Cobalt-free tyre studs reduce particle emissions

Cobalt has long been used in tyre studs due to its hardness, enabling grip in icy conditions as well as providing durability. But according to the researchers, cobalt is so tough that it chews up road surfaces and creates large amounts of airborne particle emissions. 

The study, published in Tribology International, saw alternative stud material containing iron-nickel tested on an asphalt surface. Compared to traditional studs containing cobalt, the new studs produced 20 per cent less wear and particle emissions, while still maintaining good grip on ice and packed snow.

“Cobalt is a cheap solution,” said Ulf Olofsson, a professor in the Department of Engineering Design at KTH Royal Institute of Technology. “It’s so hard that it doesn’t wear down, which is why it’s also mass produced for rock drilling tools.

“But asphalt is soft enough that cobalt-containing studs grind and pulverise it into ultra-fine particles that go deep down into the body when inhaled.”

According to Olofsson, winter studs only need to be 20 to 30 per cent harder than asphalt to make driving on ice safer. Including cobalt in the stud material is overengineering, leading to more road damage and particulate matter.

“The studs on the market today are double the hardness of road material and nine times the hardness of glacial ice at -40C,” said Olofsson. “That’s overkill.”

Although mostly permitted across Europe, studded tyres are banned in several countries, including Germany, the Netherlands and Poland. In the Nordic countries, non-exhaust PM10 emissions significantly exceed those from exhaust due to the frequent use of studded tyres. 

Studies have shown that studded tyres save roughly 70 lives each year in Sweden, but some cities in the country have still banned them on certain roads due to the health risk posed by airborne asphalt particles.

According to Olofsson, Swedish road surfaces have a lifespan half as long as those in Germany, where studs are banned. The professor said the next phase of the research will explore the longevity of the cobalt-free stud materials.