Drag Coefficient (Cd)

Total drag depends on the coefficient multiplied by the car's frontal area. Air resistance rises with the square of speed, so it dominates consumption at motorway speeds. Electric cars often use smooth wheels, flush door handles and closed grilles to reduce drag.

Shape, underbody panels and details such as mirrors affect how the airflow separates from the body.

Roof boxes, open windows and bike racks significantly increase drag and consumption. Manufacturers publish Cd values, but the frontal area is equally important for comparison.