On the structural vibrations of bicycles: influence of materials and construction technology on the modal properties

Structural vibrations of bicycles and bicycle components have drawn the interest of research-ers and designers since many years, mainly because they have a large influence on rider com-fort. For the improvement of comfort in-plane vibrations (with displacements in the sym-metry plane of the bicycle) are the most important and sometimes in plane modes have been studied. In recent years also the out-of-plane structural modes of vibration have been considered, because the cyclists’ experience and recent researches show that they may interfere with the typical modes of vibration of the vehicle in motion (capsize, weave and wobble) that determine stability and safety. In this paper the modal analysis approach is used for identifying the out-of-plane modes of some bicycles with similar geometric properties: a utility bicycle with steel frame, a sport bicycle with Ergal frame and two sport bicycles in carbon. The tests are carried out with hammer excitation. The results show that in the range 10-125 Hz all the tested bicycles have some typical modes (e.g.: torsion mode, frame bending). The dependence of the natural frequencies and modal dampings of the typical modes on the material and construction technology is analyzed and discussed. The new modes that sometimes appear when the structural properties of frame and fork are modified are presented and analyzed. Finally, the possible influence of the identified structural modes on bicycle stability is discussed.