Tread for a heavy-duty vehicle tyre, having a tread surface in the new state that is intended to come into contact with a road surface when a tyre provided with this tread is running, this tread comprising: - at least one cavity forming a hidden channel intended to form an additional groove after a predetermined amount of partial wear, this hidden channel being delimited by two facing lateral walls (221, 222), these two lateral walls being connected together by a lower part forming a bottom and by an upper part, - each hidden channel being extended towards the tread surface in the new state and along its entire length by a sipe of small width that opens into the upper part of said channel, - at least one hidden channel having a plurality of extensions that extend from this hidden channel towards the tread surface so as to place the hidden channel and the outside of the tread into communication at least starting from an amount of partial wear of the tread, - each extension being a secondary channel having two openings, a first opening at or close to the tread surface of elongate shape with a minimum dimension I0 and a maximum dimension Lo, and a second opening that opens into the hidden channel, - this tread, being appropriate for conferring a preferred direction of rotation on the tyre provided with this tread, being characterized in that, for at least one hidden channel provided with extensions, each first opening of these extensions is formed entirely by a side of the sipe that extends said hidden channel and in that the first openings of the extensions that place a hidden channel into communication with the outside are all oriented such that the part of each first opening that is furthest away from the sipe that extends the hidden channel is the first to come into contact with the road surface. - at least one cavity forming a hidden channel intended to form an additional groove after a predetermined amount of partial wear, this hidden channel being delimited by two facing lateral walls (221, 222), these two lateral walls being connected together by a lower part forming a bottom and by an upper part, - each hidden channel being extended towards the tread surface in the new state and along its entire length by a sipe of small width that opens into the upper part of said channel, - at least one hidden channel having a plurality of extensions that extend from this hidden channel towards the tread surface so as to place the hidden channel and the outside of the tread into communication at least starting from an amount of partial wear of the tread, - each extension being a secondary channel having two openings, a first opening at or close to the tread surface of elongate shape with a minimum dimension I0 and a maximum dimension Lo, and a second opening that opens into the hidden channel, - this tread, being appropriate for conferring a preferred direction of rotation on the tyre provided with this tread, being characterized in that, for at least one hidden channel provided with extensions, each first opening of these extensions is formed entirely by a side of the sipe that extends said hidden channel and in that the first openings of the extensions that place a hidden channel into communication with the outside are all oriented such that the part of each first opening that is furthest away from the sipe that extends the hidden channel is the first to come into contact with the road surface.