Post
by MikeK » Wed Feb 11, 2015 10:42 am
Maybe I can help expand on what connyro said jooleyen...
I think what the trend is, is trading width for length. A couple advantages to doing that, and of course, a couple disadvantages. Fatter skis, even with a similar surface area as a long skinny ski, float better on the snow, particularly soft snow... it's just the mechanics of how snow works. Sidecut and other things aside, the tradeoff then is weight (wide skis, even short often have more surface area, more materials and thus more mass), glide, and tracking. A skinny ski is kind of like a skinny tire in the snow - it will cut down through the snow, even if it isn't deep, and 'slice' a straighter track. A wide ski will sideslip more (think of the extreme, say if you had a rectangular plate for a ski - it would be just as likely to slide forward as it would be side to side). The glide affect can be from multiple things, but cambers aside, it you aren't sinking much in the snow, or you are in a track, you simply have less frontal area to push against. All these things are compounded by cambers (the shape of the bottom of the ski from the side) and sidecuts (the shape of the ski from the top).
As far as turning, a shorter ski will be easier to turn than a longer one - it's a matter of where the edge forces act on the ski - you can easily see this by the new 'modern, rockered' skis which turn up the tips and the tails. This effectively makes the ski like a shorter ski (edges move closer to the foot) and they are already slightly shaped in the reverse camber that occurs under load, but also gives you the float of a longer ski in deep snow. You can also notice this effect by dulling your tip or tail edges - it will change how the ski rotates and make it grab less farther away from your foot, essentially making it easier to turn.
So onto sidecuts - these help the ski turn. It's easier to put a radical parabolic side cut into a ski that is wider and still maintain adequate flotation area. Skinnier skis will have less: it's a function of material available, width needed to maintain float, and tracking. Sidecuts will make the ski want to turn when it's edged. The less radical, the better the tracking, the more radical, the tighter they want to 'carve' when edged. You'll also need to kick them perfectly straight back or they will want to wander. Some people cannot stand this and would rather give up turning for tracking - again, there is no reason you couldn't have a wide, straight ski - there were ones designed like that basically as big snowshoes. But most modern XCD skis try to have some balance of turning ability and gliding/tracking ability.
Cambers don't really have much to do with width but you'll notice most of the wide, larger sidecut skis will have a single camber i.e. no wax pocket. This is similar to a downhill ski and that it's easy to push the ski flat and then reverse camber it (the ski bends into a banana shape under load with causes it to follow that arc). Double and 1.5 cambers are what typical XC skis are and were. They have a wax pocket created by a second bend in the skis under your foot. It's typically hard to flatten this out because it needs to support your weight and keep the wax or scales off the snow when you are gliding (that pocket is what gives the glide)... so again it becomes a tradeoff between turning ability and kick and glide. The skis that are more suited to kick and glide will often maintain that double camber and make better use of the things I mentioned above that allow it to excel at that, and the skis that have single will often take advantage of the turning aspects. There are of course skis which blurr this very much, and those are right in the middle of the range (the current Fischer E109 and Madshus Eon are two of these examples).
The other thing with stiff double cambers is they don't do well in deep snow - it takes a lot of pressure to flatten the ski to get a 'kick', so you wind up sinking and slowing down. Fatter, single camber skis can stay above the snow and although they glide less on hard snow, will glide better in deep snow due to the flotation AND the ease of which they engage.
Wide skis also have more surface area underfoot for the wax or waxless pattern to engage the snow, leading to more grip for climbing.
