Saving Fuel Myths

Check MythBusters for that one (it's some obvious link, mythbusters.org, perhaps). I think they also looked at pickup truck tailgate up/down at some point.

In slow-moving traffic or non-moving traffic, the aerodynamic effects are small, so keeping the windows open instead of using air-conditioning would save fuel.

In highway traffic, using air conditioning would result in lower fuel use than keeping windows open. Of course, using the vents with air-conditioning off would save more fuel.

Jeff

Mythbusters did that one. IIRC, they found out that the AC uses more power than the wind resistance of open windows.

I recall them doing the truck with the tail gate down or up...They found the truck got better gas mileage with the tail gate down than up, and more with that tail gate removed...

I did not see the car with the windows down. I just have to wonder the drag when someone rolls their two front windows down.

The reason they found that the AC used more power was because the test speed was limited to 35 MPH due to the track causing excessive side loads on the tires at speeds higher than that. 35 is too slow for windows open drag to have much affect and the vehicle was an SUV that already isn't aerodynamic so the percent drag change from open to closed was less than it would have been on a more aerodynamic car such as the EV1, Honda Insight, or Toyota Prius.

It was one of their more flawed tests. In the original test they drove around on a very small oval track and didn't exceed 50 mph. Hardly a fair test of highway economy. They did the test over in a later episode. As I recall, after the second test they concluded that at low speed, windows down, A/C off was best, at high speed A/C on windows up was best, except that windows up, A/C off was best at any speed. Personally I have never been able to tell much difference in summer/winter fuel economy and don't worry about the A/C's effect on fuel economy.

Ed