The time of year is rapidly approaching where the unaware driver may find himself careening down an icy road, bouncing off the curb, trimming down mail boxes and coming to rest against a parked car. According to the US Department of Transportation there are about 190,000 accidents due to icy roads annually. This includes only those serious enough to be reported. It is likely there are more minor accidents, like skidding off the road into the ditch, that are never reported.
Every driver knows that icy roads are slippery. In his book, “Mechanics of Pneumatic Tires“, Samuel K. Clark establishes a numerical measurement to this slippery condition by listing a chart of Coefficient of Road Adhesion (Cr). Within that chart he shows dry asphalt and concrete having a Cr of .8 to .9; ice has a Cr of .1. Traction is reduced by 80 percent to 90 percent compared to a dry road surface. Since this book was published in 1981 tire manufacturers have made some significant progress in tires designed for winter driving. [Read more…]