Patent ID: 7766062

Claim:
A pneumatic radial tire, comprising a tire tread including at least two layers of a base tread and a cap tread arranged externally in a radial direction of said base tread, wherein said base tread is formed by a base tread rubber composition including at least 2-20 parts by weight of a kraft paper ground product relative to 100 parts by weight of a rubber component, said base tread has its ratio E*a/E*b of a complex elastic modulus in a circumferential direction E*a to a complex elastic modulus in a tire radial direction E*b set to fall within a range of 1.6-2.27, each of said complex elastic moduli E*a and E*b being measured at a temperature of 70° C., a frequency of 10 Hz, and a dynamic strain of ±1% at a tire maximum width position in a state where the tire is attached to a rim and filled to a prescribed internal pressure, and a ratio E*a/E*c of said complex elastic modulus E*a of said base tread to a complex elastic modulus in the tire circumferential direction E*c of said cap tread is set to fall within a range of 1.1-10, each of said complex elastic moduli E*a and E*c being measured at a temperature of 70° C., a frequency of 10 Hz, and a dynamic strain of ±1% at a tire maximum width position in a state where the tire is attached to a rim and filled to a prescribed internal pressure.