karls10jk

Unless the Willys is decked out with armor or on 37's, I wouldn't want the 4.88's for the highway and 70mph.

domano 68

Any other thoughts? Also what does the red arrows indicate on the above chart? Thanks!

resharp001

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Here is something to consider when your regular commute involves highway AND mountains. You're either going to be revving a bit higher on a flat highway on the top end, or revving higher due to having to downshift to lower gear in the mountains. I've not owned a 6-sp wrangler, but I will tell you that revving 2700-2800 rpm on the interstate isn't bad and is about perfect for me. It's a fine line of getting up to 3k+ for an extended cruise is where the engine noise gets a bit aggravating to me.....you know, long road trips with cruise control and engine at 3k. Either way when you get out of that little green zone on the tac (above 2500 rpm), you're not gonna see the "eco" light come on much.

OD is overdrive, not relevant to the 6-spd. Guessing whoever made those charts was lazy and just duplicated that part from the auto? idk I don't look at the manual chart much and have to say I never noticed that.

OMJK17

Maybe a dumb question, but ideally for flat highway driving, is there a RPM that the 3.6L operates with the best fuel economy?

I only ask because I'm gonna be upgrading my 2017 JKU with a 3.21 to 34" and likely eventually 35" tires. It's an automatic and primary highway and city driving, moderate hills as we are at the foothills of the Adirondacks. I know a re-gear is in my future, I was also unsure about 4.56 or 4.88. I want to do it once and be done. Looking for the best possible fuel economy.

resharp001

Auto or Manual? (**edit...sorry, I see you say it's auto) Since there are limited gearsets available, it's often a compromise. In your situation, 4.88s are pretty aggressive for 34s. That gets you down to 4.10 or 4.56, and since you have foothills it's most likely you lean to 4.56. If you were strictly going for fuel economy it would probably be 4.10s due to the lower RPMs on flatter land relative to the tranny stress heading up the hill. 4.56 is pretty much the sweet spot for "35's" and the 3.6L auto. 6-spds typically get away with 1 set lower.

You're driving a jeep. All I could really say is ANYTHING you do after you start modding is going to make it less fuel-efficient. I'd opt for a higher revving engine over lower revving and more stress on the transmission. I used to be more concerned about RPMs, but my jeep, solo, gets better fuel economy with screaming RPMs at a lower gear through mountain climbs than the jeep gets towing my trailer on the interstate on flatter land in 5th gear and lower RPMs. There is a point though that the engine noise gets a bit loud, and for me that is cruising around 3k rpm regularly. That is subjective though.

Jay2013jk

Not being a smartA.. on the tach is a green area.. this is the optimum RPM range for economy.. now looking at the chart on this link:

https://www.google.com/search?client...aboqHtQammUM2M

you could surmise what would put you in the optimum RPM range. FYI.. most 35" are not full 35s most are slightly less. Good Luck with the re-Gear.

OMJK17

Thank you. That’s where I was kinda confused in the chart. I didn’t know if green was good but blue was the best, or if green was exactly where I want to be. Thanks for the help!

OMJK17

Another gear related question. It's pretty clear that tire size is an important factor. How much of an impact would the weight of the tires or weight of the jeep in general be in regards to gear selection?

resharp001

Weight of tire/wheel combo is going to have a big impact on performance, but it's not the difference between choosing an additional step up/down the gearset ladder IMO.