The past few weeks have been the highlight of the year for ski enthusiasts, who have enjoyed both the World Championships and the Vasaloppet. What incredible races we’ve witnessed! Klæbo’s six World Championship gold medals, Alvar’s Vasaloppet victory, Jonna’s domination in the sprint and decisive performances in the relays, Ebba and Johaug’s battles down to the second, and finally Frida’s ice-cold composure in the 50 km race.
A common denominator for all these great performances is that no one would have won without gold-standard skis. In today’s tight competition, no one wins without competitive equipment. This doesn’t mean that you must have the absolute best skis of the day, but they must be competitive relative to your own capacity. A stronger skier can often manage with slightly worse skis, while others really need top-notch equipment to stand on the top of the podium. Performance is truly the combination of both the skier’s and the waxing team’s efforts. So it’s no wonder that waxing teams put an enormous amount of work into skis, structure, and wax.
Having good skis is, of course, about craftsmanship in the waxing cabin, but just as much about choosing the right equipment for the conditions of the day. This is a matter of measuring differences—differences that are often very small. The ability to measure these differences and make the important aspects measurable is something we are passionate about at Skisens, so naturally, we feel strongly about this topic as well.
How do you actually measure glide, and how precise must the measurement be? The margins that determine the outcome are incredibly small—for example, the 1.3-second difference between Ebba and Johaug in the 10 km race. In terms of pure glide friction, this corresponds to a difference of about 0.2% (you can read about our calculations here). Then, of course, grip also plays a role, making everything even more complex. But for simplicity’s sake, let’s focus only on glide—where a difference of 0.2% is incredibly small, likely below what any waxing team can ensure.
To get a sense of how small these margins are, we can look at how a glide test is conducted. Last fall, Skisens had the privilege of participating when the Swedish Ski Association conducted tests to update guidelines for roller ski wheels. You can read a report on these tests on the Swedish Ski Association’s website. The rolling resistance was measured in three ways: with a dedicated measuring instrument, with Skisens ski poles, and through conventional paired tests—the most common method for selecting skis on snow.
During the paired tests in Falun, the same two test skiers skied twice, and glide was compared over a 100-meter glide stretch with an entry speed of about 35 km/h. The results showed that a difference in glide distance of 100 cm corresponded to a difference in glide friction of approximately 10%. This means that to select a pair of skis that are 0.2% better than another, we must measure glide differences at the centimeter level. For anyone who has done glide testing, this seems nearly impossible. To illustrate how difficult it is, the standard deviation for the difference between two repeated rolling tests with identical skis in the experiment above was 37 cm over 15 repeated attempts with experienced test skiers competing at a high national level.
According to this reasoning, 37 cm would correspond to a difference of about 3.7%. Considering how this would affect a 10 km race under the conditions of the World Championships in Trondheim, it could translate to a 30-second difference. By repeating the glide test multiple times, this uncertainty can be reduced, but reaching a precision below 10–20 cm is very difficult, meaning that an uncertainty of about 10 seconds over 10 km will likely remain—which, incidentally, is greater than the difference between first and second place in both the men’s and women’s races in Trondheim.
Everyone who has performed glide tests knows how difficult it is to select skis with this level of precision. It’s common to experience different results in repeated tests. One of the main reasons for these variations is the challenge of ensuring the same entry speed. Figure 1 illustrates how the glide distance in a glide test with skis differing by 5% in glide friction is affected by variations in entry speed. With the same entry speed, the difference in glide distance after 100 meters is about 0.5 m. However, it is also clear that the variation in entry speed affects the glide distance more than the friction itself. If the difference in entry speed is 1 km/h in favor of the slower skis, this will have a greater impact than the difference in glide friction. To select the right skis, one must carefully observe how the glide of the two skis changes throughout the glide test. Experienced test skiers are very skilled at this, which is why most teams manage to get it right so that we, as spectators, get to witness seemingly fair competitions.
Figure 1. Difference in glide distance between two skiers of equal weight, where one skier has skis with 5% higher glide friction.
The solid line represents an ideal test scenario where both skiers have the same entry speed, while the dashed lines represent stochastic variation in entry speed within the range of ±1 km/h.
To further understand the immense amount of work waxing teams must put in, we can emphasize that all tests conducted by these teams are relative measurements—that is, performance comparisons. This is an extremely time-consuming approach where one can never truly know how close they are to an optimal value.
An ideal scenario would instead be to work with absolute measurements, in this case, glide friction.
With full respect for the complexity of true craftsmanship, measuring glide friction over time could help build a knowledge base on what levels of glide friction are achievable in different snow conditions. It could also provide insights into the quality of skis used by different teams. Perhaps the sport could even embrace more transparency by implementing a testing system similar to fluorine testing, where the friction of race skis is documented. In the long run, this would likely lead to a fairer sport, giving smaller federations the opportunity to compete on equal terms with larger ones.
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