Ski geometry

Ski geometry is the shape of the ski. Described in the direction of travel, the front of the ski, typically pointed or rounded, is the tip, the middle is the waist and the rear is the tail. Skis have four aspects define their basic performance: length, width, sidecut and camber. Skis also differ in more minor ways to address certain niche roles. For instance, skis for moguls are much softer to absorb shocks from the quick and sharp turns of the moguls and skis for powder are much wider to provide more "float" in deeper, softer snow.

The length and width of the ski define its total surface area, which provides some indication of the ski's float, or ability to remain on top of the snow instead of sinking into it. Cross-country skis must be narrow to reduce drag, and thus must be long to produce the required float. Alpine skis are generally not designed to reduce drag, and tend to be shorter and wider. Skis used in downhill race events are longer, with a subtle side cut, 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. For off-piste skis the trend is towards wider skis that better float on top of powder snow. The ski width of all-mountain and off-piste skis has generally increased since the 1990's when 85 mm width was considered a wide powderski. From 2010 and onwards, many well known ski manufacturers sell all-round freeride skis for the general public starting in the 90mm range and going up to 120 mm or more.

Camber is the ski's shape as viewed from the side. Typically skis are designed so that when the tip and tail are on the ground, the waist is in the air. Without camber, when the skier's weight is applied at the waist, the weight would be distributed on the surface closest to the foot, diminishing along the length. Camber distributes weight onto the tips and tails, extending the surface area bearing the skier's weight, and thereby improving the amount of ski edge in contact with the surface. The technique was first introduced by ski makers in Telemark, Norway, and remained largely unchanged through the 20th century.

In 2002, skier Shane McConkey led development of the Volant Spatula, an alpine ski developed for skiing deep powder snow. The Spatula uses reverse camber with the tips and tails rising above the waist in an effort to improve floating on soft snow. Referring to the shape of the runner on a rocking chair, these designs became known as rockers.

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