OverlanderJK
Resident Smartass
I don't think anyone makes a 5.38 for a D30 anymore. 5.13 is the deepest I think.
Do Yourself a Favor - Regear Your 2012-Up JK!!
- Thread starter wayoflife
- Start date
I don't think anyone makes a 5.38 for a D30 anymore. 5.13 is the deepest I think.
You don't need to worry about your motor, it's the size of the pinion in a Dana 30. Going with a 4.88 will be a good choice.
Sorry, I'd have to disagree, a 5.13 pinion in a Dana 30 is really really small and will be a weak point. 4.88 is the highest I would go especially if you lock up your front.
AcB-jk
New member
OhhSeven
New member
I think you can get them from east coast gear supply. Not that you'd want to.
AcB-jk
New member
4.88 gears should hopefully run the 35's no problem. Anything else I would need to swap the gears besides the gears and an overhaul kit?
AncientTrail
New member
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:
Do you not in this case measure from the middle of the axle to ground x2 to get actual tire size which would be lower than 37?
This stuff is confusing LOL!
:beer:
Measuring from the center of the wheel to the ground x2 is just the easier way to explain what you need to do. If you measure from the ground to the edge of the tire where the sidewall makes a 90 deg turn to become the tread, you will get the same number needed or at least close enough and without having to do math.
AncientTrail
New member
So wouldn't you enter a lower number than 37 in the above chart, the actual tire size under load? My 35's measure less than 35 from center of wheel to the ground.
My Pro Cal instructions say to -24 from the measured tire size number and set pins according to that info. Example: my measured tire size is 16.5 x2= 33. Pro Cal says -24 from that number and set pins accordingly. Would I not enter the 33 as the tire size in the above gear chart to get my crawl ratio?
Thanks for taking the time to help :beer:
blackbettie
New member
I completely agree with a re-gear in the case of 35's or larger on both motors. I decided to run 4.56s with my 35s. I could have/should have run 4.88s... 
but that's water under the bridge now. my question is anyone out there running 4.56s on 37's? How everything going, any axle seal problems or c gusset issues. Thinking of going 37in Nitto Trail Grapplers.
but that's water under the bridge now. my question is anyone out there running 4.56s on 37's? How everything going, any axle seal problems or c gusset issues. Thinking of going 37in Nitto Trail Grapplers.
kpig
Member
I did the same thing and regeared 4.56 with 35s. Now that I have toyo 37s which are pretty heavy (measuring 35.75"), I really wished I had done 5.13s. It's not really that bad on flat highway. I'm running about 2600 rpms at 70mph, but when I hit a small grade, the auto tranny wants to drop into 4th and even 3rd to maintain speed. Off road it's not terrible in 4lo with the 4:1 ratio. I will probably regear to 5.13 when I finally decide on swapping axles, but for now it's ok. I have EVO c gussets and Purejeep truss with no issues so far. Good luck.
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blackbettie
New member
Well that gives me some hope! So it's def looking like a C gusset swap is in order with 37s then... Thanks for the info!
ERAUGrad04
Caught the Bug
I just had to chime in on this thread now that I made the jump to 5.13s. HOLY COW what a difference! I only have about 400mi on the so far, but the difference is incredible! Driving back to the Bay Area today from ORE in LA, I was shocked at how little down shifting was occurring and how happy the engine was being more in its power band. For nearly the entire drive home, I kept the speed at 60mph (due to gear break in), but it basically parked itself in Overdrive and stayed there. Also, the transmission seems to be much happier too. The shift points are actually lower now with the new gears. Before, with the 4.10s, it would wind up a gear before shifting into the next. Now, it's happy as a pig in mud keeping the shift points below 3,000rpm and there is no lugging.
Thanks again as this thread was one of the "nudges" that helped push me to the 5.13s. :beer::beer::beer:
Thanks again as this thread was one of the "nudges" that helped push me to the 5.13s. :beer::beer::beer:
t8er
New member
So my jeep is getting regeared over easter. I have 35's but 37's will go on this summer I was debating 4.88 since it'll still be highway driven and I go to FL every year. I'm still torn on bumping to 5.13. It's also getting sleeves and gussets on the front axle. Anyone running a 3.6 6 speed with these gears that can give me real world performance? I'm also in Denver.
Being that you have a 6-speed, you could definitely get away with 4.88's but, being that you're in Denver, I personally would still go with 5.13's IF you are for sure thinking about upgrading to 37's. The higher ratio will help a lot on the mountain passes and really, while you will run on the higher side of the RPM range on the highway, it's really not that much higher. But, that's just my opinion.
Rancho
Caught the Bug
Spot on. I love my 5.38's and 37's (or taller) for going over Vail Pass, Rabbit Ears etc.
:beer:
:beer:
AZMyke
New member
What do you think?
I have a 2015 JKU and re-geared to 4.56 when I thought I'd go with another set of 35s ... instead I went with 37s which will measure out to 36.8. I know this won't be a rock-crawler combination, but at 70-mph the gearing chart puts the RPMs at 2330. It's a DD and will see the trails on a recreation basis using moderate trails and in 4Lo I should be alright? I've trussed the front and rear and plan to go bigger on the brakes. My thoughts are ... if this doesn't work out so great I'' regear in about a year or so. Thanks for any thoughts provided.
I have a 2015 JKU and re-geared to 4.56 when I thought I'd go with another set of 35s ... instead I went with 37s which will measure out to 36.8. I know this won't be a rock-crawler combination, but at 70-mph the gearing chart puts the RPMs at 2330. It's a DD and will see the trails on a recreation basis using moderate trails and in 4Lo I should be alright? I've trussed the front and rear and plan to go bigger on the brakes. My thoughts are ... if this doesn't work out so great I'' regear in about a year or so. Thanks for any thoughts provided.
OverlanderJK
Resident Smartass
First your tires won't measure to 36.8 and second, you have trusses, you will be fine.
ERAUGrad04
Caught the Bug
5.13s are ideal for 37s with the 3.6. That said, if it were me, I'd probably drive the 4.56s and see how it is. I was originally using 4.10s with 37s and it was bearable, but not ideal. I later upgraded to 5.13s and it was well worth it.
I would think 4.56s and 37s is very similar to 4.10s with 35s, which is very doable. At least I thought so anyway.