25 February 2025
What causes car tyres to wear down? Jülich physicist Bo Persson has investigated the conditions under which rubber tyres wear on asphalt roads. The study, which investigates tyre wear both theoretically and experimentally, was published last week in The Journal of Chemical Physics.
More than one hundred thousand tonnes of microplastics are produced every year in Germany alone by tyre abrasion from cars – by far the largest source of tiny plastic particles that harm humans and the environment. This might be set to increase further with the switch to electromobility. Although electric cars emit less particulate matter than combustion engines, they are also typically heavier due to their large batteries. This leads to more tyre abrasion.
Is it possible to predict wear rates and the size of wear particles? What other external conditions do they depend on? Which material properties play a role here? Jülich physicist Bo Persson has been focusing on these kinds of questions for almost 30 years. In 2023, he was awarded the Tribology Gold Medal for his ground-breaking contributions to the field of tribology.
In his latest study, he and his colleagues Ruibin Xu and Naoshi Miyashita investigate how pressure, speed, and environmental conditions influence the wear rate of tyres.
The scientists experimentally investigated the wear rate of tyre tread rubber in a series of measurements in which the rubber slides on concrete paving surfaces at different contact pressures and sliding speeds. They found that the wear rate is proportional to the contact pressure – but independent of the sliding speed. Dry conditions were more destructive than wet conditions, with water leading to lower wear rates.
The scientists analysed their results using an innovative theoretical approach. Previous theories assumed that the wear rate is proportional to the friction work – the product of two factors. One factor is the normal force, in the case of a vehicle its weight, and the other is the friction coefficient, which in turn depends on a variety of factors, including speed.
The theory of Persson and his colleagues, however, is based on a new variable – the stored elastic energy that builds up due to stresses in the contact areas between the tyre and the road surface. This energy steadily increases as the tyre moves over the road – up to a point. As soon as this elastic energy is high enough, it breaks the necessary bonds in the rubber – and an abrasion particle is formed, which detaches from the tyre. The wear rate is thus independent of speed.
But the theory is not yet complete. The authors will now expand the theory to include plastic flow, a deformation process that plays a role in the wear of non-rubber materials. “Our study is not the final theory of wear,” says Persson. “But it does present a new approach to this problem.”
Original publication: Rubber wear: Experiment and theory, The Journal of Chemical Physics, B. N. J. Persson, R. Xu, N. Miyashita, https://doi.org/10.1063/5.0248199
Emeriti at Peter Grünberg Institute (PGI-1)
