The sidecut is a general term for the curvature of a ski, snowboard, or skiboard that is seen when looking down from the top. The sidecut depth is measured as the distance between the waist of the board and an imaginary straight line that strikes both of the contact points at the tip and tail. The sidecut radius is the radial measurement of the curve that matches the inner curvature of the ski, snowboard, or skiboard. For instance, with a radial sidecut, a circle with a particular radius will perfectly fit the curvature of the sidecut. This particular radius is the given specification from the manufacturer. However, it is not necessary that the radius be constant. Mathematical functions, such as a parabola or a clothoid, are often used to describe the curvature of a sidecut. Also, multiple radii are stitched together in a piecewise fashion as well.
Alpine skis have undergone three distinct changes in sidecut design. The earliest skis from the 1800s all the way to modern examples in the late 1990s featured a very small amount of sidecut that produced a ski that was almost rectangular in profile as seen from the top. Starting with the Elan SCX in 1995, and very rapidly thereafter, these designs dramatically increased sidecut, a design known as the parabolic ski, or later known as a shaped ski. Shaped skis ruled the hills from about 1997 to 2010, when the rocker ski design of much greater width began to appear in force. From about 2012 on the rocker design dominated ski design, with shaped skis being found primarily in beginner equipment.
Snowboards and skiboards have generally had much more sidecut than alpine skis, roughly similar in layout to a parabolic ski. These designs evolved independently and were engineered from the start to select a design that produced smooth turns. Alpine skiing had previously been based on a skidding style of turns known as "stemming" that did not require much (or any) sidecut, and did not experiment with other designs as styles changed. Snowboards had to invent their equipment and techniques fresh, and found the deep sidecut was best through experimentation.
Alpine skis were for many years shaped similarly to cross-country skis, simply shorter and wider. Experiments with deeper sidecuts had been carried out with limited success, but the much deeper sidecuts of snowboards led to further experiments. In 1993 the Elan SCX introduced a radical sidecut design that dramatically improved performance of alpine skis. Other companies quickly followed the Elan SCX design, and it was realized in retrospect that "It turns out that everything we thought we knew for forty years was wrong." Since then, "shaped" skis have dominated alpine ski design.
Early ski designs
The first true downhill skis, made in Telemark, Norway by Sondre Norheim, were handmade from single pieces of hardwood and featured a relatively modest sidecut of about 4 to 5 mm. Alpine ski development after this seminal introduction proceeded in a series of stepwise improvements; laminate woods, metal edges, metal laminates (see the article on the Head Standard) and finally the fibreglass torsion box design were introduced over a period of 100 years. Throughout, little engineering effort had been spent on considering the ski shape, as other issues like torsional stiffness and "chattering" were problems that needed to be solved. Skis of the 1970s were largely identical in shape to those of the 1800s.
Skis with narrower waist profiles had been experimented with, but had never become widely used. In 1939, Dick Durrance ordered a custom ski from Thor Groswold's factory in Denver with a 7 mm sidecut, and this became a new standard for slalom skis. During the winter of 1948/49, Jerry Hiatt and Thor's son Jerry decided to experiment with even bigger sidecuts. Taking a pair of the company's standard hickory Rocket skis, they cut away wood until they produced a 15 mm sidecut. When they tried them out, they found they turned quite easily in a series of rounded turns. Ironically, this was considered poor form in the era of the stem Christie, where good form was a series of sharp J-shaped turns. The two abandoned the design, speculating that they ended up as firewood.
In any event, wooden skis of this era did not offer much torsional stiffness; when rolled on-edge by the skier's boots, the tips and tails of the ski would tend to twist in the opposite direction in order to lay flatter on the snow. This reduced the amount of performance the sidecut would normally add. Hiatt and Groswold's experiment required such a deep sidecut that the waist had little vertical stiffness, another problem for the design.
A radical change in design did not occur until the mid-1970s introduction of the first modern snowboards. With no previous designs to set the mould, snowboard designers had to experiment to find the right layout. The 1975 Burton Backhill had a 17 mm sidecut, giving the board a very short turning radius. The Backhill was extremely low-tech in comparison to contemporary ski designs, consisting largely of a sheet of plywood. A contemporary ski's torsion box design greatly improved torsional stiffness and would allow even greater sidecut to be effective. But in spite of the snowboard demonstrating that modern skis could carry much wider sidecuts, and that such a sidecut resulted in excellent turn performance, little came of this development. The snowboard market was ignored by the major ski companies through the 1970s and 80s.
Experiments with slightly greater sidecut on skis did appear during this period, including the Head Yahoo and especially the Atomic Powder Plus. Further developments followed due to changes in competitive giant slalom, as the gates were moved further apart and resulted in much more turning. K2 responded with the GS Race with a 10 mm sidecut, and several similar designs followed. In spite of reports that these skis were easier to turn, they were considered specialty items and the designs offered only to the race and performance markets.
One particularly notable experiment was made at Olin during the early 1980s. In 1984, one of the Olin executives asked ski designer Frank Meatto if it were possible to make a beginners ski that would make skiing easier to learn. Meatto and co-designer Ed Pilpel decided to experiment with a radical sidecut as a way of improving turns. They designed a ski with a 31 mm sidecut, but it had tips that were 128 mm wide and they wouldn't fit into their presses. They solved this by cutting the ski in half longitudinally, leaving the curve only on the inside edge, which powers the turn. The result was effectively one-half of the parabolic designs that would follow. The ski was so narrow underfoot that additional platforms had to be added to mount the bindings. The company produced 150 pairs to demonstrate at the SIA trade show in 1986, but no one purchased the odd-looking asymmetrical "Albert" design.
The company that finally drove the evolution of ski design was Elan of Slovenia. Designers at Elan produced an experimental design with screws that could be adjusted to produce different amounts of sidecut, and asked members of the company ski team to try them at different settings. This quickly demonstrated that a radically increased sidecut around 22 mm clearly improved turning performance. A series of test skis followed, which the Elan team immediately started racking up win after win on in giant slalom events.
In 1993 a number of these "Sidecut Extreme", or "SCX", skis were sent to the US for testing. The results on student skiing was dramatic, and the company began designing their skis specifically for the training market. By the end of the year the improvement of the "parabolic" design was obvious to everyone, and the SCX was named "ski of the year" in the trade press. By 1995 older designs were being sold off at pennies on the dollar in bargain bins as skiers turned en masse to the new designs. By 1997/98 the conversion was complete, and only parabolic designs were being produced.
Over time the name of these skis changed. Originally termed parabolic by their designer Jurij Franko, the term carver soon became common as these skis were being sold largely on their ability to allow even beginners to perform the efficient carved turn. This changed again to shaped ski by the early 2000s, as the design was applied to a wider variety of ski types and some level of parabolic shaping became universal from training skis to downhill racers.
One disadvantage to the parabolic shape was that it was much wider at the tip and tail, producing a design with considerable rotational inertia. To offset this effect, the skis had evolved to be much shorter, reducing the moment arm. In spite of the larger "shovels" at the tip and tail, the overall area of the ski was reduced, which led to them tending to sink in soft snow. This left powder skiing and off-piste skis among the few markets not being served by parabolic designs. Several skis aimed at the powder market had appeared over the years, including the Volant Chubb and other "fat-boy skis" from the early to mid 1990s.
Free skier Shane McConkey was skiing on the Elan designs in 1996, but found they sank in the snow. As an experiment to get more "float" on the snow, he tried mounting ski bindings on waterskis while skiing in Alaska. He began working with Volant on skis that combined their metal-based production method, producing the aluminum-based Volant Huckster. In 1998 he was testing the Huckster with his friend Scott Gaffney, who reported that his bent Chubbs skied better than the new design because the tips didn't sink in the snow. McConkey took the design and used it to produce the radical Volant Spatula in 2002, which featured not only a banana-like reverse-camber but also a negative sidecut radius. On firm snow the skis were difficult to turn at all, but in powder the tips and tails bent up to produce the curved shape that caused them to carve. McConkey moved to K2 Sports and introduced the similar Pontoon design circa 2006.
By 2010 the rocker design was becoming the "in" design, and starting to displace parabolics on the larger mountains. By 2012 the change to rocker designs was well underway, and by 2013/14 almost all new skis claim to be rockers. Many of these have moderated their camber and sidecut to be more traditional, allowing them to be used on the trails as well as powder, but retain the very wide bases and other features of the rocker design. These may be referred to by any number of names depending on the brand and marketing, with terms such as "full rocker", "all mountain rocker", "hybrid" and others.
Different types of skis have different sidecuts. Skis with drastic sidecuts tend to make quicker sharper turns and have a smaller turn radius. For example a world cup slalom ski would have an extremely large tip (probably around 120 mm) a narrow waist (in around 60mm) and a large tail (slightly narrower than the tip). The drastic shape of this ski would allow it to make extremely quick turns (radius between 11m and 14m) without skidding. The disadvantage to a pronounced sidecut is that the ski will be less stable at high speeds, preferring short, quick turns. Also, skis with a drastic sidecut will perform poorly in moguls. Most skis have a moderate amount of sidecut. This allows reasonably fast turns (radius around 17m on most skis) while still maintaining some stability at higher speeds. Another possibility is a very slight sidecut. This is commonly found on giant slalom skis and competition level mogul skis. The straighter sidecut allows skis to make long, fast, highly stable turns (radius around 30m for giant slalom, even more for most mogul skis). In mogul skis, the narrow width, straighter sidecut, and light weight allow the ski to be maneuvered through the tight troughs in the bumps. Jumping skis are very wide and have virtually parallel sides, as the ski jumper is more concerned about maintaining a fast and straight trajectory, and not turning at all.
As powder-specific constructions are becoming more popular, some extremely unusual sidecuts are beginning to appear. For example, the K2 Pontoon's widest point is the tip. It then gradually gets narrower all the way down to the tail. Also, some skis like the Volant Spatula and Goode Scoop have a reverse sidecut. In a reverse sidecut, the tip and tail are a normal size, but the ski becomes extremely wide at the waist, giving it an ovaline shape. These constructions are thought to provide maximum floatation in extremely deep powder, but they are useless on hard snow. Most people, however, prefer traditional sidecuts, even in powder.
- Seth Masia, "The Evolution of Modern Ski Shape", Skiing Heritage Journal, September 2005, pp. 33-37
- Masia 2004, p. 18.
- Masia 2005, p. 33.
- Masia 2005, p. 35.
- Masia 2005, p. 34.
- Jeffrey Covell and Frederick Ingram, "The Burton Corporation", Gale Directory of Company Histories
- Masia 2005, p. 36.
- Arttu Muukkonen (translated by Janne Niini), "The Story of Rocker Skis", interview with Shane McConkey, 1 April 2009
- "Shane McConkey changed powder skiing forever"
- Mike Rogan, "Understanding Rocker", Ski, 27 August 2012
- "Rocker for Skis Explained", REI