Pneumatic tire with a pair of sidewall short fiber reinforcing layers

Abstract

A pneumatic tire comprises a radially innermost belt ply having an axial width of from 0.8 to 1.2 times the tread width, a carcass with turnup portions having a radially outer end at a height of not more than 0.15 times the tire section height H, and a short fiber reinforcing layer having a thickness of from 0.3 to 1.0 mm disposed along the axially outer surface of the carcass in each of a pair of sidewall portions between the axial outer edge of the radially innermost belt ply and the radially outer end of the carcass turnup portion. The short fiber reinforcing layer is a compound of: 100 parts by weight of a base rubber compound containing 40 to 70 parts by weight of butadiene rubber and 60 to 30 parts by weight of natural rubber and/or isoprene rubber; 10 to 30 parts by weight of short fiber; and not more than 30 parts by weight of carbon black whose iodine number is in the range of from 30 to 90 mg/g. The short fiber in the short fiber reinforcing layer is oriented so that the oriented direction of at least 90% of the short fiber is in the range of from +20 to -20 degrees to the circumferential direction of the tire. The short fiber reinforcing layer has a directional complex elastic modulus such that the complex elastic modulus E*a in the circumferential direction is not less than 5 times the complex elastic modulus E*b in the radial direction.