I need you to confirm or deny!*

My friend Nathan says driving with your car windows down is less fuel-efficient than running the A/C. He says the increased drag requires more extra power than the A/C motor. But he rides a bike everywhere, so I need to get a second opinion on what he tells me.

*From an actual question a student e-mailed me about the International Law review session he missed.

5 comments:

Spice said...

It depends. My Prius is pretty aerodynamic (and pretty pretty, BTW), so having the windows down is more efficient than running the A/C, or at least so says many articles and message boards I've read about my beloved Otto II.

towwas said...

They covered this on Car Talk once - and what they come up with was, like, above some speed (can't remember what it was, but it was highwayish) it was more efficient to run the AC. I say, when it's hot out, I run the AC. I hate being hot and sweaty in the car.

grrrbear said...

They covered this on Mythbusters a season or two ago. Basically, up until about 40 miles per hour, it's more efficient to have your windows down. Above that, the additional drag caused by the open windows overcomes the advantage of not running the AC compressor.

Of course, when it's above 75 degrees outside I roll with the AC regardless. What's the point of opening the window only to have 90 degree air come in?

J.Po said...

I was JUST going to say you should write to Mythbusters. But thankfully, Grrbear stepped in!

I just saw the Mythbusters where they proved that driving really close to a semi increases fuel efficiency b/c of drag (we used to do that in swimming - get in someone's wake during a race). They pointed out the dangers in trying said technique in the real world.

Burrito Eater said...

If it is above 60F use the AC if it is below 60F use just the car fan if it is below 30F consider the heat. Plus you have to figure in the power needed to roll down windows and if you have a big ol' yellow lab with its head out the window.