A ski is a long flat device worn on the feet designed to help the wearer slide smoothly over snow. Originally intended as an aid to travel in snowy regions, they are now primarily used for recreational and sporting purposes. Also, a ski may denote a similar device used for other purposes than skiing, for example, for steering snowmobiles.
Snow skis glide on snow because downward pressure, as well as heat from surface friction, melts a thin layer of snow directly under the ski. This creates a very thin layer of water directly under the ski upon which the ski glides. Ski wax is used to decrease drag by increasing the water repellent properties of the base.
The original Nordic ski technology was improved during the early twentieth century so that skiers could make turns at higher speeds. New ski and binding designs, coupled with the introduction of ski lifts
and snow cats to carry skiers high up on mountains, enabled the development of most prominent category of the sport, alpine skiing
Skis were originally wooden planks made from a single piece of wood. They are now usually made from a complex assembly of components including glass fiber
, other polymers
, Hardened plastic or composite materials
, though many may still contain wood cores.
Most skis are long and thin, pointed and curve upwards at the front to prevent digging into the snow. The user is attached by bindings which in turn hold the ski boots. Beginning in the early 2000s, many ski manufacturers began designing their skis and bindings together, creating an integrated binding system. These systems serve two purposes. Firstly, they often use a railroad track style design, to allow the toe and heel pieces to slide, which in turn allows the ski to flex deeply, without an unflexed spot underfoot due to the binding. Secondly, it allows the consumer to purchase both skis and bindings from the same manufacturer, thus increasing sales.
Types of ski
Many types of skis exist, all designed for different situations, of which the following are a selection.
Like all skis, the original alpine "downhill" skis were little more than glorified planks of wood. Eventually metal edges were added to better grip the snow and ice of a ski trail and for durability. Downhill ski construction has evolved into much more sophisticated technologies. The use of composite materials, such as carbon-Kevlar
, made skis stronger, lighter, and more durable. In the late 1980s and early 1990s, spearheaded by ELAN, manufacturers began producing parabolic "shaped" skis (when viewed from above or below, the center or "waist" is significantly narrower than the tip and tail). Virtually all modern skis are made with some degree of side cut. The more dramatic the difference between the width of the tip waist and tail, coupled with the length stiffness and camber of the ski, the shorter the "natural" turning radius. Skis used in downhill race events are long with a subtle side cut as they are built for speed and wide turns. Slalom skis—as well as many recreational skis—are shorter with a greater side cut to facilitate tighter, easier turns. Many ski manufacturers label skis with their design turn radius on the top. For a racing slalom ski, they can be as low as 12 meters (40 ft) and for Super-G they are normally at 33 meters (108 ft). However, for off-piste
skis there is a trend toward wider skis to better float on top of powder snow. This means skiers have a huge range to choose from depending on individual needs and application.
The ski is turned by applying pressure, rotation and edge angle. When the ski is set at an angle the edge cuts into the snow, the ski will follow the arc and hence turn the skier; a practice known as carving a turn. While old fashioned "straight skis" which had little side cut could carve turns, great leg strength was required to generate the enormous pressure necessary to flex them into a curved shape for carving, a shape called "reverse camber". Now, when a modern, hourglass-shaped ski is tilted on to its edge, a gap is created between the ground and the middle of the ski (under the binding) as only the sides near the tip and the tail touch the snow. Then, as the skier gently applies pressure, the ski bends easily into reverse camber. Influenced by snowboarding, during the 1990s this shaping of the ski became significantly more pronounced to make it easier for skiers to carve turns. This makes skiing much easier to learn, because the skis turn with much less effort when placed on edge. Such skis were once termed carving skis, shaped skis, or parabolic skis to differentiate them from the more traditional straighter skis, but nearly all modern recreational skis are produced with a large degree of side cut.
- For other turning techniques, see Skiing.
The ski binding anchors the foot firmly to the ski at heel and toe. As a safety feature, it is spring-loaded to detach the ski from the foot once a set pressure tolerance is exceeded, usually caused by falls or collisions. Modern bindings utilize a standard spring system to minimize the amount of force applied to joints such as the knee during backward twisting falls.
Twin-tip skis are skis with turned-up ends at both the front and rear. They make it easier to ski backwards, allowing reversed take-offs and landings when performing aerial maneuvers. The turned-up tail allows less application of aft pressure on the ski, causing it to release from a turn earlier than a non-twin-tip ski. Twin-tip skis are generally wider at the tip, tail, and underfoot and constructed of softer materials to cushion landings. Bindings are typically mounted closer to the center of the ski to facilitate the balance of fore and aft pressure while skiing backwards or "switch", and built lower to the ski for easy rail sliding. Some skis are also manufactured with special materials or a different side cut design under and close to the foot to facilitate rail sliding (also referred to as "jibbing"). The popularity explosion of twin-tip skis created a push for the inclusion of more terrain park elements at ski areas across the globe. In the past five years twin tips have become popular among youth skiers, ages 14-21. Once considered a passing fad, twin-tip skis have become a staple ski in the product line of all major ski-producing companies worldwide, with a few specializing in twin tips. Line Skis, started by Jason Levinthal, is the first company to market only twin-tip skis. The first twin-tip ski was the Olin Mark IV Comp introduced in 1974. The first company to successfully market a twin-tip ski was Salomon, with their 1080 ski. These skis are often used by freestylers.
Alpine touring ski
The Alpine touring ski
is usually a modified lightweight downhill ski with an alpine touring binding
. Like the backcountry ski it is designed for unbroken snow. For climbing of steep slopes, skins (originally made of seal fur, but now made of synthetic materials) can be attached at the base of the ski and the binding opened at the heel. For skiing downhill the bindings are locked. The ski is used with alpine touring boots which are rigid but lighter than downhill skiing boots.
is a double width ski that attaches to both feet in modern front entry boots. More common in use during a brief boom in the 1980s, today the monoski is used by only a few thousand enthusiasts worldwide. The monoski is produced by a half dozen companies worldwide in limited quantities. Due to its extra width and flotation in deep snow, enthusiasts claim it to be a superior powder ski.
The Telemark ski
is a downhill or touring
ski, where the binding attaches only at the toe. The Telemark ski was the first ski with an inwards-turned waist which made it much easier for skiers to turn. It was pioneered by Sondre Norheim
. The fact that the foot is only attached to the ski at the toes, means that specialized more flexible ski boots are used, and a specific turning technique involves pushing one foot forward and lifting the heel of the other foot.
are very light and narrow, and usually have parallel edges, though some newer skis have a slight sidecut
. The boots attach to the bindings at the toes only. There are three binding systems most often used: Rottefella's NNN, Salomon's SNS profil, and SNS pilot. The ski bases are waxed to reduce friction during forward motion, and kick wax
can also be applied for adhesion when walking uphill. Some waxless models may have patterns on the bottom to increase the friction when the ski slides backward. There are two major techniques, classical (traditional striding) and freestyle or skating which was developed in the 1980s. Skating skis are shorter than classical skis and do not need grip wax. Skating is also the technique used in biathlons
Skis for mountain/backcountry/cross-country free range skiing
which are designed for skiing on unbroken snow where an established track is lacking. These skis are characteristically quite wide (10 cm and greater), and often fitted with cable bindings
to provide general sturdiness, and to better extract ones feet from deep snow banks, in case it should be impossible to reach the bindings by hand. This is also the model used by military forces trained to fight in winter conditions, and the most closely related to the historical ski. The widest backcountry skis are often called 'Big Mountain' skis.
These skis are specifically designed for moguls
. They are typically softer, less wide and less waisted compared to a common carving ski.
Ski jumping ski
Skis for ski jumping
. Long and wide skis, with bindings attaching at the toe.
Use on vehicles
Skis are sometimes used in place of tires on vehicles
intended to travel over snow. The best known example of this is the snowmobile
, but larger vehicles such as aerosans
, snow coaches
, and snow planes
have also employed skis.