Abstract: A belt tensioning device having an improved damping mechanism for damping movements of the pivoted structure rotatably carrying the pulley with respect to the fixed structure. The damping mechanism includes a strap and a ring mounted on their respective fixed and pivoted structures and with respect to one another such that the strap engages the ring with a gripping action sufficient to provide (1) a relatively high resistance to frictional sliding movement between the strap and ring in one direction correspond to the direction of untensioning of the belt with the pulley and (2) a relatively low resistance to frictional sliding movement between the strap and ring in an opposite direction corresponding to the direction of belt tensioning.