| 摘要 |
PURPOSE: A pneumatic radial tire having a semi-groove against heavy load is provided to increase the durability by radiating heat efficiently during traveling with forming semi-grooves circumferentially in the tread shoulder rib, and to improve traveling stability by restricting uneven wear. CONSTITUTION: Grooves(G1,G2,G3,G4) are formed in a pneumatic radial tire with the same depth, and semi-grooves are formed circumferentially on a tread shoulder rib. Semi-grooves having the specific width and depth are placed to accelerate radiation of heat and prevent lowering of durability from belt separation. The width of the semi-groove is within the range of 0.7mm to 2.5mm, and the difference between the depth of the main groove and the depth of the semi-groove is within the range of 1.6mm to the depth of the main groove divided by two. The endurance of the tire is increased by relieving concentration of stress on the edges of second and third belts(B2,B3) with reducing stiffness. Uneven wear of the tread shoulder rib is prevented by restricting tension from being transmitted to the tread portion with the semi-grooves.
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