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So, I recently bought a 2015 Jeep Wrangler Sport Unlimited with a 3.21 gear ratio (should have done more research). The Jeep came stock with 29's with a 16inch rim. I want to go with 33's on the stock rim, but have read mixed opinions about the tire size on the 3.21 gear ratio. Has anyone been in my situation and went to 33's if so how is it going with the new tires with performance?

Thanks for your time.
 

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There will be lots of opinions. Lots of people run 33’s and 35’s with 3.21’s and their world hasn’t ended. You’ll have to give it more gas but you’ll get there.
 

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I had 3.21's and auto in my 2013 sport unlimited and ran 33's with no issues.

 

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about 20,000 miles. 285/75-17 on 17x8.5 rims with 4.5" backspacing
 

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So, I recently bought a 2015 Jeep Wrangler Sport Unlimited with a 3.21 gear ratio (should have done more research). The Jeep came stock with 29's with a 16inch rim. I want to go with 33's on the stock rim, but have read mixed opinions about the tire size on the 3.21 gear ratio. Has anyone been in my situation and went to 33's if so how is it going with the new tires with performance?

Thanks for your time.
I'm running 35's with 3.21 gears on my 2015 3.6. It's not going to win any street races, but not a pooch at all! It feels like a sports car compared to my 2008 Rubicon with 33's!
20200318_150126.jpg
 

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I had 3.21's and auto in my 2013 sport unlimited and ran 33's with no issues.


I too ran "33s" on my 2013 Auto JKU for a probably 3 1/2 years, driving in the mountains for 2 years with the 3.21 gears.

On flat ground it was fine.
On the highway into a headwind it would often kick down into 4th, and sometimes into 3rd at 70-75mph.
In the mountains it would OFTEN kick into 4th on the slightest inclines, 3rd on moderate inclines, and even into 2nd gear which was VERY annoying, and dangerous if the roads were slightly wet/damp/snow covered.
Passing would require planning, and being in the 4th or usually 3rd gear.

Upgraded to 4.56 gears.
Flat ground is the same, fine.
Highways, it RARELY goes into 4th. On modest inclines it will usually stay in 5th.
Have only kicked down into 3rd once or twice on steep climbs, with a strong headwind, b/c I insist on trying to cruise uphill at 70+mph. Has never kicked into 2nd at 55-60mph with the 4.56 gears.

Cruises at around 3000-3100 rpm on the highways all day long. No issues at all. Passing is just a matter of a bit more throttle :)

Can you live with 3.21 and 33s? If on flat ground definitely. If on the highway with climbing I would definitely recommend 4.56. If you tow or go off roading, definitely would recommend regearing.
 

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We had 32" tires (stock size) with the stock 3.73 gears. It was drivable, but it really was geared too tall. It made it harder to drive, on road and off, and it was on the slow side by our standards.
Part of it depends on your standards, what you expect out of it as far as performance. As mentioned, many people run 35's with 3.21 gears and I assume they are happy with it. I know I would not be, but they are.
Other aspects are where you live, how you drive, and whether you have a manual or automatic. The auto hides some of the overgear because it does all the downshifting for you. But the other side of an auto is if you are overgeared the torque convertor may not lock up enough.
 

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Had 3.21's with manual trans running 245/75/17 (2016 JKU) and thought it was absolutely hideous! Totally hated that combo as I live in hill country and was constantly shifting for the slightest grade. Before I had it regeared put on some 285/75/17's (with spacers) and it was flat out pathetic. I knew it was getting regeared to 4.56 in a few days so it wasn't a big deal. Can't imagine driving it around with 3.21's and 34's! I guess it doesn't bother some folks but it darn sure bothered me as my Jeep was a total slug imo. Love driving it now with the 4.56's and was worth every penny doing the regear.
 

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I upgraded to 285/70r17(32.7in) KO2s on a 2012 JKU Rubicon that has stock 4.10 gearing and auto trans. Performance is fine in all terrains. I couldn't imagine running that size tire on a 3.21 ratio.
 

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The good thing is regearing isn't that expensive in the scheme of Jeep ownership. And while regearing it is a great opportunity to make other improvements, like adding TrueTrac LSD's or lockers.
Your best option is to figure out what size tires you want, try them, and if you aren't happy with the lack of performance at that point just regear.
The reality of bigger tires is, bigger tires will make your Jeep slower. It changes the gearing, makes it taller, you can't avoid that. Will you be OK with the decrease in performance and the way it drives? Hard to say. I know I would not be. But some are OK with the decrease in performance, with the way it drives over geared like that.
 

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Most people go from stock 32” to 33” on 3.21. I will be interest to see how you feel after jumping from 29” to 33”. Might feel worse to you than others.


Sent from my iPhone using Tapatalk
 

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I wouldn't, but I am in the minority I'm sure. 33" on 3.21 WITH the automatic, not ideal really. As said, it can be done. I would be more concerned with the longevity of the Auto trans.

Big question: Is this your daily driver?

33" tires on heavy steel wheels, 3.21 and an auto will no doubt put additional strain on that auto trans, regardless of a speedo and shift point recalibration. I may take some heat for this, as people who have already done it like to chime in with "I have never had a problem in 80,000 miles!" etc, but the facts are the facts in the long term.

Just make sure you ask yourself: What is the point of this? If it is for looks alone, remember, it only makes your Jeep slower, wear parts faster, and more expensive to run...

Unless you are going to MOAB this summer, your Jeep will get you anywhere on 29" tires.

All that being said - do what makes you happy! :)
 

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So, I recently bought a 2015 Jeep Wrangler Sport Unlimited with a 3.21 gear ratio (should have done more research). The Jeep came stock with 29's with a 16inch rim. I want to go with 33's on the stock rim, but have read mixed opinions about the tire size on the 3.21 gear ratio. Has anyone been in my situation and went to 33's if so how is it going with the new tires with performance?

Thanks for your time.
I ran my JK for a while with 315's and 3.21's, till I found a good deal on a set of crate axles.
Put them on and drive your Jeep, if you feel the need to change the gears down the road, just save up a few bucks and get it done.
Some members here will have you believe your vehicle won't run without a gear change, that's just not the case.
There are more folks who do things to their Jeeps for looks than there are hard core wheelers.
You will be fine.
 

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Most people go from stock 32” to 33” on 3.21. I will be interest to see how you feel after jumping from 29” to 33”. Might feel worse to you than others.


Sent from my iPhone using Tapatalk
mine was a basic sport with the baby tires.
 

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285/70/17 JLUR take offs on my 3.21 sport, no issues at all. needs a little more gas at times but ive hardly noticed an issue in 2 months/ 2000~ miles
 

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It's not the best... But you'll survive until you decide you are happy with it, or you want to upgrade.
 
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