Ways to improve mileage in a JKU?

[libarata]

Yeah, drafting helps too. I did that on our last roadtrip until the trailer I was drafting in eastern PA blew a retread and the Jeep got blasted with highway rubbery.
It was downright scary.

I always feared that, but the improved MPGs were worth it. When I finally moved to an area that sold non-ethanol petrol, my non-drafting MPGs went up to about 25 at 50mph. Oh, I also drive five under, which nets me 25-27mph in my 99 Forester when NE is in stock.

 

[jungblud]

I always liked the bumper sticker 'You go fast, I"ll go anywhere.' Why so fast? Where is the fire?

 

[GFA]

The gearing is the main problem with your milage. I was going to change my gears but decided my milage is more important than more grunt. RPM = Less MPG. ALWAYS

I agree 100% that I'm over geared and that it is the root of my poor mileage. I'm stuck with the gears though as I'm not re doing them again, I can't see putting more money towards it that would sacrifice drivability for an added 2-3mpg's on the highway. I would however add the Ripp if I were certain it would be a significant improvement in drivability and a modest increase in MPG's. It's hard to bite that bullet though since there would still be a turd underneath all that sugar coating. Reliability of a supercharger is also a concern of mine as some of my travels have taken me a long long way from help if it were needed. I will be due for tires by the end of the upcoming winter though so I might try some light 315's or 35/12.5/17's to see if it makes a difference for the better. I doubt it would hurt as long as they're light.

I ran it for about 5k miles on the current 285's before re gearing and it was painful to drive. Constantly shifting even with the slightest change of grade, downshifting to second at 70mph and the complete inability to tow my m416 using overdrive at any speed. This was before the gobi also. It's marginally better after the re gear but it does not make up for the fact that it's under powered from the start. I was very surprised that my wife's Lincoln MKX pulls the m416 significantly better than the jeep did in it's stock form...

I did a bit of drafting going thru Tennessee but most truckers don't like it as you have to get very close to them so that the winds coming around them don't rock you around. It's amazing the difference you can feel once you decide to pass them, it feels like starting up a steep grade after just coasting down another.

I think I've decided to keep this one until we actually know what the next wrangler will be and what it has to offer. If it's not a significant improvement over the current wrangler then I'll either get a final year model JKU or possibly trade out to something different.

Thanks for everyone's input, it's been a big help.

SB

 

[GFA]

I always liked the bumper sticker 'You go fast, I"ll go anywhere.' Why so fast? Where is the fire?

I don't mean to offend any mid westerners here but when I'm going from NC to CO or MT I can't get through Kansas or Iowa fast enough. States like them are the bowels of America IMO, they play a huge part in our country but are meant for passing through...

Seriously though, it's nearly 1700 miles from here to Denver, a 10mph difference in speed getting there and back can mean adding 2 days to my trip in an area I'd like to see vs 2 days in one I'd rather not. Im not at a point where I can take off several weeks at a time so every day counts. I'm all about slowing down and taking it in when I'm in the areas that are scenic to me but corn fields are not one of them.

Damn jeep, I don't know why I'd rather drive it than my V8 F150 that's more comfortable and gets 16-17 at an effortless 75mph...

 

[kojackJKU]

Just sumptin about them. I am running your same tire package and I have no issues with driveability. I am a 2011 auto with 3.73s. Works the bees knees, not a rocket ship but that's not what she's for.

 

[I Leak Oil]

Your gearing is your biggest obstacle to getting better mileage. Others have already said it so I figured I'd just throw in my two cents to reinforce that fact. I know it's the most expensive of all the potential solutions presented here but that doesn't change the reality of it. Those are damn tall for your tire size and highway driving.

 

[Septu]

What about finding a friend or someone local to swap tires with for a couple days. Don't do any wheeling, but just see what 35s would be like with some highway driving.

 

[kojackJKU]

with 5.13s he should put on a 37"

 

[Dan Grec]

arly 1700 miles from here to Denver, a 10mph difference in speed getting there and back can mean adding 2 days to my trip in an area I'd like to see vs 2 days in one I'd rather not.

I think your math is a little wonky.

1700 miles @ 60mph average is 28.3 hours of driving time.

1700 miles @ 70 mph average is 24.25 hours of driving time.

So that extra 10mph average will only "save" you 4 hours of drive time, not even close to "2 days"

The difference is only 3 hours between 70mph and 80mph.


At highway speeds, almost all the energy the engine is producing is to overcome wind resistance, especially so on a vehicle with a co-efficient of drag like the Wrangler.
The energy required to overcome wind resistance increases with the cube of velocity (i.e. to the power of 3) - so you'll require much less energy to drive even a little bit slower, which is why slowing down helps mileage much more than anything else (tires, weight, etc.)
(The energy required to move more mass only increases with the square of mass (i.e. to the power of 2), so removing weight is still not as good as slowing down).

-Dan

 

[GFA]

I think your math is a little wonky.

1700 miles @ 60mph average is 28.3 hours of driving time.

1700 miles @ 70 mph average is 24.25 hours of driving time.

So that extra 10mph average will only "save" you 4 hours of drive time, not even close to "2 days"

The difference is only 3 hours between 70mph and 80mph.


At highway speeds, almost all the energy the engine is producing is to overcome wind resistance, especially so on a vehicle with a co-efficient of drag like the Wrangler.
The energy required to overcome wind resistance increases with the cube of velocity (i.e. to the power of 3) - so you'll require much less energy to drive even a little bit slower, which is why slowing down helps mileage much more than anything else (tires, weight, etc.)
(The energy required to move more mass only increases with the square of mass (i.e. to the power of 2), so removing weight is still not as good as slowing down).

-Dan

Your math is correct in that it takes 24hrs of actual drive time at 70mph not including fuel stops and food or congestion on the roads. That's easily 30hrs in the real world. What I forgot to mention is that I make the trip out and back in two days, so roughly 15hrs each day which is at my physical limit of drive time for one day. I can not safely add another 2 hrs of drive time per day so it would add an extra travel day in each direction although it would be a short one at only 4 hrs each.

The rest of your post makes sense and makes me think that even though 35's would slow down rpms by about 150 or so, it won't help any. Still gotta push the brick through the air..
SB

 

[Flagster]

fly and rent a truck/rv/jeep
that is a long drive/lotto gas for one camping trip a year

 

[K2ZJ]

How are you calculating mileage and did you correct your speedometer after the gear change?

 

[GFA]

fly and rent a truck/rv/jeep
that is a long drive/lotto gas for one camping trip a year

I thought of doing that but we did about 560 miles of dirt through multiple states. Once we reached the Badlands in SD we tried to keep off of asphalt until we made it to great falls MT which accounted for nearly 400 of them. The rest were in Utah and Colorado. The journey truly was part of the trip, just not the 1800 miles getting there and back. That part sucks..

I think I'll be making a moab trip for a week in the spring and flying/renting is the plan then.

How are you calculating mileage and did you correct your speedometer after the gear change?

My speedo is spot on after using the flash cal to adjust and mileage was calculated at each fill up. My MPG display is about 1.5mph off of actual.

I shouldn't complain I guess, my average mpg over 7600 miles was just under 14 as 4000 miles of the trip were done at less than 65mph where I usually get 14-17. It's just the highway mileage at 65-70 that's the killer. I'm looking for gas stations at the 200 mile mark

SB

 

[kojackJKU]

fly and rent a truck/rv/jeep
that is a long drive/lotto gas for one camping trip a year

what you talkin bout willis? fly instead of drive? silly talk.

 

[Septu]

fly and rent a truck/rv/jeep
that is a long drive/lotto gas for one camping trip a year

It's not only the destination, but the journey that is part of the fun.