CdA explained in five sentences

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.  


Related Posts


How often do you ask yourself questions like: What if I would be 10% more aero? What if I lose those 2 kilograms? How much

Read More »