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Ski, Wax and Snow: Three Elements for Faster Gliding

The Science of Gliding

White landscape, powder snow and perfect slopes are all the ingredients for the best winter day. Whether it is with cross-country (XC) or alpine skis, snowboard or touring skis, everyone is looking for the fastest glide.

However, we all have had the feeling of “slow” or “heavy” snow while skiing. Especially for athletes, having a fast glide would make the difference between winning a gold medal at the Olympic Games or not arriving on the podium. For this reason, a correct ski waxing is considered as a performance factor.

But firstly, how can we glide on snow? What are the factors that we should consider during gliding?

Five different frictions

While gliding, the friction between the surface of the ski and the snow melts the snow underneath, forming a thin layer of water on which it is possible to glide. When talking about ski sports, the overall friction μ is defined as

μ= μploughdrylubcapdirt

  • μplough  is the resistance due to plowing of snow out of the way, dry the deformation of the snow over which the ski is traveling
  • μlub the lubrication of the ski with a thin layer of melt water
  • μcap the capillary attraction of water in the snow to the ski bottom
  • μdirt the snow contamination with dust [1].

The science behind gliding is very complex. In fact, three different elements (snow, wax and ski) must have the most efficient interplay to guarantee the best glide. As the snow characteristics, i.e. temperature and grain size (Figure 1), are not possible to change in the skiers’ favour, skis and waxes are to be in continuous evolution.

Snowflakes photographed by W. Bentley at the end of the 19th century
Snowflakes photographed by W. Bentley at the end of the 19th century.

As mentioned, the glide occurs on a water film. The thickness of this perfect surface of water ranges between 4 and 12 μm [1]. However, when the snow is too cold, the layer freezes and slows down the ski. On wet snow, the water layer becomes too thick, increasing μcap (Figure 2).

Figure 2. Different gliding speeds depend on the snow temperature and the ski waxing [3].
Figure 2. Different gliding speeds depend on the snow temperature and the ski waxing [3].
Consequently, the combination of ski material/wax is chosen and designed in order to act on the water layer.

Speed vs snow temperature

Before concentrating on skis and waxes, let’s quickly review the characteristics of snow. Falling snow comes in different shapes, from star-like flakes to needles. But soon after it starts accumulating on the ground, its metamorphosis begins to take place due to temperature or mechanical action.

Figure 3. Snowflakes shape and snow penetration [3].

Depending on the snow shapes, temperature and origin (artificial or natural), different waxes have to be utilized due to differences in penetration (Figure 3). For instance, old snow is usually faster, as snowflakes are already transformed and the creation of a water film is easier [1].

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Ski material

Since the bone-made skis of prehistoric humans, skis have undergone a large evolution. Depending on the sport for which the skis are used (XC or alpine skiing and so on), the size and shape vary, but the core materials are mainly the same.

Strong, stiff, flexible, hydrophobic, light and resistant to vibrations are the common properties that need to be considered while designing a ski (Figure 4).

Figure 4. Schema of the different layers that constitute the ski [4].
Figure 4. Schema of the different layers that constitute the ski [4].

The core part of the ski can be made of laminated wood, Kevlar, foam or aluminium honeycomb in different proportions [4, 5]. Depending on that, we would have “harder” or “softer” skis that would react differently to different snow conditions, as well as influence the muscles of the skier in different manners [6].

The ski’s outside part is usually made of fiberglass or carbon fibres [4, 5], while the ski base, the part in contact with the snow, is made of ultra-high-molecular-weight polyethylene (UHMWPE), a semi-crystalline and hydrophobic polymer material [7].

The porous surface should be impregnated with wax, which is melted by means of an iron (Figure 5).

The base is frequently sintered, while it contains performance-enhancing additives and solid lubricants as polytetrafluorethylene (PTFE) and graphite [8, 9]. Graphite, in particular, permits the dissipation of the static charges that form between the base and the snow, which increases the friction. All the above-mentioned layers are glued together by a resin [6].

Figure 5. 1) Ski base without wax. 2) The wax is ironed in order to be absorbed by the UHMWPE. 3) At room temperature some wax comes out from the pores. 4) At colder temperature on the snow more wax comes out [3].

It is common for new skis to get their base ground by means of a sanding machine. Depending on the size and direction of the grooves running along the length of the ski, the skis can be used in different snow conditions (Figure 6).

Figure 6. Different ski base grooves, showing a notable variety in directions and sizes. The top left, for example, with its thick and wide grooves, is used when the snow contains a high percentage of water, i.e. after rain by the end of the season [7].

Chemistry of wax

The wax concept is easy. Having a hydrophobic surface is important to avoid the suction of the water into the ski surface. In this way, lower friction between the ski and the snow is created. The first waxes used were of vegetable or animal origins (candle wax, vegetable oil) [3].

In the 1950s, wax companies produced the first petroleum-based waxes, using paraffin. A higher or lower number of C atoms distinguishes between hard and soft waxes (Figure 7), respectively. Hard waxes are used during cold and abrasive snow conditions, while soft waxes are applied for fresh and powder snow.

Figure 7. Schema of the different layers that constitute the ski [10].
Figure 7. Schema of the different layers that constitute the ski [10].

Already in the late 1970s, fluorocarbon products were introduced as wax, where fluorine substituted some of the H atoms, lowering the friction coefficient and increasing hydrophobicity. As a result, fluorinated wax led to a 4% increase in performance [11]. Fluorinated waxed skis are in fact “self-cleaning”, as water and oily dirt do not stick to the surface and the water rolls the dirt away (Figure 8) [3].

Figure 8. Fluorocarbon is a hydrophobic material to repel moisture. In low humidity or low moisture, a highly fluorinated wax may reduce speed as it essentially increases dry friction.
Figure 8. Fluorocarbon is a hydrophobic material to repel moisture. In low humidity or low moisture, a highly fluorinated wax may reduce speed as it essentially increases dry friction.

However, using fluorinated wax is toxic and constitutes a potential risk for the health of ski waxers, causing respiratory illnesses above all [12]. In addition, it has been shown that fluorinated wax can pollute watersheds, lakes, rivers and ski venue fields, after the snow melts [13].

For environmental and health reasons, the International Ski Federation announced a ban on all fluorinated waxes during competitions starting from the 2020/2021 season. Today, new eco-friendly ski waxes are introduced to the market, replacing the fluorocarbon with natural materials with comparable characteristics.

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In the classic technique of XC skiing, the skis have to both glide and grip. Kick wax, also known as grip wax, can create static friction to help the athlete build grip while propelling him/herself forward. The kick wax is placed only on the grip ski area (roughly where the foot is positioned).

The rest of the ski is waxed using the previously described glide wax. Since the classic skis are characterised by a camber, when the bodyweight of the athlete is fully on the ski, the ski is pressed down and the kick wax is in contact with the snow, permitting the grip. When the athlete is gliding, less body weight is on the ski that rises permitting the gliding.

The grip wax comes in different forms (hard wax or a klister), again depending on the snow conditions. Hard waxes are paraffin-wax-based substances with admixture (rubber, resin or colophony) (Figure 9), while klisters are sticky waxes composed of rosins, solvents and fats [14].

Steps to find the perfect “wax potion”

Ski waxers are looking for the fastest combination (ski plus wax) for their athletes. The skis and waxes are tested in different ways. In XC skiing, for example, one type of gliding test requires you to start gliding in a tuck position from rest on a slight downhill and consequently choose the skis that reach the longest distance before stopping.

Another method is through “sensation”. The athletes/ski waxers choose the skis based on the feeling of gliding when they are skiing. In general, four different steps are necessary when preparing the skis for a competition [3]:

  1. The day before the competition, different skis are tested for flexibility and hardness, based on their material (around 10-15 skis per athlete) [16]
  2. If necessary, the chosen ski is groomed for creating grooves that permit the water during friction to flow away
  3. Different waxes are tested few hours before the competition according to the weather conditions and temperature (base wax)
  4. The last layer of wax is applied few minutes before the race starts (for competitions in classic technique, in this phase the kick wax is applied)

Beside the theory of ski wax chemistry, the experience of ski waxers helps in choosing the best “potion” for having the fastest skis that still have to match the best physical condition of the athlete in order to win.

"I am fascinated by how the development of new sports equipment allows pushing the boundaries of human limits further, reaching new records."
Veronica Bessone
Veronica Bessone
PhD in Sport Biomechanics, Bioengineer
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*This article is the work of the guest author shown above. The guest author is solely responsible for the accuracy and the legality of their content. The content of the article and the views expressed therein are solely those of this author and do not reflect the views of Matmatch or of any present or past employers, academic institutions, professional societies, or organizations the author is currently or was previously affiliated with.

References:

[1] Colbeck S.C. 1992. A Review of the Processes That Control Snow Friction, CRREL Monograph, 92 (2): 49
[2] La storia di Wilson Bentley: l’uomo dei fiocchi di neve. Accessed on 5th February 2020
[3] Dominator: Educational Series. Accessed on 5th February 2020
[4] Ogso Ski Collection
[5] Mechanics of Sport: Ski. Accessed on 5th February 2020
[6] Clarys J.P., Van Puymbroeck L., Publie J., Bollens E., Cabri J., De Witte B. 1986. Influence of ski materials on muscle activity. J Sports Sci.; 4(2):129-39.
[7] La preparazione dello sci da gara. Accessed on 5th February 2020
[8] Colbeck S.C., & Perovich D.K. 2004.Temperature effects of black versus white polyethylene bases for snow skis. Cold Regions Science and Technology,39:33
[9] Schamesberger R. 1995. Ski Coating made from polyethylene E. Patentamt, Editor.
[10] Ski Wax King Size – nordicx.com. Accessed on 5th February 2020
[11] Breitschädel F., Haaland N., Espallargas N. 2014. A Tribological Study of UHMWPE Ski Base Treated with Nano Ski Wax and its Effects and Benefits on Performance. Procedia Engineering. 72:267-272
[12] Hoffmann M.D., Clifford P.S., Varkey B. 1997. Acute effects of ski waxing on pulmonary function. Med Sci Sports Exerc; 29(10):1379-82.
[13] Grønnestad R., et al. 2019. Levels, Patterns, and Biomagnification Potential of Perfluoroalkyl Substances in a Terrestrial Food Chain in a Nordic Skiing Area. Environ Sci Technol: 53(22):13390-13397.
[14] Kuzmin L., Fuss F.K. 2013. Cross country ski technology, Routledge Handbook of Sports Technology and Engineering, Routledge, ISBN 9781136966590
[15] Pellegrini B., Stöggl T., Holmberg H.-C. 2018. Developments in the biomechanics and equipment of Olympic cross-country skiers. Front Physiol.; 9:976.
[16] Con scioline di tenuta (classico). Accessed on 10th February 2020

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