Final answer:
The towing device that uses rubber belts to suspend part of the load while towing vehicles is the tow sling.
Step-by-step explanation:
The towing device used for lifting and towing vehicles where part of the load is supported on rubber belts is known as a tow sling. It is also sometimes referred to as a sling lift. The tow sling is wrapped around the vehicle's front or rear end, and then lifted by a boom on the tow truck. This method, however, is getting less common due to the potential of damage to the vehicle being towed, especially to the bumpers. More modern tow trucks use wheel lifts or underlifts, which lift the vehicle by the tires or use a metal yoke without causing damage to the bumper.