Abstract: An adjustable bottom bracket mechanism, comprising: a bottom bracket, an axial connection portion and a mounting portion. The bottom bracket includes at least one shaft through hole and is configured for connection of a seat tube. A lengthwise extension direction of the seat tube is defined as a first direction. The axial connection portion includes at least one axial through hole and axially corresponds to the at least one shaft through hole. The mounting portion is connected to the axial connection portion and adjustably fixedly connected to the bottom bracket in a first position or a second position. When the mounting portion is in either of the first and the second position, axes of the at least one shaft through hole and the at least one axial through hole are located on the first direction.

Abstract: An adjustable bottom bracket mechanism, comprising: a bottom bracket, an axial connection portion and a mounting portion. The bottom bracket includes at least one shaft through hole and is configured for connection of a seat tube. A lengthwise extension direction of the seat tube is defined as a first direction. The axial connection portion includes at least one axial through hole and axially corresponds to the at least one shaft through hole. The mounting portion is connected to the axial connection portion and adjustably fixedly connected to the bottom bracket in a first position or a second position. When the mounting portion is in either of the first and the second position, axes of the at least one shaft through hole and the at least one axial through hole are located on the first direction.

Abstract: A sprocket assembly of the present invention includes a first sprocket and a bigger second sprocket. The first sprocket has a small-diametered tooth having a beveled edge. The beveled edge is tapered from a first face to a second face along a transmission direction. The second sprocket has a big-diametered tooth, which is clockwise adjacent to the small-diametered tooth having the beveled edge, having a thinner section. The thinner section is stepped at an outer face of the second sprocket. A chain of a bicycle selectively surrounds the first sprocket or the second sprocket, and a travel path thereof shifts quickly and easily via the beveled edge and the thinner section.