Do Yourself a Favor - Regear Your 2012-Up JK!!

[wayoflife]

When we bought our 2012 Jeep JK Wrangler, we had always planned to upgrade it's axles to a set of Dynatrac ProRock 60's. Of course, being that money doesn't grow on trees, we decided to use the time until we could afford the upgrade to extensively test just how well a set of 37" tires would do with the new 3.6L Pentastar motor running factory 4.10 gears. For almost 2 years, we took our Jeep just about everywhere we could, driving it to and from the trail, on the highway and around town, up and over mountains, hard and fast through the Mojave Desert, up and over steep ledges in Moab and, crawling it over big rocks on trails like the Rubicon. And, after racking up over 45,000 miles on the odometer, what I can tell you is this... it can be done and it does work surprisingly, okay. For someone who's never driven a re-geared equivalent, they may not even know what they're missing.

Having said all that, recent circumstances forced us to upgrade our front axle sooner than we had planned for and, while we were at it, decided to just bite the bullet, take advantage of Off Road Evolution's $999 special and have our Jeep re-geared with a set of 5.13's at the same time. After testing them out extensively on the 2013 JK-Experience, all I can say is - why in the hell didn't we do this sooner!!

While the 3.6L motor has a good amount of power and will do a decent job of compensating for larger tires, it simply can't make up enough of a difference especially in situations like on long or steep hill climbs. Here, your transmission will try to help make up the difference by dropping gears and running your RPM's up close to 6 grand just to keep you moving. Of course, this will cause your engine and transmission to run really hot and in some cases, cause your Jeep to go into limp mode - ask me how I know. With a set of 5.13's, this will no longer be an issue as you'll have plenty of power to do the same job in a higher gear and running at a lower RPM. Of course, this is to say nothing about the fact that on the rocks, a set of 5.13's will also significantly improve your crawl ratio - running 37" tires on 4:10 gears, you'll go from a 3.36:1 to a full 4.21:1! Of course, for those would might complain about the increase in RPM at highway speeds, what I can tell you is that it's really insignificant. In fact, the difference you'll see when compared to a stock Rubicon running 32" tires and 4.10 gears is only about 200 RPM as you can see in the calculators below:

2012 Jeep JK Wrangler Rubicon - 32" Tires w/4.10 Gears

2012 Jeep JK Wrangler Rubicon - 37" Tires w/5.13 Gears

Trust me, if you're planning on running 35", 37" or bigger tires on your 2012-Up JK, you really will be doing yourself a BIG favor to get it re-geared at the same time. If you live in the SoCal area, be sure to take advantage of Off Road Evolutions $999 special too as it really is a deal that is hard to beat :yup:

 

[Sithwindu]

So the pr 44 and bolt ins killed it on jkx?! Making me want to regear now heh ill have to give 5.13's a try

 

[wayoflife]

So the pr 44 and bolt ins killed it on jkx?! Making me want to regear now heh ill have to give 5.13's a try

Yep, running 37" Nitto Trail Grapplers with 5.13 gears was a winning combination! It's definitely what I would recommend even on a 2012-up JK.

 

[UnIuckychucky]

Few things

Changing your Ring and pinion is helpful but the higher you go the weaker it becomes. You are able to run 37s on a Dana 30 as long as you don't go higher than 4:56 gear ratio.
also are you going to keep running 37s for a couple of years because you now have a pro rock 44 and your getting a rear 60 from Moby. Seems kinda pointless to have 2 jeeps that are both on 40s and exactly the same.

 

[Sithwindu]

I'm runnin 35 mud grapplers on my 2013 jku, went to a mudfest this past sat and felt I could really use a bit more power 3.73 isn't giving me the power this engine wants to output!!

 

[wayoflife]

Changing your Ring and pinion is helpful but the higher you go the weaker it becomes. You are able to run 37s on a Dana 30 as long as you don't go higher than 4:56 gear ratio.

:cheesy: Believe me, you're talking to a guy who knows this first hand. In a Dana 44, I would not recommend running anything higher than a 5.13 even if a higher ratio like a 5.38 will provide better performance results. In a Dana 30, I typically don't recommend anything higher than a 4.88.

also are you going to keep running 37s for a couple of years because you now have a pro rock 44 and your getting a rear 60 from Moby. Seems kinda pointless to have 2 jeeps that are both on 40s and exactly the same.

Well, that's kind of become the plan now even though I would prefer to have 2 Jeeps running 40's

 

[kRay.JK]

But what about a 3.8L motor :grayno: - lost cause to have the best of both worlds?

 

[NFRs2000NYC]

You don't think 5.13s are a bit too high for a 2014 with 35 (34" effective?) I'll be getting mine with 4.10s, and figured if it's not enough, I'll bump it to 4.56, but Im afraid 5.13 would be a bit too high...unless I misunderstood your post and you weren't specifically telling people to get 5.13s but just to regear?

 

[pvanweelden]

But what about a 3.8L motor :grayno: - lost cause to have the best of both worlds?

Regearing will also help the 3.8 (will help any motor)

Anytime you increase wheel size, regearing at the appropriate ratio, will maintain stock performance.

But it is not cheap, so plan accordingly, and if you plan on sticking with a certain tire size, definately regear.

 

[wayoflife]

But what about a 3.8L motor :grayno: - lost cause to have the best of both worlds?

Depends on what size tire you are wanting to run. With an old 3.8L and 37" tires, the ratio you would want to run is 5.38 but, that will leave your pinion really small and a weak point. Because of this, I wouldn't recommend that you run anything more than a 5.13 on that setup. Trust me, I've run both on my 2007 and speak from experience here.

You don't think 5.13s are a bit too high for a 2014 with 35 (34" effective?) I'll be getting mine with 4.10s, and figured if it's not enough, I'll bump it to 4.56, but Im afraid 5.13 would be a bit too high...unless I misunderstood your post and you weren't specifically telling people to get 5.13s but just to regear?

My only point was to recommend that you regear. As I had stated multiple times, 5.13's is what I would recommend with 37's but would probably go with 4.88 if I were running 35's.

 

[cozdude]

thanks for the little info write up Eddie! you have me thinking about how i need to regear my '11 finally and not save for a place to live when my parents kick me out. after the regear im sure they would lol

 

[wayoflife]

Regearing will also help the 3.8 (will help any motor)

Anytime you increase wheel size, regearing at the appropriate ratio, will maintain stock performance.

But it is not cheap, so plan accordingly, and if you plan on sticking with a certain tire size, definately regear.

For sure, on a 3.8L motor, re-gearing was always a must in my book. My point to writing this article was more to inform folks with 2012-up JK's which have the new and more powerful 3.6L motor of the benefits of re-gearing.

thanks for the little info write up Eddie! you have me thinking about how i need to regear my '11 finally and not save for a place to live when my parents kick me out. after the regear im sure they would lol

LOL!! You would definitely see the benefits of new gears.

 

[NFRs2000NYC]

Quick question, when you use your gear chart, do you input tire size by "model" ie a 35 or actual size mounted on the jeep ie 34.2?

When I put mine in, it's showing 2900 rpms at 75...you think that's livable?

 

[NFRs2000NYC]

One more thing, not that I care too much, but out of curiosity, how much did your MPG suffer from the 37s and the gears over stock? Im not looking at actual mpg like 15 or 19, Im interested in the loss difference. Did you lose like 5 mpg or like 1?

 

[hothondaguy]

thanks for this insight, i eventually will be running 35's all the time and will probably be looking towards 4.88's. the whole gearing stuff is a bit confusing to me...but this helps out alot.

 

[DynoMax Exhaust]

I went 5.38's in my Dynatrac 60's.... more because I thought I was going to get a 3.8 equipped JK.
I have a 2013, on 37's and I am happy with the set up. I am already eyeballing 40's. :brows:

 

[wayoflife]

Quick question, when you use your gear chart, do you input tire size by "model" ie a 35 or actual size mounted on the jeep ie 34.2?

When I put mine in, it's showing 2900 rpms at 75...you think that's livable?

View attachment 49576

The only time I ever refer to "actual" tire size is when calibrating my speedometer. For the purposes of all other discussion, I always refer to what is printed on the sidewall. The numbers you see on the chart are approximate and based on an apples to apples comparison. In other words, it would be unfair to compare a tire that has 32" written on the sidewall with an actual measurement of a larger tire. Does that make sense?

2900 RPM at 75 MPH is totally livable in my book. You need to remember, with a bigger built up Jeep, it's always a good idea to gear in a manner that will help compensate for things like weight, rotating mass and wind resistance.

One more thing, not that I care too much, but out of curiosity, how much did your MPG suffer from the 37s and the gears over stock? Im not looking at actual mpg like 15 or 19, Im interested in the loss difference. Did you lose like 5 mpg or like 1?

Not much, maybe like 1-2 MPG... maybe not even that much. It's hard to say because I'm not the most conservative driver.

 

[wayoflife]

thanks for this insight, i eventually will be running 35's all the time and will probably be looking towards 4.88's. the whole gearing stuff is a bit confusing to me...but this helps out alot.

Well, let me know if you have any other questions.

I went 5.38's in my Dynatrac 60's.... more because I thought I was going to get a 3.8 equipped JK.
I have a 2013, on 37's and I am happy with the set up. I am already eyeballing 40's. :brows:

I'm pretty sure that's what Mel is running in his new 2013 EVOLander. It did really well on the JKX but, I'm betting he's got his eyes on a set of 40's too

 

[hothondaguy]

does it matter much if you have an Auto vs Manual? we have 2013 with auto. currently primarily running the stock wheels and tires, but i have a set of pro comp 315's and moab wheels that i picked up on a forum for cheap that we use for excursions. i will eventually run 35's but gotta save some money first. and the 999 special is that the installed out the door pricing?

 

[wayoflife]

does it matter much if you have an Auto vs Manual? we have 2013 with auto. currently primarily running the stock wheels and tires, but i have a set of pro comp 315's and moab wheels that i picked up on a forum for cheap that we use for excursions. i will eventually run 35's but gotta save some money first. and the 999 special is that the installed out the door pricing?

It does make a difference and, in case it was missed by me, we have an auto. If you have a manual, you may not need as high of a ratio but, you would still want to regear. Chris at Off Road Evolution has a 2013 with a manual, 4.10 gears and running 37's and was having a hell of a time trying to keep up with us on the JK-Experience.