Major Test: What to Think About When Choosing Winter Tyres

Choosing tyres for winter is not an easy task. Photo: Katja Kircher

A major debate is underway as to which winter tyres are best, studded or non-studded. But there is more to making a decision as a consumer than just that question. On ice and snow, non-studded tyres made for Nordic conditions differ greatly from those produced for Central European conditions. These differences are amplified as the tyres become worn.

“Worn European winter tyres generally grip poorly on smooth ice, and they performed at the same level as summer tyres in our tests”, says VTI Senior Research Leader Mattias Hjort.

VTI tested the grip performance of 50 worn winter tyres on snow and ice. The aim of the study was to determine how the ability of the various types of winter tyres to grip the road degrades with age and wear. Comparing studded and non-studded winter tyres was emphasised. Twenty-seven completely new tyres were tested in addition to worn ones. All the tyres were tested on level ice and packed snow. The tests were conducted at VTI’s tyre testing facility in Linköping, although tests on real cars have also been run on test tracks in Norrland and Finland. The tests measured mainly braking and steering performance, although acceleration performance was sometimes tested as well.

The tyres were divided into three main categories: studded tyres, non-studded tyres of the Nordic type, and non-studded tyres of the Central European type. The worn tyres were selected after mapping the condition of used tyres from four different tyre hotels. One of the most common sizes, 205/55-R16, was chosen. The tests indicated that studded tyres are significantly better than non-studded tyres in terms of their steering capability on ice, and that Nordic tyres were significantly better than Central European ones. Brake tests on smooth ice in VTI’s tyre testing facility indicated, among other things, the following:

• New tyres: Nordic non-studded tyres yielded 25% longer braking distances than did studded tyres. European non-studded tyres yielded roughly 50% longer braking distances than did studded tyres.
• The worn studded tyres yielded roughly 25% longer braking distances than did the new studded tyres.
• Worn tyres: Nordic non-studded tyres yielded roughly 10% longer braking distances than did European studded tyres. European non-studded tyres yielded roughly 30% longer braking distances than did studded tyres.

The differences between the tyre types diminish when they are worn but, despite major deterioration, worn studded tyres still clearly grip the ice better than do worn non-studded tyres. In these tests, the worn European tyres performed on par with summer tyres that were several years old. In terms of their grip on snow, the differences between the different types of winter tyres are smaller on snow than on ice. Tests of worn tyres indicate that the European tyres lose the most in terms of performance.

“The extent of the differences between the tyre types depends largely on the surface in question, and studs become more important on really slippery ice. On such surfaces, the tests showed that even quite worn studded tyres performed much better than did completely new non-studded winter tyres”, says Hjort.

So what do you recommend for the winter, studded or non-studded?

“I would love to give a simple answer to that, but it depends entirely on how, where, and when you drive your car. From the standpoint of gripping the road, the studded tyres are clearly better on slippery icy surfaces, but they do have the disadvantage of promoting road wear and particle formation. If you go with non-studded, I would recommend tyres of the Nordic type, as there are big differences between them and the Central European tyres on both ice and snow”.

What tyres are best for the environment?

“Non-studded winter tyres. Studded tyres cause more noise and road wear, which contribute to poorer public health. Wear particles from studded tyres also contribute to the pollution of fields near roads and of bodies of water that receive road run-off water. Stud-caused wear damages vehicles and the road environment. The need for road maintenance increases, leading to increased carbon dioxide emissions”.

Studs roughen things up

The studs cause the pavement to wear, as is most obvious from the grooves that form in the roadway. This wear roughens the pavement, making the roadway provide better friction under wet conditions. Snow and ice can also be roughened and even be worn through by studded tyres. A Norwegian study found that at least 50% of vehicles on our roads should have studded tyres to improve road grip on ice. A similar study from Finland estimated the requisite share at 25–50%.

We use particularly wear-resistant pavements in Sweden because of our use of studded tyres. Our pavements have a high stone content, are relatively coarse and are making them noisier than those in, for example, Central Europe.

Generally, grooved roadways are not associated with a greater risk of accidents. However, accident risk does increase under wet road conditions and on ice and snow, but when road conditions are dry the risk decreases, as most drivers drive more carefully on grooved roadways.

Hazardous particles

The test with worn winter tyres did not focus on particles, but VTI has prior experience in that area. We know that inhalable particles are generally hazardous to our health. Higher mortality as well as more people stricken by coronary vascular disease and by respiratory diseases such as degraded lung function are just some of the effects associated with the presence of inhalable particles. The wear particles that studded tyres produce are coarser than, for example, particles from exhaust, and affect respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma to a greater extent than smaller particles do. The smaller particles in turn exhibit a clearer correlation between long-term exposure and effects on mortality and coronary vascular disease.

The results of one study comparing particles generated by pavement wear from studded tyres with other traffic-related particles indicate that the wear particles do not appear to be less harmful to human respiratory tract cells.

How the tested tyres were chosen

The worn winter tyres were chosen after mapping the condition of used tyres in four different tyre hotels, two in Stockholm, one in Linköping and one in Malmö. All the worn tyres had tread depths of five to seven millimetres. The average age of the tyres was five and a half years. Tyres produced by different manufacturers and both expensive and inexpensive tyres were included in the tests.

Report
VTI report 875: Test of ice and snow grip for worn and new winter tyres – A comparison of different types of winter tyres
Authors: Mattias Hjort, Olle Eriksson
Link to report (in Swedish with a summary in English).

Contact, tyres: Mattias Hjort mattias.hjort@vti.se VTI, Sweden

Contact, particles: Mats Gustafsson mats.gustafsson@vti.se VTI, Sweden