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A key consideration when designing a vehicle body are the aerodynamics, which have an impact on fuel consumption, top speed and acoustic levels. The drag coefficient (Cd value) as measured in the wind tunnel sums up the vehicle’s aerodynamic qualities. A number of variables influence the Cd value, including the vehicle shape (saloon, estate or hatchback). The design of the underbody also has an effect. Aerodynamic drag is caused by the displacement of the air surrounding the vehicle and the friction between the air and the vehicle’s surface.
The following formula is used for calculating aerodynamic drag:
Aerodynamic drag = vehicle speed squared x frontal area x Cd value x ½ air density.
The typical streamlined Volkswagen body design combines with narrow gaps and joints to reduce buffeting and keep drag low. This in turn translates into favourable fuel consumption and lower CO2 emissions. The most critical variable is vehicle speed, however, as doubling the speed quadruples the aerodynamic drag.