Roof Rack Drag Coefficient

The drag coefficient is often used to measure this for a car.

Roof rack drag coefficient.

The drag coefficient is a measure of how easily the car moves through the air. The net drag coefficient yes there s a formula for that naturally depends on your vehicle and what you re carrying but the effect on fuel economy is unequivocally negative. Drag is a force that moves parallel to the airflow. Adding a roof rack to a car creates more drag.

While there have been studies of their impact on individual vehicles depending on the configuration the fuel consumption penalty can be 0 to 25 percent on passenger cars this is the first study to estimate impacts at the national level. This is because as the air flows over the top of the vehicle following the smooth lines of the hood and windshield then collides with the roof rack and causes turbulence. While roof racks are very useful in carrying extra storage on a vehicle they also increase the frontal area of the vehicle and increase the drag coefficient. This is because the air flows over the top of the vehicle following the smooth lines of the hood and windshield then collides with the roof rack and causes turbulence.

According to the epa a good rule of thumb is that a loaded roof rack reduces fuel economy by five percent. Creating more drag creates more work for the car. While roof racks are very useful in carrying extra storage on a vehicle they also increase the frontal area of the vehicle and increase the drag coefficient. Use of roof racks requires vehicles to expend more energy due to aerodynamic drag.