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Old 10-27-2011, 02:23 PM   #1
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Gearing for a 2012 MANUAL

I’ve done a pretty good bit of research on this and other forums regarding gearing as it pertains to bigger tires, gas mileage, powerband, etc. However, most of the info I've found for the 2012, specifically, has been kinda sporadic.

Given its flatter power curve and added hp, the 3.6 Pentastar engine would seem to alter a lot of what I’ve read about gearing in the earlier model years. Maybe a little, maybe a lot. I don’t really know.
I’ve looked at the power curve charts, although they seem to me to be a fairly broad generalization, considering all the variables that make one Jeep so different from the next.
I’m going to be running 35’s on a 2012 MANUAL JKU.
I won’t be rock climbing, or trying to summit the north face of Eiger. I will not be towing anything.
I will do some recreational off-roading…probably on woods trails. I will get into some mud and snow. Nothing too hardcore.
I’ll also do a good bit of long-distance freeway/turnpike driving, so keeping mpg loss to a minimum is desireable.
Taking all of this into consideration, I’m looking at upgrading my gearing to 4.88. Again, that comes from looking at posts that deal mostly with other year models, and mostly with automatic transmissions. I skipped the 4.56 because I’ve read that they are less available and more expensive. Correct me if I'm wrong.

Would I be happier with 5.13’s?
I understand that I’ll be running at higher rpm’s at freeway speeds, either way. As long as it’s not gonna overly abuse the engine, trans, etc I’m okay with that.
My plan is to find a mechanic/shop that I can trust to do the job right, then order the parts through them.
I also intend to buy everything new. Front/rear gears, bearings, pinion nuts, shims, etc. Not sure exactly what I’ll need…that’s one of my questions to you, the knowledgeable. Is it called a master kit?
Not sure where I got that from…
I do remember a post from earlier this year in which oilwell stated it was quite likely that the rear pinion bearing and some other parts were liable to be trashed during the gear change, and that it would be better to spend a little extra $$ and get the job done right, as opposed to skimping and having something fail post installation.
My philosophy as well.
To boil it all down, let me ask this:
What gearing would best optimize highway driveability, while still giving me decent gas mileage, based on my having the 3.6 with a manual transmission?
Like doing a handstand on a tightrope, I know.

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Old 10-27-2011, 02:45 PM   #2
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From spending time on here the 4.10's and 35's -- 6 speed -- is a great compo with the 2012.

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Old 10-27-2011, 02:47 PM   #3
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I have read the same- new pentastar with Rubi 4.10's should have no problem turning 35's, automatic or standard transmission.
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Old 10-27-2011, 02:50 PM   #4
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Thought I might be high w/the 4.88 choice. Kinda hard to extrapolate all the info for 3.8's into the Pentastar.

Anybody have ideas on mileage, highway rpm's?

Thanks for the info.
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Old 10-27-2011, 02:56 PM   #5
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I hear 4.10's are supposed to be really good with the new engine.

I'm assuming you have 3.73's....
Since you have 6 gears...you may still be OK. I say try it and find out before you spend $1500 on gear ratios.

Use this for RPM's....
http://www.grimmjeeper.com/gears.html
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Old 10-27-2011, 03:00 PM   #6
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Originally Posted by panthermark View Post
I hear 4.10's are supposed to be really good with the new engine.

I'm assuming you have 3.73's....
Since you have 6 gears...you may still be OK. I say try it and find out before you spend $1500 on gear ratios.

Use this for RPM's....
Gear Ratio Calculator
Good advice.

Yes, 3.73's. Decided on before my tire size, unfortunately.

Anyway, I thought 4.88's might be a bit much (kind of...I've been smacking it back and forth in my head like a tennis ball), but didn't expect it to be okay with 4.10's. In fact, I was a bit worried it might need the elusive 4.56's.

'Preciate the link.
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Old 10-27-2011, 03:05 PM   #7
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Originally Posted by panthermark View Post
Use this for RPM's....
Gear Ratio Calculator
Jesus. Didn't realize I'd need a master's from MIT to use this thing.

Thanks, though.
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Old 10-27-2011, 03:08 PM   #8
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I wouldn't do anything any differently than you would with a pre-'12 model. The 3.6 is actually weaker than the 3.8 at the extreme low end where you will be when leaving a stop light. If you had 4.10s from the factory I don't think I would suggest spending money to change them, but since you're out the money anyway I would still do 4.88s.
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Old 10-27-2011, 03:10 PM   #9
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It isn't too bad once you've done it a few times.

It is much easier with an auto because you can select Dodge NAG1 and it fills out the 1st set of number for you.

For #1 - your ratios are:
1 4.46
2 2.61
3 1.72
4 1.25
5 1.00
6 0.797

For #2
High = 1
Low = 2.72 (You don't need low unless you wanna know crawl speeds)

For #3
Ignore

For #4
I'm assuming 3.73....or 3.21....or put in what you want to play with.

For #5
Put in your tire size.

Calculate
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Old 10-27-2011, 03:12 PM   #10
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Originally Posted by oilwell1415 View Post
I wouldn't do anything any differently than you would with a pre-'12 model. The 3.6 is actually weaker than the 3.8 at the extreme low end where you will be when leaving a stop light. If you had 4.10s from the factory I don't think I would suggest spending money to change them, but since you're out the money anyway I would still do 4.88s.
You have a 2012 6 speed with 3.73's on 33's....how do you like it? I know that you are really big on torque...but with that said...and given the short first gear....is it "that bad". (And not compared to you diesel! )
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Old 10-27-2011, 03:14 PM   #11
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Thanks for the time saver, panther...

Kinda surprised me when I saw it. Thought it'd be like the tire size / speedo calculator.

Based on the chart, I'd be turning 2641 rpm @ 70 mph with 4.88's...only about 440 rpm over what my Liberty Renegade produces right now.

Interesting.
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Old 10-27-2011, 03:19 PM   #12
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Originally Posted by oilwell1415 View Post
I wouldn't do anything any differently than you would with a pre-'12 model. The 3.6 is actually weaker than the 3.8 at the extreme low end where you will be when leaving a stop light. If you had 4.10s from the factory I don't think I would suggest spending money to change them, but since you're out the money anyway I would still do 4.88s.
That's good to know. I do have kind've a heavy foot. And not a lot of patience. And a motorcycle that goes 0-60 in about 3 seconds.

What would be a good brand of gears to buy? I've read a lot of good things about Yukons, probably 'cause that's what a lot of Jeepers buy. Know next to nothing about others, though.

I'd rather have reliability and pay more...
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Old 10-27-2011, 03:23 PM   #13
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It isn't too bad once you've done it a few times.


For #2
High = 1
Low = 2.72 (You don't need low unless you wanna know crawl speeds)
I don't know if the OP has a Rubi or not, and maybe this is only an EU spec, but for the Rubi you should calculate Low = 4.00. Just to keep in it in mind.
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Old 10-27-2011, 03:24 PM   #14
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just posted similar 2 minutes after you

see thread 60 mph at 1500 rpm with 3.73
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Old 10-27-2011, 03:25 PM   #15
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I have a 2012 6 speed with the 3.21. I was thinking about going to the 4.10 to increase the towing capacity. I am really happy with the 3.21 on the road. Havn't gone off yet and haven't upgraded tires yet. Let us know how the new ratio works out.
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Old 10-27-2011, 03:33 PM   #16
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I don't have a diesel. ??

Just driving around it's OK. Offroad it's marginal, but better than it was. The day after we got it we took it out in the pasture to play and it wouldn't even idle across the pasture in 4H, I had to either use 4L in 2nd or 3rd gear just so it would drive around by itself. When we took it out a couple of weeks ago it had about 4k miles on it and was able to idle around in 1st gear fine unless I was going up a significant hill, but it was also a lot cooler that day than the previous time. I don't know if the improvement was the break in miles or the cooler air.

If I had 35s I think I would want more gear than 4.10. You are going up 6% in tire size, 30% in moment of inertia of the tires and 10% in gear ratio. Just to break even with all of that I think you would want to go to a 4.30 or 4.56 gear, but availability and cost are an issue with those. If it was a car, I would say it is best to compromise to the numerically lower gear, but with a 35" tire I would go the opposite way and make sure you can turn them.
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Old 10-27-2011, 03:33 PM   #17
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I don't know if the OP has a Rubi or not, and maybe this is only an EU spec, but for the Rubi you should calculate Low = 4.00. Just to keep in it in mind.
Yup....I know...
But yes, people should keep that in mind....
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Old 10-27-2011, 03:35 PM   #18
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I don't have a diesel. ??

Just driving around it's OK. Offroad it's marginal, but better than it was. The day after we got it we took it out in the pasture to play and it wouldn't even idle across the pasture in 4H, I had to either use 4L in 2nd or 3rd gear just so it would drive around by itself. When we took it out a couple of weeks ago it had about 4k miles on it and was able to idle around in 1st gear fine unless I was going up a significant hill, but it was also a lot cooler that day than the previous time. I don't know if the improvement was the break in miles or the cooler air.

If I had 35s I think I would want more gear than 4.10. You are going up 6% in tire size, 30% in moment of inertia of the tires and 10% in gear ratio. Just to break even with all of that I think you would want to go to a 4.30 or 4.56 gear, but availability and cost are an issue with those. If it was a car, I would say it is best to compromise to the numerically lower gear, but with a 35" tire I would go the opposite way and make sure you can turn them.

I know you talk about an older gasser pick-up truck (can't remember what year...)...but I thought your work/fleet truck was a diesel?
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Old 10-27-2011, 03:37 PM   #19
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Nope, no diesel for me.
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Old 10-27-2011, 03:41 PM   #20
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If I had 35s I think I would want more gear than 4.10. You are going up 6% in tire size, 30% in moment of inertia of the tires and 10% in gear ratio. Just to break even with all of that I think you would want to go to a 4.30 or 4.56 gear, but availability and cost are an issue with those. If it was a car, I would say it is best to compromise to the numerically lower gear, but with a 35" tire I would go the opposite way and make sure you can turn them.
So the 4.88's aren't too much, then. Okay. I've read a lot of posts (the majority, in fact) where folks who got 4.10's wished they'd gotten 4.56's, etc. (or 4.88's due to cost/availability).

What would I be looking at needing to do the whole regearing from the ground up? Obviously gears & bearings. What else? Rear pinion nuts...?

I'd like to at least be conversant about the topic before I start talking to mechanics.
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Old 10-27-2011, 03:45 PM   #21
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see thread 60 mph at 1500 rpm with 3.73
Use the link in post #5

If you have an auto from 2007-2011, use Dodge 42RLE. If you have a 2012 auto, use Dodge NAG1

If you have a manual, you can use the gears listed in the earlier post....the only difference is that 6th gear used to be 0.84 from 2007-2011.

Input your low transfer case as either 2.72 or 4 (if you have a Rubi).
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Old 10-27-2011, 04:21 PM   #22
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I have a 2012 6 speed with the 3.21. I was thinking about going to the 4.10 to increase the towing capacity. I am really happy with the 3.21 on the road. Havn't gone off yet and haven't upgraded tires yet. Let us know how the new ratio works out.



Once I get the Jeep, I'll post stuff for a bunch of installs: lift, bumpers, gears, side rails, etc.
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Old 10-27-2011, 09:23 PM   #23
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So the 4.88's aren't too much, then. Okay. I've read a lot of posts (the majority, in fact) where folks who got 4.10's wished they'd gotten 4.56's, etc. (or 4.88's due to cost/availability).

What would I be looking at needing to do the whole regearing from the ground up? Obviously gears & bearings. What else? Rear pinion nuts...?

I'd like to at least be conversant about the topic before I start talking to mechanics.
I think you will be disappointed if you go with 4.10s based on how mine drives with 3.73s and 33" tires

If you are starting with a new Jeep that has 3.73s you will need at a bare minimum the gear set, a shim set, a crush sleeve, a rear pinion bearing (probably a few of them by the time you're done) and a pinion nut for each axle.

If you do the job yourself you will also need the tools to remove and install bearings, a dial indicator with magnetic base, a dial type in-lbs torque wrench, a ft-lbs torque wrench, something to generate a helluva lot of torque with to crush the crush sleeve and some gear marking compound.

If you start with 3.21s add new carriers and carrier bearings to the list.

It seems like I'm forgetting something, but I think that's a decent list to start with.
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Old 10-27-2011, 11:55 PM   #24
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I have a 2012 and I am running 4.88s with 37s and a stick and it is almost identical to a stock Rubicon with 4.10s and 32s (I am off less than 100RPM at 70mph vs. a stock Rubi). I had an '07 with a stick, 37s and 5.13s and it was a good match. I have extensive JK experience and am professionally qualified to offer the following advice.

With the 3.6 and a stick, if I was running 35s, I would go 4.56. You just DO NOT NEED to overgear on these new drivetrains. 5.13s and 35s would be way, way too low in my opinion. I can tell you I wouldn't be happy with 5.13s and 37s on this Jeep, it would have been too low. If I had an auto, I would do 35s without regearing because of the new tranny's ratio spread.

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Old 10-28-2011, 12:14 AM   #25
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Originally Posted by oilwell1415 View Post
I think you will be disappointed if you go with 4.10s based on how mine drives with 3.73s and 33" tires

If you are starting with a new Jeep that has 3.73s you will need at a bare minimum the gear set, a shim set, a crush sleeve, a rear pinion bearing (probably a few of them by the time you're done) and a pinion nut for each axle.

If you do the job yourself you will also need the tools to remove and install bearings, a dial indicator with magnetic base, a dial type in-lbs torque wrench, a ft-lbs torque wrench, something to generate a helluva lot of torque with to crush the crush sleeve and some gear marking compound.

If you start with 3.21s add new carriers and carrier bearings to the list.

It seems like I'm forgetting something, but I think that's a decent list to start with.
Hey dude, thanks for the information. It's invaluable. I found out earlier today that my Jeep was just inspected and is staged for shipping.
'Bout goddamn time.

I'll probably drive it for a little while with the 3.73's, get a feel for it before I go for the gear change. Plus, I've literally got a garage full of stuff to start installing when it gets here.

If it seems like a dog @ 3.73, I'm pretty sure I'll go with the 4.88's. Last thing I wanna do is spend the $$ to change gears and not be satisfied with the result.

Again, I appreciate the help.
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Old 10-28-2011, 12:31 AM   #26
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I have a 2012 and I am running 4.88s with 37s and a stick and it is almost identical to a stock Rubicon with 4.10s and 32s (I am off less than 100RPM at 70mph vs. a stock Rubi). I had an '07 with a stick, 37s and 5.13s and it was a good match. I have extensive JK experience and am professionally qualified to offer the following advice.

With the 3.6 and a stick, if I was running 35s, I would go 4.56. You just DO NOT NEED to overgear on these new drivetrains. 5.13s and 35s would be way, way too low in my opinion. I can tell you I wouldn't be happy with 5.13s and 37s on this Jeep, it would have been too low. If I had an auto, I would do 35s without regearing because of the new tranny's ratio spread.
--Sean
I hear you, sean. I'm not planning on the 5.13's. But I think – at least at this point – the 4.88's are a better way to go than the 4.56's, which are hard to find, and more expensive than the 88's. And I think 4.10's would not give me the oomph I want on long distance road trips through the mountains of PA, VA, and NC, where I travel often. I've run the #'s through a couple of different rpm/road speed calculators, and the difference between the 56's and 88's is not especially large (2268 rpm @ 65mph in 6th, as opposed to 2427 @ 65 in 6th).

Anyway, I've only just started gathering info on the whole deal. Any and all input will be put to use. I still have a lot of research to do.

Thanks for the advice.
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Old 10-28-2011, 01:10 AM   #27
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Those RPMs are at 65, but they are obviously higher if you are normally driving at 75. Your typical highway speed is more important. 2500RPM cruising speed in sixth seems to be a nice balance of power (no downshifting on grades), economy, and NVH.

Just for info, I bought mine with 3.21s knowing I would be regearing, and to be honest, it was totally fine. Also, keep in mind, there are only a few company's making the gears that EVERYONE is repackaging and selling as their own. The majority of JK gears out there are Cha gears. US Gear is supposed to be making US-made JK gears, but I heaven't seen them yet. Lastly, 4.56 gears are offered by Superior. They are $10 more (through Quadratec) tan 4.88 or 5.13s. So the expense is an ATM withdrawal, pretty negligible on a $1000+ transaction.


--S
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Old 10-28-2011, 01:13 AM   #28
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Just for info, I bought mine with 3.21s knowing I would be regearing, and to be honest, it was totally fine. Also, keep in mind, there are only a few company's making the gears that EVERYONE is repackaging and selling as their own. The majority of JK gears out there are Cha gears. US Gear is supposed to be making US-made JK gears, but I heaven't seen them yet. Lastly, 4.56 gears are offered by Superior. They are $10 more (through Quadratec) tan 4.88 or 5.13s. So the expense is an ATM withdrawal, pretty negligible on a $1000+ transaction.

--S
Didn't know that. In fact, I didn't even know Q sold gears. Thanks for the info, man.
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Old 10-28-2011, 02:48 AM   #29
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I've been thinking of re-gearing. Would 4.88 increase or decrease MPG on a Rubicon with 32.7 inch tires? If so, by how much? Would the power increase be pretty significant?
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Old 10-28-2011, 07:39 AM   #30
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Originally Posted by kbwwolf
Thought I might be high w/the 4.88 choice. Kinda hard to extrapolate all the info for 3.8's into the Pentastar.

Anybody have ideas on mileage, highway rpm's?

Thanks for the info.
Just got my 2012 JKU last night. I have 3.73 gears, 35" tires, and was doing 75 at 2,000 rpm.

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