Heavy loading tubless tire with defined polygonal section bead core

Claim 1

A heavy loading tubeless tire of the type including a bead portion to be fitted on an inclined base of a wheel rim, comprising: a bead portion which has a buried bead core bundled of a plurality of bead wires and having a polygonal section contour and which has a bead base composed of two regions: a region W 1 located at the side of a bead heel and inclined at an angle substantially equal to an angle θ of inclination of the wheel rim base with respect to the axis of tire rotations; and a region W 2 located at the side of a bead toe and inclined at a larger angle than said angle of inclination of the wheel rim base with respect to the axis of tire rotations, wherein the improvement resides: in that the width of the region W 2 at the side of said bead toe measured in the axial direction of tire rotations is within a range of 30 to 70% of the total width of the bead base measured in the axial direction of tire rotations whereas the width of said bead core measured in the axial direction of tire rotations is at least 40% as large as the total width of said bead base; and in that the polygonal contour of said bead core is composed of a bottom side a 1 , which is located at the side of the bead heel and inclined at an angle θa substantially equal to the inclination angle of the bead base in said region W 1 relative to the axis of tire rotations, a bottom side a 2 , which is located to merge into said bottom side a 1 and inclined at an angle θb larger than the inclination angle of the bead base in said region W 1 relative to the axis of tire rotations, a bottom side a 3 , which is located at the side of the bead toe and inclined at an angle substantially equal to the angle of inclination of said bottom side a 1 and which merges into said bottom side a 2 such that a convex portion of the bead core, defined by said bottom sides a 2 and a 3 and a radially inner portion of an inner side b extending radially outward of the tire from the end portion of said bottom side a 3 at the side of the bead toe, projects inward toward said bead base from an axially inward extension of said bottom side a 1 , and an upper side c opposed to said bottom side a 1 , said upper side c being disposed at an angle of inclination (θ 2 ) with respect to the axis of tire rotations that is of an inclination that is smaller than and opposite to the angle of inclination (θ 2 ) of said bottom side a 1 relative to the axis of tire rotations.