Tribology noun /trīˈbäləjē/ Def: The science of interacting surfaces in relative motion. It includes principles of friction, lubrication, and wear.
So, every time we slap our skis on to the snow, we become empirical tribologists! Studying why some days our skis glide in a pleasing manner and on some days the skis are so sluggish it might be more fun to go for a walk. Many of the Coaches Corner blog posts are devoted to tuning and caring for skis so they glide smoothly and quickly over the snow. As we enter the spring skiing season and the conditions become more wet (either in the consistency of snow or the warm springs day where the snow gets a little slushy), adding hand structure to your ski base can really make a difference.
Snow is amazingly and at times maddingly variable, and to keep our skis gliding in that pleasing situation we only have four things we can modify; ski design, base structure, glide wax, and base material – usually ranked in that order. Notice how base structure is nearly as important as ski design and often more important than glide wax. Which is why nearly all new skis come from the factory not with a mirror-smooth finish on the base material, but with a fine structure reminiscent of a old vinyl LP record. This structure is applied direct from the factory by very expensive machines called stone grinders (very high speed stones that cut into the base) and also by skilled after-market professionals.
The accepted reason tribologists offer for glide on snow is that pressure will create melting of the snow and the liquid water can act as a lubricant. In extremely cold snow there is so little melting that skiing on snow can feel like trying to ski on sand, the mechanical friction from cold abrasive crystals slow down the ski. Yet at very high speeds such as on downhills the heat from friction increases and suddenly skis can feel (relatively) fast again. In wet saturated snow the amount of water creates too much friction from adhesion and the skis become very slow.
The structure applied to the base of the ski is intended to manage the effect of water and promote glide. With the amount of snow variation between the two extreme examples it becomes clear why there isn’t one structure design that is universal. But did you know that you can temporarily modify the structure on your skis to optimize glide for different conditions?
Hand structure tools, also known as rilling tools, are devices that will make an impression into the ski base that will modify the existing structure and create a temporary and new structure pattern. The temporary aspect is because (most of) these devices only press into the base material, which is resilient. With time the base material will rebound to the original pattern. This can take weeks, which can be great for stable skiing conditions. If snow conditions change, hot waxing one or more times will make the hand structure disappear. Note that still available are some hand structure tools that will cut into the base; the use of these tools is rarely needed (high demand competition in extremely wet saturated and coarse snow) as the very deep structure will remain until the skis are re-stone ground so they should mostly be avoided. An example is the Swix Super Riller Linear, which has the distinction of being the first commercial rilling tool on the market.
The positive effect that hand structure can have is illustrated by these two examples – the US Cross Country Ski Team technicians only use two broad-range stone grinds and in almost all race situations every ski goes to the start with a hand applied structure. The other example is the number of manufacturers making these tools – in addition to the very recognizable brands of Swix and Toko, there is Red Creek (Sweden), Speedy (Finland), SRB (Germany), all of which are used at World Cup events. Wax specific brands such as Vauhti and Start, or rollerski brands such as Jenex/V2 have small offerings as well.
Applying a hand structure is almost too easy! Note that nearly all of them only fit skis of racing width, often with a maximum ski width of about 47-48mm.
Choose the appropriate roller or bit. Most companies make devices using a single roller, some use two rollers. The use of two rollers isn’t necessarily an advantage, They are able to make complex patterns with just one pass, but sometimes the right solution is not complex and only one roller is needed and a blank roller is used in the second slot.
OK, now apply the tool to the ski base, press down using appropriate pressure (a variable!) and run the tool from tip to tail. If using on a classic ski the tool has to be removed and re-applied to respect the grip zone. This application takes only seconds to do! Simple, right?
An example of factory structure. The same ski with hand structure.
A hand structure does have to work in conjunction with the existing pattern from the stone grind, so the results can vary. Even without a aftermarket grind, each ski company uses a different factory base grind. For example a hand structure that is good on a Fischer factory base grind might be different when it interacts on a Salomon factory base grind. And a stone grind that is intended to be best in warm and damp conditions cannot be modified to work in very cold conditions, but a very fine stone grind for cold conditions can be modified with a hand tool to work in warm conditions.
The improvements in glide are most notable as the moisture content increases. There are many conditions where a proper hand structure can yield better speed than glide wax or even ski choice! However, deep impressions from some roller designs intended for wet conditions can also increase the overall surface area of the ski base, which can actually make skis slower in very wet snow that is new and has very fine crystals so it's a delicate balance. The designs also provide places for dirt to accumulate, and in wet, coarse, and dirty snow the initial improvement in speed is negated in a few kilometers due to increased contamination. A hand structure too aggressive for the conditions can make skis slower! It is better to err on the conservative side when in doubt, as a hand structure more conservative will at least do little harm.
Note that some roller patterns are best for skate skiing, some for classic, and some can be good for both. An example is simple linear tools, such as 1mm or 2mm linear tools (that just press a straight line down the base) – these are often a first choice for classic skis, but for skate skis they are usually better when used in conjunction with another design.
Cross linear/oblique patterns are some of the most broad spectrum hand structures and very safe on skate or classic. They also tend to do best on new snow. The so-called “screw”, “V”, or “Xmas Tree” patterns more often (but not always!) are best for skate skis, and for coarse or older snow. Some patterns can be applied more than once, or even backwards. An example would be the Red Creek +5/-5 oblique tool; already a great choice in very wet fine grained snow, it can be applied several times and even backwards as the snow gets progressively more wet. While hand structure tools can be expensive, they can last almost indefinitely. It is best to start with tools from one brand and learn to use them well, as they can often be combined. The use of a linear 1mm or 2mm on the tail of a ski could better improve performance than going “up the ladder” in pattern choice, especially if the primary tool provided improved speed but the track
become slightly wetter or more glazed.
Some examples of different rollers
Best of all, if you “get it wrong”, or the snow conditions change, just hot wax your skis once or twice and your skis are back to the base stone grind and ready to experiment in the April sun once again!
Have a great Spring,
Coach Karl and Kelly
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