Riding Technique
Aerodynamic drag
What does Aerodynamic drag mean?
The air's resistance to a moving rider and bike. The force grows with the square of speed, so the power to overcome it grows with the cube.
Aerodynamic drag is the force the air puts on you and your bike as you move through it. Wikipedia’s bicycle performance page notes that air drag power “increases with the cube of the speed.” The drag area, written CdA, combines your frontal area with how smoothly air flows around you, so a lower riding position reduces it.
Why does it matter on an e-bike?
At e-bike speeds, drag is most of the work. In our physics model for an upright 120 kg rider and bike with a drag area of 0.5 m², drag is about 78% of the power needed at 20 mph and 87% at 28 mph. Holding 28 mph takes about 2.4 times the power of 20 mph.
That is why speed cuts range so sharply. Our e-bike speed vs range guide shows the full table, and the fastest e-bikes guide explains why the cube law limits every fast e-bike.
Also known as: air drag, drag area, CdA