Bridgestone Corporation

Teruyuki Tominaga

Hisao Ushikubo

Misao Kawabata

Yasuo Himuro

Toshio Hayakawa

Automobile tire

When a radial tire is used at high speed (e.g. 250 km/h or more), tire blocks deform outward due to a centrifugal force applied to mass at the center of each block, so that contact pressure rises and therefore the tire is heated into blow out. To overcome this problem, the rubber thickness (gage) of the block partitioned by circumferential grooves and transverse grooves is reduced at the central area of the block. To reduce the rubber thickness, a shallow groove extending along the circumferential groove is formed in the middle of the block or a hole is formed at the center of the block.

Pneumatic radial tire suitable for use at high speed

A low profile pneumatic radial tire comprises at least one carcass ply containing cords arranged substantially at 90.degree. relative to a circumference of a tread, and a belt consisting of at least two belt layers which are composed of metal cords inclined relative to the circumference of the tread and intersected with one another between the adjacent belt layers and which are arranged upon a crown of the carcass. The tread surrounds the crown, and is provided with a pair of circumferential main grooves which are disposed symmetrically with respect to an equatorial plane of the tire and which divide a treading portion of the tread into a central region and axially opposite side regions and which are separated by a distance ranging from 45 to 65% of a maximum width of the tire in the state that the tire is assembled onto a normal rim and inflated at a normal internal pressure. The width of the belt ranges from 110 to 130% of a distance between intersections of an imaginary straight line which tangentially contracts with a top surface of a wear indicator projecting from a bottom of each of the circumferential grooves and which is drawn in parallel with a tire rotary axis and a tire contour line at axially opposite side regions of the tread, and the thickness of a tread rubber at maximum width edges of the tread ranges from 30 to 80% of that at the intersections.

Low profile pneumatic radial tires

To improve high-speed durability of a low-section pneumatic radial tire without producing tire separation at both belt ends and expansion at both tread sidewalls after the tire has been worn off to some extent, the tire belt structure disposed between the tire tread and the carcass is composed of two belt layers and a plurality of auxiliary layers. The auxiliary layers comprises a first auxiliary layer extending over the belt layers and at least second and third auxiliary layers arranged on both axially outside end of the tread in such a way that an axially outer end of each of the auxiliary layers extends to near the tread sidewall and an axially inner end of each of the auxiliary layers extends to or beyond under at least an axially outermost circumferential groove formed on the tread in step fashion extending from tread center to tread end or vice versa. Further, these auxiliary layers are formed by winding a ribbon including at least two heat-shrinkable fiber cords coated with a coating rubber in spiral fashion on the circumferential surface of the belt layers.

Growing community of inventors

Kodaira, Japan

Teruyuki Tominaga