Conserve gas. Windows down or AC on?

We all simply guesstimate the most fuel efficient way to drive our cars. But do we really know the most efficient method during the hot summer months to drive? We ask ourselves; Windows up and AC on or windows down and enjoy a bit of a forced breeze. Well the question is now answered with two tests completed.

The first test required two new vehicles of the same year, make, and model. A simulation using computer models which monitored airflow through the engine to estimate fuel consumption; similar to how most factory installed, on board computers estimate fuel consumption. The results were amazing. The vehicle that had the windows down and AC off got an average of 11.4 to 11.3mpg. The vehicle with the windows up and AC on got an average of 11.7 to 11.8mpg. The car with the AC on got better fuel consumption in this test. The difference can be logically thought to be due to wind drag coming through the car, but this wasn't good enough. Another, more primitive test would need to be done.

The second test required two vehicles just as before. This test required each car having exactly 5 gallons of gas, starting the engine and driving the car at exactly the same speed at exactly the same time until each car ran out of gas. Pretty ingenious right? Right. Well the test showed that the car with the windows down was able to go 15 miles more than the car with the windows up and AC on. So which method do you believe; the computerized guesstimate or the hands on real time test?