Effect of the use of a noncircular chainring on the power delivered by recreational cyclists

There is no agreement on the effect that noncircular chainrings have on cyclists when compared with circular ones. In this research, the effect of the use of noncircular chainrings by recreational cyclists is assessed in terms of power delivery indicators. Two complementary approaches based on experimental tests and numerical models are used to study the differences between the results obtained by using circular and noncircular chainrings. The first approach intends to estimate the changes in the transmission system in terms of mechanical advantage when using different chainrings. The model considers that the point of tangency between the chain and the noncircular chainring varies during the rotation. The second approach aims at comparing the power delivery capacity when using different chainrings. A series of constant power tests until exhaustion is performed with each chainring to obtain the power-time relation at different exertion rates. As a result of this work, a refined model for obtaining the mechanical advantage of the transmission of the bicycle was proposed and validated. Additionally, the effects of the change of the chainring on the cyclists were assessed on a pilot test with two recreational cyclists, registering a change in the behavior of the power delivery capacity during intensive efforts for short periods of time.