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post #1 of 19 Old 03-24-2015, 05:35 PM Thread Starter
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What gear for 37s

I need to know what diff gears to use with 37 13.50 20 on a 2014 Wrangler sport with an automatic. Mostly highway driving at 65mph with light trail use.
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post #2 of 19 Old 03-24-2015, 05:38 PM
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I'm personally going to go to 4.88's in my 2014. At 70 mph the chart shows to be about 2750 rpms which is a hair higher than my stock 4.10s on the stock rubicon tires.

I'm currently running 37 mt/r k with 4.10s and at 70 mph I'm at 2250 in 5th gear and it sucks. If I down shift to 4th it hits about 2700 and feels perfect power wise.

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post #3 of 19 Old 03-24-2015, 05:55 PM
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Since you have a Dana 30 up front 5:13 is as high as you can go. You will still have to turn off overdrive at highway speeds but there will be enough power for you to get around town without it being too much of pain. You will have no problems in 4lo

I have 5:13 gears on mine and I am running 37x13.5r18 Toyo Open Country MT's. Mine is 2007 with the crappy 3.8. Not sure what differences there are with the 3.6
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post #4 of 19 Old 03-24-2015, 06:22 PM
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Look at gear charts. The sweet spot (fuel economy vs performance) is 4.88 for the 3.6. With the 3.8 you needed to gear as low as possible.
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post #5 of 19 Old 03-24-2015, 07:50 PM
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if I were you I would do the 5.13's with your automatic. if you had a standard I would say 4.88's.

as mentioned above I have the 3.8 which is lower on HP and torque compared to the 3.6. i'm running an automatic and 5.38 gears which is almost perfect. I wouldn't have minded being able to go a little lower.

www.4ws.com has great deals on gear packages. they are also a site sponsor.

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post #6 of 19 Old 03-24-2015, 07:56 PM
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Quote:
Originally Posted by CamoCop View Post
if I were you I would do the 5.13's with your automatic. if you had a standard I would say 4.88's.

as mentioned above I have the 3.8 which is lower on HP and torque compared to the 3.6. i'm running an automatic and 5.38 gears which is almost perfect. I wouldn't have minded being able to go a little lower.

www.4ws.com has great deals on gear packages. they are also a site sponsor.
You do realize that the newer auto trans 5th gear is lower than the manual trans 6th gear right? http://www.wanderingtrail.com/Mechanical/gearratio.html

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post #7 of 19 Old 03-24-2015, 08:06 PM
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lol, no I didn't. my buddy is running 4.88's /w 35" tires on his 2013. usually the auto tranny's are geared higher than the manual tranny's.

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post #8 of 19 Old 03-24-2015, 08:37 PM
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Everytime someone asks for gear advice the answers are always all over the place. I would try to drive someone elses Jeep with lower gears to see how you like it.
The 12+ autos do better geared taller than the earlier ones. I personally like my auto with 4:10s/35"s and I would hate it if it was too low(been there on another vehicle). We do have 75mph speed limits though.
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post #9 of 19 Old 03-25-2015, 05:30 AM Thread Starter
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Thanks guys for responding, hey Ronson what is your RPMs at 65 MPH?
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post #10 of 19 Old 03-25-2015, 04:46 PM
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Quote:
Originally Posted by Ronson View Post
Everytime someone asks for gear advice the answers are always all over the place. I would try to drive someone elses Jeep with lower gears to see how you like it.
The 12+ autos do better geared taller than the earlier ones. I personally like my auto with 4:10s/35"s and I would hate it if it was too low(been there on another vehicle). We do have 75mph speed limits though.
I understand your point but driving a Jeep with big tires and a gear ratio that is too low like some of the 3.21 + 35+ folks is not much better. Performance is really subjective for many, so it's better to look at the right gear chart and make your own decision unless you are just looking for some to help you rationalize not regearing.
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post #11 of 19 Old 03-25-2015, 06:58 PM
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Quote:
Originally Posted by spinlock View Post
I understand your point but driving a Jeep with big tires and a gear ratio that is too low like some of the 3.21 + 35+ folks is not much better. Performance is really subjective for many, so it's better to look at the right gear chart and make your own decision unless you are just looking for some to help you rationalize not regearing.
I totally agree and that chart Is very useful, especially with the specific model year specs Included.
By too low I meant numerically low. I've had vehicles that would barely go 60 and get 7mpg. Geared tall is just as bad. A buddy of mine is constantly shifting from high to low range on easy dirt roads because he can't pull a hill in high range with 3.08s and 33s.

I will have to see what rpms I pull at 65. I do know I can get the "eco" light to come on at 75mph if I have a steady foot on flat ground.
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post #12 of 19 Old 03-25-2015, 11:47 PM
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We find the 4.56 gears work best with 2012-current 3.6 auto jeep's on 37's. If it's just a trail rig then I am sure you can go lower. Most of our customers use their jeeps on the hwy.

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post #13 of 19 Old 03-26-2015, 01:13 AM
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2012 Unlimited auto here with 37s and 5.13s. Ran with the OEM 4.10s for a while and it was tolerable from a performance perspective, but at freeway speeds, was searching between OD and 4th too much.

@jdemonto, that really surprises me that you find 4.56s to work well with 37s. I think the 5.13s are perfect.

@OP, what many do not consider, and what a mathematical chart cannot tell you, is that the larger the tire/wheel combo, the more your drivetrain will be having to overcome inertia. Especially with the auto, that means you actually want a ratio that is slightly lower (numerically higher) than the numerical charts suggest should give you the same RPM. In other words, the same RPM will feel different, and perform different with 32s than it will with 37s because of the additional rotating mass creating a flywheel effect. I have the info somewhere for the RPM on my setup. I'll search for it and edit if/when I find it.

Edit: Well, I searched and can't find a specific RPM, but I do know that at 70 MPH, my current setup runs only about 250 RPM higher than it did with stock Rubicon tires and 4.10s.

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Last edited by UnlimiDozer; 03-26-2015 at 01:52 AM.
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post #14 of 19 Old 03-28-2015, 05:08 PM
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Quote:
Originally Posted by UnlimiDozer View Post
2012 Unlimited auto here with 37s and 5.13s. Ran with the OEM 4.10s for a while and it was tolerable from a performance perspective, but at freeway speeds, was searching between OD and 4th too much.

@jdemonto, that really surprises me that you find 4.56s to work well with 37s. I think the 5.13s are perfect.

@OP, what many do not consider, and what a mathematical chart cannot tell you, is that the larger the tire/wheel combo, the more your drivetrain will be having to overcome inertia. Especially with the auto, that means you actually want a ratio that is slightly lower (numerically higher) than the numerical charts suggest should give you the same RPM. In other words, the same RPM will feel different, and perform different with 32s than it will with 37s because of the additional rotating mass creating a flywheel effect. I have the info somewhere for the RPM on my setup. I'll search for it and edit if/when I find it.

Edit: Well, I searched and can't find a specific RPM, but I do know that at 70 MPH, my current setup runs only about 250 RPM higher than it did with stock Rubicon tires and 4.10s.
I was about to regear to 4.88s myself and started thinking about this ^^^ myself. Do I want "stock performance" on a big heavy 37? Gonna need a few more horses to get those bad boys moving and keep them moving especially on long hills on the freeway.

I currently have a 2013 auto w/ the 3.6, 4.10s, and 33.75" Duratracs and I'll still get 4000-5000 RPM drops on windy days and long hills on the freeways here in D/FW.

I'm thinking 5.13s for me when I make the jump to 37s...

Last edited by flomingo; 03-28-2015 at 05:10 PM.
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post #15 of 19 Old 03-28-2015, 06:34 PM
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I'm running 37's on a 2012 manual and went for 5.13's. All the folks I know with autos and 37's are at 4.88 with the 3.6L.

Chart should tell you all you need to know.
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post #16 of 19 Old 04-05-2015, 02:29 AM Thread Starter
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Thank you Jonboy for posting the chart, very helpful.
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post #17 of 19 Old 04-13-2015, 10:28 AM
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I think your choice is between 4.88 and 5.13. If you can't find anything to drive with your engine/transmission, 37's, and those gears to compare, you'll have to take what I call a leap-of-faith decision. I was between 4.56 and 4.88 for my 35's, went 4.56 on faith and it worked out perfectly. Good luck.

PS................based on your opening post, I think 4.88 is your probable best gamble.

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post #18 of 19 Old 04-13-2015, 10:59 PM
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I went 5.13 with 37s, but I chose to go a little lower geared (numerically higher) to get the benefits crawling rocks on the trail. I would personally not run 37s just for "mostly street and occasional light trail".

Also before tossing 37s onto a Sport, make sure you read around to understand what other parts you may need to beef up or address (or realize they are going to break or wear much faster).

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post #19 of 19 Old 04-14-2015, 08:09 AM
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Here is 65 with 4.56 gears in 5th gear on the edge of the Eco

2013 3.6 auto 37" nittos

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Last edited by jdemonto; 04-14-2015 at 08:18 AM.
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