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Old 04-30-2014, 10:29 PM   #1
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General gearing question

I have been reading a lot of lift and gearing threads. I see not everyone agrees on what size gear to go with depending on the tire size. I do get that each person has different needs, rock crawling vs DD with highway use.

So the question. I like the drivability of my 3:21 gears I'm open to the idea of 3:73's. Is there a formula that takes into account the size of the tire and which gear size to go with to get me back to or close to my original gearing?

And I'm done......

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Old 04-30-2014, 10:33 PM   #2
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There is no exact formula. It highly depends on your preference for fuel economy vs performance. Look at the gear chart and make the choice based on your preferences.

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Old 05-01-2014, 12:56 AM   #3
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Do you have a Jeep yet? Please list what year your Jeep is, what size tires, etc. Also fill out your Jeep profile.

You re-gear according to tire size and engine. Nobody can give you accurate advice without this info.

I've never heard of anyone going from 3.21 to 3.73. Not worth bothering.
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Old 05-01-2014, 08:08 AM   #4
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There are charts available that provide the information you are seeking. See below link. Ratio ultimately depends on your driving preference and agree that going to 3.73 from 3.21 not worth it and is a waste of money. I had 3.21 and went to 4.88 with 35" tires.

http://www.jeep4x4center.com/jeep-ti...atio-chart.htm
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Old 05-01-2014, 10:05 AM   #5
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Sorry, I have a 2014 JKUS I am in the process of doing my homework for a future lift.

I didn't mean to imply that I was going to swap out my 3:21 for 3:73's. I just meant that I like how it's geared now so I wanted to stay in the same range.

I have decided on a 2.5" lift but haven't decided on tire size. I like 35's but on some rigs they seem to be overwhelming but the 33's look too small on other rigs, so I might try to go somewhere in the middle. Not that I have a lot of choices. I do notice that rim size seems to add a lot to the perception of being too big or too small.

At this point I'm really f@@king indecisive..... There are just too many options...

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Old 05-01-2014, 11:37 AM   #6
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A 2014 with an automatic transmission and 35's, the sweet spot would be 4.56. With a manual transmission, you could get away with 4.10. That being said I don't think you can find 4.10 from say Yukon or G2 (the ring & pinion manufacturers). 3.21 will be DREADFUL with 35's and not great with 33's.

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Old 05-01-2014, 11:41 AM   #7
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Thanks, That chart was what I was looking for.
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Old 05-01-2014, 11:43 AM   #8
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A 2014 with an automatic transmission and 35's, the sweet spot would be 4.56. With a manual transmission, you could get away with 4.10. That being said I don't think you can find 4.10 from say Yukon or G2 (the ring & pinion manufacturers). 3.21 will be DREADFUL with 35's and not great with 33's.

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Some would say 4.56, some would say 4.88. I've heard many say to figure out which gears you need, and go one lower (numerically higher). Just depends on your elevation and needs. If 37's are even a remote possibility for the future, do the 4.88.
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Old 05-01-2014, 11:47 AM   #9
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I also should have stated I have an A/T.

Thanks for all your help.
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Old 05-01-2014, 02:18 PM   #10
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Some would say 4.56, some would say 4.88. I've heard many say to figure out which gears you need, and go one lower (numerically higher). Just depends on your elevation and needs. If 37's are even a remote possibility for the future, do the 4.88.
Not for 35's. 4.88 would be too deep on a 2014. I do agree with the 4.88 though if 37's are in your future.

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Old 05-01-2014, 03:31 PM   #11
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Not for 35's. 4.88 would be too deep on a 2014. I do agree with the 4.88 though if 37's are in your future.

-Dan
So you think if you are going with 35s on either a '13 or '14 you would go with 4:56 if 37's don't seem to be in your future.
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Old 05-01-2014, 07:39 PM   #12
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I'm 4.10s with a 33"
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Old 05-01-2014, 09:13 PM   #13
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So you think if you are going with 35s on either a '13 or '14 you would go with 4:56 if 37's don't seem to be in your future.
Correct. Some guys don't want the trouble of running 37's and will run 35's the rest of the Jeeps life. 4.56 would be optimal. In the optimal rpm. You would get back whatever MPG you lose, your OD/6th gear and your crawl.

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Old 05-01-2014, 09:14 PM   #14
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I'm 4.10s with a 33"
On a 2012+? If so that's about perfect for 33's. You probably could get by with 35's with a superchips flashpaq.

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Old 05-01-2014, 09:26 PM   #15
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I'm new to to to all this so I'm trying to get as much information as I can, so some of this might be repetitive.

Currently on my stock setup, if I'm driving at 70mph my tach says I'm turning about 1800rpm. In the current setup I'm happy with the performance, it's not a mustang. But looking at the chart Chaz provided they recommend running a gear that will keep the rpm's around 2600-2800. Which with 35" tires would be 4:11's. But I see a lot of people going quite a bit lower in their gear. Is it just preference, performance advantage or time tested trial and error?
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Old 05-01-2014, 10:56 PM   #16
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Originally Posted by Famtruckster14 View Post
I'm new to to to all this so I'm trying to get as much information as I can, so some of this might be repetitive.

Currently on my stock setup, if I'm driving at 70mph my tach says I'm turning about 1800rpm. In the current setup I'm happy with the performance, it's not a mustang. But looking at the chart Chaz provided they recommend running a gear that will keep the rpm's around 2600-2800. Which with 35" tires would be 4:11's. But I see a lot of people going quite a bit lower in their gear. Is it just preference, performance advantage or time tested trial and error?
4.88 would be better for off road and areas with lots of hills. 4.56 better for highway driving. 4.88 and 4.56 really isn't that much different. I would do 4.88 for 35's, but I wheel a lot + lots of the wheeling is up to a mountain area and back down.
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Old 05-02-2014, 12:23 PM   #17
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If you're concerned about MPG- get 4.10s. They'll run 35s just fine. See if you can fine a Rubi on 35s at a dealer somewhere and take it for a spin.
If you want it back to stock feel on 35s or you want a little more performance get 4.56s. Better for off-roading, better for city driving, still fine on the highway. I think most people get 4.56s because for the same money (typically) you get better performance.
People obsess over the 2500-2900 RPM range- stop staring at the chart and get in your Jeep. Hit the freeway and run your Jeep to 2500 RPMs. "Downshift" your auto into 4th and run it to 2800. You'll won't feel or hear any difference- it isn't a Honda and it won't sound like one. The torque curve is flat as a pancake anyway- the Pentastar doesn't start cranking until 3000 RPMs. So unless you're worried about MPG get 4.56s and enjoy the ride.
And for the record 4.56s were fine on 33s too. (I had 305/70s in a KM2 which really were 33.5".) When I put on 35s I thought there would be some huge difference. Yah, no. There was a small difference- but nothing the average person would even notice.
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Old 05-02-2014, 01:31 PM   #18
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Good thread, i was sort of wondering the same thing. So basically, if i understand this correctly....

If you have a 4.56:1 gear ratio, for every 4.56 revolutions of your....transmission? your wheels rotate once.

So the smaller the ratio, the better the fuel economy, the greater the number, the better the torque.......right?
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Old 05-02-2014, 10:08 PM   #19
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Thanks for all the help.

My Jeep is a DD and it's pretty flat here outside Chicago. I might only get the opportunity to go off-road a couple times a year. I think that 4:10 or 4:56 is the way to go, for me. I don't foresee me going any bigger than 35's at the most, might even go slightly smaller.

So I'm assuming that I will need to swap both front and rear gears. This may sound stupid but are they geared the same? Also if I'm opening up the diff should I also just put in a trutrac type locker or other option? Also do you need them front and rear?
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Old 05-02-2014, 11:58 PM   #20
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Yes, both diffs have to have the same gear ratio. And yes it is wise to have whatever traction device you want installed at the same time. You can do one or both.

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Old 05-03-2014, 12:38 AM   #21
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Sounds like you're not going to be wheeling much. So if you're going to lock it, only need to do one. Better to do the rear since it's a D44, but you'll want a selectable. Don't lock the D30.
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Old 05-03-2014, 09:09 AM   #22
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Not sure what you mean by "selectable", ARB air locker, Eaton electric or TruTrac?

Also if I get the ARB or Eaton does the diff basically become an open diff when it's not engaged and is that a concern either way since it's a DD? Or should the ARB / Eaton go in the front an put a TruTrac in the rear? Or for the money of an ARB / Eaton should I just put TruTrac's front and rear?

Or am I just over thinking this and in my situation it's overkill? I don't want to spend a ton of money but want it done right and don't want to spend it twice.
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Old 05-03-2014, 09:21 AM   #23
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I have the eaton and it rocks . I have no experience with the others but have heard nothing bad about them
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Old 05-03-2014, 10:52 AM   #24
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I have an ARB in my rear, hands down the best. it does require an air source though. So for someone that isn't going to be wheeling as much, I'd go with the Eaton.

Any selectable will work as an open diff until you activate it.
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Old 05-03-2014, 07:07 PM   #25
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So the smaller the ratio, the better the fuel economy, the greater the number, the better the torque.......right?
Actually, no. It's not quite that simple. There are other factors. If you drive in the city (frequent stop and go, avg. <50mph) or if it is very hilly where you live, then 4.88s will almost certainly net you higher mpg. It'll definitely net you more low-end torque. On the other hand if you're setting your cruise control at 70 on mostly flat lands then 4.10s or possibly 3.73s will net you higher mpg as well as more high-end torque (in the upper rpm range) - so long as your transmission is not hunting, meaning downshifting constantly, which kills mileage. You also have to consider wind-drag, increased mass and friction of wider tires.

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