Study on the Frictional Property of Studless-Tires on Icy Roads, Part 3: Relationship between the Frictional Property of Studless-Tires on Icy Roads and the Friction Coefficient-slip Ratio Curves

For elucidating the tread wear mechanism of studdless tires on the icy road, we have conducted, μ-S curve analysis which principally yields the relationships between the friction coefficient, μ, and the slip ratio, S, and deformation analysis of small rubber blocks located between the sipes. Then the following results were obtained. 1) μ-S curve can be formulated by the following regression equation; μ=(a•Sb-c)•exp(-Sd)+c•exp(Se) Where, μ is friction coefficient, S is slip ratio, and a, b, c, d and e are coefficients. 2) Resulted relationships between the shape of μ-S curve and tire performance on the icy road indicate that the tire performance enhances with loosening the sharpness of the μ peak shape. 3) The deformation analysis of small rubber blocks have reached an modified formula in which the degree of small rubber block deformation can be shown by an addition of bending deformation and the compression-shearing deformations. Using this formula, an amended equation of relationships between an inclined angle of the block and friction coefficient can be obtained, μ rock value obtained from dimensions of small rubber blocks of test tires with various number of sipes and from their modulus has corresponded with one obtained from substituting 100% for slip ratio in, μ-S curve regression equation. This verifies the effectiveness of the formula.