1 Why is aerodynamics important
Cyclists use most of their energy in overcoming air resistance. At a speed of 30 kilometers per hour, between 70% and 80% of the pedaling power is used to overcome this air resistance. Since air resistance increases by the power of three by speed, at 40 kilometers per hour more than 90% of the power delivered is used to overcome air resistance.
2 What stands CdA for
CdA is an abbreviation for the coefficient of aerodynamic drag. The CdA consists out of two components, Cd is coefficient of aerodynamic drag and is a function of the shape of the cyclist, their posture and the bike. The A is the frontal area (expressed in m2) of the cyclist and bike.
3 What are normal values of CdA
CdA values can range substantially between cyclists and between their positions. CdA’s of riders on a road bike with hands “on the tops” are around 0.5, while pros on a time trial position can reach CdA values even below 0.2.
4 What are the gains of a lower CdA
Gains of a lower CdA are substantial. A very generic rule is that every reduction in CdA by 0.01 means that nearly 10 watts less power is needed to cycle 40 kilometers per hour.
5 How to improve my CdA
Since the posture of the cyclist him/herself causes 80-90% of the aerodynamic drag, this is where improvements should be sought. Well-known recommendations include head down, elbows narrow and cornered, knees to the bike etc. Since improvements are rider specific, only wind tunnel test can detect where real improvements exist.