With the heat of summer definitely upon us, it’s time to think about fuel efficiency as far as how it relates to driving with the windows down or turning on the air conditioning in your car. Well as it turns out, that question has two answers. The bottom line is that it relates to how fast you are driving.
It is true that running the air conditioning in your vehicle does decrease fuel mileage. It is also true that driving with the windows down increases drag on your vehicle, which decreases fuel mileage.
The Mythbusters on the Discovery channel tested this myth; twice as a matter of fact. The Mythbusters are Jamie Hyneman and Adam Savage. The pair was awarded honorary doctorate degrees from The University of Twente for their research on the “windows down vs. AC on” myth. Their aim is to confirm or debunk various theories or urban legends.
The first time they tested the theory that driving with the windows down is more fuel efficient than driving with the air conditioning on they were criticized for not exploring the point at which the speed of the vehicle with the windows down can cause the drag to be powerful enough to offset the fuel consumption caused by the air conditioning. The ultimate findings were that when driving at less than 50 mph, it is more fuel efficient to drive with the windows down. If driving more than 50 mph, it is more fuel efficient to roll up the windows and turn up the air conditioning.