Considering the price of gas these days, it makes sense to maximize your gas mileage. One of the most commonly used tips for improving mileage is to roll your windows down rather than use your air conditioning (AC). But, is that really the better option or just a widespread myth?
The Short Answer
Yes. Studies have shown that opting for open windows instead of AC will improve your gas mileage.
This had been debated for years due to a lack of solid data from either side. However, the issue was resolved when General Motors (GM) and the Society of Automotive Engineers (SAE) conducted a study in 2004. That study used a 4.6-liter V8 sedan and an 8.1-liter V8 SUV. It concluded that both engines had a noticeable decrease in fuel consumption when the windows were rolled down as opposed to turning on the AC.
The Tricky Part
Although this reliable study recommends rolling down your windows for cooling, it still has some tricky aspects to it.
First, keeping your AC off has a much bigger impact on an SUV's gas mileage as compared to its impact on a sedan's — especially at higher speeds. Most likely, this is due to the difference in engine size and power, as well as the SUV’s ability to displace wind.
Second, the study also indicates that it's still bad for mileage to keep your windows rolled down. Basically, the best way to maximize mileage is to bake in a hot car; that isn't a viable option for most people. It all comes down to personal preference: if heat doesn't bother you, then opt for open windows. If you prefer to drive in an optimal temperature, and you are not concerned with the potential savings of open windows, then use the AC.
There are many ways to increase your gas mileage, and choosing open windows instead of using the AC is a great option. However, the best way to improve your gas mileage is to drive with closed windows whenever weather permits it.