Uncoupling pulley having a longitudinal axis, and including a wheel rim having a first zone, to receive a belt connecting the wheel rim to a first power transmission element, and second zone situated in the axial extension along the direction defined by the longitudinal axis of the pulley, of the first zone; a hub to be secured to a second power transmission element; one of the power transmission elements being driving, and the other being driven; a ring mounted below the second zone of the wheel rim and around the hub, so the ring can rotate, around the longitudinal axis, relative to the wheel rim and/or the hub; an elastically deformable element mounted between the hub and the ring; and a unidirectional clutch having an end fastened to the ring and the remaining part of which is mounted below the second zone of the wheel rim and above the ring.