Backbone (Spine) Frame

The backbone is the main top member of a motorcycle frame running back from the steering head. A backbone frame, or spine frame, relies on one large tube or pressed-steel beam for strength, and the engine hangs underneath it, often as a stressed member.

This design is cheap and simple to build and leaves room for a step-through layout, so it is used on many small motorcycles, mopeds and scooters, the Honda Super Cub being a famous example. Some larger bikes have used variations of it as well.

Because so much load goes through a single structure, check the area around the steering head and engine mounts for cracks and rust on older bikes, especially pressed-steel frames.