JP2661920B

PURPOSE:To enhance performance under ice and snow and separation resistance in the title tire by arranging on outside of the tread, an outer layer portion formed with a foaming rubber having a specified glass transition point and a predetermined foaming ratio and average bubble diameter in such a way as to have a preset volume rate with respect to the entire volume of the tread. CONSTITUTION:The outer layer portion 3A of a tread 3 is formed with a foaming rubber 11 having volume of 10% or more of the entire tread and including a rubber component with glass transition point of -60 deg.C or less. The foaming rubber 11 includes a closed bubble 13 with a foaming ratio Vs of 5-50% and an average bubble diameter of 5-150mum, and as well it contains 20 or more closed bubbles with a bubble diameter of 30-200mum per a unit area 1mm . An inner layer portion 3B is formed inside the outer layer portion 3A, and thereat, the inner and outer layer portions 3B and 3A are fitted in contact with each other at a first junction A close to a shoulder 4, and as well the inner layer portion 3B and a side wall 8 are covered with a reinforcing layer 10 at a second junction B. This constitution enables performance under ice and snow and separation resistance to be enhanced.