A heavy duty radial tire is to be mounted on a 15 degree drop center rim. In a mounted state that the tire is mounted on the rim and inflated to 0.5 ksc but not loaded, the inside diameter BC of the bead cores at the radially innermost point thereof is set to being not more than the diameter BT at the heel point of the bead portions. In a demounted state that the tire is demounted from a rim, the bead bottom is tapered towards the axial inside of the tire at an angle .theta. of from 1.0 to 1.9 times the angle .alpha. of the tapered bead seat of the rim. In the mounted state, the bead core has a radially inner surface tapered at the substantially same angle as the bead seat, and the axial distance BP of the axially inner end of this tapered inner surface from the bead heel point is set in the range of from 1.3 to 2.1 times the maximum width BW of the bead core measured in the direction parallel to the bead seat. A straight line drawn between a point P2 at which the carcass main portion starts to contact the bead core and a point P3 at which the carcass main portion and a radially extending straight line passing the axially inner end of the radially inner surface of the bead core intersect each other, is inclined at angle .beta. of from 45 to 60 degrees with respect to the tire axial direction.