In cycling, several resistances are opposed to the motion : the resistance due to the gravity that occurs when the ground is inclined; the rolling resistance which represents the contact of the tires of the bicycle with the ground; and the aerodynamic drag that characterizes the air resistance to the moving system (the cyclist and his bicycle).<\/p>\n\n\n\n
On level ground, at speeds greater than 40 km\/h, the aerodynamic drag (RA<\/sub>, in Newton) represents approximately 90% of the total resistances opposed to motion. Which means that about 90% of the mechanical power produced by the cyclist is used to overcome this resistance. It is dependent on several variables, the air density (\u03c1, in kg\/m3<\/sup>), the drag coefficient (CX<\/sub>, dimensionless), the projected frontal area of the cyclist and bicycle (Ap<\/sub>, in m2<\/sup>) and the square of the velocity relative to the fluid (v, in m\/s) :<\/p>\n\n\n\n As you can see from this formula, the greater the cyclist’s velocity, the higher the aerodynamic drag. The air density being dependent on atmospheric conditions (the barometric pressure, itself dependent on the altitude, the temperature and to a lesser extent the humidity) and the velocity having to be as great as possible, it remains therefore two modifiable parameters : CX<\/sub> and Ap<\/sub>.<\/p>\n\n\n\n CX<\/sub> represents the complexity of the general shape of the moving body in a fluid, the position of the cyclist and the movement of the air on the cyclist and his bicycle. It is not measurable directly, but different methods make it possible to estimate it.<\/p>\n\n\n\n Ap<\/sub> represents the projected frontal area of the moving body. Imagine that you are exactly in front of a cyclist on his bicycle in front of a white wall, the projected frontal area represents the whole visible area of this cyclist on his bicycle (Fig. 1 and Fig. 2). There are different techniques to directly estimate Ap<\/sub>. The advantage of quantifying it is that this value provides direct information on the aerodynamics of a position. To read more about this subject, consult our review on the subject<\/a>.<\/p>\n\n\nR_{A}=0.5 \\times\\rho\\times C_{x} \\times A_{p} \\times v^{2}<\/pre><\/div>\n\n\n\n