Help me Understand the 3.21 vs 3.73 vs 4.10 Axle Ratio on JKs - Page 4 -
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post #46 of 54 Old 09-09-2013, 05:12 PM
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Originally Posted by JIMBOX
Any gear ratio deeper than 4.10 is great, even for 33' tires-

The major determining factor is whether or not your jeep is a DD-

Ifit is then you should stay in the 4.88/5.13 range--5.38s are wonderful, but will be a little nerve racking at 75/85 mph freeway travel-

With an auto, the deeper you go the better you fly !

Thanks, I probably should have mentioned that I have a 2012... 5.13 sounds kinda high?!?!

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post #47 of 54 Old 09-09-2013, 05:17 PM
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Numerically high, geared low.

I'm lazy and haven't read through the thread, I presume somebody coughed up the regear charts for the '12s here somewhere?

Time for coffee break!!!
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post #48 of 54 Old 09-10-2013, 07:17 AM
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Originally Posted by SubAtomicGenius View Post
I'm lazy and haven't read through the thread, I presume somebody coughed up the regear charts for the '12s here somewhere?
Yup charts for both engines are on page three.
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post #49 of 54 Old 04-13-2014, 02:36 PM Thread Starter
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How Low Should You Go?

After months of searching, reading, and research I finally found a comprehensive answer to my question, “How do I determine my ideal crawl ratio---one that will serve me best for my specific vehicle and off-road driving needs?”

"A low crawl ratio is very important to a rockcrawling Jeep or in any other situation where low speed control is needed. The ability to idle over rough terrain at a quarter mile per hour in total control doesn’t usually come with stock gearing, especially with manual transmissions. A low crawl ratio is also an asset on descents, where using engine breaking is preferred over using the foot brakes. The availability of low gearing doesn’t hurt at high altitudes, when the rarefied air has sapped half your engine power. A deep crawl ratio is less important to a desert Jeep, a mudder, or one that is used primarily in easy situations.

The “ideal” crawl ratio is a debatable topic and one that is subject to a great deal of personal preference. There are some rigs down to 350:1. They can idle in gear and tire movement is barely perceptible. Even without going to these extremes, it’s possible to go so low that first gear is essentially useless 99.9 percent of the time. Also, the needs of a manual trans and an automatic are quite different.

The crawl ratio needed depends on the type of terrain encountered and how much low-end torque your engine develops. A big, torquey engine can get by with a higher ratio than can a four-cylinder. The key is to be low enough that the engine can essentially ideal over obstacles at a very low speed without constantly stalling or forcing the driver to slip the clutch. Automatics are a little more forgiving in that regard. Generally, manuals need lower crawl ratios than automatics.

After quizzing a large number of 'wheelers, I'll go out on a limb and give some crawl ratio ranges. For general purpose wheeling with a manual transmission, a range of 40-60:1 will offer good all-around performance. For automatics in the same situations, 35-50:1 works well. For die-hard rockcrawlers with stick shifts, 60-100:1 and beyond can be beneficial. For automatics in the same situations, 45-60:1 works well.”

Citation: Allen, Jim. "Chapter 5/HOW LOW SHOULD YOU GO?" Jeep 4X4 Performance Handbook. St. Paul: Motor/MBI, 2007. N. pag. Print.

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post #50 of 54 Old 04-13-2014, 04:12 PM
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Gear for the year, engine, transmission, tire size and typical usage which for almost everyone is driving on pavement despite what many web wheelers claim. Then try it out offroad. If a lower ratio is needed or more choices would be advantageous, then a rubicrawler can be installed which addresses both of those needs. Doing otherwise leads to a rig that is great offroad but is suffers on the street.

It comes down to if you want a trailer queen or a good all around Jeep. Proper differential gears for the typical usage nets a good all around Jeep and a rubicrawler or other similar doubler allows a daily driver to be taken to the next level of offroad prowess without hurting the typical usage. Ridiculously low (high numerical value) gears are great for a trailer queen.

All that being said, JK's require lower (higher numerical value) gears than previous generations of Jeeps, especially 07-11 models, particularly the automatics.

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post #51 of 54 Old 04-13-2014, 04:19 PM
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YUP, that's the main reason I've modified mine for a 61/1 crawl ratio and since it's notta DD, I don't have any troubles on the freeway, plus

I'm so much more able to tow my off-road trailer on-& off-road-

Ya gots to figure these things out, they're not done for you !


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post #52 of 54 Old 04-14-2014, 09:55 AM
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There is a major difference between 2011 and 2012 automatics. Honestly, anything over 3.73 is overkill for the 2012+ models unless you're running 35" or larger tires OR if you never drive on the highway. I would say that most guys here probably do drive on the highway and probably are running 33s or smaller and therefore I would strongly advise not to run 4.56-5.13 gears. Not only will your RPMs be wayyyy too high on the interstate but your driveshafts will also start spinning a lot faster which can open whole new cans of worms that get expensive real fast. Don't ask me how I figured this out...

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post #53 of 54 Old 04-14-2014, 12:24 PM
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the new auto has a full step lower first gear than the out going 42le. so these 2012 autos+ is like going from 3:21 to 4:10. This is why the new rubi auto with the optional 4:1 can turn those 35"s like they are 30"s, you can easily get that traction control light going on with out even trying. this one thing makes the Rubi option almost worth it out of the box. If this trans was in the 3.8 people would not think so little of 3.8.

real crawl ratio in auto is bit hard to measure as well. with the slip before converter lock. the w580 uses this in every gear as well, not just OD. so 1st even at 3.56(?) is more like total slip to total lock. that is the advantage of the auto off road.

to bad the later jk's did update that antiquated trans sooner.

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post #54 of 54 Old 04-14-2014, 05:16 PM
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FWIW, I run 4.88 gears in my automatic 2014 JKU, which is my daily driver. I have 315/70-17 Duratracs. I love this combination. I have a Sahara, so I don't have the lower ratio transfer case, but it still works great for what I do. Yukon zip lockers in both axles also help.

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