Investigation of Riding Position Effects on Time-Trial Bicycle Drag Coefficient at Different Yaw Angles

Abstract

Time-trial bicycle racing is highly influenced by aerodynamics, perhaps more so than any other form of bicycle racing. Companies competing in this class of racing spend millions of dollars trying to optimize the geometry of the bicycles and the gear each rider wears in order to reduce aerodynamic drag. The idea behind this project was to investigate other ways to optimize the aerodynamic efficiency of the rider, considering that the rider contributes the majority of the drag force of the bicycle-rider system. A large contributor to drag is the frontal area of the object of interest (a silhouette of the object in the fluid flow direction). This illustrates how much the rider’s body contributes to overall drag. If small riding adjustments could be made to the rider’s body during riding, drag may be significantly reduced. This idea and the fact that the direction of wind impacting the rider can vary influenced the concept of this project. It was hypothesized that adjusting the time-trial handlebars on the bicycle to place one of the rider’s hands further aft than the other would influence the upper body to rotate slightly. This could then reduce the frontal area of the rider in the wind direction, therefore reducing the aerodynamic drag. To simulate this situation, a non-contact 3-D digitizer was used to scan a rider aboard a bicycle in a normal riding position and in the above-mentioned, asymmetric position. This 3-D scan was then imported into the computational fluid dynamics (CFD) program Star-CCM+ and several simulations were run. Each of the two riding positions was simulated at differing yaw angles, ranging from −45° to 45°. The initial simulations seem to prove the theory as the asymmetrical riding position experiences decreased drag at significant yaw angles while the normal riding position does not. These results are encouraging and it is desired to continue refinement of the scanning and simulation methods as well as to validate these findings in a wind tunnel.