Canting is often thought of as a means of attenuating edge contact angle. Canting is better used as a means of restoring mobility to the ankle joint lost through leverage as applied by the boot shell and cuff.
Additionally, canting is used to account for the predisposition to action in a particular direction, as created when the column of support from the hip to the foot is put under compression/load.
Too many use cant to affect they way they ski in the present, rather than how they might ski in the future.
When you stand one footed, barefoot, on a flat, level surface, your CM will move ‘sideways’ until it is directly over the foot. This movement affects the original angle between the ‘vertical’ tibia, and the ‘horizontal’ floor, such that the angle is now somewhat acute. With no structure around the foot, ankle, and lower leg, the tibia distal simply slides across the talus proximal. The torso is more or less upright and plumb, and the head is more or less over the base of support.
At the same time, if you relax somewhat on that foot, you may notice that your pelvis and torso may rotate, generally clockwise if on the left foot, anti-clockwise if on the right (as viewed from overhead. At which point, your upper body is now pointing in a different direction than your foot.
If you put a ski boot on that foot, and repeat the task, the following will occur: As the tibia/floor angle changes, the boot sole will initially tip to its lateral edge. The boot sole will then flatten. As it does so, the ankle joint will collapse to the medial side, due in part to the load applied from above, and the fulcrum presented by the lateral aspect of the boot cuff. Not only has range of motion been lost, but the leverage present assures that mobility of the ankle joint has now been lost, at least until the load has been removed.
Generally, the torso will tilt to one side, and the arms may be recruited to assist in balancing. The affected knee will no longer be in line with, or ‘leading’ the hip and ankle; rather, it will ‘kink’ to the medial side.
If one inserts a cant of appropriate dimension under the boot sole, thick side medial, the leverage on the ankle joint is greatly reduced, and rotation reduced, thus restoring mobility.
There is a small subset of skeletal conformity for which this strategy may not work. In the event of significant tibia vara, or bowed legs, it may be necessary to reverse the cant to ‘thick side out’. In the event that canting is applied to reduce ‘edginess’ or a ‘grabby’ ski, odds are very good that ankle mobility has been further leveraged by the attempt to fix something that is not directly due to a canting need.
If you are of the mind that effective, performance skiing is driven either by the hips or the knees, and want to ski that way, then canting thick side out may be a good choice. You may then deal with the ‘thousand natural shocks the flesh is heir to’, including chronic muscle and back pain, tendon irritation etc. Otherwise, there are very few athletes who will truly benefit from that configuration.