Heavy duty radial tire with belt reinforcing rubber layer having axially inner and outer rubber portions

A heavy duty radial tire comprising a carcass which extends from a tread portion to each of bead cores in a pair of bead portions through a pair of sidewall portions, and a belt layer disposed inside the tread portion and radially outward of the carcass and comprising a plurality of belt plies, wherein:

• said belt layer comprises a first belt ply disposed on the radially innermost side and having belt cords arranged at an angle of 10 to 45° with respect to the tire circumferential direction, a third belt ply disposed radially outward of said first belt ply and having belt cords arranged at an angle of 10 to 45° with respect to the tire circumferential direction in the slanting direction reverse to that of said first belt ply, a second belt ply disposed between said first and third belt plies and having belt cords spirally wound at an angle of at most 5° with respect to the tire circumferential direction, and a fourth belt ply disposed radially outward of said third belt ply and having belt cords spirally wound at an angle of at most 5° with respect to the tire circumferential direction, in which the axial width W1 of said first belt ply and the axial width W3 of said third belt ply are at least 85% of a tread ground contact width Tw, the axial width W2 of said second belt ply is at least 70% of the tread ground contact width Tw and is smaller than the widths W1 and W3 of said first and third belt plies, the axial width W4 of said fourth belt ply is at least 5 mm, and the distance K from the tire equator to the axially outer end of said fourth belt ply is from 35 to 40% of the tread ground contact width Tw,
• a pair of reinforcing rubber layers are disposed between said first and third belt plies so as to extend axially outwardly from each of the axially outer ends of said second belt ply, and
• each of said reinforcing rubber layers comprises an axially inner rubber portion which is continuous with the axially outer end of said second belt ply and which has a substantially constant thickness T1 of 1.5 to 4.0 mm and a complex elastic modulus E*1 of 8.0 to 14.0 MPa, and an axially outer rubber portion which is continuous with said axially inner rubber portion and which has a thickness T2e of at least 2.0 mm at the axially outer end of said third belt ply and a complex elastic modulus E*2 of 6.0 to 12.0 MPa which is smaller than the complex elastic modulus E*1.