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Old 08-27-2014, 04:07 AM   #1
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2014 Unlimited Auto Sport with 37's gears?

New to the forums.
Just purchased new Jeep Wrangler Unlimited Sport with Auto.
Ordered 37" Toyo MT tires.
Smittybilt bumper / tire carrier in the rear and rock bars, OR Fab 3/4 and winch in front. 3.5" Rock Krawler long arm lift.

I have read a number of threads but none have really addressed my situation:
I drive entirely on the street, automatic, heavy bumpers/winch.
Should I go with 4.88 or 5.13 on the gears?

50% of my driving at 65 and 50% around town at 30.
Not planning to take it off road, but the pics on this forum look great, so I will give it a try! Spend winters in the CO mountains is why I went with JKU.

Sure appreciate everyone's input.

thanks,
Eric in Austin, TX

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Old 08-27-2014, 06:49 AM   #2
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I am running 5.13's with my auto. I am on 35's but will be going to 37's thats why I went 5.13's ( wanted to make some strength upgrades before 37's). Mine is a DD and i have no complaints.

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Old 08-27-2014, 02:13 PM   #3
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Thank you Robert! What is a "DD"? Assuming your jeep is also automatic and has the same motor?
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Old 08-27-2014, 02:34 PM   #4
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DD is daily driver. If his Jeep is an 09 it is a different engine. I believe on the newer engines 4.88 or 5.13 would be fine for 37s. You also would want to explore ball joints, Cs and axle armor as those bigger tires are a lot of extra stress. Your gas mileage will suck even more. Not sure how long your daily commute is, but you may end up not really happy with the decision to go that big if its a lot of miles. Just curious why you did a long arm on a limo?

Google Wrangler gear chart and you will find a breakdown - make sure you look at the one for the 3.6 engine.
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Old 08-27-2014, 07:22 PM   #5
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What gear ratio would you recommend on a JK with 3.8L and 37" tires?
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Old 08-27-2014, 08:07 PM   #6
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Quote:
Originally Posted by ekrohn View Post
New to the forums.
Just purchased new Jeep Wrangler Unlimited Sport with Auto.
Ordered 37" Toyo MT tires.
Smittybilt bumper / tire carrier in the rear and rock bars, OR Fab 3/4 and winch in front. [COLOR="rgb(0, 191, 255)"]3.5" Rock Krawler long arm lif[/COLOR]t.

I have read a number of threads but none have really addressed my situation:
I drive entirely on the street, automatic, heavy bumpers/winch.
Should I go with 4.88 or 5.13 on the gears?

50% of my driving at 65 and 50% around town at 30.
Not planning to take it off road, but the pics on this forum look great, so I will give it a try! Spend winters in the CO mountains is why I went with JKU.

Sure appreciate everyone's input.

thanks,
Eric in Austin, TX

For whatever it's worth, with the pentastar V6 in the 2014, 4.88 should do the trick.
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Old 08-27-2014, 08:24 PM   #7
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4.88 Would be fine with the newer motor, i run 4.88 and 33's in the 10 auto, and you wouldnt believe the difference it made in pep and wheel-ability
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Old 08-28-2014, 01:00 AM   #8
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I sure appreciate all the feedback! Thank you
I'm going 4.88 from the graph it looks the closest to stock ratios.

I did the long arm on a limo as I just didn't know any better at the time.
I was told that it pushed the rear wheels back an inch and how important that was.
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Old 08-28-2014, 02:51 AM   #9
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Quote:
Originally Posted by 88Hatchy View Post
What gear ratio would you recommend on a JK with 3.8L and 37" tires?
Well for me it was a Hemi and 4.88's. If I change axles like I am thinking about doing then it will be a Hemi and 5.13 or 5.38's in a D60/14bolt setup.

According to the gear charts for a manual trans 5.13 should do the trick for a daily driver and for an Auto 5.38's or if they will fit and not be fragile 5.86's. I forget where the D44 gear ratio limit is. If you have a D30 front start with replacing it and armoring a D44 if you want a long and happy life with 37's

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Old 08-28-2014, 11:58 AM   #10
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You have three things working against you.

  1. Extra weights from the bumpers, winch, rock rails, and 37" tires will be around 550 - 600 Lbs.
  2. The rotational inertia of the massive and heavy 37" tires
  3. Altitude in Colorado. At 5000 feet, you will lose about 15% to 18% of your power.
If I were you, I would go with 5.13 gears.
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Old 10-23-2014, 11:08 PM   #11
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I went with the 5.13 gears and a Super Chips programmer which I put on setting which requires 93. The jeep is far from quick, but drives pretty good even with the big tires.

With the large tires I cannot seem to drive it faster than about 70 on the highway which it being pretty sloppy and risky. 65 more stable. So I think the 5.13's are the way to go since you're not going to drive it 80 anyway.

I really did not notice any difference in power when I went from stock wheels and gears to 37's and new gears. The Super Chips did wake it up and I would recommend it for sure.

Thanks for all the help!
Eric in Austin
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Old 10-24-2014, 04:00 AM   #12
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Quote:
Originally Posted by ekrohn View Post
New to the forums.
Just purchased new Jeep Wrangler Unlimited Sport with Auto.
Ordered 37" Toyo MT tires.
Smittybilt bumper / tire carrier in the rear and rock bars, OR Fab 3/4 and winch in front. 3.5" Rock Krawler long arm lift.

I have read a number of threads but none have really addressed my situation:
I drive entirely on the street, automatic, heavy bumpers/winch.
Should I go with 4.88 or 5.13 on the gears?

50% of my driving at 65 and 50% around town at 30.
Not planning to take it off road, but the pics on this forum look great, so I will give it a try! Spend winters in the CO mountains is why I went with JKU.

Sure appreciate everyone's input.

thanks,
Eric in Austin, TX
3.6 engine, with 37's, the optimum gear ratio would be the 4.88, but with your's being the heavier 4 door, with heavy bumper, and winch, plus driving in the mountains, then the 5.13 would be more appropriate for you.....

Also with 37's, you will need C Gussets, trusses, and heavy duty Ball Joints with grease zerks.
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Old 10-24-2014, 04:24 AM   #13
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Quote:
Originally Posted by 88Hatchy View Post
What gear ratio would you recommend on a JK with 3.8L and 37" tires?
A 2 door with no extra added weight, the 3.8 engine, with auto, and 37,s would be the 5.38.
Same, but with manual, would be the 5.13..........

Plus the axle MODS, mentioned in Post # 12.
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Old 10-25-2014, 02:47 AM   #14
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4 door, 3.6, auto, 37" tires, heavy front and rear bumpers, winch, Rock Krawler 3.5 lift.
Went 5.13 + Super chips and it drives pretty decent.

Have not done any axle mods done.
Really don't know anything about these but will start to research and inquire when I'm in the shop next. Thank you for the heads up!

Eric
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Old 10-25-2014, 09:41 PM   #15
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Can I ask
I have a 2013 4 door auto and running 35" tyres, looking at 4.88 Yukon gears .
I have a ARB rear locker num RD117 will the ring and pinion be ok with this locker?
Also I have a procal set for lager tyres but will I have any issues with the change of gears and my auto?
Thanks for any advise
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Old 10-25-2014, 10:51 PM   #16
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I thought the gear chart said for a 3.6L auto on 35's and 37's were best at 4.56 and the 3.8L on 35's was 4.88 and 5.13 for 37's.

Where is that gear chart? Anyone have it?
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Old 10-25-2014, 11:06 PM   #17
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I ask because I plan on going to 37s one day and Purchasinf a PR44 next year while on 35's. Would rather not have to regear again and the chart said Id be safe at 4.56
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Old 10-26-2014, 01:29 AM   #18
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If your not taking it offroad why waste money on a winch?

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