PURPOSE: To improve the rigidity and steering stability without impairing antiskid property by forming a tread rubber into a two layer structure of cap rubber and base rubber having larger dynamic modulus of shearing elasticty than the former so as to be a rubber composite of respective fixed physical properties.

CONSTITUTION: A tread rubber 3 is formed into a two layer structure of cap rubber 4 on the grounding face side and base rubber 5 on the contact face side with a belt 2. The cap rubber 4 is formed out of a rubber composite having the dynamic modulus of shearing elasticity GC' of 1.5-2.0MPa at temperature 60°C, and the base rubber 5 is formed into a rubber composite of which the oil mixing quantity 1s under 10 weight part against 100 weight part of rubber content and the dynamic modulus of shearing elasticity GB' is 1.6-3.0MPa at temperature 60°C larger than GC'. Consequently, the tread grounding face is soft, the contact area with road surface is maintained so as to be high in antiskid property, the whole tread is high in rigidity so as to be hardly deformed, the steering stability can be improved.