INTRODUCTION: Adjusting the binding position of a cross-country ski is a popular tuning element in ski racing. By altering the load application point on the ski, the pressure distribution between the front and rear contact zone will change. Using the high-precision tribometer developed by our group, we investigate the effect of the load application point on the friction coefficient of both modern cross-country skis and an adjustable test ski without human influence from the skier. METHODS: Firstly, the friction of a cross-country ski was tested by altering the binding position 10 cm in front and behind the normal position. Secondly, pressure zone measurements of the ski at different load application points were performed to understand how the ski characteristics changed. Thirdly, the parameters of average contact pressure, slider spacing and load split were tested independently with an adjustable full-size test ski. RESULTS: Moving the binding backward on the cross-country ski showed a decreasing trend in friction for a temperature of -2°C and -10°C. A minimum friction coefficient was seen at a load application point of 17 cm behind the middle point. The trend appears to reverse on melting snow conditions (T air = +5°C), but the standard deviation at each binding position was considerably larger. By isolating the variables on the adjustable test ski, a decrease in the spacing between the contact zones showed a clear trend in decreasing friction. A spacing of 20 cm had 10% reduced friction compared to a spacing of 120 cm. Increasing the average contact pressure by shortening the contact zones or increasing the normal load led to a decrease in friction. Higher contact pressures than 22 kPa led to a slight increase in friction again due to more ploughing in the snow track. The effect of load split between the front and rear slider showed a sinusoidal trend as the load was moved from the rear slider to the front slider, with one distinctive minimum of around 70% and a maximum of around 25% of the load on the front slider. DISCUSSION/CONCLUSION: On cold and dry snow conditions, the results from the adjustable test ski points towards benefits of having shorter contact zones and smaller spacing than the racing ski tested. Also, the load split with today`s binding placement is far from optimal. Higher load towards the front zone gave the lowest friction and is explained by inducing a lubrication water film earlier, so that the rest of the second slider gets a reduced friction. The performance benefits for an athlete could be discussed based on lower friction vs the feeling of the dynamic response of the skis.
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