The effect of spatial position on the aerodynamic interactions between cyclists

Aerodynamic drag contributes the majority of the resistance acting on elite cyclists. At speeds of 50km/h, over 90% of an athlete's power output is expended overcoming drag. As a result, reducing the drag of cyclists significantly improves their performance. To date research on cycling aerodynamics has primarily focused on a single rider, despite the fact that many cycling events are mass start or team based, which necessarily involve athletes travelling in close proximity. Fundamental investigations of multiple less complex bluff bodies have shown strong aerodynamic interactions that significantly affect the forces they experience. Whilst practical experience has shown this to also be true for cycling, such effects are not well understood. This paper reports the results of wind tunnel experiments that measured the variation in aerodynamic drag for cyclists in various two rider formations. Both drafting and overtaking formations were investigated; being inline parallel and perpendicular to the flow respectively. Loads experienced by both riders were mapped as a function of their relative spatial position. Results show that drag and side force are strong functions of spatial position. For two riders drafting directly inline there was a maximum drag reduction of 49% for the trailing rider and over 5% for the lead rider. During overtaking a drag increase of over 6% was recorded with riders positioned side-by-side.