In individual time-trial cycling races (TT), the interest of the cyclists in improving aerodynamics increases because the rider has to overcome the wind drag effect without the advantages of drafting for riding behind another cyclist. For this reason, in some races, the riders use aerobars (Figure 1) to support the elbows closer to the bicycle with aerodynamic advantages [1]. The aerobars postures are associated with a drop in the power delivery capacity [2-4] and an increased difficulty to sustain the posture for long periods due to discomfort. It is possible to find some suggestions for the definition of posture when riding in aerobars [5-7]. Nevertheless, studies on the effect of postural parameters in aerobars postures are scarce.In this context, a methodology was developed to study the influence that variations in the body posture when riding in aerobars have on the performance of cyclists and their interaction with the bicycle [8]. The methodology is based on an optimization problem that minimizes race time subject to constraints associated with the interaction between the bicycle and the cyclist. This interaction is represented through the pressures and the vibration levels in contact areas. The methodology was implemented in a numerical code for the posture optimization of cyclists.Five cyclists were included in the study with their bicycles. The power delivery capacity and drag area, vibration transmission, and pressure in contact areas were measured. The postures were defined by the aerobars’ height fit limits of each bicycle (named ABhigh for upper bound and ABlow for lower bound). A 20-km race and various road inclinations and wind speeds were considered in the study.Two types of results were obtained for the optimization of aerobars’ height to minimize race time. Figures 2 and 3 exemplify the results. The optimal posture is identified considering that it leads to the best time while satisfying all the constraints. If none of the postures satisfy the constraints, the race condition is considered as unfeasible, and it is not plotted. The optimal aerobars’ height is presented using colored regions corresponding to the percentage of the aerobars’ height fit window (100% is ABhigh, and 0% is ABlow). The dotted line represents the threshold that would be obtained between the regions for selecting ABhigh or ABlow if only the race time was considered (i.e., without including interaction constraints).For the first type of result, the optimal solutions always lie in the boundary postures (i.e., ABhigh or ABlow). In contrast, for the second type, for some race conditions, the optimal height lies in the intermediate postures. The intermediate heights are identified as optimal for the race conditions in which the constraints restricted the selection of posture. This occurs because the race time as a function of aerobars height is monotonous in the range of analysis. For this reason, if only performance is considered, the posture selected is one of the boundary postures. When the constraints limit the solution, they force selecting an intermediate height even if it is not associated with the best race time. It is worth highlighting that the final selection of the aerobars’ height depends on each bicycle’s fit window as the postures can be fixed in certain positions and not in the exact height proposed by the optimization solution.It is concluded that postures with intermediate aerobars’ heights are identified as optimal solutions for conditions in which the interaction constraints modify the solution. For the other cases, the optimal solution lies on one of the boundary postures.

Posture Optimization for Individual Time-Trial Cycling Races

Paper Proceedings: https://asmedigitalcollection.asme.org/IDETC-CIE/IDETC-CIE2021/volume/85369

ASME 2021 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE2021)

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