Adding an aftermarket rear spoiler to your car may be costly in more ways than one. It could increase drag and decrease fuel economy.
We are often asked whether rear spoilers reduce drag. This is an important question because reduced drag increases miles per gallon (MPG) and reduces emissions. Studies show that improving the drag coefficient (cd) by 0.01 can improve a car’s fuel economy by 0.2 mpg. This is why we recommend rolling windows up at highway speeds and removing roof racks (or at least the cross beams) when not in use. We also recommend GasPods for sedans and other cars.
Today, we want to talk to you about rear spoilers, which have remained a fixture in the automotive parts aftermarket not only because of car culture and popular culture (just look at the box office receipts for the Fast and the Furious film series), but also because many people believe that rear spoilers reduce drag and thus increase fuel efficiency. So what do rear spoilers do? And should you add an aftermarket rear spoiler to your car?
To begin, let’s talk about what a spoiler is and what it does. A spoiler is comparable to an aircraft wing – it redirects airflow. Obviously on an aircraft it is designed for lift, whereas on a vehicle it is designed to provide down force. Why would a car want down force? A spoiler designed for racing can provide down force to keep the rear of the car planted, providing more traction and grip. Spoilers only work at higher speeds when there is enough air flowing over them. The addition of down force will increase friction and grip, meaning that you will likely see more fuel consumption and decreased fuel economy as a result.
So why do a lot of passenger vehicles have rear spoilers? In many cases, they are cosmetic. Most spoilers on mainstream passenger vehicles are not designed to provide performance or reduce drag (although for some cars they may smooth air flow in the rear of the car). High end sports cars, however, may have spoilers designed to increase performance at various speeds.
Will adding a spoiler to your vehicle increase MPG? Probably not. Unless you find a spoiler designed to reduce drag that was wind tunnel tested for your specific vehicle, it is highly unlikely to increase MPG. In fact, it could very well make your fuel economy worse. No matter what, it will cost you a lot of money that you could instead invest in techniques and gear that are proven to improve your fuel economy. Our own testing confirms that automobile aerodynamics can be very tricky. But saving money on gas is simple and easy.
If you are really interested in increasing your MPG, here are three surefire ways to make it happen: (1) Improve your driving habits by following our driving tips; (2) perform regular vehicle maintenance, such as properly inflating your tires every two weeks; and (3) for certain types of cars, add proven aerodynamic enhancements, such as “GasPods.”
Questions? Please write us at firstname.lastname@example.org. We would love to hear from you!