Abstract: A derailleur gear unit includes a ratchet wheel rotatably mounted around a pivot base and formed with a plurality of teeth. A retaining disk is fixedly mounted around the pivot base, and a shank extends from an outer periphery of the retaining disk and is formed with a catch. A first shifting lever includes a first end portion, a mediate portion rotatably mounted around the pivot base, and a second end portion. A pawl member is pivotally mounted on the first end portion of the first shifting lever and includes an arcuate guiding track slidably abutting on the catch, and a detent meshing with one of the teeth of the ratchet wheel. A second shifting lever includes a first end portion pivotally mounted around the pivot base and a second end portion. A pushing rod located radially opposite to the detent of the pawl member is mounted on the first end portion of the second shifting lever and meshes with one of the teeth of the ratchet wheel.

Abstract: A sprocket assembly includes a larger diameter sprocket having a plurality of teeth formed on an outer periphery thereof, and a smaller diameter sprocket having a plurality of teeth formed on an outer periphery thereof. A driving chain meshes with the plurality of teeth of the smaller diameter sprocket and is able to shift from a first center of a space defined between the teeth of one pair of adjacent teeth located at the smaller diameter sprocket to a second center of a space defined between the teeth of one pair of adjacent teeth located at the larger diameter sprocket. A distance between the first and second centers is made not equal to an integer multiple of the pitch of the driving chain such that the driving chain is bent between the first and second centers and is deflected from a moving direction thereof which is along a tangent line drawn from the first center of the smaller diameter sprocket, and such that the driving chain has a deflection point relative to the first and second centers.