The former is a parameter indicating the relative importance of the inertial
and viscous effects in determining aerodynamic forces. If its value is low, the
latter are of great importance, while if it is high aerodynamic forces are primarily
due to the inertia of the fluid. In this case (for vehicles, if Re >3,000,000), the
dependence of the aerodynamic coefficients on the Reynolds numberis very low
and can be neglected. This is usually the case for road vehicles, at least for speeds
in excess of 30 ÷40 km/h