Just in case anyone is interested the speed at which you lose out on gas mileage from having your window open is around 40-45 mph. It depends on the frontal area of the car and how much drag will be created. Just incase anyone wanted some useless engineering facts. We did it in class a yr ago so just thought I would share some knowledge with the rest of you guys.

 

I'm a graduating civil engineering major, however, in our fluids class we did lots of these calculations with cars. Since our prof was a guy who liked cars we spent a week on how to find real stats of these sorts of things. Like if a golf ball has dimples to improve the reynold's number and such would it benefit you to take a hammer to your car and make dimples? Anyhow, based on the drag equation it came out that on an average day that 40-45 mph is where having the windows down creates significant drag. These calculations were based on a volkswagon bug (the new one) b/c that's the shape and area he had. But i'm sure it's pretty comparable since they are both sub compacts.

Oh and w/ the dimples, your car is already designed to have a high reynold's number so no bashing up your car w/ some hail damage or ding's will not increase your speed. Only reason I say this is b/c a poll was taken in our class and half the class said yes it would help, but ppl don't do it b/c then our cars would look like crap. At least they were half right.