Speed computation (non-kinematic) uses a*v^3 for air resistance

[radim-asamm]

There is this comment explaining how speed for segments ("way segment") is calculated

    // Solves a * v^3 + c * v = d with a Newton method
    // to get the speed v for the section.

Where a represents drag coefficient * reference area for a cyclist. Is the use of cubic term a good model? In many common situations, air resistance (or drag) is modeled as being quadratic with respect to speed, not cubic.

[vodie]

The air resistance is quadratic, but the required power is cubic. For twice the speed you need the eightfold power for the air resistance.

[poutnikl]

P = F . v = (F_rolling + F_slope + F_drag ).v = (A + B.sin(alfa)+ Cv^2 ). v = (A + B.sin(alfa)).v + Cv^3

[radim-asamm]

I see. Thanks!