Aerodynamic Drag
Aerodynamic drag is the air-resistance force that acts opposite to a vehicle’s motion relative to the surrounding air.
Why speed and wind matter
Drag force depends on air density, the square of relative air speed, drag coefficient, and frontal area. Relative air speed includes wind: a headwind increases the air speed seen by the vehicle, while a tailwind reduces it. Because the force contains speed squared, a modest speed increase can cause a much larger rise in aerodynamic force.
The propulsion power needed to overcome drag is force multiplied by road speed. In still air on level ground, the aerodynamic power requirement therefore rises approximately with the cube of speed. This is why sustained high-speed driving can increase EV consumption sharply even when acceleration is gentle.
Drag coefficient alone does not state the complete aerodynamic load. Vehicle size matters through frontal area, and the product CdA combines the two. Cooling airflow, ride height, open windows, roof racks, external accessories, and vehicle attitude can also change the effective drag of a particular configuration.
For formulas, CdA, and the effect on range, see Understanding EV Range.