Calibrated continuous‑beam modelling of a motorcycle handlebar, to analyze bar‑end weight influence on vibrations and guide design improvements

This thesis presents the development and experimental calibration of a continuous beam model of a motorcycle half handlebar, aimed at analysing how bar end weight characteristics influence system vibrations and at guiding design improvements. The work is motivated by fatigue failures of the command block electronics and rider discomfort at the handgrip, both induced by engine excitation dominated by the first and second orders at the rev limiter (185 Hz and 370 Hz). An experimental modal analysis on eight configurations – from the bare half handlebar to the fully equipped OEM layout – first clarified how the system modes evolve with the counterweight type and with the presence of additional components such as the clutch pump and handgrip. Afterwards, the handlebar and counterweight stem were described analytically through a continuous beam formulation and implemented in a parametric MATLAB simulator. The model was calibrated against additional, ad hoc tested configurations by tuning the base torsional stiffness, component rotational inertias, stem stiffness and modal damping ratios, achieving frequency errors below 5 % and MAC values above 0.90 for the first two modes. Three modal criticality indices – proximity to the engine order forcing peaks, ISO 5349 filtered handgrip vibration, and command block vibration – were defined to objectively compare different counterweight designs. Applied to four candidate solutions, the indices identified a prototype that retains the OEM stem while reducing the counterweight mass by nearly 50 % (55 g instead of about 100 g). This configuration lowers the worst case command block vibration by approximately 40 % with respect to the current OEM solution, without compromising handgrip comfort. The calibrated continuous beam model and the criticality indices together provide a predictive, transferable methodology that supports the early design of handlebar counterweights, reducing the need for extensive experimental prototyping.