Pneumatic tire for heavy duty vehicles

A pneumatic tire for a heavy duty vehicles, comprising a tread divided by two circumferential zigzag grooves in a tread center zone and remaining side zones consisting of circumferentially continuous ribs, said tread center zone including block patterns of elongated blocks circumferentially discontinuous with traverse grooves, said traverse grooves being provided in their substantially mid portions 30-70% of their lengths with platforms rendering said traverse grooves shallower 30-70% than their original depths, widths of said traverse grooves measured perpendicularly to their lengthwise direction being 0.2-0.3 times of the traverse length of said blocks, each said side zone T.sub.s having a width which is 20-42% of an effective width BW of a belt, and 75-100% of said width of each said side zones being firmly reinforced by said belt, thereby forming in a surface of said tread a pattern of blocks and ribs when said tire is relatively new, said pattern being capable of converting as a whole into another pattern of ribs formed by said circumferential zigzag grooves having branch grooves when said tread has worn more than 30-70%.