Understanding the "science of slippery": Engineering breakthrough points tire maker to new winter safety



    TORONTO, Oct. 9 /CNW/ - It's a winter experience every Canadian driver
has had: Approaching an intersection, you touch the brake pedal and instead of
slowing down, the car sails merrily ahead as if you had no brakes at all. You
are driving on ice, and you're out of control.
    If you're lucky, you have gotten away with little more than a racing
pulse and mental reminder to drive with greater caution. But thousands have
suffered more dire consequences each winter, and the annual toll of injury and
property damage has made driving on icy roads among the most dangerous things
many Canadians will ever do.
    Indeed, statistics from Transport Canada show that while injuries or
fatalities resulting from all highway collisions dropped steadily between 1988
and 1997 (the most recent figures available), the tally of injuries and
fatalities resulting from collisions on icy or slippery surfaces remained
constant during the same period.
    But what makes ice slippery when you drive? And did you know that it is
actually more hazardous to drive on ice when the temperature is between minus
6 degrees C and 0 degrees C than it is when temperatures are colder?
    That simple notion - that a "danger zone" exists when ice can be more
slippery - is the result of research from engineers in Japan who set out to
improve the performance of winter tires. Understanding what makes ice slippery
was the first step in creating a new generation of winter tires better able to
deal with this dangerous condition.
    Tire engineers have long understood that the very act of driving a car on
ice makes the ice more slippery. The weight of the car and the friction of the
tire rolling over the surface of the ice acts to melt the ice under the tire.
The layer of water between the ice and tire acts like a lubricant, reducing
the traction the tire can achieve. The tire engineers at Yokohama Rubber
Company Ltd. studied the phenomenon and discovered that the thin film of water
created by the tire actually grew when the temperature was between minus 6 C
and 0 C. The engineers learned that it was between these same temperatures
that the vehicle's ability to stop or turn became seriously impaired.
    Measuring the thickness of a film of water seven times thinner than a
human hair became crucial to understanding how to deal with the threat it
posed to safe driving. The Yokohama engineers determined that a layer of water
thicker than 10 micrometres between the tire surface and the ice presented a
crucial challenge to winter tires: Tires that could cope with the thinner
layer of water created at colder temperatures suddenly couldn't handle water
10 micrometres or greater and began to hydroplane. (1.0 micrometre is
one/one-thousandth of a millimetre). The danger zone varies a little by
vehicle, and is a function of the weight of the vehicle, the temperature, the
tire size and contact patch, among other factors.
    The next question was how to get rid of a film of water so thin it could
barely be measured.
    Despite how they appear to the naked eye, neither ice nor the rubber
surfaces of a tire are completely smooth. Viewed under a microscope, tiny
undulations in both surfaces can be seen - undulations that capture water
between them. The challenge for the Yokohama engineers was to find a way to
eliminate that water. They turned to two technologies that literally help the
tire to absorb the water between the ice and tire surface.
    The first creates tiny suction cups that pick up water; the second
literally absorbs water and then releases it. Both technologies are actually
part of the solid rubber areas of the tire and so small that they aren't
visible without a microscope.
    "Shelled microbubbles" are just that: Microscopic bubbles in the rubber
compound with hard shells. The shell is broken when the tire rotates and the
shell contacts the road, creating a tiny, round void in the surface like a
tiny suction cup. The void creates suction as it contacts the ice surface,
pulling water up into the space. As the tire rotates past the point of
contact, centrifugal force expels the water from the void. The process is
repeated with each degree of tire rotation as thousands of the tiny bubbles
absorb and drain water.
    Absorptive carbon flakes throughout the rubber compound accomplish a
similar objective using capillary action. The absorptive carbon flakes, like
the shelled microbubbles, are liberally distributed through the rubber
compound. Looking like fabric folded in an accordion pleat inside a tiny void
in the rubber, the elements form a series of parallel channels. Like the
bubbles, these voids are broken by contact with the road surface. As the void
contacts the road, some of the thin film of water is drawn up into the folds
by capillary action. The water drains from the voids as the tire rotates, and
the process is repeated.
    The absorptive compound can handle from 10 to 60 micrometres of water
created in the danger zone, says Yokohama. Two new tires from the company -
the Yokohama Ice Guard IG 20 for automobiles and the Yokohama Geolandar I/T
G072 for light trucks and SUVs - incorporate the new absorptive technologies
and go on sale in the Canadian market this fall.
    Other aspects of tire design continue to be important in winter tires,
the engineers say. Tread design that optimizes performance in snow, helps
evacuate slush and that gives the tire safe characteristics when the road is
dry are also important. But identifying the critical danger zone in
temperature, understanding the thin layer of water beneath the tires and
dealing with it have given tire engineers a new weapon with which to fight one
of Canada's most dangerous winter driving conditions.




For further information:

For further information: Additional information and illustrations of the
new technologies is available from: Brad Sherwin, Marketing Communications
Manager, Yokohama Tire (Canada) Inc., (604) 464-6700 xt 1119,
brad.sherwin@yokohama.ca; Doug Mepham, MacDonald & Co., (613) 966-4969,
doug.mepham@bellnet.ca

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