Abstract
Under crosswind conditions, road cyclists experience an extra drag force and a destabilising lateral force. In these conditions a group of cyclists manages to reorganise its spatial formation to minimise these forces forming an echelon, i.e a diagonal single pace line of riders staggered across the road, a configuration which is markedly different from those adopted in wind-free conditions. To study the effect of the crosswind on drag and lateral forces on the riders we performed wind-tunnel experiments using a scale model cyclist and measuring the forces by means of a load cell. Several configurations with one, two, and four cyclists have been investigated varying yaw angles. Results show that, in a basic 4 rider configuration at a 50 ^{circ } yaw angle, a sheltered rider within the echelon experiences less than 30% of the drag of the guttered rider behind the echelon, struggling against the crosswind. Furthermore, we show that an echelon is worth being adopted under crosswind conditions only beyond a 30 ^{circ } yaw angle. At this critical 30 ^{circ } yaw angle the drag on the guttered rider doubles when the gap to the front group increases from 10 cm to 1 m (in real scale). These results can be of interest in defining road cycling race strategies and they allow some significant configurations to be identified and further investigated in more complex experiments.
Highlights
In cycling, the wind is a key factor as it generates extra drag forces for the riders
Given that the drag amounts to almost 90% of the total resistive forces for a cyclist at racing speeds [1, 2], it is interesting to know how much the drag and the lateral forces of one cyclist under windy conditions decrease through the shelter provided by a group of riders and which positions in the group are most beneficial in terms of force decreasing
Among the studies highlighting the effects of the Reynolds number on the cyclist aerodynamics we mention Terra et al [24] that experimentally investigated the Reynolds number influence on the wakes of the arms and legs of a model cyclist varying the velocity in the range 5-25 m/s ( Re = 2.3 × 105 - 1.2 × 106 ) by means of PIV measurements in wind tunnel
Summary
The wind is a key factor as it generates extra drag forces (aerodynamic resistance) for the riders. Slipstreaming effects and drag reduction in cycling groups and even larger pelotons with no wind are well known and have been highlighted by several previous wind-tunnel experiments [3, 4] and numerical simulations [5]. Barry et al [8] studied the drag interactions of a four cyclist group by means of wind-tunnel experiments and they showed a significant reduction of the drag of about 50% for the sheltered riders with respect to an individual cyclist. Belloli et al [9] investigated drafting effects by wind-tunnel tests for two cyclists
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