The Bicycle Frame
The bicycle frame is the main load bearing structure of the bicycle and in order to select materials for its construction or to make an efficient frame design the loads carried by the various components must be evaluated under realistic conditions.

The diagram shows the frame geometry of a conventional bicycle. It is important to determine which components are in tension, which in compression, which experience bending forces, and what the magnitude of the forces and moments on the components are under normal use conditions. This is done by considering the structure as made of tubes with pin-joints rather than welds. The pin joint does not allow a moment transfer from one tube to another and so they are all either in tension or compression. When the system is in static equilibrium under the applied forces, each element must experience zero net force and zero net moment.

From: McMahon & Graham,
"The Bicycle & the Walkman," Merion (1992)