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Unread 04-05-2014, 09:52 AM   #1
okeedoky0
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Best gearing for 2012 JK on 35's?

I own a 2012 JKU with a 3" BDS lift and 315/70/17 tires. I currently have 3:21 gears. I recently added a Smittybilt Atlas rear bumper and tire carrier and have a full size tire mounted. With the added weight I am noticing some sluggishness in my get up and go. What would be the best gear ratio to run with 35's ... 3:73, 4:88? I will be adding a heavier front bumper soon and for trips the back is packed full of camping gear. What affect will regearing have on mpg. I currently get around 15. This is a daily driver both in town, on the hiway, and off road.

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Unread 04-05-2014, 10:09 AM   #2
ancientspear
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http://www.jeepforum.com/forum/f96/p...ml#post9821516

Tip: Stay in green if daily driving is more important to you than rock crawling (blue). It will net you better fuel economy. Gear in the yellow range on an auto transmission and it will be searching for gears a lot when traveling in hills with cruise control but you're already noticing the sluggish aspect the chart describes with 35's and 3.21.

Consult the chart. You have the 3.6L, remember stock tires are 32", and gear selection is different for Auto and Manual transmission. Your stock setup probably returned 21-ish highway 70mph while my stock auto Rubicon (3.6L and 4.10 gears on 32's) averages 18.5 at that speed but drops down to 13.5 when driving 77-80. Using this chart you can see where my RPMs are hovering at 70mph (about 2500) and how much running at 3000 RPM affects mileage at those higher speeds. Highway test time on my rig... > 15,000 miles from hot and humid GA weather to sub -40 winters in my province.

A friend of mine had 4.88 on his auto 12 with 35's but is now regearing for 37's by going to 5.13. He loves climbing stuff in the trails and is more agressive than the average driver so you can see why he's trying to stay in the 2700 range at 70mph in the chart for his gearing for given tire size. For me, I would probably look maintain my current RPM at 70mph if I increase tire size to 35+.
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Unread 04-05-2014, 11:32 AM   #3
okeedoky0
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Thanks. I looked over the chart and read through the whole thread. Lots of different opinions depending on what the use will be. Mine is an Auto. Like I said its a DD and will only be O/R 10-20% of the time. How do I tell what my stock front and rear axles are? 2012 JKU Sport. What manufacturer is recommended keeping in mind I have a low budget?
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Unread 04-05-2014, 01:42 PM   #4
Yamaha90
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i'm selling my D30/D44 JK axles and they have factory 4.10's in them. not bent no damage. They would bolt right in if you're interested.

I ran 35's on these 4.10 in the 3.8L auto for the past 100,000 miles. The 4.10's and 35's for my powertrain were just fine. Not a race car but manageable to drive around town and on the highway.
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Unread 04-05-2014, 08:22 PM   #5
SLADE
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4.56 if you see a lot of highway (65mph+)

4.88 if you see mostly 2 lane with an occasional highway.
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Unread 04-05-2014, 08:51 PM   #6
SubAtomicGenius
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I agree with the 4.56's.
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Unread 04-06-2014, 03:43 AM   #7
Prot
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I have a 2014 JKU with an automatic. I have the 3" bds lift and 315/70-17 Duratracs along with bumpers, winch, tire carrier, etc.

I went with 4.88 gears. They are only 200 rpm's higher than 4.56 at 70 mph. I occasionally tow an enclosed trailer, so the gears help a lot. This is my primary vehicle that I drive daily, usually around town at low to moderate speeds. I have tried it on the interstate and it is fine.

If you are thinking about lockers, get them put in at the same time as the gears so you don't pay labor twice.

Your sport has a d30 up front and d44 in the rear.

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Unread 04-07-2014, 03:46 PM   #8
mrwhipple
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I really like the 4:56s with the 35s. Very responsive all around and plenty of low end off-road.
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Unread 04-07-2014, 04:39 PM   #9
sean0168
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Just a FYI I have the stock 410's in my 14 JKUR auto with 35's and I can tell you on the highway my max speed is 75mph. If I try to go any faster it shifts out of OD and I am down to 12-12.5 MPG. Pretty frustrating as I drive up north a lot and most cars are cursing at 80+. I have done the procal already but one of the reasons I went with the rubicon was in hopes of not needing a regear. Summer is on the way and now will be pulling a boat so I may have to look at new gears. GRRRR!
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Unread 04-07-2014, 04:40 PM   #10
ROCKR8R
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Personally, I would set up for 37's in the future so I would go with 4.88, however that is me. 4.56 or 4.88 will be your best bet

PM me if you would like a quote.

-Dan
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Unread 04-07-2014, 05:14 PM   #11
SubAtomicGenius
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I would not set up for 37's due to the front D30.
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Unread 04-07-2014, 05:36 PM   #12
ROCKR8R
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Quote:
Originally Posted by SubAtomicGenius View Post
I would not set up for 37's due to the front D30.
I have no qualms with running 37's on the D30.

-Dan
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Unread 04-07-2014, 09:01 PM   #13
maniacal_rick
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I run 4.56's with 35's and a 3.6/manual. No issues in any driving conditions. I believe that 37's will be no problems either. If I had an auto, I would get 4.88's.
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Unread 04-07-2014, 10:42 PM   #14
KYgreenYJ
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I have 35's with a 3.6 and 4.10's, if the jeep didn't come that way, I'd probably go with 4.56's. It really is not bad how it is, but its also not my daily driver. I think 4.88 would be a little low for the highway, but would probably be the best off-road, with the option of upgrading to 37's later.
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