MPG - Windows Down or A/C

[CALDWELL]

hey fella's, today i have a question about traveling with the windows down, or A/C on, and the effects to mpg.

In August my family is taking a trip to Corolla, NC ( OBX ). I was talking to my mom ( who will be driving with me. ), she was asking what kind of gas mileage my X gets.

I told her that i recently took a trip from home ( S. Philadelphia suburbs ) to Harrisburg, PA with 3 of my friends in my truck. the trip was 132 miles, and I used 1/4 of a tank getting there. I was traveling @ an average speed of 76 MPH. I had the windows down, and a full load of people, and the A/C was off. I would guess that i was getting around 22 mpg +/-. I thought that was pretty impressive.

HP / MPG MODS - K&N Airbox Mod - Magnaflow muffler

* hoping to have complete 2.5'' exhaust by then also

Now I know that the A/C will use more fuel, and decrease my mpg. My moms thought was that if the windows are up, and the A/C is on. the X is more aerodynamic, and will have less drag. which would compensate for having the windows down, even though our trucks are like bricks moving down the street


I just wanted to get some thoughts or answers, to prove my mother wrong lol. I want to drive front windows down for the trip. do you really need A/C @ 70mph with the windows down ? well i guess that may be preference...


thanks fellas

 

[nssj2]

well you're both right. Keep in mind though, driving style is the biggest player in MPG. The generally accepted rule of thumb is that below 40mph, windows down AC off is the most efficient. Anything above 40 should have the windows up and AC on. To give you an idea of how much drag is involved at 40ish mph, try to open your door (seatbelt on is highly recommended). I can't even open mine above 25.

 

[snickstx]

An interesting read.

http://green.autoblog.com/2007/08/29/mythbusters-mistakes-in-ac-vs-windows-down-episode/

I guess it depends on if you're driving 45 or 70 most of the way. I'm always windows up, A/C on...but I'm in Texas. I wish I had A/C in the seats.

 

[alexk]

I did the same trip in my x last august except I went to nags head. I filled up once I got off the bridge into delaware and drove all the way down there and still had just under a quarter tank of gas. By the time I filled up I calculated 22 mpg. Mine was a v8, I did about 75-85 the whole way down and I was using the front and rear AC. I had one other person and 2 kids with me, the third row was folded and filled with stuff.

 

[Ronin8002]

I use the A/C most of the time highway or around town. Only exception is if the weather is nice (in the 70's) then I'll open the sunroof and roll down the windows...but only around town...not on the highway.

To me it's worth using a little extra gas to have a comfortable, quiet ride and not arrive at my destination looking like I just thrashed myself at the gym.

FWIW I believe Aldive (RIP) got all of his 30+ MPG results with windows up and A/C on.

 

[F15E_WSO]

Saw this on mythbusters (was not an SUV) and having the windows down was LESS fuel efficient. So run the AC!

Also I suspect you will spend more on the first round of drinks on what might be saved on a trip like this; don't sweat the little things (pun intended)

 

[gtyates]

I also agree. At highway speed it is a disadvantage to drive with the windows rolled down. And it is a heck of a lot more enjoyable to travel with a/c on!!

 

[CALDWELL]

Ok so the general idea is to run the AC for optimum mpg...

I thought the AC would do worst then the windows down. I never use my AC so i really wouldnt know. I love driving with the windows down

windows down is easier to spot hot chicks lol, and to let them know they look good with the PA system i have in my X lol

 

[DLinkOZ]

Saw this on mythbusters (was not an SUV) and having the windows down was LESS fuel efficient. So run the AC!

Also I suspect you will spend more on the first round of drinks on what might be saved on a trip like this; don't sweat the little things (pun intended)

You beat me to the Mythbusters reference. As soon as I saw the title of the thread, I knew what I wanted to post... but no, I'm beat to the punch.

 

[Doomie17]

i got the cure for best milage. windows up a/c off. but what was said before driving style plays more in the equation

 

[IZwack]

IMO - AC off, windows down (a bit) for max MPG. Of course I havent tested it but I'm pretty sure the coefficient in air drag vs the drag on the AC compressor is smaller. This is part of how I got 55 mpg on my Civic (but I never cracked the windows more than halfway down when on the highway - but its okay to roll them down all the way driving around town).

If you live near mountains, I'd do this test: Find the steepest, longest highway incline you can find. With the windows up and AC off, approach the mountain at 60 mph. Without using cruise control and keeping your foot steady on the gas (dont move it up or down), turn on the A/C when the vehicle is halfway up the hill. Notice how the vehicle slightly lags when the A/C kicks in. Of course part of this is inertia because the pump must go from 0 RPM to just about the same RPM as the engine. But still, take note of the lag. Then do the same test - approach the same incline with the windows up and AC off at 60 mph. Keeping your foot steady on the gas (again) and halfway up the hill, open the windows at the same time and notice the lag (if any).

Visit ecomodder.com - thats pretty much one of the biggest hypermiling forum, plenty of lessons on that site, even some hypermilers using pickup trucks and so on.

 

[EasyRhino]

Windows up/AC on.

Also, you surely know that determining gas mileage by estimating % of a tank used is innacurate, at best.

 

[IZwack]

Also, you surely know that determining gas mileage by estimating % of a tank used is innacurate, at best.

What method do you use? And where is percentage significant?