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Got the 3.21 Gear Ratio - doomed?

14K views 78 replies 29 participants last post by  andrewoc15 
#1 ·
My new JKUS S came with the 3.21 gear ratios which were explained to me to be better for gas mileage and OK if you aren't going to be towing. My answer to both those questions was that yes, I will be commuting a 100 miles a day and no I don't have any intensions of towing anything, may be a bike rack in the hitch, but that's it.

2 months into it, I go through my first off roading trip and learn a lot more about lifts, larger tires etc. and then I see this chart while researching thing (thanks mommymallcrawler for providing it!!)

So, now it means to get more clearance I first have to get preferably a 4.10 ratio, then a lift and with it larger tires?

My Sport S has a Dana 30 in the front and Dana 44 in the rear. Any reason with the config that I can't go to 4.10 in this? 3.73 would not be worth it.

Also, is there really a big difference between 3.21 and 4.10 when larger tires are put in, let's say 33s or 35s? What am I going to give up if I gear up to 4.10?

Please help!!!

All insights would be appreciated!!

Thanks in advance.
 
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#3 ·
I have 3.73's which are a good match for 33's, but I'm also in the much lighter 2 door. If you ever plan on 35's then you'll need to step up to at least 4.56 if you want good performance in your 4 door with 35's maybe even 4.88's.

If you are going to re-gear I would only want to do it once and imo 4.10 will cost you a good buck and if you step up to 35's you'll probably want to re-gear yet again, but if you stay at 33's then you'll be fine with 4.10's.

The dana 30 can take whatever gears you decide to go with, you'll just need to do a carrier change is all which is pretty cheap.

You give up a bit of fuel mileage as your rpm's will be a bit higher at highway speeds, but your Jeep will feel like a slug especially with 35's and 3.21's, not good for off roading hence the re-gear.
 
#4 ·
#5 ·
If you are only interested in rolling in 33's, you can pretty much get away without a lift and just do some trimming of your factory fenders. Definitely a re-gear to 4.10 eliminates sluggish performance with the bigger tires. This will be your cheapest route.

If you do however want to play big and step up to 35's.. then that is going to start chewing up some coins. You will need at least a 2.5 Lift to gain proper clearances for a 35. A 4.56 re-gear will get you closer to factory specs on performance. With the D30 axle upfront, definitely advise on c-gussets and of the axle to reinforce it from the stress of rolling a big tire. Artec Full Armor kit will take care of the D30 stiffening. A D30 axle sleeve is not critical but the gusset and truss definitely advisable for 35's.

Of course, you will need to address your tire carrier as well for the 35's. That is just your admission ticket to the big jeep play ground. From their, you start emptying every pocket to scratch the mod itch :bop:
 
#9 ·
Thanks folks...a quick follow up....will be getting a winch and a metal bumper with some rock sliders (BTW good idea if I am going rock crawling anyway?)...SO my thinking is to get 33s with a 2.5 inch AEV lift...logic..don't need the lift to fit 33s but will get me extra clearance with all that extra weight induced sagging I might get....BUT, if I did all of the above, I should change the gear ratio to 4.10 , right? 35s won't be practical for me with my commute.
 
#12 ·
You'll actually probably be OKAY with the 3.21's. Will run better with 3.73's, or 4.10's with 33's.

You will gain clearance on the body of the Jeep with the lift, but you will not gain overall clearance between the axles and the ground.

If you want to compensate for a heavier front bumper and winch, look into a RK or TF 1.5" kit. You'll probably net more than that, with a lot less money spent.
 
#10 ·
with a 100 mile daily commute I would advise against going to 35's, regear etc... I would recommend a leveling kit and 33's (285/70r17 in something light like a duratrac) and stick to your 3.21 gears. That is until you decide to buy a new DD and turn the jeep into a wheeling toy... a lifted JK on 35's is not your best choice for a 100 mile daily commute and a JK on 33's with a small lift will be capable enough to have fun with without killing you onb a daily basis. Just my $.02
 
#11 ·
33's without a lift isn't a good idea if you want to get into off roading. The tires won't rub the fenders on paved streets, but you start flexing off road and you are going to have a problem especially with a wider tire. Once you either put wheel spacers on or go to a wheel with say 4.5" of backspacing then the tire will stick out past the fenders which will cause fender rubbing when flexed even more.

I run a Teraflex leveling kit (2" front and 1" rear) and 2" extended bump stops and although my tires don't rub my fenders off road when flexed they do come close
 
#13 ·
You will gain clearance on the body of the Jeep with the lift, but you will not gain overall clearance between the axles and the ground.

What gets you the clearance between the axles and the ground then, if not the lifts?
 
#14 ·
larger diameter tires is the only way to increase clearance to the axles
 
#18 ·
Not getting a daily driver...my jeep is it...have to make some compromises to make it work as a DD and off roading rig. Also 35s don't seem like a practical idea for me.

So half an inch incremental height from 33s doesn't seem much, but don't I need the lift anyway, especially if I am going to add the heavier bumper with a winch given how little space is left between the 33s and the fenders?
 
#22 ·
In that case I would get a set of light 285/70r17's, a Teraflex spacer leveling kit (or something comparable) set of quick disconnects for your sway bar and have fun.
Try your 3.21's and see how you find it, you'll probably be ok with that combo. 3.73 or 4.10 would give you a little more power but a regear isn't cheap ($1500+) so I would run it as is first and then decide if you feel it's worth it or not
 
#19 ·
With 33s though, should I get it regeared though....3.73 or 4.10? If I don't what am I going to feel...sluggish drive or lack of power when on climb etc.?
 
#24 ·
I have the 3.21 gears in my 13 Sport as well. I have 33" tires. The only time i notice anything at all is when trying to accelerate going over hills at highway speeds. It does seem to struggle a bit. Other than that though i haven't really noticed anything. 35s would be a different story.

Cant really speak to the offroading effects of the 3.21. I haven't done a whole lot yet to know the difference though i think obviously lower gearing would be better.
 
#25 ·
In my opinion based on running at the Cliffs and planning to only run at similar places, I'd say keep your stock setup for your daily commute and get a set of 33" mud terrains to swap out for when you're going off roading. That should give you enough ground clearance for just about anything at the Cliffs at least. You probably won't need the lift unless you just feel like riding a bit higher and enjoy throwing money at your Jeep on impulse buys (we're all guilty of this at some point :D). You'd be better off getting the 33"s and Swaybar disconnects first, then see if you need the lift due to rubbing. None of this would make a Regear necessary until you decide you want more grunt off road and then I'd say 4.10 w/ 33"s would do well but you'll feel it in your commute MPG.
 
#29 ·
You may find it acceptable, but trust me - the engineering disagrees with you. 3.21 gears in an auto with heavy 35s - you do not have quite the power you think you do. Yes it goes from point A to point B - but once you do your regear, you will have a major AHA moment and realize just how marginal the performance was.
 
#28 ·
Folks who are driving 3.21 with larger than stock tires should hook up with a Jeep club or local folks running properly geared rigs to do a test drive and see what you are really missing. If I put you at the wheel of my rig I can guarantee you IMMEDIATELY would tell the difference. You folks with 3.21s probably would not even believe it is a Jeep if all you had to compare to is 3.21.

Do not settle for poor performance - regear if needed. It is also better for your engine and transmission. You paid a lot of money for your rig - upgrade it right to run bigger tires. You are not "doomed" - you just need to spend the coin to give your Jeep some guts.

In my opinion, the 3.21 majorly sucks even with 32 inch tires - I drove my sons briefly when I was in Ohio. An improperly geared rig will NOT (repeat NOT) feel "just like stock" on bigger tires - do not fool yourself.
 
#36 ·
x2. I just traded my 2005 TJ with Duratrac 33's and 3.73's on a 6 speed manuel for a 2014 JK Sport with Nitto Trail Grappler 295/18's and 3.21's and factory/dealer installed 4" lift on a 6 speed manuel one month ago. And the 3.21's suck. I drive 40 miles highway everyday to work and the difference between the two are incredible. My 14 Sport gets horrible gas mileage (13.5 mpg) and never put in 6th gear because even on flat pavement it has no power. I don't care so much about mpg or I never would have bought a Wrangler to begin with, but I do care about lack of power. As soon as I can come up with the money then definitely going to regear to either 4.10 or 4.56.
 
#32 ·
Isn't there a reverse ratio calculation of some sort? Swore I saw it somewhere. If I have x.xx gears with x size tire now it will be equal to x.xx gears with new x size tire?

I have 3.73s now and getting ready to get 35s. I will regrear to either 4.56 or 4.88s if I lose any power. I have to be able to pass when I want to.
 
#34 ·
Thanks MMC I understand the chart. I found the thread by forum member baby blue sound. How did he get this calculation is what I'm referring too below.

"""3.21s will be no good on 35's. I'm an effective 3.55 ratio now after going 37s with my 4.10 gears and I don't like it at all. You'll be an effective 2.93 ratio on 35s with your 3.21 gears, don't think you'll like it one bit. """"
 
#35 ·
You folks are missing out on one very important thing. The bigger the tires the more they weigh. The change from stock to 33s is hardly noticeable for most and then on to 35s is very noticeable and then 37s are a dramatic change .Its a combination of the increased size and weight which increases proportionately with tire size.

Most people will be happy with .
3:21 and 33s
3:73s and 35s
4:10s and 35s maybe a light 37 in flat country.
4:56 and 37s are good DD ,35s a good trail ratio
4:88 and 37s is good ratio for trail and DD
5:13 is preferred for heavy trail use and mountains for 37s.
5:38 is for 37s and up ect.

Location and use are also very important. If you want to rock crawl or run in the mountains you need low gears. If you trail ride some and mostly DD odds are you will be happy with the a small step up in tire size and the stock gears. 3:73 are very popular for most that will not go any larger than 35s on a DD/ weekend trail machine.

Ive got 40k DD/ weekend trail ride miles on 3:21s and 33s and have zero issues and have been very happy with preformance. I am going to a heavy 35 and re gearing to 4:56 to lean more towards trail use than DD. Putting 35s on wifes DD with 3:73 JKU and have no reservations at all. It will be a 100% mall crawler and 3:73s area good enough for that.

I think some folks have never driven any of the older Jeeps with smaller engines with the same gears. My 95 had 2.5 and 4:10s and was still very capable but was a joke compared to this 3.6. My 79 with 304 sounded mean and pulled good but had less power than this 3.6
I guess its all in what you have experienced and what you know as acceptable or usable.
 
#37 ·
A basic question to understand this completely.....how does the performance change when you reggae...reading the posts, my guess is that the RPM at which gears shift goes up?!? So, if 1st gear moved into 2nd gear at 2000 RPM in a 3.21 gear ratio, with a 3.73, that gear won't shift into 2nd the RPM reaches 3000 (let assume)??? If so, what does that let you do better....push through obstacles with more force???
 
#38 ·
#40 ·
Very useful information through out....thank you all...

One other curiosity, doesn't 4LO essentially do the something similar on trails that a higher gear ratio would do? I've only been on trails once in my 2 month old JKU, thus learning it all right now, we had in 4LO throughout and it powered its way through everything..I was impressed!!
 
#43 ·
4lo does effect your final drive ratio but only when in 4lo, as would lower gears. (Lower gears are actually numerically higher, higher gears are numerically lower, 4.88 gears are actually lower than 3.21)
While shifting into 4lo helps to reduce your final drive ratio a regear effects your final ratio 100% if the time, 2 hi, 4hi or 4lo.
Often with bigger tires your final drive ratio becomes too high and power loss becomes an issue both on road and off making a regear a great way to spend money
 
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