When a tread thickness from a second belt ply 7B is defined as T, a minimum position Qt in which the tread thickness T becomes a minimum value Tmin is provided in a region Y which is away from a tire equator C by a distance of 0.5 to 0.7 times of a tread grounding half width WT/2. A ratio Tmin/Tc between said minimum value Tmin and the tread thickness Tc at the position of the tire equator C is 0.92 to 0.97, and a ratio Tb/Tc between a tread thickness Tb at a position of an outer end of the second belt ply and said tread thickness Tc is 0.95 to 1.10. When a tread thickness from a carcass 6 is defined as K, a minimum position Qk in which a tread thickness K becomes a minimum value Kmin is provided in said region Y. A ratio Kmin/Kc between said minimum value Kmin and a tread thickness Kc at a position of the tire equator C is 0.97 to 0.998, and a ratio Kb/Kc between the tread thickness Kb at a position of the outer end of the second belt ply and said tread thickness Kc is 1.2 to 1.5.