Help me Understand the 3.21 vs 3.73 vs 4.10 Axle Ratio on JKs - Page 2 - JeepForum.com
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Unread 06-16-2013, 08:00 AM   #16
Butterjeep
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I would regear your diffs first. Your Jeep will be more enjoyable on road as well. The 3.21's should never be available but many Jeeps never make it off road so a lot of people don't realize the gearing shortcomings. There's a gearing chart (just do a search) that will help you out. I run 3.73's and I feel like I need a regear so I am sure 3.21's are frustrating out on the trail.

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Unread 06-16-2013, 08:45 AM   #17
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When I get my Jeep, I want more aggressive tires, but I want to retain every bit of the 3.73 final gears. So, I'm going with a BFG 275/65/17 (<I think those are the right #s) That tire is .8" wider and supposidly only .1" taller. I think I'll run that tire with a stock suspention until I see shortcomings per my application, and go from there.
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Unread 06-16-2013, 04:28 PM   #18
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what part of southern indiana are you in? far from Jeffersonville or Sellersburg?
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Unread 06-16-2013, 06:07 PM   #19
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Quote:
Originally Posted by TrailRated2011 View Post
My 2011 JK 2dr Sport model w/manual transmission has an axle ratio of 3.21. Would simply buying and installing a Terra Low 4:1 system be a 100% remedy to my current crawl being way too fast? Pros/Cons? Would doing this just create another issue somewhere else?

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It would be easier and probably cheaper to install new axle gears. Give you more pep on the street too.
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Unread 06-17-2013, 01:02 PM   #20
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Originally Posted by Butterjeep View Post
I would regear your diffs first. Your Jeep will be more enjoyable on road as well. The 3.21's should never be available but many Jeeps never make it off road so a lot of people don't realize the gearing shortcomings. There's a gearing chart (just do a search) that will help you out. I run 3.73's and I feel like I need a regear so I am sure 3.21's are frustrating out on the trail.
Excuse my asking, Butterjeep, but the comment about 3.21s you made has me wondering. Should I decide to pull the trigger and buy a new Wrangler, it will be more for fun and enjoying what is above the Jeep rather than what is below it. Meaning that it will be more of a convertible than a rock crawler. Under these circumstances, my original thought was 3.21 rather than 3.73 to conserve a little fuel on the road. Since I retired, we do take several trips a year of 300+ miles and, I would also look at an occasional trip to the woods in search of Bambi, but nothing more hardcore than some Mississippi mud! So, should I still consider 3.73s?
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Unread 06-17-2013, 01:53 PM   #21
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That reallydepends on the tire size you intend to run. If you will keep them stock then you can probably get by with the 3.21. If you want to get bigger or more aggressive tires you will want the 3.73.

I would make sure to really test drive both options before buying. I personally can't imagine having 3.21's in one of these jeeps.
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Unread 06-18-2013, 07:20 AM   #22
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Thanks, Dune! It makes sense that tire size would make a difference. I will probably keep tires pretty much to stock specs but will def try to drive both ratios before making a final decision.
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Unread 06-19-2013, 09:03 AM   #23
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Originally Posted by Sixtyplus View Post
Excuse my asking, Butterjeep, but the comment about 3.21s you made has me wondering. Should I decide to pull the trigger and buy a new Wrangler, it will be more for fun and enjoying what is above the Jeep rather than what is below it. Meaning that it will be more of a convertible than a rock crawler. Under these circumstances, my original thought was 3.21 rather than 3.73 to conserve a little fuel on the road. Since I retired, we do take several trips a year of 300+ miles and, I would also look at an occasional trip to the woods in search of Bambi, but nothing more hardcore than some Mississippi mud! So, should I still consider 3.73s?
The mpg difference from 3.21 to 3.73 is negligible, the feeling of acceleration however I would say is evident.

my $.02 Jeep only offers the 3.21 to raise the EPA fuel econ rating.
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Unread 06-19-2013, 10:17 AM   #24
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Also remember that while you say you will keep the stock tires, that will probably change. You will really like the jeep and enjoy getting outdoors into the back country and start getting the mod bug. You want just a little more clearance or slightly better tires and before you know it you are rolling on 35's with a 3" lift kicking yourself because you bought a jeep with 3.21's.
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Unread 06-19-2013, 07:37 PM   #25
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Originally Posted by bogleparsons View Post
The mpg difference from 3.21 to 3.73 is negligible, the feeling of acceleration however I would say is evident.

my $.02 Jeep only offers the 3.21 to raise the EPA fuel econ rating.
I would say always go with the lowest gears you can, so for our Jeeps, it's 3.73 or 4.10's if you get a Rubicon. The tiny difference in gas mileage is not worth it. Even on extended road trips, the lower gears help. Our Jeeps are not aerodynamic and that plus some weight and a good headwind would be all it takes to make you hate 3.21's. Even with 4.10's, you'll still be able to break every speed limit in the country by quite a bit, so it's not like your freeway speeds will suffer.

Even if you keep your tire size stock, go low. The lower gearing helps driveability and allows you to enjoy your Jeep so much more, and all it costs is a negligible difference in mileage.
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Unread 06-19-2013, 07:39 PM   #26
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Quote:
Originally Posted by Sixtyplus View Post
Excuse my asking, Butterjeep, but the comment about 3.21s you made has me wondering. Should I decide to pull the trigger and buy a new Wrangler, it will be more for fun and enjoying what is above the Jeep rather than what is below it. Meaning that it will be more of a convertible than a rock crawler. Under these circumstances, my original thought was 3.21 rather than 3.73 to conserve a little fuel on the road. Since I retired, we do take several trips a year of 300+ miles and, I would also look at an occasional trip to the woods in search of Bambi, but nothing more hardcore than some Mississippi mud! So, should I still consider 3.73s?
Also, if you're slinging through some Mississippi mud, you'll want the extra leverage of the lower gears. Hopefully, my posts and everybody else's posts have convinced you that 3.21's are unacceptable!
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Unread 06-20-2013, 07:48 AM   #27
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I think the comments from everyone seems to be 100% for 3.73s! Where we live we are always out in the country! Though I really have no desire to lift and go to monster tires, an upgrade would be to a more aggressive tread pattern to enable me to check on our back forty.

Thanks for all the input! I'm convinced!
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Unread 06-20-2013, 07:55 AM   #28
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Quote:
Originally Posted by RockyClymer
I don't post too often, but thought I would try and give some help here.

Axle ratio is simply that, the number of times the drive shaft turns to make one turn of the tire (or axle shaft if you prefer). So your rigs drive shaft will have to turn 3.21 times for one tire rotation. So an axle ratio of 4.10 would mean the drive shaft has to turn 4.1 times for a complete revolution of the tire....that is almost one more turn for the same tire rotation! Quite a bit of difference when you think of it, the result is that your engine will run faster for the same speed, or, by running the engine slower, you will get a much slower wheel rotation and hence be able to "crawl" slower for the same speed than when using a 3.21...

Crawl ratio is simply the combination of the lowest transmission ratio in low range, the ratio of the transfer case in low range and the axle ratio discussed above. Simply stated, the lower the combination (obtained by the multiplication of all three) the "higher" the crawl ratio...as above, this means that for a given engine speed (rpm) the vehicle will go or crawl slower. An example (for my JK) first gear in low range is 4.46, I have installed a RockTrac 4.0 transfer case and my axle ratio is 4.88 - so, multiplying these, 4.46 x 4 x 4.88 = 87, my crawl ratio is 87. On your vehicle, and making some assumptions, your first low gear is 4.46 (same as mine on the 6 spd) your transfer case is 2.7 (std JK) and your axle ratio is 3.21. 4.46 x 2.7 x 3.21 = 38, so your crawl ratio is 38 compared to my 87 or about 43% of 87....this roughly means that for the same engine rpm, my vehicle will go a little less than half the speed yours will....this is a significant difference when rock crawling.

Third point, what does it mean? Could mean a lot of things, but a few basics. Going slower when rock crawling gives a lot more control over wheel placement and and tire speed control...that is not "jack rabbiting" as you explained it. You gain a lot of tire spin control with the higher crawl ratio just through throttle control. Going slower can allow your tires to "dig" in or "bite" at the rock or obstacle instead of just spinning. Going downhill the higher gear ratio will allow the engine compression to provide much more braking effect...again, more control using the throttle.

This is a real short story, so hope it helps. For more info, discussion you may PM me.
Awesome answer!!!!!! I learned some stuff
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Unread 06-24-2013, 06:27 PM   #29
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Made a Decision Today: Re-gearing

Made a decision today: National 4WD Centres in Smiths Falls, ON, Canada is re-gearing my 6 sp. manual 2011 2dr. Sport JK (33 in. Duratracs) from 3.21 : 1 Axel Ratio to 4.56 : 1.

Special Recognition goes to Capital Dodge in Ottawa ON, Canada who pointed out another great solution---The Bully Dog Triple Dog GT Gas Tuner. See http://www.bullydog.com/documents/40...tion_Sheet.pdf
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Unread 07-04-2013, 07:07 AM   #30
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