Characterization of Tire Road Wear Particles in the Field and at Laboratory Scale

During normal driving conditions, wear particles are formed due to the friction between tire tread and road surface. To derive realistic particles for study purposes, basically, two approaches can be taken: Either collection outdoor under real usage conditions or indoor under very controlled conditions. The first approach is challenging due to many disturbing factors, while the second might be biased by choosing specific conditions. This article describes how both approaches are used in combination to ensure field relevance of high-quality characterization insights.

Particle samples collected from the environment always contain material from both surfaces—the tire tread and the road, which is why in this context we refer to TRWP (Tire Road Wear Particles), which consist of combined material—roughly 50%/50% (by mass)—from both sources. To capture those TRWP outdoor under real usage conditions a special vehicle was used which is equipped with a vacuum cleaner system in the wheelhouse. For further evaluation the samples were further refined and analyzed. For better assignment of the collected material to the dedicated test tire a TiO₂ marker was used. A trend between driving conditions and detected particle size was observed which must be further investigated.

Under lab conditions the generated particles can be assigned explicitly to the specific compound and to the operation conditions. The particles are observed with optical methods direct at the sample wheel or separately offline after collection. The obtained images are processed applying methods from the field of “Particle Object Tracking”, such as Feature-Point-Detection and Blob-Analysis. As an outcome, individual rubber particles are identified, tracked and characterized. Finally, the size distribution of the particles can be concluded from the entity of all particles, whereby information about the shape of each individual particle is available. Through these insights on size and shape environmental impact of TRWP can be determined more accurately and—most importantly—suitable mitigation approaches can be derived.