Fig. 5.
The thickness of the ski is proportionate to its elasticity and the weight of the runner, being about 1¼ inches at the binding and 3⁄8 inch at the front bend and the heel. A stiff ski runs rather less comfortably than a thinner and more flexible one, but it is safer to choose a ski of ample thickness near the binding, especially if it is to be used for jumping.
The turn up at the front of the ski should begin at about one-fifth of the distance from the tip to the heel end. It should be very gradual, for a sudden bend makes the ski run more slowly and far less smoothly. The under side of the tip need not be more than five inches above the ground.
There is a slight upward arch between the front bend and the heel. It should be no more than ¾ of an inch high at its highest point, below the heel of the boot, only just sufficient to prevent the ski when resting on soft snow from bending downwards in the middle under the weight of the runner. The height of this arch should therefore vary slightly according to the length and stiffness of the ski, and to the runner’s weight.
Of course any twist in the ski will prevent it from running true. A simple way of making sure that a ski is free from any such twist is as follows: draw a few lines across its sole, at right angles to a line down the middle of it, and, holding the ski so that a very much fore-shortened view of the sole is obtained, see if all these lines are parallel.
Nothing is more uncomfortable and difficult to run on than a ski which has become warped and has a downward bend in the middle. To prevent this happening and to preserve the upward arch, a pair of skis, when not in use, should be placed sole to sole and bound together at the front bend and the heel, with a block of wood about 1¾ inches thick put between them 8 inches or so behind the binding, just where the boot-heel rests on the ski.
Most skis are made with a groove running along the middle of the sole from the front bend to the heel. This groove greatly increases the ski’s steadiness in straight-running, and on no account should be omitted. A smooth-soled ski makes turning easier for the runner who has not learnt the right way to do it, but this slight advantage by no means compensates for the wobbliness in straight-running which it entails. If you want easy steering, choose extra-flexible skis, but not grooveless or extra-short ones.
Most of the ordinary foot-bindings are fixed to the ski by means of a hole bored from side to side through its thickest part. See that this hole is made almost entirely in the upper half of the ski’s thickness, well away from the sole. When lifted by a strap passed through this hole, the ski should point downwards at an angle of about 45 degrees.
In order that they shall be stronger in relation to their weight and less flexible, skis are sometimes made with a convex, instead of a flat upper-surface. The increased stiffness makes them less comfortable for ordinary running but safer for jumping. The convexity should always stop short of the beginning of the front bend.
[Fig. 6] shows that it depends on how this convexity is obtained as to whether and how it is an advantage or otherwise. Supposing the wood in each case to be of exactly the same quality, b will obviously be not only stiffer but heavier than a, c will be stiffer but no heavier, d will be equally stiff but lighter. It is evident, then, that one cannot say off-hand that the convex shape is either better or worse than the flat, but only that, weight for weight, the convex shape gives greater stiffness and strength, the flat gives more elasticity.