10s and turning 2600 rpm at 70 gets old and burns through gas. Limit your tranny to 4th for auto or 5th for manual and you'll have the same effect without the added cost.
This is the most sensible post I've read about the 3.21 / 3.73 / 4.10 OEM gearing debate, and it not only caused me to back off the regearing ledge after snagging a JKUS 3.21 off the lot (for a smoking 7% below invoice deal, mind you), but this post also caused me to go from long time lurker to new board member.

Now is it as simple as you say, just use your auto tranny limiter to select lower gears for more power, and you're golden? (Notwithstanding the fact that there's no limit below 1st). 'Cause then isn't having the 3.21's for better fuel economy + the new selectable tranny a "best of both worlds" setup? (Assuming you're not lifting or adding more rubber).
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Old 03-29-2012, 04:02 PM   #45
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My 2012 Unlimited Sport has the 3.21 gears in it. I have concerns that this will not be acceptable for running 33's. A few threads I have found say this is not as much of an issue on the 2012 with the 5-speed auto.

I'm already talking to my dealer about ordering one with 3.73 gears in it. Would it be worth it to go ahead and trade? Or should I stick with the 3.21?

I won't be going any bigger than 33's. I ran 33's on my 2010 JKU and it worked out great with the 3.73 gears.
The difference between the OEM 32s and 33s would have minimal effect on performance. If you are happy with the 3.21s now, you will remain happy with 3.21s and 33s. You can also get lighter 33s (like the duratrac 33x12.5x15) which will make the change essentially transparent.
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Old 03-29-2012, 04:04 PM   #46
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The difference between the OEM 32s and 33s would have minimal effect on performance. If you are happy with the 3.21s now, you will remain happy with 3.21s and 33s. You can also get lighter 33s (like the duratrac 33x12.5x15) which will make the change essentially transparent.
Indeed, I have 2010 with 3.21 gears and 33x12.5R15 DuraTracs. I noticed no change in performance from the stock 32s.
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Old 03-29-2012, 04:09 PM   #47
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This is the most sensible post I've read about the 3.21 / 3.73 / 4.10 OEM gearing debate, and it not only caused me to back off the regearing ledge after snagging a JKUS 3.21 off the lot (for a smoking 7% below invoice deal, mind you), but this post also caused me to go from long time lurker to new board member.

Now is it as simple as you say, just use your auto tranny limiter to select lower gears for more power, and you're golden? (Notwithstanding the fact that there's no limit below 1st). 'Cause then isn't having the 3.21's for better fuel economy + the new selectable tranny a "best of both worlds" setup? (Assuming you're not lifting or adding more rubber).
No, for at least three reasons.

(1) You're effectively giving yourself a 4 speed (rather than a 5 speed) transmission. Your best bet is always to use the gearing that best spreads your gears out among the powerband.

(2) Downshifting generally will cause a bigger RPM jump than one or two steps up in gears. For example, you could find yourself spinning 2100 RPMs on the highway and wish you were more at around 2300 RPMs, but downshifting sends you to 2700 RPMs.

(3) Gears don't just matter for high RPM performance. A good gearing match allows the engine to get the power going and lug less when starting from a standstill. This is why I can't (or would be miserable if I did) put on 40" tires with my 3.21s and then just use only my first two or three transmission gears. Getting started from every stop sign would be a PITA.

That said, if you're not getting bigger tires and you're happy with your 3.21s, I wouldn't bother changing anything. There are downsides to spinning higher RPMs--there's no free lunch.
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Old 03-29-2012, 04:12 PM   #48
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Originally Posted by rtljeep View Post
This is the most sensible post I've read about the 3.21 / 3.73 / 4.10 OEM gearing debate, and it not only caused me to back off the regearing ledge after snagging a JKUS 3.21 off the lot (for a smoking 7% below invoice deal, mind you), but this post also caused me to go from long time lurker to new board member.

Now is it as simple as you say, just use your auto tranny limiter to select lower gears for more power, and you're golden? (Notwithstanding the fact that there's no limit below 1st). 'Cause then isn't having the 3.21's for better fuel economy + the new selectable tranny a "best of both worlds" setup? (Assuming you're not lifting or adding more rubber).
With the exception of 1st, essentially, if you want "gears" just drop it one gear and hold it at 4000rpm. You will burn more gas with more throttle input, but at least it is driver controlled and temporary. Having 4.10s all the time takes that control OUT of your hands. The only reason I wanted 4.10s is so that I can run 35" tires, which would bring me back down to 3.whatever. Believe me, I have sports cars with short gearing, and it is fun, but it does have it's downsides, MANY downsides. I got 3.21s because I didn't know better (my first jeep) but I have absolutely no problems passing, merging, cruising at 80, etc. Maybe you guys drive more aggressively than I do, but the Jeep is my cruising vehicle. If I need to extra power (ie deep snow, etc) drop it down a gear and the effect is exactly the same...all it is is torque multiplication.
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Old 03-29-2012, 04:16 PM   #49
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No, for at least three reasons.

(1) You're effectively giving yourself a 4 speed (rather than a 5 speed) transmission. Your best bet is always to use the gearing that best spreads your gears out among the powerband.

(2) Downshifting generally will cause a bigger RPM jump than one or two steps up in gears. For example, you could find yourself spinning 2100 RPMs on the highway and wish you were more at around 2300 RPMs, but downshifting sends you to 2700 RPMs.

(3) Gears don't just matter for high RPM performance. A good gearing match allows the engine to get the power going and lug less when starting from a standstill. This is why I can't (or would be miserable if I did) put on 40" tires with my 3.21s and then just use only my first two or three transmission gears. Getting started from every stop sign would be a PITA.

That said, if you're not getting bigger tires and you're happy with your 3.21s, I wouldn't bother changing anything.
Just to rebut a little bit...

1)You don't care about power in 5th or 6th. Both are highway gears only and don't matter. If you want to pass, you drop to 4th.

2) So? You get instantly more power, you do what you need to do, and go back to smooth, quiet comfort cruising. The 2012 tranny is VERY smooth and pretty quick to react, so it is not a chore.

3)Again, we established that 1st gear is essentially the one that matters in terms of a REAL difference between the 4.10s and 3.21s. The initial roll is what is going to matter. Yes, if your plan is for 35"+ I agree, gears should be equipped accordingly. However, for a daily driven vehicle, mechanically, there is actually no benefit, and technically, a slight drawback.

This is NOT meant as a flamefest, just objective information.
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Old 03-29-2012, 04:24 PM   #50
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Just to rebut a little bit...

1)You don't care about power in 5th or 6th. Both are highway gears only and don't matter. If you want to pass, you drop to 4th.

2) So? You get instantly more power, you do what you need to do, and go back to smooth, quiet comfort cruising. The 2012 tranny is VERY smooth and pretty quick to react, so it is not a chore.

3)Again, we established that 1st gear is essentially the one that matters in terms of a REAL difference between the 4.10s and 3.21s. The initial roll is what is going to matter. Yes, if your plan is for 35"+ I agree, gears should be equipped accordingly. However, for a daily driven vehicle, mechanically, there is actually no benefit, and technically, a slight drawback.

This is NOT meant as a flamefest, just objective information.
Right, but it's all about the balance.

Hypothetically, let's say the 2012 wranglers--equipped with the 3.6 and current trans and tires--could ONLY be had with 5.36s or (imaginary) 1.xx gears. They'd both suck, right?

So the question was whether the 3.21s was the "best of both worlds." I say no. Given the power curve of the 3.6 and the results when it's mated with the current trans, I think the 3.73s would probably be more along the lines of a "perfect balance." The 3.21s are a little short, the 4.10s are maybe a little tall.

And I disagree that highway power generally isn't important and, when I want it, I can downshift. It's true that I can downshift of course, but my only two states of mind on the highway aren't "perfect happy" and "need to pass immediately." Sometimes I just want to pick up the pace a little bit without flooring it. For that, adding 200 or 300 RPMs to where the 3.21s sit you would be helpful.

Just my two cents.
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Old 03-29-2012, 04:52 PM   #51
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Right, but it's all about the balance.

Hypothetically, let's say the 2012 wranglers--equipped with the 3.6 and current trans and tires--could ONLY be had with 5.36s or (imaginary) 1.xx gears. They'd both suck, right?

So the question was whether the 3.21s was the "best of both worlds." I say no. Given the power curve of the 3.6 and the results when it's mated with the current trans, I think the 3.73s would probably be more along the lines of a "perfect balance." The 3.21s are a little short, the 4.10s are maybe a little tall.

And I disagree that highway power generally isn't important and, when I want it, I can downshift. It's true that I can downshift of course, but my only two states of mind on the highway aren't "perfect happy" and "need to pass immediately." Sometimes I just want to pick up the pace a little bit without flooring it. For that, adding 200 or 300 RPMs to where the 3.21s sit you would be helpful.

Just my two cents.
Interesting view, but I personally think the 3.21s are the best of "both worlds." They provide optimal fuel economy with pretty good power. The 4.10s provide optimal power with so so fuel economy. The 3.73s are kind of neither, they don't give you optimal fuel economy, and they don't give you any drastic increase in power (although some.)

The point of this thread TO ME, is not to knock any of the ratios. I think they all have their purpose. If I did it all over again, I would have opted for higher gears so I can run 35"s without issue. However, if someone is going to run OEM or 33" rubber, I think the fact that they can downshift (except 1st obviously) severely negates the argument.

I do hear you on the extremes of comfort cruising vs passing immediately, although I must say I recently drove 300 miles to Lake Placid through the mountains, and never did I lack power. I was following my friend in an FX35, a much faster vehicle, and could keep up without much issue. It didn't feel very stable above 80 with the mountain winds, so I backed off to 75 max, but from 70-90 the truck pulls very well. 50-65 it just acceptable, but again, that is in top gear.
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Old 03-29-2012, 05:31 PM   #52
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It didn't feel very stable above 80 with the mountain winds, so I backed off to 75 max, but from 70-90 the truck pulls very well. 50-65 it just acceptable, but again, that is in top gear.


Couldn't tell ya the last time I saw 90 mph.
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Old 03-29-2012, 07:19 PM   #53
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Couldn't tell ya the last time I saw 90 mph.
I didn't even pay attention. I was following my friend and he kept accelerating so I did as well. Before I knew it, I looked down and was doing close to 95 . When I realized, I quickly backed off and dropped it to 75. The other day I was driving normally (doing 70 in a 65) and it was incredibly windy here. The Jeep was swaying hard and it was REALLY dangerous. I dropped it to 55 and then the swaying seemed to have stopped. Gotta watch those crosswinds.

I've done 157 in my s2000 and 170 in my M3. I'm not a top speed demon anymore, more of a twisties guy now.
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Old 03-30-2012, 12:55 AM   #54
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I own a '12 2door with 3.21. I have not driven a '12 with any other gearing, but I really like how my jeep performs with stock tires. I do wish the transmission had a tow or performance setting as it does try place me in too high of gear when cruising at a steady speed. Seems to try to go to 1500 rpm whether going 30 or 55. So when I am going to be driving on 55 mph on state highways, I hit the old - lever on the tranny to limit to 4th gear. I tow nearly 2,000lbs frequently and it has not been a problem. If given the option again, knowing what I know, I would probably go for the 3.73 for additional flexibility in tire choice. I would have to try the 3.73 at 70 first. Would I spend the money to regear for stock tires, no. If I was getting the JKU, I would definitely go for the 3.73 so that I had a 3,500lb towing capacity and to deal with the additional weight.

I think that some of the very aggressive gearing advice comes from the previous 4 speed automatic. 1st is much lower on the 5 speed and 5th is a bit lower than 4th is on the 4 speed.
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Old 03-30-2012, 09:56 AM   #55
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I personally think this is the best approach. I have a '12 Auto with 4.10s and turning 2600 rpm at 70 gets old and burns through gas. Limit your tranny to 4th for auto or 5th for manual and you'll have the same effect without the added cost.
Pulling out into traffic is a lot nicer with 4.10's than 3.21's.

Unless the vast majority of your driving is high speed cruising, I think 4.10's make for a much better daily driving experience.

I think the talk about fuel economy is overblown. I seem to be within 1mpg of the numbers posted by people with 3.21's. That may matter to Chrysler who has to maintain a certain average fuel economy over their entire fleet (which is probobly the only reason 3.21's are standard), but it doesn't to me.
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Old 03-30-2012, 12:37 PM   #56
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With 3.73 and 33 Duratracs 6th gear is still pretty useless on a decent grade, with 3.21 it must be pretty much useless on anything but flat ground with a tailwind. I wish you could get 4.10 as an option for the Sport...
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Old 03-30-2012, 01:13 PM   #57
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With 3.73 and 33 Duratracs 6th gear is still pretty useless on a decent grade, with 3.21 it must be pretty much useless on anything but flat ground with a tailwind. I wish you could get 4.10 as an option for the Sport...
True but let's be honest, wether you have 2.11 or 9.99s, if you are going up a decent grade you should NOT be in top gear.
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Old 03-31-2012, 05:23 PM   #58
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I have a 2012 Sport S 2 dr with the 3.21s. I just pulled my 5x8 utility trailer with a yard of top soil (total weight should be some where near 3000 lbs). some pretty good hills, no problem, it actually out preformed my previous 05 ZR2 blazer with 3.73s. So for me the 3.21s are just fine.
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Old 03-31-2012, 11:48 PM   #59
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In one of these threads I saw a chart showing that 1st with the auto is a little higher than 1st with the manual. I have a 2012 Sport with 3:21s and the manual, and it's a little boggy off the line. Plus at 80mph in 6th (stock tires) you're taching all of 2K. So 3:21s with the manual are really one bump too low in 1st and 6th. But it looks like with the auto it's OK. Alls I can tell you is I would rather have the 3:73s.

Is it a deal breaker? No, and the low range does seem to get a bit stronger as it breaks in. But I'm curious if the aFe intake and exhaust will up low rev torque enough to make the 3:21 pay. Otherwise a re-gear is not off the table.
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Old 03-31-2012, 11:59 PM   #60
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I have the 2012 sport with 3.21s. I have 32's now, but my buddy got his 35's in 2 weeks ago and we mounted them on my jeep just so I can check how the 3.21s handled the 35's. I had them on for 2 days till my buddy got his lift on. and honestly. The jeep help up well. A lot better than my old 07 jk with 4.10s. It didnt struggle on shifts and it didnt skip a beat going up hill. The 285HP and 30+ torque hp than 07-2011 really make a difference. For me, I dont feel the need to change gearing.


The whole gear changing thing was more popular with the 202HP 3.8L engine. the 2012 is a whole other animal.

My buddy has a 2010 rubicon with 4.10s and the 35's. Mine still had more get up with the new engine and 3.21s with the 35's

But it also might be fine for me because im used to running 35's with 4.10s on my old jk. So To feel my 2012 with 3.21s held up a little better is more than enough for me!!

__________________
2012 JKUSPORT|2.5" RC LIFT|35" DURATRACS|AEV FRONT BUMPER|IPF|JKS|TERAFLEX|
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