Windows up or down for better gas mileage?

Dear Car Talk

Dear Car Talk | Aug 01, 1990

Dear Tom and Ray:

Please answer a question that has been bothering me for over five years. I have asked everybody I know, and no one has given me a logical answer. I want to cool the passenger compartment of my car as efficiently as possible. Do you get better gas mileage (all factors being equal) by using the "2/60 method" (two windows rolled down, driving 60 mph), or by using the car's air conditioner?

RAY: Great question, Mary! As a matter of fact, the Society of Automotive Engineers has wasted some of it's valuable time studying this very dilemma. The answer is that you get better mileage by rolling up the windows and using the air conditioner.

TOM: The reason has to do with aerodynamics. The more aerodynamic your car is, the less wind resistance it creates. Wind resistance makes the engine work harder and therefore wastes fuel. That's why you're seeing new cars being shaped more and more like what medical science has always known is the most aerodynamic of shapes; the suppository.

RAY: Anyway, when your windows are all rolled up, wind slides around your car. That's when it's most aerodynamic. When you roll your windows down, wind comes inside the car, blows against the seats, the passengers, the back window, and generally makes the engine work harder.

TOM: And according to the studies, you waste more energy through the loss of aerodynamics than you do through powering an air conditioner.

RAY: We also prefer the air conditioner to the window method because it also allows you to arrive at your destination without looking like my brother before his hair stabilizes in the morning (eek!).

TOM: Speaking of aerodynamics, we'd like to know if anyone has done any research on the fuel efficiency of pop-up headlamps. It's easy to see how they improve aerodynamics and fuel efficiency during the day when they're hidden. But don't they do twice as much damage at night when they create two huge wind-resistant baffles in the front of the car? It seems like the aerodynamic equivalent of driving with two medium size pizza boxes strapped to your front bumper! Seriously, if anyone knows of any research on this topic, please send it to us in care of this newspaper.

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