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2014 Unlimited Auto Sport with 37's gears?

3K views 17 replies 12 participants last post by  monte417 
#1 ·
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
 
#2 ·
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.
 
#4 · (Edited)
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.
 
#9 ·
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

Lunatic Fridge
 
#7 ·
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
 
#8 ·
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.
 
#10 ·
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.
 
#11 ·
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
 
#12 · (Edited)
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.....:thumb:

Also with 37's, you will need C Gussets, trusses, and heavy duty Ball Joints with grease zerks.
 
#14 ·
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
 
#15 ·
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
 
#18 ·
If your not taking it offroad why waste money on a winch?
 
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