The invention discloses an automatic downshifting and variable speed transmission bicycle, comprising a bicycle stand, wherein the bicycle stand is installed with a bottom bracket; the bottom bracket is installed with a bottom bracket sprocket set, and the bottom bracket sprocket set is composed of three chain discs of different sizes; a rear axle of the bicycle is provided with a tower footing, and the tower footing is fixedly installed with a sun gear; one side of the sun gear is provided with a planet carrier, and the planet carrier is installed with planetary twin gears. The invention is easy to start, can run at high speed, has multiple functions, and is reliable in operation, with convenient maintenance and low cost, and is energy saving and environmental-friendly; it has a good market prospect and brings great convenience to cyclists.

A bicycle rear-wheel sprocket pairing for engaging in a meshing, force-transmitting and form-fitting manner with a bicycle roller chain, wherein the rear-wheel sprocket pairing is rotatable about a sprocket axis. The sprocket axis defines an axial direction running along the sprocket axis, a radial direction running so as to be orthogonal to the sprocket axis, and a circumferential direction encircling the sprocket axis. The rear-wheel sprocket pairing comprises a larger sprocket and a smaller sprocket which for rotating conjointly with the larger sprocket in a slip-free manner about the sprocket axis is connected to the larger sprocket so as to be coaxial with and axially directly adjacent to the latter. The larger sprocket has an even tooth count of equal to or less than twenty-two teeth, and the difference in the tooth count between the larger and the smaller sprocket is exactly two teeth.

A bicycle rear-wheel sprocket pairing for engaging in a meshing, force-transmitting and form-fitting manner with a bicycle roller chain, wherein the rear-wheel sprocket pairing is rotatable about a sprocket axis. The sprocket axis defines an axial direction running along the sprocket axis, a radial direction running so as to be orthogonal to the sprocket axis, and a circumferential direction encircling the sprocket axis. The rear-wheel sprocket pairing comprises a larger sprocket and a smaller sprocket which for rotating conjointly with the larger sprocket in a slip-free manner about the sprocket axis is connected to the larger sprocket so as to be coaxial with and axially directly adjacent to the latter. The larger sprocket has an even tooth count of equal to or less than twenty-two teeth, and the difference in the tooth count between the larger and the smaller sprocket is exactly two teeth.

A bicycle sprocket comprises a sprocket body, a plurality of sprocket teeth, and a torque transmitting profile. The sprocket body has an outer periphery and an inner periphery positioned radially inwardly from the outer periphery with respect to a rotational center axis of the bicycle sprocket. The plurality of sprocket teeth is disposed on the outer periphery of the sprocket body. The torque transmitting profile is positioned around the inner periphery of the sprocket body. The torque transmitting profile includes at least ten internal spline teeth. The at least ten internal spline-teeth include at least one first internal spline-tooth, at least one second internal spline-tooth and at least one third internal spline-tooth. The at least one internal first spline-tooth, the at least one second internal spline-tooth and the at least one third internal spline-tooth are different in shape from each other.

A bicycle sprocket comprises a sprocket body, a plurality of sprocket teeth, and a torque transmitting profile. The sprocket body has an outer periphery and an inner periphery positioned radially inwardly from the outer periphery with respect to a rotational center axis of the bicycle sprocket. The plurality of sprocket teeth is disposed on the outer periphery of the sprocket body. The torque transmitting profile is positioned around the inner periphery of the sprocket body. The torque transmitting profile includes at least ten internal spline teeth. The at least ten internal spline-teeth include at least one first internal spline-tooth, at least one second internal spline-tooth and at least one third internal spline-tooth. The at least one internal first spline-tooth, the at least one second internal spline-tooth and the at least one third internal spline-tooth are different in shape from each other.

A bicycle drive includes a multi-sprocket arrangement for rotatable mounting on a rear-wheel axle an engagement with a bicycle chain having inner link plate pairs and chain outer link plate pairs. The multi-sprocket arrangement includes a sprocket having, between an axial inner side and an oppositely situated axial outer side, a flat sprocket body and a plurality of teeth formed on a circumference of the sprocket. The plurality of teeth include at least one tooth of a first tooth group, the axial width of which is dimensioned to be greater than a chain inner link plate spacing and smaller than a chain outer link plate spacing, and a second tooth group, the axial width of which are dimensioned to be smaller than the chain inner link plate spacing.

A bicycle drive includes a multi-sprocket arrangement for rotatable mounting on a rear-wheel axle an engagement with a bicycle chain having inner link plate pairs and chain outer link plate pairs. The multi-sprocket arrangement includes a sprocket having, between an axial inner side and an oppositely situated axial outer side, a flat sprocket body and a plurality of teeth formed on a circumference of the sprocket. The plurality of teeth include at least one tooth of a first tooth group, the axial width of which is dimensioned to be greater than a chain inner link plate spacing and smaller than a chain outer link plate spacing, and a second tooth group, the axial width of which are dimensioned to be smaller than the chain inner link plate spacing.

A drive chain system comprising a chain with an alternating succession of inner chain links and outer chain links, each inner chain link having a pair of inner link plates contacting the lateral faces of two rollers and each outer chain link having a pair of two outer link plates contacting the inner link plates of adjacent inner chain links. A pin connects two outer link plates and two inner link plates and a roller, wherein the inner surfaces of a pair of opposite outer link plates comprise protrusions in the area between the adjacent inner link plates. The system comprises a chainring with a plurality of teeth, which teeth taper laterally towards their respective tip.

A drive chain system comprising a chain with an alternating succession of inner chain links and outer chain links, each inner chain link having a pair of inner link plates contacting the lateral faces of two rollers and each outer chain link having a pair of two outer link plates contacting the inner link plates of adjacent inner chain links. A pin connects two outer link plates and two inner link plates and a roller, wherein the inner surfaces of a pair of opposite outer link plates comprise protrusions in the area between the adjacent inner link plates. The system comprises a chainring with a plurality of teeth, which teeth taper laterally towards their respective tip.

A bicycle rear sprocket assembly comprises at least one sprocket having a total tooth number that is equal to or larger than 15. The at least one sprocket includes at least ten internal spline teeth configured to engage with a bicycle hub assembly.