Companies like HED or Zipp have published tunnel test data where they evaluate the benefits of an aerodynamic Wheel. These benefits are strongly dependent of the yaw angle.
Yaw angle is the angle is not only the angle of incidence, but it depends also on:
Vfrontal =Vwind x cos (α); Eq. 8
Vlateral =Vwind x sin (α); Eq. 9
Vaparent= Vwind - Vfrontal.; Eq. 10
In order to show the values of the yaw angle in typical conditions, the next figures are shown:
For a typical constant speed of 35 km/h, and two wind speeds: (10 y 20 km/h), the following yaw angles are obtained for different wind angles of incidence.
It can be checked that for the specified conditions and a 10 km/h wind speed, yaw angle is always lower than 20°.
In the case of a 20 km/h wind speed, a yaw angle of 30°, can appear only if the angle of incidence is between 30° and 90°. In any case, a yaw of 35° is never reached.
Moreover, in the following graphic it is shown how the yaw angle varies with the wind speed when wind angle of incidence is 60°, when the cyclist speed is again 35 km/h.
Finally, in the following graphic the conditions (wind speed and angle of incidence) where for a cyclist speed of 35 km/h the yaw angle are higher or lower than 20° are represented.
The wind tunnel data tests published are usually done only for yaw angles up to 20°. This does not mean that for higher yaw angles the performance of the wheels is necessary worse. Just there are not published data.
But what is demonstrated is the benefit of the aerodynamic wheels below 20°.
The wind tunnel data test published are usually done only for yaw angles up to 20°. This does not mean that for higher yaw angles the performances of the wheels are necessary worse. Just there are not data published.
But what is demonstrated is the benefit of the aerodynamic wheels below 20°, and in this range, the higher the yaw, the better the performance of an aerodynamic wheel.
In the following 3D plot, yaw angles for 35 km/h speed, depending on wind speed and angle of incidence, are represented. Values higher than 20° in yellow and red.