Current research on microplastics (MPs) primarily focuses on investigating environmental samples, often lacking in identifying the actual sources and emission quantities. Little is known about the quantity of bicycle tire abrasion in real-use scenarios. Mountain biking, a popular outdoor sport produces tire wear particles (TWP) directly in natural environments. This study quantifies microplastic abrasion from mountain bike tires in real-life usage. We measured the weight loss of mountain bike tires gravimetrically over their period of use to quantify abrasion throughout their lifecycle. We found an abrasion rate of 3.62 g (median) per 100 km per mountain bike. The rate was higher for the rear tire (median 2.32 g
IQR = 1.58 to 3.59 g) compared to the front tire (median 1.32 g
IQR = 1.06 to 2.64 g). After higher abrasion rates of the new tire, rates decrease, and average abrasion stabilizes at around 1.43 g (median front and rear
IQR = 1.07 to 1.60 g) per 100 km per tire. This dynamic is due to the abrasion of excess material and sharp edges produced during manufacturing. Gravimetrically measuring material loss proved effective in assessing MP abrasion from mountain bike tires. Combining these findings with average bicycle kilometrage statistics for Germany results in an emission of 59 to 88 g of tire material per mountain biker per year. Calculated emissions from cycling (rider-number * average kilometrage * abrasion rate) would contribute <
1 % to the total annual MPs emissions, significantly lower than motorized vehicle tires, which contribute about 30 %.