Heavy duty pneumatic low-sectional radial tire

Abstract

A heavy duty pneumatic low-sectional radial tire having an aspect ratio of not more than 0.8 is disclosed, which comprises a pair of bead portions, a pair of side portions, a tread portion extending across the side portions, and a reinforcement for a tire casing composed of at least one carcass ply extending across two bead cores and turning up around the bead core and containing cords embedded therein in a substantially radial direction of the tire, each cord having a modulus of not less than 4,000 kg/mm.sup.2, and a belt of at least two layers, each layer containing metal cords embedded therein, superimposed around a crown portion of the carcass and crossing with each other at a relatively small angle with respect to the equatorial line of the tire. In this tire, a carcass line of the tire casing at a temporarily mounted posture on a normal rim under an internal pressure of 0.5 kg/cm.sup.2 depicts a bow-shaped profile in tire section defined by a curved line, whose curvature being smaller with distance from a chord PQ at the outside thereof, where the PQ is a line segment connecting a point P to a point Q, the point P is an intersection of the carcass line and a normal line of the carcass line passing an alienating point of the bead portion from a rim flange or an inflection point of the carcass line when the intersection is located inside the inflection point and the point Q is an intersection of the carcass line and a radial line of the tire passing the point P. The bow-shaped profile of the carcass line is substantially symmetrical with respect to a substantially perpendicular bisector of the chord PQ as a symmetrical axis inside and outside thereof.