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Researchers at the University of Bayreuth have, for the first time, provided concrete figures on the abrasion of mountain bike tires in off-road conditions. Their , published in Science of The Total Environment contribute to a better understanding of the global microplastic cycle.

Microplastics are now found almost everywhere—in household products and food, in the human body, in soils, water, and air. This has negative effects on ecosystems and is likely to impact the health of living organisms, including humans. A significant proportion of the microplastics in the environment is released by road traffic, particularly through tire wear from motor vehicles. However, other means of transport that also contribute to tire abrasion have been little studied so far.

Investigating alternative modes of transport, such as bicycles, helps to understand how much microplastic enters the environment and through which pathways, ultimately promoting more environmentally friendly mobility.

For years, it has been known that tire wear from motor vehicles is a major contributor to microplastic pollution. Approximately 11 grams of microplastic are released per 100 kilometers driven, accounting for about 57% of microplastic pollution from road traffic and roughly 35% of total microplastic pollution in Germany.

In contrast, cycling is considered an environmentally friendly mode of transport and is also a popular recreational activity. Mountain biking, in particular, has been growing in popularity, with around 20% of the German population now participating in this sport—sometimes in pristine natural environments. However, no data has been available on the quantity and significance of tire abrasion from mountain biking.

To gain a broader understanding of the environmental impact of cycling, researchers at the Chair of Sport Ecology at the University of Bayreuth have now conducted the first study on the abrasion of mountain bike tires.

For the study, a team led by doctoral researcher Fabian Sommer equipped nine mountain bikers with brand-new tires. The participants then followed their usual riding habits while tracking their routes via GPS. At predetermined intervals, the tires were weighed in the lab to measure and document material loss due to abrasion.

On average, the study found that tire abrasion amounted to approximately 3.5 grams per 100 kilometers, equating to a per-capita abrasion rate of up to 88 grams per year. When scaled up to the total microplastic pollution in Germany, mountain bikes contribute to less than 1%.

The researchers also observed that the abrasion rate was higher during the first 500 kilometers of riding with new tires compared to after the 500-kilometer mark. According to the researchers, this could be due to the rounding of tire edges and the relatively quick wear of excess material from the manufacturing process—the small hair-like structures found on new tires.

"Our study provides the first reliable data on the amount of tire abrasion from mountain bikes under real-world conditions. The results show that while mountain bike tires release microplastics directly into nature, the amount is significantly lower compared to motorized vehicles. This highlights another advantage of cycling as a sustainable mode of transport," says Sommer.

As part of ongoing research, a follow-up study is now being conducted, focusing on tires from road bikes, gravel bikes, and mountain bikes/e-mountain bikes. This study aims to provide additional insights into the dynamics and rates of tire abrasion for these different types of bicycles.

In addition, environmental samples will be analyzed in collaboration with the laboratory of Prof. Dr. Christian Laforsch from the Collaborative Research Center 1357 Microplastics at the University of Bayreuth to better understand the impact of microplastics on the environment.