Abstract
Bicycle transmission systems represent a key component in the design of bicycles, as they determine the nature of pedaling effort that riders have to provide. Multi-gear systems enable riders to choose between multiple transmission ratios and are typically divided into external and internal. The present work aims at designing a three-speed automatic internal shifting hub for regular (non-electric) bicycles, starting from an already existing alternative with only two gear ratios (i.e., speeds), which is taken as reference. The complete kinematic design and a preliminary dimensioning are implemented and described in detail. The novelty of the design lays in the number of available gear rations (three), which is an unprecedented result for automatic internal shifting hubs for regular bicycles, as it is unmatched by the models available on the market. The higher number of gear rations increases the number of available combinations of torque and pedaling cadence to achieve a certain velocity, granting more riding flexibility and ultimately enabling easier rides. This is proven through validation by numerical simulation of a driving cycle, which shows that lower and more constant pedaling forces are required when using the novel three-speed automatic internal shifting hub with respect to the two-speed reference model.