Rolling resistance, vertical load and optimal number of wheels in HPV design

Even if it makes a smaller contribution than aerodynamic drag, rolling resistance plays a non-negligible role in the efficiency of human powered vehicles, whether they are designed for daily commuting or to set speed records. The literature, experimental evidence and models show that the rolling resistance coefficient of cycling wheels strongly depends on the supported load, suggesting that the number of wheels and the load distribution could play a role in vehicle design and in road-test data analysis. Starting with an in-depth look at the relationship between a single wheel and overall vehicle rolling resistance coefficients, an analysis is proposed and discussed with the aim of minimizing the rolling resistance of a vehicle. Finally, a parametric surface response model for rolling resistance is obtained as a function of wheel size and the number of wheels. The overall analysis overturns the popular assumption according to which "the more wheels, the more rolling resistance", at least according to a strict definition of the phenomenon.