Tread Wear of C3 Bus Tyres Around a City in Italy

Tyre wear is a major contributor to microplastic pollution. Heavy-duty vehicles, due to their higher weight and longer distances driven compared to passenger cars and vans, have the highest share of tyre wear from road transport. Heavy-duty vehicles cover a wide range of applications—from urban stop-and-go buses to long-distance lorries—and their maximum mass can vary from around 3.5 tonnes to more than 40 tonnes. However, experimental wear data on heavy-duty vehicles, and particularly on buses, for both original and retreaded tyres are scarce. Additionally, there is no standardised methodology for measuring their tyre wear. In this study, we measured the tread wear of regional buses operating around the city of Varese (Northern Italy) between 2019 and 2025. The tread depth reduction was 1.7–1.9 mm per 10,000 km for 22.5-inch tyres and 2.6–2.9 mm per 10,000 km for 19.5-inch tyres. Based on the annual distance driven (40,000 km for 22.5-inch tyres and 25,000 km for 19.5-inch tyres) and the tread characteristics, we estimated a mass loss of 550–800 mg/km per vehicle. These are some of the first wear emissions in the literature for new and retreaded tyres at both drive and steering axles.