Pneumatic radial tire for heavy load

A pneumatic radial tire for heavy load vehicles comprising a pair of bead portions in each of which a bead core is embedded, a radial carcass ply extending from one bead portion to the other bead portion and turned around the bead core from an inner side to an outer side of the bead core in a width direction of the tire and at least six belt layers disposed on an outer side of this radial carcass ply in a radial direction of the tire, wherein

• the following relations are satisfied:
• W56>W34>W12, where W12 is a maximum width of first and second belts of the belt layers, W34 is a maximum width of third and fourth belts of the belt layers and W56 is a maximum width of fifth and sixth belts of the belt layers;
• and
• 1>D12/D34>0.6, where D12 is a cord diameter of the first and second belts and D34 is a cord diameter of the third and fourth belts, and
• a steel cord of each belt layer has a double twist structure in which a plurality of steel filaments are twisted to form a cable and two to ten cables are further twisted,
• wherein the first and second belts are disposed adjacent to the outer side of the radial carcass ply, the third and fourth belts are disposed on the first and second belts and the fifth and sixth belts are disposed on the third and fourth belts,
• wherein
• a cord of the first and second belts has an arrangement angle θ2 of not more than 10 degrees with respect to a circumferential direction of the tire,
• a sheath cable of the cord of the first and second belts has a twist angle θ1 with respect to an axis center of the cord having a range of 3 degrees ≦θ1≦13 degrees, and
• the following relation is satisfied:
• 2.0>θ2/θ1>0.4.