A bridge frame is a frame of a motorcycle built over the engine block.
In contrast to most other frames, the engine block itself has a bearing task in a bridge frame. As a result, the frame can be easily constructed. It is about the engine block because there are other parts to be attached: the tank, the footrests, the rear frame with the saddle, trunk rack etc.
There are different types of Bridge Frames:
The spine frame is a bridge type frame made of pressed steel sheet.
The diamond frame is an open spine frame in which the engine block forms a supporting part. This type of frame was first applied to the Vincent-HRD motorcycles that came out in 1936. In our time it is applied to, among other things, the Honda CX models, starting in 1977. The old-fashioned bicycle frames where the first engine cubes were hung were called diamond frame, to the triangle formed by the frame tubes. The name "Diamond frame" was used for the first time on bicycles, and was named by the triangular construction used by John Kemp Starley's safety bicycle.
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