The reason is not quite obvious, for at first glance it would appear that the ski would meet more resistance from the snow in the edged position than in the flat, but this is not the case, for, when the ski is edged, most of the resistance is exerted obliquely against its sole, and so tends to make the ski rise to the surface of the snow and relieves the pressure. When, however, the ski is flat, the resistance acts directly against the side of it, and there is no lifting tendency to diminish the rapidity with which this resistance increases as the snow is compressed.
Fig. 22.
Moreover, since during a turn the runner must lean inwards to keep his balance, the ski cannot remain in its normal position in relation to the leg unless it is more or less edged inwards ([Fig. 22], a). That the leg and ski should remain as nearly as possible in their normal relative positions is an advantage, for the more nearly they do so the less is the strain on the ankle. If the weighted ski is held quite flat during a turn in which it is outermost, that ankle is placed in a very unstable position ([Fig. 22], b), and is liable to give way and so edge the ski on that side towards which it is moving ([Fig. 22], c); it will then cut more deeply into the snow and be brought instantly to a standstill.
Fig. 23.
In all that I have said so far about side-slip, I have assumed that the ski is moving more or less broadside on, with its heel travelling outside the track of its tip and its pivoting point well forward, and this is what either one or both skis actually do during the greater part of any swing or turn; for, in turning, a ski usually passes through the positions of either b or c, [Fig. 23]. A ski may also, as, for instance, in turning downwards from a slow traverse, move so that the curve in which its point travels is outside that of the heel ([Fig. 23], d) and its pivoting point is near the heel. In each of these cases, though one end is side-slipping faster than the other, both ends are slipping to the same side, and the ski, as I have said, has therefore to be edged to the opposite side.
If, however, the ski begins to turn as in d, and finishes as in b or c, it must of course be edged first to one side and then to the other, as in e, and for a moment be flat. At this moment the pivoting point of the ski is at its centre, and its heel is side-slipping in one direction as much as its point is in the other, as in a. If ever, therefore, a ski, in turning, continues to pivot on its centre ([Fig. 23], a) instead of only doing so for a moment, it must obviously be held quite flat, as otherwise either one end or the other will cut below the surface of the snow and be checked suddenly.