Pneumatic radial tire for heavy duty vehicle

A pneumatic radial tire for heavy duty vehicles having a pair of bead portions each comprising:

• a bead core disposed circumferentially of the tire on a plane which is substantially perpendicular to a rotational axis of the tire,
• a rubber stiffener disposed radially outwardly of said bead core and shaped in the form of a triangle in cross section,
• at least one carcass having a fold-back portion folding back at said bead core in a radial direction substantially perpendicular to said rotational axis to cover said bead core and in part said rubber stiffener, and
• at least first, second and third chafer plies disposed around said carcass to reinforce said bead portion and having embedded therein a plurality of first parallel cords, a plurality of second parallel cords and a plurality of third parallel cords, respectively, with the cords of adjacent plies arranged to cross each other in diagonally opposite directions, the cords of said first, second and third chafer plies being all composed of organic textile material,
• said cords of said first, second and third chafer plies extending with respect to said radial direction at chafer angles of .theta..sub.1, .theta..sub.2 and .theta..sub.3, respectively, defined by the following equations,
• 35.degree..ltoreq..theta..sub.1 .ltoreq.55.degree.,
• 35.degree..ltoreq..theta..sub.2 .ltoreq.55.degree.
• 70.degree..ltoreq..theta..sub.3 <90.degree.,
• said first, second and third chafer plies having a first chafer height h.sub.1 measured in said radial direction from a laterally outward and radially outermost end of said first chafer ply to a heel point at which a bead base of said bead portion and a flange portion of a rim having mounted said bead base thereon are intersected with each other, a second chafer height h.sub.2 measured in said radial direction from a laterally outward and radially outermost end of said second chafer ply to said heel point and a third chafer height h.sub.3 measured in said radial direction from a laterally outward and radially outermost end of said third chafer ply to said heel point, respectively,
• said carcass having a fold-back height H measured in said radial direction from a radially outermost end of said fold-back portion thereof to said heel point, the first, second and third chafer heights h.sub.1, h.sub.2 and h.sub.3 being selected within ranges defined by the following equations, ##EQU4## said third chafer height h.sub.3 which has the maximum chafer angle .theta..sub.3 with respect to said radial direction being radially taller than the other chafer heights h.sub.1 and h.sub.2 respectively having said chafer angles .theta..sub.1 and .theta..sub.2 each smaller than said chafer angle .theta..sub.3.