Why Ski Base Matters – Part No. 1
If ski waxes and surface coatings worked exactly as they are often presented to work—that is, if they formed a continuous layer covering the entire ski-base surface, regardless of how complex the structure pattern is, and if this layer survived for several tens of kilometres—then the ski-base material itself should matter very little during a race.
Under such conditions, the ski base should hardly ever come into direct contact with the snow. The actual sliding interface would be formed primarily between the snow surface and the wax/coating layer.
In reality, however, the sliding interface and the associated wear processes are considerably more complex.
Modification of the Structure Pattern
The application of multiple wax layers and surface coatings modifies the original stone-ground structure.
The exact modification depends on the structure geometry, wax properties, application method, scraping and brushing procedure. In general, however, wax tends to make the structure shallower and its sharp features more rounded.
After scraping and brushing, wax is not distributed uniformly across the surface. A significant amount can remain accumulated in the deeper parts of the structure valleys, while the highest surface features are much more strongly exposed.
Consequently, the geometrical structure actually interacting with the snow can differ substantially from the freshly stone-ground structure.
Wear Process During Sliding on Snow
The real contact between ski and snow occurs only over a fraction of the nominal ski-base area.
Different friction regimes determine the number, size and total area of these real contact points, as well as the local pressures acting within them.
The complete interaction is complicated because both the snow and, to a much smaller extent, the ski-base surface can undergo elastic deformation, plastic deformation, fracture and wear. Nevertheless, several general relationships can be identified.
The smaller the real contact area and the fewer the individual contact points, the higher the local pressure within those contacts.
Higher local pressure becomes especially important when the snow is hard, transformed and compacted and when deformation deeper inside the snow cover is limited.
As a general tendency:
fewer and smaller contact points produce higher local pressures;
harder and more compact snow produces less deformation within the snow cover;
reduced deformation concentrates the mechanical interaction closer to the ski/snow interface;
higher local pressure and harder snow generally increase mechanical wear of the exposed ski-base surface.
Wear of Wax and Coatings
Wax and coating material is therefore not removed uniformly from the ski base.
Wear starts preferentially at the real contact points—normally the highest and most exposed irregularities of the structured base surface. These are the locations carrying the highest local loads and experiencing the strongest mechanical interaction with the snow.
At such points, the effective lifetime of a wax or coating layer can be very short.
The opposite situation exists deep inside the structure valleys.
Wax accumulated there is geometrically protected from direct mechanical contact with the snow and can therefore remain for a relatively long time. Its long persistence, however, does not necessarily demonstrate that it is providing an equally long-lasting low-friction sliding layer.
In fact, it may persist precisely because it is located outside the most important real contact zones.
This leads to an important distinction:
wax lifetime on the ski base is not the same thing as wax lifetime in the real ski–snow contact interface.
The highest structure features can lose their wax or coating very quickly, while material retained in deeper valleys remains almost untouched.
The ski-base material, its surface morphology and its mechanical and physicochemical properties can therefore become relevant to sliding performance much earlier than would be expected from the apparent persistence of wax on the ski.