This screen shows the application of simple beam theory to a 60cm length of tube - a representative length of tube in a 60cm bicycle frame. This calculation simulates a load being placed on one end of the tube while the other is held (a cantilever). The load can be varied by using the slider. What is a typical load experienced in service by a frame? For a fit rider probably 3-4 times their weight, up to 2500 Newtons for a 70 Kg rider.

Although the stresses in a real bicycle frame are much more complex than this, this simple analysis allows a basic design to be made, which could then be augmented by a more detailed Finite Element Analysis or building and testing protoypes.

As the load increases, so does the deflection (how much the beam bends). The beam's upper surface is put in tension as it is loaded, and when the stress exceeds the material's tensile strength, it will break (The Maximum Fibre Stress readout will turn red at this point). However once the Yield stress of the material is exceeded then there will be permanent deformation i.e. the tube will be bent. Therefore a substantial safety margin should be built in to the design. Maybe a factor of 2 or 3, which means that loads of 1000N should be seen as a working maximum.

The Selector bar at the top of the page allows you to pick different materials - try changing the material your tube is made of, and see how it affects how the bar responds to bending, or jump to the Tube Designer.

This means that bicycle frames made of different materials will have different stiffness. The Rinard frame deflection test gives test data for various different frame materials. The deflections quoted here are for a full frame not just a single tube and will be correspondingly smaller.