© The tread-pattern presents a plurality of circumferential zig-zag grooves that divide the tread-band into a plurality of ribs, and a series of sipes (4) which divide at least the axially inner ribs, into a plurality of blocks (3) that are reciprocally locked, one with respect to the other, in the transversal direction. The above-said grooves, are comprised by an alternated succession of narrow notches (1) and large elliptical shaped cavities (2), with the greater axis constituting one side of the zig-zag, with having the cross-section, the slant of the sidewalls and the base-profile, variable with continuity.