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Old 01-22-2020, 02:41 PM
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Curious. WHat was FCA thinking with the 3.21 ratio in JK/JKU?

I have a 3.73 rear end with 285's and it is fine on the freeway at 75-78mph most of them time running 285's. I drove a 3.21 over the weekend while in the DFW. What a dog. Multiple downshifts at 70mph driving into a 15mph headwind. Is this the ratio they standardized their MPG for the EPA? On that note, shouldn't they have different MPG for 3.21, 3.73, 4.10?

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Old 01-22-2020, 02:51 PM   #2
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3.21 is a slight improvement from YJ/TJ that suffered with a 3.07 gear.

I don’t believe they need to EPA certify power train combinations with different axle ratios.
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Old 01-22-2020, 03:05 PM   #3
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I believe it is fleet mpg they are worried about. Individually .5mpg might not be a big deal but when it includes every vehicle it adds up.
EPA mpg is not done in real world environment. I think it is basically done in a controlled environment at 50mph or some thing like that.
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Old 01-22-2020, 03:24 PM   #4
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I read something years ago from somebody that ran GM's fuel economy program stating that across the entire range of their available rear end gear ratios, the EPA MPG variance was between 0.4 and 0.5 MPG -- and that's comparing the shortest ratio to the tallest ratio. He also said it was reasonably linear across the range, so very tiny differences from one ratio to the next, up or down. I think at the time 3.42 was GM's highest and 4.10 was the lowest available ratio.

However, that was in the context of whether mileage-conscious buyers should worry about axle ratios.

For the manufacturer, it wouldn't surprise me that it's a mileage-rating-driven decision. Lately we're shafted with that god-awful AC refrigerant yf1234 in just about everything made because the EPA doles out a microscopic CAFE credit for every vehicle it goes into. The impact of that credit is much smaller than the difference a 3.21 gear could make on the final rating.
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Old 01-22-2020, 03:56 PM   #5
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CAFE is what determines drive lines across the entire product line. Unfortunately, FCA is usually close to the bottom of those corporate standards, mainly due to things like Wranglers, SRT's, Challengers, Chargers, etc. The high performance vehicles need to be balanced with the eco friendly vehicles. 3.21's got them another point or two.
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Old 01-22-2020, 04:50 PM   #6
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My JKWW has 3.73 gears on 285/75 tires. Yes, it's OK at any speed. It's even fairly fast off the light. On the other hand, my wife's stock JK has 3.21 gears on factory tires and it's a rocket ship compared to mine. So I'd have to ask what size tires did that DFW jeep have?
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Old 01-22-2020, 04:58 PM   #7
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That decision must have been made by the same person who decided to put the PCV valve in an unreachable place, hid the spark plugs under an air intake that takes 2 hours to remove, and sub'ed the heater core casting to the lowest bidder.
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Old 01-22-2020, 05:17 PM   #8
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My JK has 3.21, bought it used otherwise I would have gone with 3.73. Maybe because it is lighter than a JKU, but I added 285/70's and it drives just fine. I can zip off the lights, cruise at 75 without constant downshifting, and still get 20mpg. Ideal, no. Completely acceptable as a DD / light offroader, yes.

There is no other reason to have 3.21 except to meet mileage requirements. For those that keep the tiny tires, they most likely don't notice it much.
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Old 01-22-2020, 05:35 PM   #9
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Have stock tires and totally hate the 3.21 in my manual trans JKU. Lots of hills around here and I have to constantly shift for even slight grades hitting them at 60 mph. Worst gearing of just about any vehicle I've ever owned. Heaven forbid you actually need to tow something? Talk about stressing the clutch and power train! IMO an extremely poor choice of gearing from the factory all in the name of grabbing a few more tenths of mpg.

Mine is getting regeared soon as we get some warmer weather!
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Old 01-22-2020, 05:42 PM   #10
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My JKU Auto is 3.21 with stock 29" wheels, very good DD and leght to medium off-roader.
I can do 23MPG highway on a hot day with AC on and 25 in moderate wheather/speed.
City without traffic 19-20.
It wasnt my choice though, bought it off the lot.
But if I can achieve 23 MPG on "california regular juice" im sure EPA testers can do the same, still rated for 20MPG highway, maybe they take the average of all models.
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Old 01-23-2020, 10:34 AM
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It had the KO2 265/70/17, (31.5" tire) same tires my Winter Edition came with. In a controlled environment (flat surface, no wind, no extra weight in or on the rig) its probably fine. Now add real bumpers, not plastic. Add a 15mph head or crosswind. Small grade uphill. 4 adults and luggage... and it's horrid.

In West Texas, the wind never, and I mean never, stops blowing. The only upside is it is flat as can be here. DFW pretty much the same, but there are plenty of hills between Lubbock and DFW. Downshift, upshift, downshift, downshift again...

3.73 is not incredible, but its ok. Regear eventually.
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Old 01-23-2020, 11:09 AM   #12
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I'd say, as a bidness man, that the vast majority of the 1-million+ people who bought non-Rubicon JKs new got them with 3.21s, and the vast majority of those people had no idea what that even means and either loved or hated their Jeeps based on something other than the axle ratios. Jeep wins by getting to score a little bit higher in EPA CAFE testing, getting to charge $495 (in 2014, more now I'm sure) to the people who actually do care and order 3.73, gets to charge $10,000+ to people who want to go all the way to 4.10 (or love the Rubicon sticker), and the vast majority of their buyers don't know or care what they have. Sounds like a sound decision to me.

That said, I had a stock airport rental JKU Sport S 3.21 once, in Moab. It worked fine, and I had a blast for five days, admittedly doing only mild rock climbing. Since I got my own JK with 4.56s I haven't done that again and would probably find it less enjoyable. But most people never get to compare the two.
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Old 01-23-2020, 11:39 AM
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It isnt the number so much as it is the driveability. Its a flying brick to start, now add weight, wind, etc and its a terrible design... for the consumer... who is buying them. And yes, 3.73 was lumped into the Winter package... so I am sure it was more than $495!
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Old 01-23-2020, 12:05 PM   #14
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I'm always surprised by the number of stock JKs that fly past me on the freeway doing 85+ mph (while I'm cruising the slow lane at 65). Soccer Moms/Dads want to drive in the fast lane and they want good gas mileage (for a Jeep). Like NoGABiker says, they have no clue about axle ratios - they just know you push the pedal on the right to go and the one on the left to stop, and that theres a noisy thing under the thing in front of them that they think can be opened, only because they saw the guy at Jiffy Lube do it.
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Old 01-23-2020, 03:11 PM   #15
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With 3.21 and auto im in "ECO mode" till 77-78MPH it can go to 100 easily, i think for Wrangler balance betwen "on road" and "offroad" capabilities is important. Sports with 3.21 are more "on road" and less "offroad" jeeps, wich basicaly is perfect for ppl like me who daily drive their jeeps and go offroad where any SUV or Pickup can go.
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Old 01-23-2020, 04:07 PM   #16
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Quote:
Originally Posted by USStrongman View Post
It isnt the number so much as it is the driveability. Its a flying brick to start, now add weight, wind, etc and its a terrible design... for the consumer... who is buying them. And yes, 3.73 was lumped into the Winter package... so I am sure it was more than $495!

In total agreement here. Hell stock and 4.10's is just barely adequate. A good head wind or moderate hills still has you down shifting. I wanted to re-gear even before I went to larger tires.
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Old 01-23-2020, 08:33 PM   #17
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Quote:
Originally Posted by USStrongman View Post
Curious. WHat was FCA thinking with the 3.21 ratio in JK/JKU?
We have the 3.21 in my wife's 2013 JK Sahara. I've driven it and it scoots right along. No need for anything else, IMHO. I guess the engineers figured the 285 hp engine more than makes up for the earlier generation engines that were underpowered.
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Old 01-23-2020, 08:36 PM   #18
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We have the 3.21 in my wife's JK Sahara. I've driven it and it scoots right along. No need for anything else, IMHO. I guess the engineers figured the 285 hp engine more than makes up for the earlier generation engines that were underpowered.
and even more important is the NAG1 tranny is so much better. My 2013 sport had 3.21 and 285/75-17 tires and never had an issue.
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Old 01-23-2020, 09:20 PM   #19
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Jeep wins by getting to score a little bit higher in EPA CAFE testing, getting to charge $495 (in 2014, more now I'm sure) to the people who actually do care and order 3.73,

You know what's crazy? In Canada, the 3.73 option on a '18 Sport JKU is a $125 (Canadian, no less!) option. It was a no-brainer when I was ordering to add it in.



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Old 01-23-2020, 10:08 PM   #20
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I had a 2012 and 2016 JKU with the 3.73.
I drive my Jeeps for my work about 30,000 miles a year.
I am reimbursed 57 cents a mile. It was working ok with the 3.73 and I was happy.
I bought a 2018 JKU about a year ago with the 3.21. What a difference.
Most of my mileage is on the highway. Now my mileage reimbursement is much better. I can buy another new Wrangler sooner.
If I have a need for more off-road capability I drive my CJ-7.
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Old 01-23-2020, 11:08 PM   #21
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Curious. WHat was FCA thinking with the 3.21 ratio in JK/JKU?

I had a 15 JKUS with 3:21’s w/ manual and now have an 89 w/ 3.07 with 31x10.50’s. They’re both fine, for what I do. Mostly just hunting/fishing. I prefer the high gears for the road, which is what I do 95% of the time.
If I need more I stick it into 4lo, at least it has LS.


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