Heavy duty pneumatic radial tires

Claim 1

A heavy duty pneumatic radial ply tire, comprising: a carcass having a pair of axially spaced circumferentially extending bead cores and covered by rubber to define a tire bead seat adjacent each bead core; a carcass ply having a plurality of steel cords extending from bead to bead, with the ends of the cords being turned up around the bead core from the axial inner to the axial outer side thereof, the outermost ends of the turned up portion being at a perpendicular height h0 above its bead seat of 55 to 80 mm, the steel cords of the carcass ply lying at an angle of 90° to 70° with respect to the equatorial plane of the tire; a belt having a plurality of cords lying at an angle of 10° to 30° with respect to the equatorial plane of the tire and circumferentially extending on the carcass ply; a reinforcing layer in each bead region comprising cords disposed adjacent to the outside of the turned up portion of the carcass ply; the ratio t/h of the rubber thickness t at the height h between the carcass ply and its turned up portion to the height h, decreasing gradually in inverse proportion to the values of h/h0 within the range of 0.3≦h/h0≦0.5; the rate of the decrease in the ratio t/h, decreasing gradually in inverse proportion to the values of h/h0 within the range of 0.5≦h/h0≦0.8; and the ratio t/h taking an approximate constant value from 0.1 to 0.25 within the range of 0.8<h/h0≦1.0; wherein the rubber thickness t at a height h between the carcass ply and its turned up portion is defined as the minimum distance from the point on the turned up portion of the carcass ply at a perpendicular height h above the tire bead seat to the carcass ply.