An assembly including a deformable, inextensible tread-bearing support S, which can be slipped on to a suitable rim bearing surface (11). The bearing surface (11) extends axially towards the inside of a first rim seat (13null), which is in turn extended to the outside by a protrusion or hump (15null) of low height. The first rim seat (13null) is inclined towards the outside. A second rim seat (13null) having, viewed in meridian section, a generatrix, the axially inner end of which is located on a circle of diameter DnullA greater than the diameter of the circle on which is located the axially inner end DnullA of the first rim seat (13null). The two seats being, axially to the inside, extended by frustoconical portions (17, 14) of a height at least equal to 0.01 times the minimum diameter of the bearing surface (11), and the generatrices of which form with the axis of rotation angles null at least equal to 45null. The rim bearing surface (11) is provided with at least one circumferential protuberance (115) arranged in a circumferential groove (30) of the radially inner face of the tread bearing support S, such that the protuberance (115) axially comes to bear and butt up against at least one lateral wall of the groove (30).