Odd aerodynamics?

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AmishMike

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@Advntrbound See, I am not the only one!
With a background in physics, I like to think that I understand drag coefficients, turbulence etc.. I have build 200+ mph dragsters and Bonneville cars. I have squeezed mpg out of my old 460" powered F250 tow vehicle.
That is why this is so baffling to me, it defies sense. Stock height Rubicon running 35" Geolandar A/T's, tonneau cover, no speedometer correction. I can average 19.0-20.2 mpg at 65-75 mph a/c on or off. Add full height rack, 19.9-20.4, all 4 windows down, 20.8-21.6 mpg.

I really think that the aerodynamics of this thing are simply that bad stock that anything to disrupt them is an improvement.

@Victoryrider78 I have always found that I can get better mpg without cruise control. It cannot anticipate changes in environment like hills etc. Learned that while towing 30' car trailers and it seems to hold true even with the wife's Subaru.

 

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I have always found that I can get better mpg without cruise control. It cannot anticipate changes in environment like hills etc. Learned that while towing 30' car trailers and it seems to hold true even with the wife's Subaru.
The cruise on these is programmed to help mpg - but it's not possible to do with hills and such.
There's even mention of the cruise being associated with better mpg in some of the documents I have - if I can find it again.
But here, the hills ruin that. IF you gain a bit of speed going down hill then you can let off the pressure a bit going up and allow it to lose a bit of speed, but still keep up your average speed, you can improve mpg over cruise. My wife loves to brag about the MPG her Grand Cherokee can get and I see how she does it. She watches the current mpg and tweaks her foot on the pedal in the hills. If the speed limit is 60, she'll let it gain to 65 or better going down hills, feathering the pedal, and then let it drop back going up the next hill letting it drop back to 60, maybe a tad under.
She's the extreme, but anyone can do similar if they are really concerned.
And if they are really concerned - uh, Prius? Or if it must be a Jeep - Compass or Grand Cherokee.
She's done 25-26 without a lot of trouble. My son says his Compass could do 30 if he wasn't the driver (LOL, I've ridden with him)
 
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@ShadowsPapa Yes, cruise definitely helps with mpg for the average driver who tends to be less attentive than many of us. These new vacuum meters, er I mean mpg gauges can help and show when a little less pedal pressure nets big gains in mpg while maintaining mph. In the older vehicles you had to rely on pedal pressure and being in tune with the engine.
 

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Yes the control isn't perfect. Especially here in western PA where everything is either up or down. Its more a comfort thing for me, especially if I am only gaining a 1/2 mpg. I am happy with my 21.5!!

@ShadowsPapa I wish my wife was more aware of her fuel mileage! She gets 25 in her Equinox on mixed driving. When I drive it, its about 30 mpg.
 

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I also get better gas milage than most. It's weird, since I'm running 40s.... Anyway, I think the higher lift increases gas milage due to lighter atmosphere resistance at higher altitudes. Many hours of research have gone into this hypothesis... many hours.
 


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I also get better gas milage than most. It's weird, since I'm running 40s.... Anyway, I think the higher lift increases gas milage due to lighter atmosphere resistance at higher altitudes. Many hours of research have gone into this hypothesis... many hours.
You must be at that precise level where you get less air resistance but yet do not require forced air induction. Brilliant!! It's like 4x4 Zen.....
 

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Yes the control isn't perfect. Especially here in western PA where everything is either up or down. Its more a comfort thing for me, especially if I am only gaining a 1/2 mpg. I am happy with my 21.5!!

@ShadowsPapa I wish my wife was more aware of her fuel mileage! She gets 25 in her Equinox on mixed driving. When I drive it, its about 30 mpg.
LOL - my wife would be proud to show her how she does it. She brags about it. And I get chastised if she has left her Jeep in the garage with 25.5 mpg and I take it to run some errand and bring it back with 23 mpg average.

I have been through PA twice - going to Reading to pick up a car, and coming back with said car on a trailer. Is your area hilly? I'll not forget towing that rig through some of the mountains out there, in part because of the beauty. Very different from other mountains. But I can't recall if Pittsburgh is flat - seems to me it was flatter there. Man, that was about 2007. I never did have a great memory.

I also get better gas milage than most. It's weird, since I'm running 40s.... Anyway, I think the higher lift increases gas milage due to lighter atmosphere resistance at higher altitudes. Many hours of research have gone into this hypothesis... many hours.
That explains the tanks in the back and the oxygen mask laying on the console.
 

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I lost .5MPG with a 3.5" lift completely stock diesel sport S.

Most likely the lift caused more air to hit the tires causing more drag.

Its interesting that jeep did so much engineering just to get 1-2 mpg on the highway and it can be completely disrupted with a few common modifications.
 

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@ShadowsPapa Yes, cruise definitely helps with mpg for the average driver who tends to be less attentive than many of us. These new vacuum meters, er I mean mpg gauges can help and show when a little less pedal pressure nets big gains in mpg while maintaining mph. In the older vehicles you had to rely on pedal pressure and being in tune with the engine.
In 1973, I put a vacuum gauge in my 68 Javelin. It was a base model, no clock, so I had an empty spot in the left cluster "tunnel' just right for such a gauge.
My 82 SX4 came factory with one - as it had the optional rally gauges - OP, volt meter, vacuum, clock.

You aren't the average driver who hops in, not understanding cause and effect, or how things work. To many, a vacuum gauge is a "what the heck is that for and why should I care" thing.
For me - it's a "that thing is fluttering, time to check things out - may be a valve bad or misfire"
If it's lower than usual, I check for vacuum leaks or other issues.
Volt meters and vacuum gauges are great diagnostic tools. Oh, and they can help with mpg if you are concerned at all HA.
 


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LOL - my wife would be proud to show her how she does it. She brags about it. And I get chastised if she has left her Jeep in the garage with 25.5 mpg and I take it to run some errand and bring it back with 23 mpg average.

I have been through PA twice - going to Reading to pick up a car, and coming back with said car on a trailer. Is your area hilly? I'll not forget towing that rig through some of the mountains out there, in part because of the beauty. Very different from other mountains. But I can't recall if Pittsburgh is flat - seems to me it was flatter there. Man, that was about 2007. I never did have a great memory.



That explains the tanks in the back and the oxygen mask laying on the console.
Hypothesis, not Hypoxia...
 

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@ShadowsPapa I'm north of Pittsburgh. There's a lot of hills around here, and yes most of Pittsburgh has lots of Hills... actually broke down North Hills, South Hills, East Hills and West hills lol.
 

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Hypothesis, not Hypoxia...
LOL - yeah, but she was talking about getting better mpg because of the lift and big tires putting her truck up into the thinner air, less resistance. Sounds like her truck sits way up there, maybe she's had some fighter pilots wave to her as they fly by her up there..........

>>Anyway, I think the higher lift increases gas milage due to lighter atmosphere resistance at higher altitudes.<<

Some of the Ford and Chevy trucks around here I want to stop and ask them how the oxygen level is up where they are sitting.
 

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A ford flex Limited with the 3.5L twin-turbo is shaped like a brick, and fast. Low 12s for the 1/4 mile, stock. There is actually a flex drag team called Ecobrick...cracks me up.
To put that time into perspective, a Dodge challenger RT with the V8 runs low 13s in the 1/4 mile.

 

 
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