Okay, we all know the car has less drag with windows closed.
I also read somewhere that 45 mph is the crossover point for AC vs. windows.
If you are going OVER 45 close the windows and turn on the AC for best MPG.
UNDER 45, open the windows and turn off the AC.

Now, when the windows are open I would guess that opening only the front ones would be the worst for MPG because the air coming in the front cannot get out the back.
I'd guess opening all 4 windows half way would give better mileage than opening only the front two all the way.

What about opening both windows only on one side?
Any mechanical engineers here?

 

Kenny I drive alot with my driver window open and I get much better milage than with the window up and the a/c on! Look at my last tank 50 mpg vs the rest of my tanks. Drag or no drag if I can handle it I will not use the a/c. Oh Iam avg. 50- 60 mph when I drive. Kevin

 

Hi Kenny:

___I will concur with Texashchman. If I start up A/C, I lose from 25 - 40% immediately as lean burn is for all intents and purposes, handicapped at best. With the windows down, it is more like a 5% loss at 50 mph.

___This isn’t the same as the old days when the monster heavy Buick Le Sabre w/ a 455 cu. in. 4 Barrel and a Cd of .42 was cruising down the road. I can see the 45 mph cross over point might be about right for that large and ancient of an automobile. My father owned one of those back in 1970 IIRC and when he put his foot into it, it sounded like someone flushed a toilet! At 7 mpg when pulling the trailer, it might as well been a toilet instead of a 4 barrel on top of that monster ICE

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___Waynegerdes@earthlink.net

 

Thanks for sharing your experience.
I read the 45 mph thing in Westways Magazine, the Southern California pub for the AAA.