Automobile drag coefficient

The drag coefficient is a common measure in automotive design as it pertains to aerodynamics.

Reducing the drag coefficient in an automobile improves the performance of the vehicle as it pertains to speed and fuel efficiency.

The drag coefficient is a unit-less value that denotes how much an object resists movement through a fluid such as water or air.

Lift is an aerodynamic force that acts perpendicular to the airflow around the body of the vehicle.

[3] Lowering the drag coefficient comes from streamlining the exterior body of the vehicle.

Streamlining the body requires assumptions about the surrounding airspeed and characteristic use of the vehicle.

In 2003, Car and Driver magazine adopted this metric as a more intuitive way to compare the aerodynamic efficiency of various automobiles.

{\displaystyle F={\tfrac {1}{2}}\times {\text{air density}}\times {\text{drag coefficient}}\times {\text{reference area}}\times {\text{speed}}^{2}}

This relation also allows an estimation of the new top speed of a car with a tuned engine: Or the power required for a target top speed: Average full-size passenger cars have a drag area of roughly 8 sq ft (0.74 m2).

The drag area of a bicycle (and rider) is also in the range of 6.5–7.5 sq ft (0.60–0.70 m2).

Note that the Cd of a given vehicle will vary depending on which wind tunnel it is measured in.