82: Cool your car efficiently: windows vs. A/C by matthew

The debate has long raged over whether it’s better for fuel economy to roll down the windows or to turn on the AC. You see, having the windows down decreases efficiency by creating drag, but turning up the AC decreases efficiency by drawing additional engine power (the National Renewable Energy Laboratory estimates that vehicle air conditioners use about seven billion gallons of gasoline a year, or six percent of all gas consumed). So which is the lesser evil?

Thankfully, this issue has been tested — by those mad scientists at Mythbusters, among others — and the answer is… it depends! At speeds of less than 50 mph, it’s best to cool off by rolling down the windows, because drag is relatively low. But at highway speeds, when drag is more significant, it’s better to roll up the windows and turn on the AC.

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