Pneumatic radial tire for heavy load

A pneumatic radial tire for heavy load comprising at least one steel radial carcass composed of a main carcass portion extending in a toroidal shape between a pair of bead cores and turn-up portions turning up along the bead cores from the inner side to the outer side in the radial direction of the tire, wherein the following relationships are satisfied on condition that the tire is fitted on a standard rim and inflated with an internal pressure of 50 kPa:

• 5.3% of SH<W1pt<6.8% of SH;
• 1.7% of SH<W1tm<3.2% of SH;
• 2.8% of SH<W2tm<4.3% of SH;
• and
• 1.0% of SH<W1pt−W2pt<3.0% of SH,
• where SH is a tire section height, R is a rim radius, Hf is a height of a rim flange of a standard rim, P1 is a position on the tire outer surface with a radial distance of (R+1.18*Hf) from the central axis of the tire, P2 is a position on the tire outer surface with a radial distance of (R+0.81*Hf) from the central axis of the tire, T1 and T2 are intersections of normal lines drawn from P1 and P2, respectively, to said main carcass portion and said turn-up portion, M1 and M2 are intersections of said normal lines and said main carcass portion, W1pt is a distance from P1 to T1, W1tm is a distance from T1 to M1, and W2pt is a distance from P2 to T2.