Pneumatic tire base-cap tread

摘要

A pnuematic tire having a cap tread and a base tread is defined in way of material as follows: (1) said cap tread is made of a rubber material in which 100 pts. wt. of rubber component comprising at least 50 pts. wt. of natural rubber and/or polyisoprene rubber, at most 50 pts. wt. of polybutadiene rubber containing at most 20% of 1,2-bonding units and at most 50 pts. wt. of styrene-butadiene copolymer rubber containing at most 30 wt % of bonded styrene is incorporated with 50 to 100 pts. wt. of carbon black and with a softener in an amount satisfying the inequality; 1.1X-44<y<1.1X-30, where y is the total amount of the softener in pts. Wt.; x is the amount of carbon black in pts. wt.; and an overall solubility parameter of the softener is in the range of from 8.0 to 9.0, (2) said base tread is made of a rubber material in which 100 pts. wt. of rubber component comprising at least 60 pts. wt. of natural rubber and/or polyisoprene rubber, at most 40 pts. wt. of polybutadiene rubber containing at most 20% of 1,2-bonding units and at most 40 pts. wt. of styrene-butadiene copolymer rubber containing at most 30 wt % of bonded styrene is incorporated with 2.6 to 3.6 pts. wt. of sulfur, and (3) said base tread has a volume fraction of 0.1 to 0.5 against the entire tread part.