Abstract: To prevent crack occurrence at groove bottoms on both side areas of foam rubber tread of all-season studless tires, the pneumatic tire having a tread surface portion composed of at least two outer and inner rubber layers is characterized in that the hardness of the inner rubber layer lies from 54 to 80 degrees in Shore hardness and is higher than that of the outer rubber layer, and further the outer rubber layer is made of foam rubber with a foam rate from 5 to 50% with at least 10% volume ratio with respect to tread volume. The outer foam rubber layer serves to improve tire performance on icy and snowy roads in winter, and the inner ordinary rubber layer serves to reduce change in groove width after vulcanization, that is, reduce dynamic strain concentration at lateral grooves and therefore to reduce crack generation at the lateral groove bottoms.

Abstract: A rubber composition containing a specifically limited imidazole compound or imidazoline compound, or benzimidazole or its specifically limited derivative has a large tan .delta. at high temperature range, and a tire having a tread using such rubber composition is prevented from being lowered in the value of tan .delta. due to the temperature rising during the running and has an improved grip performance during the high speed running. The use of Bronsted acid in combination with the imidazole, imidazoline or benzimidazole can obviate the drawback of poor scorch resistance of a rubber composition containing the imidazole, imidazoline or benzimidazole alone, and the resulting rubber composition has a very large tan .delta. at high temperature range, and a tire having a tread using the rubber composition has a remarkably improved grip performance during the high speed running.

Abstract: A pneumatic tire having an excellent cut resistance is disclosed, which comprises an annular crown portion constituting a tread, a pair of side portions supporting said crown portion, a pair of bead portions located at each foot of said side portions for fitting to a rim, a carcass layer composed of at least one rubberized cord ply toroidally extending between said bead portions and a liner layer disposed inside and adjacent to said carcass layer.In the tire according to the invention, a fault surface having an extremely low adhesion which intercepts the crack growth from the outside of the tire is further arranged in said liner layer at at least a part of a region extending between said bead portions.

Abstract: A novel tread pattern is disclosed, which can give high performances on wet road at both the straight running and the cornering under a low load, particularly no load, to a heavy duty pneumatic radial tire without sacrificing the performances on wet road under normal load. The tread pattern comprises at least 4 lands defined by at least 3 main grooves, wherein a pair of first group lands arranged on the outermost side regions of the tread have substantially continuous along the the circumferential direction of the tread and the remaining lands located between the first group lands have notches arranged thereon in their lateral direction.

Abstract: A pneumatic tire having a cap/base structured tread and having an improved resistance against heat build-up and an improved wear resistance at the end of the use can be obtained by forming a tread base rubber of the tire with a vulcanizate of a rubber composition comprising specifically limited amounts of short fibers of syndiotactic-1,2-polybutadiene having a maximum diameter of not more than 10.mu. and an average diameter of less than 1.mu., carbon black, sulfur and natural or synthetic rubber.

Abstract: A pneumatic tire having an improved chipping resistant property is disclosed. In the tire, the tread portion is formed with a vulcanizate of a rubber composition comprising 3-40 parts by weight of short fibers of syndiotactic-1,2-polybutadiene, 30-100 parts by weight of carbon black and 0.2-5 parts by weight of a p-phenylenediamine type antioxidant, on a basis of 100 parts by weight of a rubber selected from natural rubber, synthetic rubber and a blend thereof in an optional blending ratio.

Abstract: A pneumatic tire provided with a plurality of slots which are provided in tread grooves and extend in the transverse direction of the grooves but at a suitable spacing from each other for the purpose of confining between the slots the growth of cracks produced in the grooves, so that each crack is prevented from growing up to an extent exceeding the spacing between the slots.