New regulations for fair play in roller skiing thanks to Swedish students

The sport of roller skiing has long been plagued with a concern. The wheels of the skis roll differently, which can cause the individual’s speed to vary considerably, and as such, the finish times can be impacted by several minutes. Now students at Chalmers University of Technology in Sweden have developed a new measuring instrument and method to standardise the resistance of the wheels – and make the sport fairer. Starting this year, the Swedish Ski Association will base its official guidelines for recommended wheels on the students' measurement method.

The challenge of differences in how easily roller ski wheels roll is not a new concern – there is simply no official standard for the rolling resistance of the wheels that competitive racers are allowed to use. A few years ago, the Swedish Skiing Association introduced a recommendation that stated that the resistance should correspond to what a skier would experience on snow. This principle of resistance corresponds to what is referred to in the sport as "standard wheel 2".

At the same time, there has not been a given standard for how easily these standard wheels are allowed to roll. Subsequently, there have been roller skis on the market with wheels that roll differently, which in turn has led to unfair competition conditions.

Variations by minutes

Andreas Löfgren studies at the Department of Microtechnology and Nanoscience at Chalmers University of Technology. Together with three fellow students, he has developed a method and instrument for measuring the roller ski-wheels, to provide the sport with a reliable and user-friendly solution to quantify rolling resistance - and thus also enable more fair competition conditions.

“Based on field data from the participants in the 2024 Junior SC in Roller Ski Shooting, we could see that the person who skied on the slowest roller wheels lost approximately three minutes compared to an equally strong skater who rode on the lightest skis. This difference is so significant that it is decisive for final placements. The winner of the race crossed the finish line in just under 28 minutes and the one who crossed the finish line three minutes later finished in eighth place,” says Andréas Löfgren, who has been conducting the work together with Albert Hansson, Arvid Sandström, Jonatan Larsen, and supervisor Dan Kuylenstierna, Associate Professor in Microwave Electronics at Chalmers.

Half of the roller ski wheels outside the approved range

With the new method, the rolling resistance of the different wheels can be calculated using an electric motor that drives the wheels of the roller ski against a flywheel while being loaded with a weight.

“The instrument can determine the rolling resistance of a ski with a margin of error of 1.1 percent within about a minute. It is compact enough to be transported in a regular passenger car and the person who will use the instrument may need about 15 minutes of instruction,” says Andréas.

In collaboration with the Swedish Ski Association, the Chalmers students have used the new measuring instrument to test the resistance of commonly used standard wheels. Based on the tests, they have produced statistics and defined what is "normal rolling resistance" and have also been able to see how large the spread is between different brands. Based on the statistics, new guidelines have been developed for which wheels should be approved.

“This gave us the opportunity to see how big the spread really is. We tested twelve different wheels and half of them fell outside the approved range. Three of them rolled too slowly and three of them had too little resistance,” says Dan Kuylenstierna, who has supervised the students.

Dan himself has a great interest in roller skiing and the idea for the solution in the project originated in a conversation with one of Sweden’s most experienced roller skiers, Tobias Westman.

“Tobias has both Swedish Championship and World Championship gold medals on his list of achievements and currently runs a ski shop in Gothenburg. He told me how he meets customers every day who are faced with the problem of roller ski wheels that roll at different speeds. It was during that conversation that the idea of ​​developing a new measurement method to standardize resistance was born,” Dan explains.

Used in the Swedish Ski Association's new guidelines

Based on the test results, a list of wheels approved for competition could be drawn up and new, official guidelines for rolling resistance can be presented to associations, organisers and roller ski manufacturers by the Swedish Ski Association.

“This means a lot to us. With standardised rolling resistances, everyone knows that a "2" rolls a certain way, regardless of brand. This makes it easier to compare results and it will create fairer competitions. In the future, we hope to be able to provide some kind of license to the manufacturers who produce correct wheels. In the long term, our vision is to also implement the method internationally, and the project is being followed with interest by the International Ski and Snowboard Federation, FIS,” says Ludvig Remb at the Swedish Ski Association.

Fact box: How the measurement instrument and method work

In the measuring instrument, a roller ski wheel loaded with a standardized weight is placed against a flywheel - a mechanical device that stores kinetic energy. The flywheel is driven at constant speed by an electric motor. As different wheels roll with different inertia, differences occur in the internal friction of the system. Using sensors that sense the current and voltage passing through the electric motor, a microprocessor can calculate the system's power. The microprocessor feeds the power calculation further through a verified behaviour model – an empirically developed mathematical model that ultimately returns the roller ski's rolling friction coefficient. The measurement results have been compared and validated in collaboration with the Swedish Ski Association through measurements of real roller ski tests on asphalt in both downhill and during staking on flat terrain.

The students' technology can be used to define a standard for what should be considered normal rolling resistance.

The method is based on the principle of conservation of energy in thermodynamics, which states that energy can neither be created nor destroyed but only converted from one form to another.