Pneumatic radial tire for heavy load having lug grooves
The present invention provides a pneumatic radial tire for heavy load, having lug grooves in respective side regions of a tread surface, in which tire an amount of slip of the trailing edge of each of land portions defined by the lug grooves, with respect to a road surface, when the tire is rotated with load applied thereon is advantageously reduced without causing decrease in partial wear resistance of the land portions at a road contact surface thereof and generating cracks at the lug groove bottom. The pneumatic radial tire for heavy load, having a plurality of lug grooves 2 provided in respective side regions of a tread surface 1 to extend in the tread width direction, open at respective side edges of the tread surface 1 , and define land portions 3 therebetween, is characterized in that: in a cross section of each lug groove 2 in the width direction thereof, only a groove wall 4 on the step-in side of each land portion 3 is bent at at least one bent point in the depth direction of the corresponding lug groove 2 such that a portion 4 a of the groove wall, located on the inner side in the radial direction than the bent point f, is tilted in a direction that narrows a groove width.
1. A pneumatic radial tire for heavy load, having a plurality of lug grooves provided in respective side regions of a tread surface to extend in the tread width direction, open at respective side edges of the tread surface, and define land portions therebetween, characterized in that:
in a cross section of each lug groove in the width direction thereof, only a groove wall on the step-in side of each land portion is bent at at least one bent point in the depth direction of the corresponding lug groove such that a portion of the groove wall, located on the inner side in the radial direction than the bent point, is tilted in a direction that narrows a groove width, and an opening width W at the tread surface and a depth, of the lug groove, is in the range of 20 to 80 mm and in the range of 40 to 120 mm, respectively,
wherein the bent point is positioned within the range of 30-70% of a groove depth of the lug groove measured from a surface of the land portion;
a portion located on the outer side in the radial direction than the bent point is tilted at an angle “a” with respect to a line normal to the surface of the land portion, which angle “a” falls in the range of 0-20°;
a portion located on the inner side in the radial direction than the bent point is tilted at an angle “c” with respect to an imaginary line extended from the radially-outer-side portion, which angle “c” falls in a range of 5-15°;
a groove wall of the kick-out side of each land portion is tilted such that an angle “b” formed by the groove wall with respect to a line normal to the surface of the land portion satisfies a relationship of a−5°<b<a+5°(b≧0°); and
wherein a portion of the groove wall on the step-in side, located on the inner side in the radial direction than the bent point and excluding a round groove bottom portion, is tilted at a constant angle “c” with respect to an imaginary line extended from the radially-outer-side portion of the groove wall, which angle “c” falls in a range of 5-15°.