TOKYO — Yokohama Rubber Co. Ltd., along with researchers at Kanazawa University, has developed a way to visualize the "frictional state of contact" of rubber on ice, which YRC claims could lead to studless winter tire designs with improved grip on ice.
When running on ice, a tire is unable to make firm contact with the road surface due to the watery film generated by the icy surface, thus reducing the tire's grip, YRC said. Studless snow tires depend on tread patterns with high drainage performance and water-absorbing agents in the tread compound to counter the watery film.
Up to now when studying a tire's contact with the road, it has been difficult to distinguish the area where water is between the road surface and the rubber from the area where the rubber is in direct contact with the road surface (real contact area). As a result, it has been difficult to grasp the degree of real contact accurately.
Now, YRC said it expects its work, conducted with researchers under Associate Professor Tomoaki Iwai with Kanazawa University's Tribology Laboratory, exploring this phenomenon will enable the discovery of new compounding agents with enhanced water absorbency and facilitate the development of tread patterns that deliver higher drainage performance.
Tribology is defined as the science and engineering of interacting surfaces in relative motion, comprising the study and application of the principles of friction, lubrication and wear.
YRC's joint research with Kanazawa University led to the development of a testing machine equipped with a high-speed camera that enables visualization of a tire's contact with the ground and succeeds in identifying the real contact area. The partners also established an analytical technique for digitizing contact images, which led to evaluating the water absorbency and drainage of tire rubber numerically.
The machine is able to observe frictional behavior between a rubber sample and ice or a smooth transparent disk used to replicate ice at speeds of up to 31 mph (50kmh). Its high-speed camera can take 1 million micro-level images per second of the tire's contact area with the road surface, while simultaneously measuring the frictional force during the test.
Images taken with this testing machine are dark only in the real contact area. Rubber that includes a water-absorbing agent shows darkness over a wider area than rubber that does not include the water-absorbing agent, YRC said.
Furthermore, digitizing the image with the newly developed analytical technique to associate the contact area with the frictional force revealed that the calculated numerical value has a high correlation with the frictional force of the rubber.
Yokohama pointed out that its three-year medium-term management plan, Grand Design 2020 (GD2020), includes a winter tire strategy that aims to assert performance leadership in winter tires supplied in the Japanese, European and Russian markets.