JKOwners Forum banner

'12 Regear thread

4K views 25 replies 11 participants last post by  highoctane 
#1 ·
Merry Christmas Eve yall.

this thread is solely for all '12 JK/JKUs that have already been regeared, if possible. Any advice that can be given will be extremely helpful to those looking for guidance. Me personally, I will be regearing my JKU with 315/70/17 Duratracs TWICE! Why? So I can help give feedback to all the other Jeepers out there. Sounds stupid right?! Parts and labor are free or next to nothing so I thought it would be a good write up to get some real world numbers. First will be 4.88s running the 35's and swapping to a set of 37's. Then ill break it down and do 5.13 with both sizes.

Ive seen a few on here that have done 4.56. Whatcha think?

Yall have a safe holiday weekend and enjoy time with the fam.
:beer::beer::beer:
 
#2 ·
Is 4.88 the norm with 35s? Are you auto or manual?
 
#4 ·
With the different gearing on the '12s, 5.13s would be too low for anything much below a 40 inch tire. If you do the math, you can go a size or two higher on gears with the '12s and be good.

For instance, 35s with either tranny would be decent with 4.10s and geared fairly low with 4.56s turning aroundd 2700 rpm at 70 mps. 4.88s and 35s are turning a tick over 2900 at 70 on my '12 with an auto.

Honestly, I kind of wish I wouldn't have gone so low on mine. I have plans to go to 37s, but am on 35s now as I took the tires and wheels off my '09 that I traded in. I also pull trailers and even pull an teardrop offroad on occasion so wanted the lower gearing. However, with the power of the 3.6, 4.56s would have most likely been plenty of power even with the 37s and given better highway manners. Also, the first gear on the auto is much lower than the old 4 speed which also really helps with higher gears.

This has me curious though. My '09 Rubi with the 4:1 t case and my '12 with the 2.72: tcase feel from my butt-meter to have very similar crawl ratios. I'm going to have to figure out the math...
 
#6 ·
Ok, for kicks.

'07-'11 First gear automatic ratio of 2.84:1
'12 First gear automatic ratio of 3.59:1

'07-'11 Rubicon with 4:1 t-case - 4.10 gears has crawl ratio of 46.57 / 4.88 gears has crawl ratio of 55.43.

'07-'11 non Rubi with 2.72:1 t-case - 4.10 gears has crawl ratio of 31.67 / 4.88 gears has crawl ratio of 37.69

'12 Rubicon with 4:1 t-case - 4.10 gears has crawl ratio of 58.87 / 4.88 gears has crawl ratio of 70.07.

'12 non Rubi with 2.72:1 t-case - 4.10 gears has crawl ratio 40.03 / 4.88 gears has crawl ratio of 47.65.

Comparing this, on the low end, the '12s don't require near as deep gears. On the highway, the auto also has lower overdrive, comparable to the manual (the manual tranny OD was actually raised for '12 slightly), so higher gears can be used there as well.

I think the norm for '12s will be much higher gears that in previous JKs.
 
#16 ·
Good to know. Good thing that I haven't ordered any parts yet. ,iChat do comparison on 4.56 versus 4.88 with 35s and then info with 4.88 & 37s. Looks like Craftsman took a shit in my living room floor with all the new tools. Now, time to plan the next steps!
 
#24 ·
Ok...we have to retract our statement about the 4.56 gears...apparently there was something wrong with a batch of gears...so according to our supplier the 4.56 is out of production for some reason. We apparently got the last 4.56 set our guys had for the 2012 install in Nov...sorry guys, still good in all other gear ratios: 4.10, 4.88, 5.13, 5.38(44 only) :beer:
 
#25 · (Edited)
This question was asked already in the thread but I didn't see a direct answer to it. To run 35's, do I necessarily have to re-gear my JKU Sport 6 speed? I don't think I should make the step all the way up to 4.88 but would running 35's warrant that in any way? Just a new Jeeper kinda lost in the situation :shy:
 
#26 ·
So the guy who just posted says he's at 2700 rpm @ 70 mph with 5.13 and 37s. That's exactly what my '08 is at. I thought the OD ratio of the new auto isn't far off the 6th gear ratio of the manual, and i don't think they changed the ratios in the manual. While gears as low as 5.13 may not be needed on the highway to maintain speed, I would think it would help bring the crawl ratio back down once bigger tires are added. In an auto it may not be as important since you have the torque multiplication of the torque converter, but a manual I would think rehearing wouldn't be much different from '07-11 JKs.


Sent from my iPhone 4 using Tapatalk
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top