Abstract: In a belt tensioning device of the type including a fixed structure, a pivoted structure mounted with respect to the fixed structure for pivotal movement about a first axis between first and second limiting positions, a belt engaging pulley rotatably carried by the pivoted structure for rotational movement about a second axis parallel with the first axis and a torsional coil spring acting between the fixed and pivoted structures for resiliently biasing the pivoted structure to move in a direction away from the first limiting position toward the second limiting position with a spring force which decreases as the pivoted structure is moved in a direction away from the first position toward the second position.