Quantification of structural loading during off-road cycling

To provide data for fatigue life prediction and testing of structural compo nents in off-road bicycles, the objective of the research described herein was to quantify the loads input to an off-road bicycle as a result of surfa ce-induced lends. A fully instrumented test bicycle was equipped with dynam ometers at the pedals, handlebars, and hubs to measure all in-plane structu ral loads acting through points of contact between the bicycle and both the rider and the ground. A portable data acquisition system carried by the st anding rider allowed, for the first lime, this loading information to be co llected during extended off-road testing. In all, seven experienced riders rode a downhill trail test section with the test bicycle in both front-susp ension and full-suspension configurations. The load histories were used qua ntitatively to describe the load components through the computation of mean s, standard deviations, amplitude probability density functions, and power spectral density functions. For the standing position, the coefficients of variation for the load components normal to the ground were greater than 1. 2 for handlebar forces and 0.3 and 0.5-0.6 for the pedal and hub forces, re spectively. Thus, the relative contribution of the dynamic loading was much greater than the static loading at the handlebars but less so at the pedal s and hubs. As indicated bg the rainflow count, high amplitude loading was developed approaching 3 and 5 limes the weight of the test subjects at the front and rear wheels, respectively. The power spectral densities showed th at energy was concentrated in the band 0-50 Hz. Through stress computations and knowledge of material properties. the data can be used analytically to predict the fatigue life of important structural components such as those for steering. The data can also be used to develop a fatigue testing protoc ol for verifying analytical predictions of fatigue life.