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Discussion Starter · #1 ·
First, I’ve read literally thousands of post on this but wanted to get direct input on my situation.

I have a 2016 Unlimited Sport with 3.21 gears and the Trac-Lok rear differential. I live in western North Carolina so we have some hills but most driving is at the 2700 ft elevation. I also occasionally tow a small trailer for camping. Never really had too much of an issue with the factory 255/75r17 wheels. Bogs down a little when fully loaded up long grades but makes it fine. I average 18.5 to 19.0 mpg.

I am putting on Nitto Ridge Grappler 285/75r17 on factory wheels with 1.5” spacers. I am also installing a Rancho 2” progressive lift with Geo Brackets.

Question is on gears. 90% on road driving with some long work trips. Never any hard off road. Mostly dirt roads with some small ruts. I realize I should change gears at some point. Looking over the tables 4.10 would make the most sense but is that a wast of time? Should I at least jump to 4.56 or is that overkill? I need to really balance performance with fuel economy. Yes, I know it is a Jeep but trying to be sensible.
 

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First of all, with MPGs your main hit is going to come from the larger tires and lift and compared to that hit the difference between 4.10 and 4.56 will be minor. Talking potential for 1-2 mpg drop for tires/lift, and a fraction of an mpg difference on those two gear sets.

Considering that, most would probably recommend 4.56 for best performance. I have factory 4.10s with 315/70/17s, and it's good enough for me and I have no plans to regear. That includes driving over steep and high grades out here in the Sierra Nevada (passes up to 10k ft, freeways up to 8k) and desert ranges. I do load up for overlanding with hundreds of pounds of gear in my JKU, but no towing. If I could regear for free I probably would change to 4.56 though. It's peppy enough off the line and good enough on grades as is, but 4.56 would be better without affecting MPGs noticeably.

But keep in mind, plenty of people run your tire size even on 3.73s and call it good enough. A lot of subjectivity here.

One other thing to keep in mind for freeway driving is that your transmission can do what it's made for, in my case 4.10s in 4th gear on the AT is the same as 4.88s in 5th gear. This also allows some degree of comparison if you keep your 3.21s for a bit with the new tires. Below is a link with the transmission ratios, which you can multiply/divide with your axle gear ratios to see what different trans gears would be equivalent to. For example if you have the AT, locking it in 4th on the freeway would be like having a 3.73 gear (approximately) in 5th. 3rd gear would be like a 5.38 in 5th or a 4.56 in 4th, and so on. Obviously these single point comparisons are only worth so much, but better than nothing.

http://www.wanderingtrail.com/Mechanical/gearratio.html

The only place using a different gear doesn't work is taking off from a stop, the lower gear will always be lower in 1st off the line and give that extra pep.
 
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Hills + towing + 2700ft + 285's = 4.56. Your MPG's will go down a little but you will like it more. Some like the 4.88's but I think it's more than you need. With the auto your freeway speed, 75, will put you in the 2700rpm range and that's just fine. From 3.21 to 4.56 will be a huge jump. You will need to re prog with a pro-cal the time that it's done. To really feel the difference do the tires first.
 

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I have a 6 speed manual and pull a Trailer at times but zero hills all flat .
Also have 4:10 gears and like it a lot if i did have hills i would go to 4:56 .
My mpg is very good but I never drive over 65 mph and drive smooth .
 

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You don't say whether you have a manual or auto trans.

The way I'd look at it is that the FACTORY puts 4.10s on JL Rubicon jeeps with 285/70s and thinks that is good for everyday use and off road use. I generally trust factory engineering when it comes to such things.

The JL (auto) has a 0.67 final drive ratio and the JK (auto) has a 0.69 final drive (essentially the same), so I think this is applicable information.

But if you wanted to compensate for towing and climbing grades, carrying extra weight, etc, then I'd say you could go to 4.56. Go test drive a JL Rubicon with the v6, Auto and 285/70 tires and see what you think and let that be your guide.

When I bought my Jeep it had 31's and 4.88 gears (but a "taller" final drive ratio of 0.80 because of the manual trans). I immediately put on 285/70s and was unhappy with how it revved too high on the highway. I put on 35's and now its just about right for me.
 

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I run 4.10 on 35s that’s 2100rpm at 60mph. With 285s that’s getting up around 2400rpm. That’s a bit high for a DD.
If you NEVER plan on going bigger the 285 don’t go lower gear then 4.10.


Sent from my iPhone using Tapatalk
 

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I run 4.88s, 285/75 and love it. It’s all subjective. I don’t think you can go wrong with the 4.56s.


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4.56 for sure.

I went from 3.21 -> 4.56 in a 2013 JKU auto, 285/7017.

Run routinely at 3000-3200 rpm on the highway at 75-80 mph all day long.

Cruising up mountains never an issue, rarely kicks down into 4th.

VERY happy with how it drives.
 
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I am in the 35s and 4.56 camp with a 2015 auto JKU. Love it. Now having said that, I live in RDU and I am visiting my mom this weekend in Asheville. If I was to live here permanently I'd gear to 4.88


I get a average of 16.5 mpg but I accelerate rapidly and tend to be heavy footed. If I baby the Jeep I can get and have seen 18.5 on the interstate.
 

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I am average <13 MPG all around town driving. Thinking of going to 4.56 to get better mpg, couldn't get worse.
 

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The way I'd look at it is that the FACTORY puts 4.10s on JL Rubicon jeeps with 285/70s and thinks that is good for everyday use and off road use. I generally trust factory engineering when it comes to such things.

This is a decent point of comparison and a lot better than nothing, but the 285/75/17s OP is planning on are a bit bigger than the JL's 285/70s (34" vs 33"). And the JL's KO2s run small for the size. Edit: OP did mention he's looking at Nitto, which would be a good amount taller and heavier.


Would also need to watch out for the difference in feel of the 8 speed auto vs 5 speed when accelerating, unless OP has the MT.
 

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Discussion Starter · #12 ·
Thanks for the input everyone. My Jeep is an automatic. Forgot to mention that in the OP.

A respected Jeep builder in my area recommended the 4.10’s. He does a lot of 4.88 and 5.13 but mostly for rigs with 35’s and built more for off road. His logic is sound but it’s somewhat of a bitter pill to spend the money and only get the same ratio as a stock Rubicon. Not that I am selling it anytime or ever but I feel like already having 4.56 would be more attractive.

I’m about to just flip a coin. Not really, I’ll probably spend some time with the RPM tables and see what I can live with. 70mph is pretty standard for me.
 

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Thanks for the input everyone. My Jeep is an automatic. Forgot to mention that in the OP.

A respected Jeep builder in my area recommended the 4.10’s. He does a lot of 4.88 and 5.13 but mostly for rigs with 35’s and built more for off road. His logic is sound but it’s somewhat of a bitter pill to spend the money and only get the same ratio as a stock Rubicon. Not that I am selling it anytime or ever but I feel like already having 4.56 would be more attractive.

I’m about to just flip a coin. Not really, I’ll probably spend some time with the RPM tables and see what I can live with. 70mph is pretty standard for me.
Point well made. I'd go 4.56 for this exact reason. If your gonna spend it, get some performance outta it!
 

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I agree, re-gear and go with 4.56 gears. Jeep puts 4.10 gears on Rubi's with 32" tires, and that is just barely enough gear. If you are going with 33" tire up to 35" tires 4.56 gears work pretty well. But everyone has their own tastes and expectations.
We have 4.88 gears with 37" KO2's (which are really just over 35") on our manual trans JKU. I occasionally wish we had gone with 5.13 gears. Both on the highway where the 4.88 gears don't have the power for the hills and off road where you just can't crawl slow enough sometimes.
My sister in-law has a JK with an auto trans and 35" tires and went with 4.56 gears. She is very happy with them.
Both of us wheel fairly hard, but neither is what I would call a hard core wheeler. But gears are power. And power is good.
 

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my manual ' 09w/ 3.21 came with the larger sahara tires (31s?) when i bouth it. was ok-ish as a DD IMO. went to 4.56 and 33x11.5 with lockers when i added the ranch spot lift + geo brackets and like you. now turns 3000 at 80mph on the highway. in the hills of VT i can still accelerate now in 5th on the highway. i'm at ~15mpg after 6 months of this setup.
 

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I don't believe it's worth the money to go from 4.10's to 4.56's. I tow a small pop up trailer and have 4.56's and towed on both 35's and 37's.

In the mountains (Ashville, VA, WV and around Chattanooga) I really wished I went with 4.88's.

Based on my experience, I would recommend 4.88's if you plan on towing in the mountains.
 

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You will be just fine with deeper gearing on a DD.

32 - 4.10
33 - 4.56
35 - 4.88
37 - 5.13

My DD is 37s/5.13 (2014 Rubicon).
 
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I have a 2015 JKUR with 3.5" lift and 4.88 gears. I tow a camping trailer regularly, which is around 20' long and just under 3500 pounds loaded. I live at 1700 feet and tow into mountains regularly. I'm very glad I went with 4.88 instead of 4.56.

I can't give you useful MPG numbers. I do too many things with the Jeep to get a straight street driving number. I rarely go through a tank full just driving it normally.
 

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After reading all the Opins... I have a 13 JKU Bestop soft top w/3.73 and a 16 JKU hardtop w/3.21.. Both DD. Both 6spds... Both with 285/70r17s.. Both with the factory LSD...yes there is a difference in S.E. Pa.. the 16 @ 65mph is turning 1600-1700 rpm gets 19mpg town & short bypass hwy.. the 13 @ 65mph is turning 2000-2100 and gets 17mpg. Any gearing change would be to put 3.73s in on the 16 -- BUT - why spend the $$s..I just grab another gear on the 16 whenever, usually the 16 pulls it fine on hills.. That's my $0.02, Thanks for reading.
 

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I'll throw in my two cents....

I run 4.88 on 37s with an auto trans in 2013 JKUR. I get around 14 mpg in town and maybe 15-17 on the highway. Does great as daily driver and still has what I need for off road. As mommymallcrawler said, you'll be fine with deeper gearing on a daily driver.

no whining now...
 
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