It’s All In The Rocker!
For many skiers all you need to know about the Rocker is it’s the extra curly bit at the front and it makes skiing powder a lot of fun! Double the rocker with curly bits at the front and back, double the fun!
But for those of you that like number crunching, want to know the ins and outs of ski design and like to impress your mates in the pub – Charles Griffin, Snoworks all-mountain skier and retired physicist gives his personal insight into Rocker shaped skis. Is your brain in gear?
HOW ROCKERS WORK
On Firm Snow
If you place a non-rocker ski unloaded onto a flat surface its camber results in the ski touching the snow at two points A and B. One near the tip and one near the tail as in Figure 1 below. These points more or less coincide with the widest parts of the ski at C and D in Figure 2. Although they don’t have to do so exactly.
If the unloaded ski is now angled over at some variable edge angle called angle λ. (Represented by the Greek letter Lambda. Click for explanation) as in Figure 3 below, its edge will still be in contact with the snow at the points A and B and only those points. In other words the positions of the points of contact are independent of the angle λ. If the ski is then progressively loaded perpendicular to its top surface it will bend into reverse camber until the whole of the lower edge is in contact with the snow. Whereupon it will carve a nice tram-line.
Now do the same with a semi-rocker ski unloaded as in Figure 4 below. It will be in contact with the snow at points E and F only and along the length from E to F when loaded as in Figure 5.
Because the ski has a sidecut it is therefore wider in front of E and behind F as in Figure 6 below. When the ski is then angled over at angle λ (remember that’s the variable edge angle), the points of contact E and F move outwards from the centre of the ski: E towards the tip and F towards the tail. The more λ (edge angle) is increased, the further apart E and F move until at some large value of λ (probably about 65°) they roughly coincide with A and B in Figure 1. As before when the ski is loaded into reverse camber it carves a nice tram-line – but the length EF of the edge in contact with the snow increases as λ increases. The same applies for a full-rocker ski except that the points E and F will initially be even closer and roughly coincident with the bindings as in Figure 7.
Thus when you are skiing short turns, a narrow piste or bumps and you are using a small value of λ (a small edge angle) only a short length of the ski is in contact with the snow and the ski is therefore relatively easy to turn. When you are using a large value of λ (a large edge angle) while carving the length of edge in contact with the snow is longer as required.
In Soft Snow, Shallow Powder, Slush
In such conditions rocker skis have another advantage over non-rocker ones. Figure 8 shows the areas of a non-rocker ski that is in contact with the snow when it is only lightly pressured and has not yet been bent into full reverse camber. As the pressure is increased the shaded areas increase until when full reverse camber is reached they merge as in Figure 9. The gain in area in contact with the snow, the unshaded area in Figure 8, is relatively small because this is the narrowest part of the ski.
For a lightly pressured rocker ski the area initially in contact with the snow is the shaded area in Figure 10. As the ski is pressured into full reverse camber this area increases until it too is the same as Figure 9. The increase in area is the addition of the unshaded bits in front of E and behind F which because of the ski’s sidecut will together be larger than the unshaded area in Figure 8 for a non-rocker ski.
Thus in such conditions the increase in flotation achieved when a rocker ski is pressured will be greater than when a non-rocker ski is similarly pressured.
So that’s it folks, now you know why Rocker skis are pretty good at carving on firm snow and have great flotation in deep snow – according to the gospel of Charles Griffin.
Off course you can test out the theory for yourselves on any All-Terrain, Off-Piste or Backcountry Course by using the latest Salomon Q skis with Rocker available on all Snoworks Ski Courses for hire this coming season. Reserve yours now.