In Japan, as the dust produced from studded tires which scratch up paved surfaces is polluting the environment, the use of studded tires will be prohibited throughout the country in the near future. High performance studless tires are being developed for this purpose, but users are worried about their use, and traffic authorities are worried about the increase of accidents.
The authors performed a series of experiments to evaluate the braking, driving and hill climbing performance of winter tires. It was found that the braking stiffness of studless tires is better than studded tires in the slip ratio range of 20 to 40%. In friction tests using a piece of rubber and ice, water was not formed in the contact surface below −10°C. It was also found that the friction coefficient of rubber increases with softer rubber. As a result, if a tire is designed to have a soft tread and large contact area with the road surface, we may safely replace studded tires with studless tires.
The author has succeeded in educating the citizens of Sapporo on safe driving methods based on the results of these experiments. Remarkably, in the past five years, half of the drivers have stopped using studded tires without an increase in the number of fatal traffic accidents.