Aerodynamic benefit for a cyclist by a following motorcycle

In recent years, many accidents have occurred between cyclists and in-race motorcycles, even yielding fatal injuries. The accidents and the potential aerodynamics issues have impelled the present authors to perform dedicated wind-tunnel measurements and Computational Fluid Dynamics (CFD) simulations to assess cyclist drag reduction when followed by one, two or three motorcycles. The 3D steady-state Reynolds-Averaged Navier-Stokes simulations with the standard k-ε model are validated by the wind-tunnel tests. The cyclist drag reduction goes up to 8.7% for a single trailing motorcycle and to 13.9% for three trailing motorcycles at a distance of 0.25 m behind the cyclist. This distance is not uncommon in elite races, as evidenced by the many recent accidents. The effect by a single following motorcycle at realistic short distances d=0.25 m (8.7%), d=0.5 m (6.4%) and d=1 m (3.8%) is larger than that by a following car at realistic short distance d=5 m (1.4%). Therefore it could be argued that in-race motorcycles are not only more dangerous but also aerodynamically more influential. This study reinforces the necessity for the International Cycling Union to change the rules concerning in-race motorcycles, not only to avoid accidents but also to avoid unwanted aerodynamic benefits.