auto

Will rolling down windows save fuel or not?

Red Sox versus Yankees. Seat up versus seat down. Microsoft versus Apple. To the list of issues people feel irrationally passionate about, add one more: Whether it's more economical to drive with windows down or with the air conditioning on.

Gas prices are nearing $4 a gallon across the nation, and motorists want to know the truth about which will make their tank of gas last longer.

Bankrate published a story about 10 money-saving driving tips. No. 8 was innocent enough. We thought.

It said, "Go easy on the air conditioning. Roll down your car's windows and let in the summer breeze. Using the gas-hogging air conditioning as sparingly as possible will give your car's fuel economy a real boost. Air conditioning can drag down your car's fuel economy by 10 percent to 20 percent. "

It was like we insulted people's mothers.

Bankrate's e-mailbag filled with letters from people adamantly disagreeing.

It's a proven fact, they all asserted, that driving with your air conditioning on is more fuel efficient.

The reason, our readers explained, sometimes patiently, is that when you drive with the windows down, it creates greater drag on the vehicle. The vehicle uses more power to combat the increased drag, hogging even more fuel than if you simply drove with the windows up and the air conditioning on.

Drum roll, please!
Several experts were interviewed to find out just who is correct. The results are unanimous:

Driving with your windows down and the air conditioning off consumes less gas than having the windows up and the air conditioner running. This is absolutely true -- that is, when you're cruising around town.

"When you're driving across town, in stop-and-go traffic," says Frank Hampshire, director of market research with the Automotive Aftermarket Suppliers Association, or AASA, "it's more fuel efficient to drive with the air conditioning off, windows down."

Poll: Which gets the best mileage?
Some people swear they get the best mileage with the air on and windows up. Others violently disagree.
Take the poll
 
Consumer Reports' auto-test department reports that the air conditioner reduces your car's fuel efficiency by up to 10 percent. So to achieve maximum fuel efficiency, motorists should avoid using the air conditioner at speeds below 40 mph and travel with their windows down, explains Gabe Shenhar, senior auto test engineer at Consumer Report's auto-test department.

"But as your speed increases to 45 mph, or highway speeds," says Jason Toews, co-founder of GasBuddy.com, "wind drag becomes an issue. Driving with the windows down increases the drag on your vehicle, resulting in decreased fuel economy by up to 10 percent. Drive at speeds over 55 mph with windows down and you'll decrease fuel economy by up to 20 percent or greater."

Shenhar and Hampshire agree: It's all in your speed.

Tips to cool your vehicle down
There are a few ways to cool your vehicle down faster -- and cheaper -- during the hot, summer months:

Tips

Different cars react differently, and so the point at which you should roll up the windows and kick on the air will be different for each car. A 2004 study by the Society of Automotive Engineers found, for example, that the aerodynamic drag for sport utility vehicles was particularly high, especially the ones they drove on a test track at speeds above 100 kph. Automotive engineers have all the fun.

Or maybe not. During the test, one engineer shot around the track with the air cranked up. A second had the windows down. An unlucky third test driver was assigned to what turned out to be the most-fuel efficient way to travel: Driving with the windows up and the air conditioner switched off.

More: Reader reactions, poll, sound off!

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-- Updated: June 22, 2006

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