Heavy duty pneumatic radial tire

Claim 1

In a heavy duty pneumatic radial tire having an all-weather type tread pattern formed in a tread divided into a central zone and peripheral zones on both sides thereof by two main, continuous, circumferential zigzag grooves formed on both sides of an equatorial line of the tire, said central zone comprising a plurality of central blocks disposed in two rows divided by segment grooves along said equatorial line and a number of dividing grooves extending between said main grooves, each of said peripheral zones being circumferentially divided into blocks in the form of arrow feathers directed toward said equatorial line by traverse grooves communicating with said main groove at extended portions thereof opposite said equatorial line, and each of said peripheral zones being further divided by a further continuous zigzag groove substantially circumferentially parallel with said main grooves into a plurality of inner and outer peripheral blocks disposed in two rows, the improvement comprising: (a) the distance between said main grooves being 25-38% of the overall width of the tread, (b) the oblique zigzag angle α of said main grooves being 55°-78° relative to the axial direction of said tire, (c) the walls of said traverse grooves being inclined at an angle β of 20°-40° relative to a cross-sectional center line of the traverse groove and extending to a depth from the outer surfaces of said blocks of at least 20% of the depth of said traverse grooves, (d) the ratio of total area of the blocks in said central zone to that in one of said peripheral zones being 1:1.0 to 1:1.5, and (e) the ratio of the total areas of said inner and outer peripheral blocks being 1:1.5 to 1:2.5.