Noncircular chainrings have drawn the attention of the cycling community because they are designed to improve the pedaling cycle and obtain better performance. Nevertheless, there is no general agreement on their effect; for this reason, they are still under development, and further efforts to understand and improve this component are required.
In this work, a noncircular chainring with custom geometry was designed, manufactured, and tested. A numerical model was developed to study the effect of the chainring geometry on the mechanical advantage of the bicycle transmission system. A chainring with a custom geometry was designed to be manufactured. The manufactured chainring was installed on a road bicycle, and its mechanical advantage was measured through motion capture.
A custom noncircular chainring providing the target mechanical advantage profile was obtained. CNC machining was used for manufacturing the 1:1 scale functional prototype. The prototype was constructed in Aluminum 7075T6. The prototype was based on an elliptical geometry with 52 teeth. The ellipse used for the prototype had a minor axis of 97.60 mm and a major axis of 118.77 mm. The results of the experimental characterization of the chainring prototype showed a variation in the mechanical advantage obtained along a pedaling cycle within 0.194 and 0.233.