Abstract: A studless pneumatic tire having excellent running performance of the tire on icy road surfaces. The tire has a plurality of block-shaped island portions formed on a cylindrical tread extending between a pair of sidewalls. The island portions have laterally extending sipes and are separated by a plurality of main grooves extending in the circumferential direction as well as by many lug grooves. Each island portion has a first sipe and a second sipe. The first sipe extends from a first lateral end facing a first main groove to traverse a first edge region of the island portion in a substantially axial direction and branches into a plurality of branch segments, thereby forming a fork-like shape, at a first interface between the first edge region and the central region of the island portion. Each branch segment traverses the central region of the island portion and reaches a point near a second interface between an opposite second edge region and the central region of the island portion.

Abstract: Pneumatic tires according to this invention have a tread provided with blocks separated by circumferential grooves extending around the tread and lateral grooves crossing the circumferential grooves, the blocks being respectively provided with two lateral sipes, characterized in that the lateral end portions having small rigidity in block portions which are substantially separated by lateral sipes are reinforced by, for example, a platform. The invention has the effects of restraining block chipping in heavy duty tires and degrading of steering stability in passenger tires, and enhancing the performance on ice without degrading wet performance, by means of increasing sipe density and restraining lowering of the block rigidity.

Abstract: A pneumatic tire includes a plurality of blocks, each having a narrow area interposed between one set of two sipes which extend substantially in a transverse direction of the tire and wide areas positioned respectively at both sides of the narrow area across the sipes. An average distance H2 from a tire tread surface of the narrow area to bottom portions of the sipes is less than an average distance H1 from tire tread surfaces of the wide areas to the bottom portions of the sipes. Expanded portions may be provided at the bottom portions of the two sipes. A ratio W2/W1 of a length W2 of the narrow area in the transverse direction of the tire to a length W1 of the wide areas in the transverse direction of the tire may satisfy 0.50.ltoreq.W2/W1.ltoreq.0.95. A length, in the circumferential direction of the tire, of at least one side end portion of the narrow area may be longer than a length, in the circumferential direction of the tire, of a central portion of the narrow area.