Bridgestone Corporation

Seiichiro Tokunaga

Nobumasa Ikeda

Toshikatsu Naoi

A pneumatic tire comprises a carcass of at least one carcass ply, a belt comprised of at least three belt layers, and a tread provided with plural circumferential grooves and island portions defined by these circumferential grooves, in which the tread is comprised of at least two rubber layers, one of which layers being a foamed rubber layer not exposed at a side of ground contact surface of the tire. In this case, the foamed rubber layer is extended up to a buttress portion of the tire, whereby noises produced during the running of the tire are effectively reduced without the degradation of wear resistance.

Pneumatic tires including foamed rubber layer to reduce noise

Disclosed herein is a pneumatic tire having a tread pattern formed in a tread portion divided into separate blocks at an outer surface of a tread rubber layer in at least a central region of said tread portion by a plurality of main grooves extending circumferentially and a great number of lateral grooves each extending toward a cross direction to each of said main grooves and having a shallower portion as compared with said main groove. The tread portion is a cap-base composite tread portion composed of an upper rubber layer forming a pattern of blocks and a lower rubber layer bordered on said upper rubber layer just therebeneath by a face connecting groove bottoms of said shallower portions of lateral grooves and forming a pattern of ribs separated from one another by said main grooves in the lateral direction and extending substantially continuously in the circumferential direction, and said upper rubber layer is substantially composed of a cap rubber having a JIS hardness at -20.degree. C. of not more than 75.degree. and said lower rubber layer is substantially composed of a base rubber having a JIS hardness at 100.degree. C. of not less than 54.degree. and a loss tangent of not more than 0.22 at 50 Hz, 25.degree. C. and a strain of 2%.

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Kodaira, Japan

Seiichiro Tokunaga