What Ski?

Buying skis can be a daunting experience, and is a topic we are often asked about at Welove2ski. No wonder: skis are incredibly technical pieces of equipment, and you can't be blamed if you don't know the first thing about a manufacturer's 'brand new vibration performance system'. It's not as if they explain it to you either; they just tell you how great it is. Anyway, fear not, for help is at hand.

I'll do my best to keep things as simple as possible by telling you about the three key elements that are going to majorly affect your ride. These are width dimensions, length, and stiffness.

The imaginary circle that defines the turning radius. Picture: © skishoot/salomonsports.com

To give you a rough idea of the figures involved, slalom skis - designed for the quick and short turns of slalom courses - have a correspondingly short radius (FIS regulation is 13m for men). This moves up through giant slalom skis (FIS regulation is 27m), super G skis (FIS regulation is 33m) and downhill skis (FIS regulation 45m). Typically, 'cross' skis and other retail models designed for on-piste performance will have a radius somewhere between a slalom and giant slalom ski, whilst other freeride skis get bigger and bigger the more they are geared towards powder and off-piste skiing.

It's clear from those numbers that skis which are regularly required to perform tight turns will need a shorter radius. This isn't to say that your big powder ski just can't do short turns - a good skier will always be able to slide a turn on a ten pence piece - but carving them cleanly will be beyond its capabilities.

So why don't all skis just have a short radius then? Because, as with all things in ski technology, there is a trade-off. The trade-off here is that a ski with a shorter radius will have to be narrower underfoot to create a larger difference in waist width and tip/tail width (a bigger shape, or 'sidecut'). If a ski is narrower underfoot, its average width will also be narrower, and this is not always beneficial.

First, it takes longer to transfer a wider ski from one edge to the other. For performance in short turns on hard pack, a ski that is comparatively narrow will be quicker from edge to edge, and this will allow the skier to engage into the next turn more quickly, and carve sharper turns. In slalom racing - a sport where fractions of a second matter - having skis that respond quickly to changes in direction is particularly important.

Second, a ski with a narrow average width will have a smaller surface area on the snow. A greater width (and therefore surface area) is often used for freeride skis because it allows the ski to stay on top of deep snow rather than sink into it, and this allows the rider to float on the surface of the snow, maintaining manoeuvrability and momentum (the last thing you want on a flatter section of your powder run is too sink into heavy snow and grind to a halt). This is why powder skis typically have a bigger radius than piste and race skis - because they need the extra width to stay on top of deep snow.

To recap on width dimensions:

1. A big difference in tip/tail width and waist width creates a short radius, which allows a ski to carve tight turns.

2. A ski with a short radius will also be a narrow ski.

3. A narrow ski will transfer from one edge to the other more quickly than a wide ski, and will feel more responsive on the piste.

4. A wide ski will have a larger surface area on snow than a narrow ski, and won't sink into deep snow as quickly, increasing manoeuvrability and momentum.

5. A slalom ski is needed for short, quickly-linked carve turns on piste, which explains why it is narrow with a radius of about 13m.

6. A big mountain powder ski is needed for big, open turns in deep snow, which explains why it is very wide with a radius that can exceed 45m.

LENGTH

With width explained, length is relatively simple. Longer length, like width, increases the surface area of the ski on snow. This has, firstly, a similar effect to having a wide ski - greater floatation in deep snow, which is why you'd think twice about going heli-skiing on 165cm, the regular length on a slalom course. A second, linked effect is that with more surface area on the hill, your weight is more dispersed (i.e. less weight per square metre), and so friction between base and snow will be decreased. With less friction, you will accelerate more quickly and to a faster top speed down the hill.

Speed skiers use skis of over 240cm! Picture: © Skishoot

So why don't slalom specialists ski on narrow, short-radius yet long skis? The trade-off on this occasion is that as you increase the length of a ski but maintain the same width dimensions, the radius will increase (the difference in tip/tail and waist width is the same but spread over a longer distance, so the sidecut will be less), and this will stop the ski from carving turns as tightly. Simply, a longer ski will give the skier greater straight-line acceleration and maximum speed, but will enlarge the turning circle.

That's why speed skiers and ski jumpers wear skis that on occasion approach 250cm (no turning required, just straight-lining), downhillers wear skis of around 215cm (some turning required, still lots of straight-lining), and slalom skiers tear through the gates on about 165cm (lots of turning required, little straight-lining).

1. A long ski will have a larger surface area on snow than an identical, shorter ski.

2. A ski with a large surface area will not sink into deep snow as quickly as a ski with a small surface area, increasing manoeuvrability and momentum.

3. A ski with a large surface area will create less friction on the snow, increasing its acceleration and maximum speed.

4. A long ski will have a large radius, and will not be able to turn as tightly as a short ski.

5. A slalom ski is required to perform lots of turns and little straight-lining, which explains why it is short with a length of around 165cm.

6. A downhill ski is required to perform fewer turns and lots of straight-lining, which explains why it is long with a length of around 215cm.
STIFFNESS

This is an important but easy concept to follow; radius means nothing if you can't flex the ski.

Put your skis together, and you'll notice that they only touch at tip and tail, bending away from each other at the waist. This is called camber. A ski's camber exists because a carve is created from the skier's force underfoot pushing the waist of the ski away from himself, into the snow and the outside of the turn. The flexed ski creates a banana shape (a reverse camber) in the snow, and following this shape, the ski travels round in a carved turn. Forget anything you might have heard about reverse camber skis, a new innovation in powder skis.

Reverse camber creates carve turns. Picture: © skishoot/salomonracing.com

The amount of pressure you need to apply to a ski to flex it from its normal camber shape into a reverse camber in a turn depends on how stiff it is. A stiffer ski will require greater power to flex it into a reverse camber, and will be less forgiving when travelling over bumps and landing air. This can be a bonus when the pressure being applied by the skier is very large (e.g. through a fast turn in a World Cup giant slalom) for two reasons. Firstly, push a soft ski too hard and it will give in and slide away from you, whilst a stiff ski will hold its edge and continue to track through the turn even when it is pushed very hard. Secondly, a stiffer ski will snap back into its original shape more powerfully as the pressure is released, and this explosiveness can aid acceleration out of the turn.

As a rule, freeride skis are softer, as they need to be more forgiving to absorb bumps and stomp landings in the park and won't require as much pressure to carve on less stable terrain. Meanwhile, skis designed for on-piste performance (particularly race skis) are stiffer, as the skier presses much harder to push out of his turns and so accelerate out of a carve, and this is all done on a very stable, hard pack race piste, where the snow is unlikely to give way. This also explains why softer powder and park skis don't perform as well on the piste as race skis.