Quantifying the abrasion of microplastics from bicycle tires into the environment

Introduction 

Biking as a form of transportation and leisure activity in natural environments has the potential to introduce MPs directly into ecosystems, often with shorter pathways than cars. While tire wear particles (TWP) from cars are known to be a major source of microplastics (MP), little is known about bicycle tire abrasion quantities.  Our first study delivered the first real-life usage abrasion data of mountain bike tires with 3.6 grams per 100 kilometres (front and rear tire combined). This second study quantifies microplastic abrasion from different bicycle tire types (road, gravel, cross country, trail, downhill) in real-life usage and tries to identify influential parameters on abrasion rates (bike, rider, environment).  

Methods 

We measured the weight loss of bike tires to quantify abrasion throughout their lifecycle. Over 90 subjects tracked their routes via GPS ridden with provided tires to calculate weight loss with distance. This follows a similar approach tested for quantifying tire abrasion of motorized vehicles. 

Results 

We found an average abrasion rate from 0.4 (road bike, front tire) to 3.6 grams (downhill mountain bike, rear tire) per 100 kilometres and tire. At every measurement point for all tire sets the rate was higher for the rear compared to the front tire. These values are comparatively low to abrasion rates between 11 up to 95 grams per 100 kilometres from motorized vehicles. 

Discussion 

Overall, the method of gravimetrically measuring weight loss proved to be an effective way to quantitatively assess the microplastic abrasion emitted by bike tires. Tire abrasion quantities of different tire types could be explained by tire attributes (e.g. different compounds, contact area and ridden tire pressure). Different abrasion quantities of individual tires of the same type could be explained by rider and bike attributes (e.g. system weight, riding style, suspension travel) and environmental attributes (e.g. surface type, incline/decline, surface moisture, temperature). 

Outlook 

We aim to detect potential intervention points in use and production to reduce MP abrasion from bicycles. By calculating the influence of different parameters (bike, rider and environment) we will try to model the load and spatial distribution of bicycle tire-based MPs in the environment.  Our research can deliver valuable insights for a better understanding of the global MP cycle.