Aerodynamics of human-powered vehicles

Since the invention of the modern bicycle in the late 1880s, human-powered cycles have been used for racing. Air resistance can be over 90 per cent of the total retarding force on a bicycle, and consequently the aerodynamics has been a critical factor in increasing racing speeds. This paper reviews the history of aerodynamics in cycling and the physical factors that influence speed. A discussion of the aerodynamic design of both conventional racing bicycles and completely streamlined human-powered vehicles (HPVs) is included. A mathematical model that predicts vehicle speed when human power input and the other key properties are known is presented. At a steady speed of 50 km/h, a modern racing bicycle would require about 420 W of power input, while a modem HPV requires only about 75 W 18 per cent as much. The top speed for a conventional racing bicycle for 200 in is about 72 km/h, while for an HPV it is about 130 km/h (180 per cent greater). At 130 km/h a conventional bicycle would require about 5800 W (humanly impossible), while a modem HPV requires only 350W, or 6 per cent as much. Reduced aerodynamic drag is almost entirely responsible for these extraordinary differences in power and speed.