The warm weather is on its way in for the summer, so it’s time to break out this age old question: Which is more fuel-efficient, rolling the windows down or air conditioning? Some studies show windows down to be superior, but according to the Society of Automotive Engineers, both have their merits.
It is better to roll the windows down at lower speeds. When you’re driving around the city, windows down is more fuel-efficient because the drag is low enough that the AC still uses up more fuel. However, at higher speeds, like on the highway, rolling the windows down can reduce fuel economy by up to 20%, whereas air conditioning only lowers it by 10%.
It also depends on what kind of vehicle you drive. SUVs have a greater disparity than sedans and coupes—they already aren’t very aerodynamic to begin with, so rolling the windows down reduces fuel economy less than in other cars, making it seem like air conditioning is significantly worse. The more aerodynamic the car, the worse the drag is when the windows are open.