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Figure 24 comprises two photographs labelled (a) and (b). Photograph (a) shows a conventional bicycle and superimposed on the photograph is a drawing of a diamond shape that coincides with parts of the frame. The diamond is made up of two triangles sharing the frame strut from the chain-wheel to the seat as a common side. This strut slopes back at about 20 degrees to the vertical. The cross bar from the seat to the handle bar forms the horizontal. If one extended this line, it would form a triangle with a strut that projects forwards at about 40 degrees from the from the chain-wheel end. One other strut is projecting rearwards from the chain wheel end back to the centre of the rear cycle wheel. This is joined by a strut that projects down and rearwards from the seat end. These three struts form the rear half of the diamond shape. Both triangles share the strut connecting the chain-wheel and the seat. Ignoring this strut, the remaining four struts create the diamond shape. Photograph (b) shows the side view of a Lotus racing bicycle that has a solid frame rather than one made from tubular struts. The frame still has a sort of diamond shape and the same four points are connected – the seat, rear-wheel axle, chain-wheel and front forks assembly. Instead of straight lines between these points, the edges of the shape are curved in to varying amounts so that the final shape looks more like a plus sign tilted back rather than diamond.

 2.4 Bicycle structures