A/C or windows: Study, experts say both hurt gas efficiency

Dominic Genetti

With the cost of gas these days, a better way to conserve it, or at least get more miles per gallon, would be a huge plus for motorists.

Some may just roll down their windows. Some may just blast the air conditioner. Well, as it turns out — unless you’re driving with the windows up and no air conditioning — your gas tank is going to take a hit.

According to a study done by the Society of Auto Engineers, rolling down the windows in a vehicle increases the drag of the vehicle and fuel consumption. In some cases, motorists could lose the same amount or more gasoline with the windows down compared with having them up with the A/C on.

“In these newer cars, it’s going to be about the same because you’ve got a wind-tunnel,” said Chris Ragar, an auto mechanic in Hannibal, Mo., in regard to driving with windows down. “It’s going to come into your vehicle, slow you down. So you’re putting more RPMs (revolutions per minute) on your car. People don’t realize it.”

“It creates that vacuum inside the car, and so you’re going to lose fuel economy,” Chuck Huston, sales manager at Poage Chevrolet in Missouri, added.

Included in the study results were dependent on the vehicle, the transmission and engine efficiency; powertrain control strategy for fuel economy and drivability; drive cycle; ambient temperature; tire temperatures; wind velocity; and others. Additional reports said about 10 percent of gas is lost when air conditioning is used and when windows are rolled down.

“It depends on the wind; if it’s coming right at you, that’s definitely going to be an issue,” Ragar said. “If it’s behind you, not so much.”

Bill Wood of Hannibal, Mo., tried driving around with the windows down recently, but nothing seemed to beat having the luxury of A/C in the car.

“I saved a little money on gas. It was a hotter experience,” he said. “I prefer air conditioning, but it does take a little more gas to do that. It is worth it.”

Huston said getting a hybrid vehicle or a car more economically designed, like the Chevrolet Sonic or Chevrolet Cruze, would help those motorists worried about drag (the wind resistance that can hurt miles per gallon). However, if air conditioning is available, he says people are just going to use it.

“I don’t think most people care. If they’ve got air conditioning, they’re running their air conditioning,” Huston said. “Go with it, especially now.”

And if you’re a truck driver, Ragar has a little fact that could help with your gas mileage, too.

“In a pickup truck, put down your tailgate,” he said. “That’s going to help you in the long-run because that wind is drafting right into that tailgate.”