INTRODUCTION: Snow friction is a major performance factor in cross-country skiing 1. Friction is affected by ski and snow stiffness. Thus, we present a measurement method to determine the contact pressure of skis on a foundation with snow-like stiffness. METHODS: We built a stiff frame on which a cross-country ski rested atop a layer of closed-cell polyurethane elastomer (Fig. 1a). The elastomer was chosen to have a similar stiffness as measured snow 2. The force-penetration relation of the elastomer was measured. The ski was statically loaded at the binding with 0.3, 0.5, and 0.7 kN and the penetration depth of the ski into the elastomer was determined. Finally, contact pressure was calculated using the measured force-penetration relation. RESULTS: Fig. 1b shows the ski base position and the contact pressure along the ski for the three loads. The pressure distribution showed two separate peaks. For increasing loads, maximum contact pressure and penetration depth increased and shifted towards the center of the ski. Additionally, the contact area, i.e. the area with positive penetration depth, increased. DISCUSSION/CONCLUSION: Static measurements of the ski base position of a loaded ski on stiff support plates were presented and showed a different contact area for different skis 3. In this work, we observed a strongly increasing contact area and contact pressure for increasing load (Fig. 1b). The contact is strongly affected by the stiffness properties of ski and snow 4. Thus, it is crucial to measure the contact area and contact pressure on soft foundations, with a similar stiffness as snow. Changes in contact area and pressure along the ski are likely to change ski friction.
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