Examining the Aerodynamic Performance of Bicycle Racing Wheels Using CFD

Margins of victory separating the top three professional riders in the 2008 installation of the Tour de France and the 2009 Giro D'Italia were less than 2 minutes after nearly 90 hours of racing. Small time differences between the top finishers, on the order of 2% in the individual and team time trial stages, were critical in determining final finish positions. High profile events such as these serve to focus on the relevance of seemingly small performance gains associated with technological advances in cycling equipment. It is commonly recognized that main contributors to overall drag are the rider, the frame including fork and aerobars, and the wheels. Comprehensive reviews by Burke and Lukes et.al. cite many efforts to identify the most relevant contributions to overall performance improvements in bicycle racing. Greenwell et.al. have concluded that the drag contribution from the wheels is on the order of 10% to 15% of the total drag, and that with improvements in wheel design, an overall reduction in drag on the order of 2% to 3% is possible. In the mid 1980's, commercial bicycle racing wheel manufacturers started to build wheels with increasingly deeper rims having toroidal cross sections. The experimental studies published by Tew and Sayersvi showed that the newer aerodynamic wheels were able to reduce drag by up to 50% when compared to conventional wheels. Although many wind tunnel tests have now been performed on bicycle wheels, it has been difficult to make direct comparisons owing to variations in wind tunnel configurations and the testing apparatus used to support and rotate the bicycle wheels studied. In this work, a CFD methodology using AcuSolve and FieldView is presented to study the performance of several commercial bicycle wheels over a range of speeds and yaw angles. The wheels studied in this work include the Rolf Sestriere, HED H3 TriSpoke, the Zipp 404, 808 and 1080 deep rim wheels and the Zipp Sub9 disc wheel. Wheels are modeled at speeds of 20mph and 30mph, in contact with the ground, using Reynolds-Averaged Navier Stokes (RANS). Drag, vertical and side (or lift) forces and aerodynamic torque are reported for each wheel. Turning moments are also calculated using the resolved side forces to examine aspects of stability and maneuverability. Drag and side forces over the range of yaw angles studied compare favorably to experimental wind tunnel results. CFD postprocessing automation methodologies necessary for completing a study of this scope are expected to have practical relevance to all CFD practitioners.

The Author

Yves-Marie Lefebvre
Sales & Support Engineer
Intelligent Light
301 Route 17N,
Rutherford, NJ 07070, USA

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