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Published on January 1, 2009

Effect of Directional Tires on Wet Traction

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Date Published January 1, 2009

This Report has been authored by:Bobby Unser at ATA Associates #with# Edward Fritsch at ATA Associates #with# Robert J. Swint at ATA Associates #with# Harold J. Herzlich at Herzlich Consulting Inc.

Directional tires are now becoming a more common design. Their groove pattern gives the impression of more aggressive traction capabilities. The distinct angular grooving makes it desirable to control the direction of rotation by having an arrow molded onto the tire sidewall. This is to address certain performance considerations the manufacturer considers important. While having certain aesthetic or claimed technical advantages, the directional requirement creates the problem of making a cross axle tire maintenance rotation pattern more difficult by requiring a dismount/remount to maintain the arrow’s direction of rotation. A study was designed to test the ERTRO position that reversed rotation with regard to wet braking and wet lane change was not a safety related issue.