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Old 09-04-2012, 07:34 AM   #1
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"Optimal gearing" for 33's and 5sp auto

Ive pretty much decided Im getting the 5sp auto and the 3.21 gearing. I know the general consensus is "3.73's at the least" but I drive 90% highway if not more for 60-80 miles daily. That being said, the 3.73's just take away too much top end and run at too high of rpms.

However, Im definitely going to put on a 2.5 inch Teraflex leveling kit and 33's maybe even 35's for mostly aesthetic purposes.

Then of course I read a new bit of info. I read that the bigger tires with the higher 3.73 gearing "evens everything out" so its like a stock wrangler with the 3.21's? Im a little confused on that since rpms relate to the motor. I could see several contributing varibles of the 3.21's not being enough gear to sufficiently roll the 33's but I figured 285 hp could handle that.

And just so yall know, I dont plan on rock crawling or off roading etc. A Wrangler with the 3.21 gearing im sure will more than suffice for what I do outside of DDing.

I appreciate yalls responses and help. Hope yall have a good day.

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Old 09-04-2012, 08:22 AM   #2
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I'm very interested in this. I'm at the exact same point as you, looking hard at an AEV 2.5" lift. I have posted this question in this and other forums and there seems to be a split. Some people say 35s on a 2.5 lift with 3.21 gears causes a significasnt lost of power and can stress components. Others say nah, do it because if you get 33s you will soon be sorry you didn't get 35s.

I am talking to a local shop, and with all the things I am considering they have arrived at the same point I have, which is maybe I should just trade up to a Rubicon. That tells me that with 3.21s, I should stick to 33s.

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Old 09-04-2012, 09:26 AM   #3
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So your doing fine with 3.21's and 33's? is yours an Auto?
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Old 09-04-2012, 09:49 AM   #4
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Mine is a 12 with the 5 speed auto. I started with 3.21 gears and 32" tires. On the highway this set up was barely adequate for me. When I upgraded to the "combo" (33" duratracs and 15" rims) Highway driving took a hit. On a 180 mile trip from sarasota to Gainesville Fla. with 2 adults most inclines (even slight ones) caused the transmission to down shift to keep speed at 67 mph.

Since then I have upgraded to 3.73s (with truetracs front and rear). Around town the Jeep feels much more zippy and gets into 5th gear around 41 mph vs 46 with the 3.21s. Gas mileage is actually better around town by about 1mpg.

On the highway we recently went from sarasota to tampa with 4 adults in the vehicle. Never once did it have to down shift to hold speed. Gas mileage was about 1/2 mpg worse than with 3.21 gearing. But there was about 350 lbs more weight that trip as well.

Overall I am really glad I made the switch. If you were planning on going 35s I would say get the 4.10s. If you offroaded alot maybe even get 4.56s.
Hope this helps.

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Old 09-04-2012, 09:49 AM   #5
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I'm running 33's with 3.21's & an auto tranny in my '12, and for a DD these are definitely the biggest wheels I would run. 35's would be too heavy without a re-gear, in my opinion, and I'm not a speed demon by any stretch of the imagination.
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Old 09-04-2012, 09:54 AM   #6
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3.21 gears and 33" tires

I have a 2012 Wrangler Sport Unlimited with the 3.21 gears and 5 speed auto trans. The factory Goodyear Wrangler SRA tires were 32.1" in diameter and weighed 43 lbs. I installed Dick Cepek FC-II, 33 x 12.50 x 17 tires (32.6" in diameter and 54 lbs.) on the stock Rubicon wheels about a month ago. I feel a slight decrease in acceleration on the pavement but not bad at all. I think it's the added weight, width and rolling resistance of the tires and not the diameter. I take the Jeep off roading on weekends and have no issues with power and torque.

However, I question the 35" with 3.21 gears. The stock tire to the 33" tire was not a big step up in diameter. However, from stock to 35" that could make a difference. A Dick Cepek 35 x 12.5 x 17 tire weighs 68 lbs and is 34.9" in diameter. That's a big jump up in diameter and weight. I would like to hear from others that have gone with the 35" tires and have the 3.21 gears.

For now I am going to stick with the 33" tires. With a my 3" lift they look good, perform well and I don't think I'll have any issues when I go for my emissions test. I have heard that some guys keep a set of original size tires to pass the test then put the larger ones back on. I don't know the details on this I just heard some things.
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Old 09-04-2012, 10:04 AM   #7
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I agree with all that has been said so far. I run a lightweight "P" series 285/70/17 (4 ply tire) on 3.21 gears. I too DD my Jeep on the highway ALOT . I love the tires and the top end,but I WOULD NOT run ANY bigger tire without more torq from the engine(somehow? turbo,supercharger whatever?) or regearing to get more low end.
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Old 09-04-2012, 10:11 AM   #8
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I JUST CHANGE MY GEAR FROM 3.73 TO 4.88 YUKON AND Master Overhaul Kits
GOT THEM FROM DAVID Northridge4x4 Jeep Parts Online Store - Home
BRAKE IN PERIOD ROGHT NOW.I RUN 295.75.16 ITS 33".AND ALSO WHEN I CHANGE GEARS I INSTALL Synergy Jeep JK Heavy Duty Front Ball Joint Set AND Superior Jeep JK Front Axle Tube Seals
VERY HAPPY
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Old 09-04-2012, 10:16 AM   #9
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I just saw a gearing chart in a mag I got the other day I'll post it up
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Old 09-04-2012, 11:13 AM   #10
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Old 09-04-2012, 11:14 AM   #11
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I think the 4 Wheel Parts catalog has a gear/tire ratio chart in it too.
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Old 09-04-2012, 02:51 PM   #12
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I have a 2012 Wrangler Sport Unlimited with the 3.21 gears and 5 speed auto trans. The factory Goodyear Wrangler SRA tires were 32.1" in diameter and weighed 43 lbs. I installed Dick Cepek FC-II, 33 x 12.50 x 17 tires (32.6" in diameter and 54 lbs.) on the stock Rubicon wheels about a month ago. I feel a slight decrease in acceleration on the pavement but not bad at all. I think it's the added weight, width and rolling resistance of the tires and not the diameter. I take the Jeep off roading on weekends and have no issues with power and torque.

However, I question the 35" with 3.21 gears. The stock tire to the 33" tire was not a big step up in diameter. However, from stock to 35" that could make a difference. A Dick Cepek 35 x 12.5 x 17 tire weighs 68 lbs and is 34.9" in diameter. That's a big jump up in diameter and weight. I would like to hear from others that have gone with the 35" tires and have the 3.21 gears.

For now I am going to stick with the 33" tires. With a my 3" lift they look good, perform well and I don't think I'll have any issues when I go for my emissions test. I have heard that some guys keep a set of original size tires to pass the test then put the larger ones back on. I don't know the details on this I just heard some things.


Your Wrangler is essentially how I want my to look. I love it. Hows your gas milage? Do you by chance know what your rpms are at 70 mph?
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Old 09-04-2012, 02:56 PM   #13
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Please correct me if I'm wrong, by looking at those charts with the 3.8L you would want a numerically higher gear ratio on an automatic compared to manual for a given tire size. This seems to be reversed for 2012 on the charts. Numerically higher gear ratio on manual for 2012? Is that correct?
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Old 09-04-2012, 05:09 PM   #14
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I have 285/70/17s on a '12 JK auto with 3.73s, seems pretty good and gets right around 20mpg or a little higher on the highway around 72 or 73mph.
Not sure if that chart takes into account the actual tire size, 285/70/17s are suposed to be 33" tires but in reality they are 32" tall. I used a Procal to program for larger tires, started with 32.75" tire height but my speedometer did not match my GPS, after a few changes 32" was the exact size.
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Old 09-04-2012, 08:29 PM   #15
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Interesting post...I have. 2012 JK Auto and getting a AEV 2.5 lift and deciding on Duratracs285/70/17 or Nitto Trail Grapplers 295/70/17....I have 3:21 gears. Different people say different things. I hope this combination will not effect my acceleration or gas mileage too much, although I know it will have some effect. Keep me in the loop
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Old 09-04-2012, 08:35 PM   #16
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You guys think too hard about this. There's NO REASON to get the 3.21 gears--ever.

It's fine if you have them in the sense that it's a mistake that's not that big of a deal to live with, but it was still a mistake.

And if you're going to bigger than stock tires, you're only going to compound your mistake.

You should get 3.73s.
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Old 09-04-2012, 08:41 PM   #17
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MTH I bought my Jeep new and my salesman talked me out of 3:73 gears....yes I made a mistake and wish I knew about this when I ordered....it was a 90/dollar option. Anyway, I am going to live with this mistake and getting the AEV 2.5 lift, Pintlers and the tires above and keeping my fingers crossed.
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Old 09-04-2012, 08:44 PM   #18
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Originally Posted by JeezAJeep
MTH I bought my Jeep new and my salesman talked me out of 3:73 gears....yes I made a mistake and wish I knew about this when I ordered....it was a 90/dollar option. Anyway, I am going to live with this mistake and getting the AEV 2.5 lift, Pintlers and the tires above and keeping my fingers crossed.
Don't feel bad--I've got 3.21 gears because back in 2009 when I bought my jeep I didn't have a clue. I love my jeep and I'm happy, but I'd be better off with 3.73s.
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Old 09-04-2012, 08:49 PM   #19
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I know the feeling...you have a similar set up I am looking at. My tire choice is the Nitto Trail Grapplers 295/717 ot Duratracs 285/70/17...what do you think with the 3:21?
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Old 09-04-2012, 08:53 PM   #20
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Originally Posted by JeezAJeep
I know the feeling...you have a similar set up I am looking at. My tire choice is the Nitto Trail Grapplers 295/717 ot Duratracs 285/70/17...what do you think with the 3:21?
Bah, you've got a 2012. I have 33x12.5R15s on a 2010. You'll be fine--not ideal--but fine.
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Old 09-04-2012, 09:21 PM   #21
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Your Wrangler is essentially how I want my to look. I love it. Hows your gas milage? Do you by chance know what your rpms are at 70 mph?

With the set up I have I get about 18.5 MPG on the highway and only about 16.5 MPG around town. I'm not sure what my RPMs are at 70 MPH. I'll pay attention to it next time and let you know. I also realize that if I drive at about 70 MPH the MPG gets better. However, most Colorado highways are 75 MPH speed limits which means most are crusing at about 80 MPH. When I'm at the 75-80MPH range the fuel mileage decreases but I don't think it's a gear ratio thing, I really think that since I installed 3.75" of lift up front and the 3" in back, the aerodynamics have made the gas mileage suffer at higher speeds.
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Old 09-04-2012, 09:59 PM   #22
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Ive pretty much decided Im getting the 5sp auto and the 3.21 gearing. I know the general consensus is "3.73's at the least" but I drive 90% highway if not more for 60-80 miles daily. That being said, the 3.73's just take away too much top end and run at too high of rpms.

However, Im definitely going to put on a 2.5 inch Teraflex leveling kit and 33's maybe even 35's for mostly aesthetic purposes.

Then of course I read a new bit of info. I read that the bigger tires with the higher 3.73 gearing "evens everything out" so its like a stock wrangler with the 3.21's? Im a little confused on that since rpms relate to the motor. I could see several contributing varibles of the 3.21's not being enough gear to sufficiently roll the 33's but I figured 285 hp could handle that.

And just so yall know, I dont plan on rock crawling or off roading etc. A Wrangler with the 3.21 gearing im sure will more than suffice for what I do outside of DDing.

I appreciate yalls responses and help. Hope yall have a good day.
do yourself a favor and go 3.37's. Your not losing anything. Hell we run 4:10's and 37's. the new motor does just fine
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Old 09-04-2012, 11:38 PM   #23
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I drove one today with the 255/75/17's and 3.21 today. I noticed a huge difference versus the 3.73 and the same wheels. I also noticed while on the highway, if I were to pass somebody i'd really have to put the pedal almost to the floor. I think I may have to go with the 3.73s and hope for the best. I know ill be putting 33's and a lift on it and worst case I think i'll lose 1-2 mpg which wont ruin my life or anything. But i'll keep yall updated.

Hell I may just buy a Prious
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Old 09-04-2012, 11:39 PM   #24
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dont ever buy a Jeep and worry about MPG. It will always go down
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Old 09-05-2012, 09:25 AM   #25
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I agree with Chris and CDJ, if you haven't already bought it, make sure you get the 3.73 gears. My jeep was bought off the lot before I knew much about them. It just came with the 3.21 gears. I can live with it for now. I'm not concerned with the MPG, I would like to have a little more acceleration though. I may end up changing the gearing in the future, but that's an expensive mod to me.

I think that if you get the towing package, the 3.73 gears are part of it.
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Old 09-05-2012, 02:20 PM   #26
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Just called AEV direct and they said"no problem 3:21 on a 2012 auto running 35's" Amazing. I need to drive one.
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Old 09-05-2012, 02:38 PM   #27
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Ive pretty much decided Im getting the 5sp auto and the 3.21 gearing. I know the general consensus is "3.73's at the least" but I drive 90% highway if not more for 60-80 miles daily. That being said, the 3.73's just take away too much top end and run at too high of rpms.

However, Im definitely going to put on a 2.5 inch Teraflex leveling kit and 33's maybe even 35's for mostly aesthetic purposes.

Then of course I read a new bit of info. I read that the bigger tires with the higher 3.73 gearing "evens everything out" so its like a stock wrangler with the 3.21's? Im a little confused on that since rpms relate to the motor. I could see several contributing varibles of the 3.21's not being enough gear to sufficiently roll the 33's but I figured 285 hp could handle that.

And just so yall know, I dont plan on rock crawling or off roading etc. A Wrangler with the 3.21 gearing im sure will more than suffice for what I do outside of DDing.

I appreciate yalls responses and help. Hope yall have a good day.
Larger tires need less revolutions per mile, changing the RPMs required for a given speed and gear. This website has a calculator that will show you your equivalent gearing at different tire sizes: DML Tire and Wheel Calculator
I believe that when I last checked stepping up from a 32 to a 35" tire changed the 3.73 ratio to 3.42.

I'm not sure where you heard about 3.73s running at too high of RPMs. Have you test drove them? I have a 2012 with 3.73s, we took a road trip out to the desert this weekend and cruised at 65-75 easy. The trip computer was reporting a little over 19mpgs; at least, that is, until we got to the desert and took it off road. A day in the sand and dirt took us back down to 15mpgs.
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Old 09-05-2012, 03:23 PM   #28
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Like was stated before, order the 3:73. I did not now I guess I am stuck with getting a 2.5 lift, 33's which will not fill the wheel well.
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Old 09-05-2012, 04:05 PM   #29
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I'm running 33's with 3.21's & an auto tranny in my '12, and for a DD these are definitely the biggest wheels I would run. 35's would be too heavy without a re-gear, in my opinion, and I'm not a speed demon by any stretch of the imagination.
X2. My KM2s dial in at 33.9". I want 35s but will not do them until I can afford a re-gear. (which I'll do anyway)
One other thing to remember- these charts are at 70 MPH. You should take into account driving at lower speeds. 35-45 is brutal with bigger tires. The Jeep tranny stock already drops into 4th gear at a really low RPM at these speeds- once you upsize your tires it's worse. I drive mostly city- and I currently drop into 4th gear right around 35 MPH- at 1200 RPMs. Way too low- all your torque disappears. So you either suffer with the engine feeling like a tank or you have to mash the gas to get the tranny to downshift. Yes- I can do it manually- but I didn't buy a manual for a reason.
I'll be the first to admit I am probably over-sensitive to this-there are people happy with 35s and 3.21s. However I will re-gear to 4.10s even with my current tire size. Yes- its liveable/not that bad- but I'd rather have "great".
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Old 09-05-2012, 05:03 PM   #30
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I went from stock on my 12 Rubi COD unlimited to a 2.5 inch Teraflex lift and 35x12.5x17 tires. I noticed hardly any power loss and only about a half mile to the gallon drop in fuel economy. I have a 5 speed auto with 373 gears.

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