Sidecut & Radius
The sidecut is the curvature that runs along the ski’s edge from tip to tail and affects how your skis turn. Most skis have at least a moderate amount of sidecut, which allows reasonably fast turns while still maintaining higher speeds.
Sidecut is the “hour glass” shape or the inner curvature of a ski that creates the turning radius. The turning radius is the virtual circle that a pair of skis makes on edge. When you put the ski on edge, you force its slight hourglass shape onto a flat surface. The greater the sidecut (or the narrower the waist width in relation to the tip and tail), the quicker the turn.
The most variations with sidecut design have occurred with touring and freeride skis. A 5-point sidecut in the forebody and the upper tail area make up the widest parts of the ski. The is tip more radically rockered and tail is somewhat rockered, so the widest dimensions make up the ski’s contact points with the snow—along with the waist.
Turn radius is the shape of a ski determined by its tip, waist, and tail width, usually expressed in metres.
The radius of the imaginary circle, where the narrower a ski’s waist is in relation to its tip and tail, the shorter the turn radius and therefore the deeper the sidecut.
A skier can make different types of turns with any ski, but turn radius suggests the natural turning tendency of the ski on “auto-pilot”.
In reality, the sidecut shape of the skis is much more complex, for example, the radius of the ski can be different in the front and the rear of the ski or several intersecting elliptical radiuses giving each ski their own unique personality. The shape of the elliptical radius determines how quickly and aggressively the ski enters and exits a turn.
FIS has defined that the radius has to be measured as follows: “The rear and front ski lengths are measured starting from the narrowest point of the ski. In order to avoid the entire side cut radius becoming distorted by the different geometries of the tail and tip, the rear ski width is recorded at 90% of the measured rear ski length whilst the front ski width is recorded at 80% of the measured front ski length.”