Abstract: 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.

Abstract: 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.

Abstract: 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.