Process for manufacturing a tread for a tyre of a vehicle wheel, in the course of which a profiled element is formed by jointly extruding a plurality of elastomer compounds (M1, M2, M3), in a common direction of flow corresponding to the longitudinal direction of said profiled element, through a gap which is delimited on the one hand by an extrusion head and on the other hand by a receiving surface such as a roller, such that the cross section of the profiled element can be shaped in thickness along a direction called the "vertical direction" which is perpendicular to the longitudinal direction and to the receiving surface, and in width along a direction called the "lateral direction" which is perpendicular to the longitudinal direction and to the vertical direction, said process comprising a first step (a) in which, in a first portion of the extrusion head provided with first inlet channels, a first elastomer compound is introduced into the gap through said first inlet channels and comes into contact with the receiving surface to form an underlayer, and then a second step (b) in which, in a second portion of the extrusion head located downstream of the first portion of the extrusion head in the longitudinal direction and provided with second inlet channels, a second elastomer compound intended to form a tread pattern block is introduced into the gap through said second inlet channels, the second portion of the extrusion head having at least one separating partition which projects into the thickness of the gap and which extends continuously in the longitudinal direction so that said separating partition delimits, on either side of said separating partition in the lateral direction, on the one hand a shaping channel enabling part of the first elastomer compound to form, in one piece with the underlayer, a protrusion called a "wedge" which projects in the vertical direction for the purpose of providing support for the tread pattern block in the lateral direction, said wedge having for this purpose a lateral wall which runs along the separating partition and which, in a cross section normal to the longitudinal direction, extends in a direction secant to the receiving surface, and, on the other hand, a flow channel which enables the second elastomer compound to flow along the second portion of the extrusion head, in contact with the separating partition, parallel to the lateral wall of the wedge and without forming a joint with said lateral wall of the wedge, said process being characterized in that it comprises a third step (c) in which, in a third portion of the extrusion head extending downstream of the second portion of the extrusion head, an injector is provided, the injector being located in the longitudinal prolongation of the separating partition in the longitudinal direction and being provided with an injection slot through which a third elastomer compound, different from the first elastomer compound and the second elastomer compound, is injected, in such a way that said third elastomer compound is placed between, and forms a joint with, the first elastomer compound emerging from the shaping channel and the second elastomer compound emerging from the flow channel, by covering the lateral wall of the wedge so as to form an interface layer called the "decoupling interface" which isolates said lateral wall of the wedge from the tread pattern block while enabling said tread pattern block to come to bear thus laterally against said lateral wall of the wedge indirectly, via said decoupling interface.