Why Do Skis Have To Be So Long? (Snow Depth Is Key)
When you first put on a full-size pair of skis you quickly discover how difficult it is to turn round in a confined space. However, you soon learn their limitations and the tricks you need to get you out of tricky corners. But why are skis so long in the first place?
While at first long skis can be cumbersome to get used to, they do offer benefits. With the skier’s body weight spread evenly the skis can work efficiently causing less drag. Similarly, long skis offer better support in powder, while at the same time offering more stability at speed and during corners.
There are no hard and fast rules about how long skis should be. The length is generally calculated from the skier’s style of skiing and how often they go. Beginners are often given much shorter skis, which might have drawbacks in terms of performance, but are much easier to learn to maneuver.
There are several forces that come into action when you use longer skis. Some of these are advantageous and some are disadvantageous. Consequently, choosing the right ski length is always going to be something of a compromise.
As your skis glide over the snow two physical forces come into play, which works against each other.
Firstly, gravity exerts a force on your body and skis, pulling them towards the center of the earth. This creates pressure between your ski and the snow surface, which is enough to lower the melting temperature of the snow and create a very thin layer of meltwater. This acts almost like a lubricant, over which your ski easily slides. When your ski has passed over this meltwater it simply refreezes.
There is a very small amount of friction created as the ski slides over the meltwater/snow and this will generate a small amount of heat, which adds to melted snow but for the most part, it is the pressure of the ski against the snow which causes it to melt.
Secondly, the water created by the pressure of the ski base acts to slow the ski. By their physical nature water molecules want to stick together, however, they can also stick to the base of the ski in a process called capillary drag. This leaves the skier having to use extra muscle to drive himself forward and overcome this extra force.
Learn more about reducing drag as a skier.
Long skis have a larger surface area and consequently, the weight of the skier is spread over a much greater area. In certain situations, such as powder, this creates a real advantage. The small flakes in powder snow trap a huge amount of air in between them, which creates a very light density, which in turn supports little weight.
Consequently, long skis are much better able to disperse the skier’s weight over a greater area, ensuring that the skier glides near the surface of the powder rather than sinking into it.
Making a comparison to an inflatable Lilo (an air-filled pool toy) in a swimming pool illustrates the point well. If the swimmer lifts himself onto the center of the Lilo from the side the centre part of the Lilo will become submerged and the two opposite ends will lift out of the water. All the force from the swimmer is focused on the center of the Lilo.
However, if the swimmer lifts himself completely onto the Lilo, laying lengthways most of the Lilo will be out of the water supporting the swimmer. Effectively the weight of the swimmer is evenly spread over the surface of the Lilo.
A larger surface area of the ski in contact with the snow creates more stability for the skier. Gravity acts on the skier down through his body, through his feet, and down through the skis into the snow.
This is called the center of mass and the extension of the skis in both directions from the feet helps to create stability for the mass. For example, if you were wearing very short skis and you caught an edge you would have very little time to react and correct the error.
However, with the extra stability of long skis, you would have a much better chance of reacting to save yourself from falling.
In the same way, at faster speeds, longer skis offer more stability in cornering. When cornering the shape or radius of the curve is determined by the distance between the tip, the waist, and the tail of the ski. This is called the turning radius which is generally longer with long skis and vice versa.
The turning radius can also be tightened by making a more aggressive side cut to the ski or physically stiffening the ski.
With longer skis, more of the ski edge is in contact with the snow at any one time, which ensures better stability. This is particularly useful when skiing fast when you have much less time and opportunity to take corrective action.