There are many different types of skis that are available to purchase. They all have different characteristics and dimensions that drastically affect the ride of how the ski performs. Most commonly thought of are length and width under waist but there a variety of dimensions that have an equal or even more of an effect than the most commonly thought of dimensions. This report explores how the many different dimensions of the ski effect how a ski performs. These include Length, width under the waist, turn radius, stiffness, the sharpness of the edges, angle of edges, camber, weight, rocker and the tips.
Length
There are two key measurements that are the most commonly thought of when renting or buying skis. They are length and width. The length of a ski is measured from the front tip to the rear tip. The length of the ski is determined by the height and weight of a skier. A 160cm skis will ski different for a kid who is 160cm tall compared to a man who is 190cm tall. The length is all relative to the skier themselves. Increasing the length of a ski also increases the weight of the ski as there is more material used. Weight is the mass of an object multiplied by gravity.
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Firstly a long ski will gain more control at high speed. They are less susceptible to bumps and have a larger edge grip. However, they have more rotational inertia. This is a value tells us how difficult it is to change the velocity of an object around a rotational axis. This axis being your connection point to the ski. When weight moves further away from the rotational axis it is increasingly more difficult to rotate the object. When the ski length increases it places more weight further away from the skier themselves making it harder to turn the ski. This has a larger effect when the when you are jumping or are doing a turning turn in which you are not carving.
Increasing the length of the ski increases the size of the sidecut radius which will be explained further later. This is probably the largest effect that the length of the ski has on turning. This has more effect when carving the snow and there is more contact between the ski and snow.
Width under the Waist
Width is measured under the waist from one edge to the other. Increasing the width increases the surface area of the base of the ski. This spreads the pressure and force of the skier further around the ski. This makes the ski float better over powder as the pressure is spread out more.
The pressure spread out is evident through the pressure per unit area. The width creates a larger surface area. With a larger denominator, the number will be smaller meaning that that the pressure per unit area will be smaller.
While a wide ski performs better in deep snow the effects are reversed on hard packed snow. Because the ski is wider it is harder to carve because it is harder to get on the edge of you ski.
Sidecut Radius
The Sidecut radius is the shape of the edge of a ski. It is measured as if the edge of the ski was drawn around to make a whole circle. It is most noticeably seen through the difference in width between the tail, the middle and the tip of the ski.
The sidecut radius is used when the ski is tipped on an edge and used for carving of a turn. If the tip and tail are wider than the middle of the ski then you would naturally think that only the wider part of the edge will be in contact with the snow. The ski will flex so that the whole edge of the ski is in contact with the snow, as seen in the diagram below. Although this is an angle of ski diagram it works in the same way if you were to change the turning radius.
Stiffness
Stiffness is how flexible a ski is. It is a large factor on how the ski reacts to bumps at speed and any stress placed on the ski. A stiff ski is more responsive, reacts more to bumps and gives you more control at speed. However, they are less forgiving as they respond to even the slightest movement or bump in the snow. Stiffness allows you to push harder and carve better. The stiffer the ski is the harder it is to change from one turn to the next. If it is flexible it is easier to initiate the carve of turn and release the carve of the turn.
Also the turn radius is irrelevant if there is no flex in the ski. As seen in the diagram above the ski needs to flex into its position to create the most effective edge and use the turn radius to carve in the design arc of the sidecut radius.
Torsional Stiffness
Torsional stiffness is the resistance against twisting forces. The effects of torsional stiffness is very similar to the effects of stiffness. If it is torsionally stiff then it is less forgiving and harder to change from one turn to another. If it is torsionally stiff it provides more grip when placed on an edge.
The Sharpness and Angle of the Edges
The sharpness of the edge is much similar to a knife. If the edge is sharper it cuts into the snow having less resistance because there is less surface area and making it smoother. You also have more control with a sharp edge over a blunt edge. A blunt edge will provide less area grip on the snow. However, when an edge is cut the edge angle has a large part to play in the control given by the ski. A ski edge angle is usually between 88-90 degrees. The lower the angle of the edge the more advantages however they are harder to control. Lower angles allow the ski to initiate the carving turn quicker however can initiate too quickly and catch an edge and lose control whereas larger angles are more forgiving because you initiate the carve turn later and make it easier to control.
Camber
Camber is the shape of the ski from the side and is measured by the distance between the centre of the ski to the ground. When the weight has applied the flex of the ski is allow the whole ski to maintain contact with the snow below. This can be seen when you place two skis together and only there are only two contact points at the tip and tail occur and the prevalence of camber is evident from the gap between the two skis.
When weight is placed on the ski the camber will push out the length of the ski. This is evident from the fact that if a curved object is placed on a flat surface and weight is applied to make it a flat object the mass will spread out and extend the length of the object.
Rocker
Rocker is the reverse camber located between the contact point and the tips and tails. It is when both the front and rear tips bend upwards. This shortens the contact length of the ski allowing the ski to be longer. As seen by the diagram below the change in rocker affects the length of the ski. More rocker allows you to have a longer ski as the skis contact length will become shorter and the ski will take up the properties of a shorter ski. Seen to the right is the difference and combination of camber and rocker. Some skis will have no camber and just have rocker forming a U shape whereas some will have very small rocker and larger rocker forming an n shape.
Weight
The weight of the ski has very straight forward affected. If the ski is heavier it holds speed better and is less affected by bumps on the snow as it is more planted to the ground. Whereas a lighter ski is less planted as it will be easier displaced by small bumps.
Reviews of Skis and the effect of different dimensions
- Atomic Benchetler 100 - 2019 - Ski magazine
- Width - 100mm
- Length - 180cm
- Turn radius - 19.5m
The reviewer describes the ski as ‘light and playful’ meaning that it is easily maneuverable because of the weight and its camber. The camber allows the ski to come back to its natural shape because it has to flex more to get into its carving shape. It also describes the ski as being a ski for when ‘it's not crazy deep’. This means that the 100m waist is good to float above powder although it is not wide enough when the snow is incredibly deep. However, the review describes the ski as being able to ski all over the mountain but only gave it a 3.27/5 on hard-packed snow. This is due to the width as it is harder to carve on wide skis and also the turning radius is large for hard-packed snow.
Fischer RC One 86 GT - 2019 - Ski magazine
- Width - 86mm
- Length - 182cm
- Turn radius - 17m
The reviewer places this ski as 4.22/5 on hard-packed snow. This is due to its width, as 86mm is typically larger than any slalom ski but still allows for the ski to carve and is easy to ski on to the edge of the ski. This ski also allows the ski to be considered an all-mountain ski allowing it to be used in a variety of different conditions. The reviewer gives the ski a 3.17 on floatation meaning that the ski does not handle deep power well, again this is due to its width.
Different Types of Skis
All the different dimension of a ski listed above affect how the ski performs. They all affect what type of skiing the ski is best set for whether it being slalom skiing or backcountry powder skiing. For a slalom ski, a ski that has to be short and nimble the ski will be around 70mm waist underfoot, a really small turn radius of 10-12m and will be relatively short. This is because the ski does not have to be able to maintain speed but has to be able to be easily maneuverable between the gates that are close together. Whereas a downhill ski which is all about maintaining speed where the gates are really far apart will have a large turning radius of 30+m and be much longer than a typical ski. Another ski will is a powder ski that is long relative to the skier, it is wide to float over the powder, as wide as 130mm and will have rocker to help float in power as well. Some skis combine elements of all these dimensions and skis to be considered all-mountain which can do everything. There are large varieties in all the dimensions. A powder ski can almost be twice as wide as a slalom ski so the effects of dimensions are evidently seen.
Bibliography
- Name Link Author Date Accessed Date created Skis http://www.mechanicsofsport.com/skiing/equipment/skis.html
- Ski Design 101 https://skierlab.com/ski-design-101/
- Powder Magazine gear Guide https://www.powder.com/gear-guide/
- Physics of Skiing http://discovermagazine.com/2004/feb/physics-of-skiing Maia Weinstock 18/10/19 5/2/19
- What is weight https://www.khanacademy.org/science/ap-physics-1/ap-forces-newtons-laws/newtons-first-law-mass-and-inertia-ap/a/what-is-weight
- Alpine edge Ski guide http://diginfo.ru/en/alpine-ski/aliexpress-for-alpine-ski-side-edge-file-guide/
- Atomic Benchetler 100 - 2019 https://www.skimag.com/gear/atomic-bent-chetler-100-2019
- Fischer Rc One 86 Get - 2020 https://www.skimag.com/gear/fischer-rc-one-86-gt-2020
- 3 Key specifications for buying skis http://welove2ski.com/3-key-specifications-for-buying-skis
- Ski buyers guide: ski Width https://www.wagnerskis.com/journal/ski-buyers-guide-part-1-ski-width/
- How to pick the right Ski length https://www.backcountry.com/explore/how-to-pick-the-right-ski-length
- Physics of skiing https://www.real-world-physics-problems.com/physics-of-skiing.html
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