A motor-vehicle wheel assembly comprising: - a wheel hub associated with a brake disc, - a motor-vehicle wheel coupled to the wheel hub so that the wheel axis coincides with the axis of the hub, - said motor-vehicle wheel being locked on said wheel hub by means of a fastening unit fixed on the wheel hub, - said motor-vehicle wheel assembly further comprising an anti-loosening device coupled to said wheel hub, comprising: - a gear inserted within said wheel hub along an axial direction, having outer teeth cooperating with inner teeth of the wheel hub formed at an end portion of the wheel hub along an inner surface thereof, - an elastic element extending axially with respect to said gear within said wheel hub, wherein the elastic element comprises a first end connected to the gear, and a second end engaged against at least one abutment and centering surface obtained inside the wheel hub, - at least one coupling element obtained on a sector of said gear along a direction substantially parallel to an axial direction of the gear, wherein said coupling element is arranged to receive a corresponding fastening member, - said anti-loosening device having a main axis coinciding with the axis of the wheel and being arranged to create a compressed configuration, wherein said elastic element is in a compressed position, and the gear is decoupled with respect to said inner teeth of the wheel hub, and is arranged within a cavity portion formed on the inner surface of the wheel hub, so as to allow rotation of the anti-loosening device around said main axis; - wherein, following a rotation of said anti-loosening device, said coupling element is radially aligned with respect to a respective anti-rotation sector obtained on said fastening unit, - wherein, in the assembled condition of said wheel assembly, said fastening member coupled to said coupling element cooperates with said anti-rotation sector, to avoid loosening of the locking unit. - a wheel hub associated with a brake disc, - a motor-vehicle wheel coupled to the wheel hub so that the wheel axis coincides with the axis of the hub, - said motor-vehicle wheel being locked on said wheel hub by means of a fastening unit fixed on the wheel hub, - said motor-vehicle wheel assembly further comprising an anti-loosening device coupled to said wheel hub, comprising: - a gear inserted within said wheel hub along an axial direction, having outer teeth cooperating with inner teeth of the wheel hub formed at an end portion of the wheel hub along an inner surface thereof, - an elastic element extending axially with respect to said gear within said wheel hub, wherein the elastic element comprises a first end connected to the gear, and a second end engaged against at least one abutment and centering surface obtained inside the wheel hub, - at least one coupling element obtained on a sector of said gear along a direction substantially parallel to an axial direction of the gear, wherein said coupling element is arranged to receive a corresponding fastening member, - said anti-loosening device having a main axis coinciding with the axis of the wheel and being arranged to create a compressed configuration, wherein said elastic element is in a compressed position, and the gear is decoupled with respect to said inner teeth of the wheel hub, and is arranged within a cavity portion formed on the inner surface of the wheel hub, so as to allow rotation of the anti-loosening device around said main axis; - wherein, following a rotation of said anti-loosening device, said coupling element is radially aligned with respect to a respective anti-rotation sector obtained on said fastening unit, - wherein, in the assembled condition of said wheel assembly, said fastening member coupled to said coupling element cooperates with said anti-rotation sector, to avoid loosening of the locking unit.