A power-assist drive system for a vehicle (e.g., a bicycle) is provided. The system includes a drive unit assembly attached to a frame of a vehicle and a motor having an output shaft, and a drive gear rotatably associated with the output shaft. The system further includes a driven unit assembly including a driven gear configured to be attached to a wheel hub of the vehicle, and a brake disc coaxially attached to the driven gear. The drive gear may be configured to operably engage the driven gear to transmit power from the motor to the wheel hub. A brake caliper may be integrated with the drive unit assembly. The system may further include a battery and a speed controller configured to receive an input signal to selectively direct electrical power from the battery to the motor to drive the wheel via the drive gear and the driven gear.

A bicycle component includes a hub shell for a wheel of an at least partially muscle-powered bicycle, wherein the hub shell is rotatably supported by at least one bearing device. An adapter unit is disposed on one end of the hub shell. The adapter unit includes an inner stopper having an inner stop face for transferring a clamping force to the bearing device and an outer stopper with an outer stop face transmitting at least part of the clamping force. The adapter unit includes a first and a second stopper component transmitting the clamping force.

A bicycle component includes a hub shell for a wheel of an at least partially muscle-powered bicycle, wherein the hub shell is rotatably supported by at least one bearing device. An adapter unit is disposed on one end of the hub shell. The adapter unit includes an inner stopper having an inner stop face for transferring a clamping force to the bearing device and an outer stopper with an outer stop face transmitting at least part of the clamping force. The adapter unit includes a first and a second stopper component transmitting the clamping force.

A front fork, which suspends a front wheel is a compression type and includes a pressure tank at a lower end portion thereof. The front fork includes, at the lower end portion, a caliper bracket which supports a brake caliper which constitutes a disc brake and a sensor mounting portion on which a wheel speed sensor is mounted. The caliper bracket includes a pair of an upper caliper support portion and a lower caliper support portion. In a vehicle side view, the pressure tank is disposed between the upper caliper support portion and the lower caliper support portion, and the sensor mounting portion is disposed inferior to or superior to the pressure tank.

A front fork, which suspends a front wheel is a compression type and includes a pressure tank at a lower end portion thereof. The front fork includes, at the lower end portion, a caliper bracket which supports a brake caliper which constitutes a disc brake and a sensor mounting portion on which a wheel speed sensor is mounted. The caliper bracket includes a pair of an upper caliper support portion and a lower caliper support portion. In a vehicle side view, the pressure tank is disposed between the upper caliper support portion and the lower caliper support portion, and the sensor mounting portion is disposed inferior to or superior to the pressure tank.

An electrical component box disposed from above to below a main frame, and a fuel tank disposed in the upper part of the main frame and above the electrical component box, are arranged to the vehicle rear with respect to a head pipe comprising a motorcycle. In this case, the top of the electrical component box is open. In the gap between the electrical component box and the fuel tank, a gap cover is arranged to hide the gap from the outside.

An electrical component box disposed from above to below a main frame, and a fuel tank disposed in the upper part of the main frame and above the electrical component box, are arranged to the vehicle rear with respect to a head pipe comprising a motorcycle. In this case, the top of the electrical component box is open. In the gap between the electrical component box and the fuel tank, a gap cover is arranged to hide the gap from the outside.

A front fork capable of reducing an unsprung weight of the arm-shaped front fork, optimizing rigidity, and improving appearance is provided. A front swing arm includes a left and right arm portions, and a bridge portion integrally connecting the left and right arm portions, a first lightening hole, a second lightening hole and a third lightening hole are provided in the arm portion, the first lightening hole, the second lightening hole and the third lightening hole are covered with a reflector provided to be exposed to an outer side surface of the arm portion from outside.

A front fork capable of reducing an unsprung weight of the arm-shaped front fork, optimizing rigidity, and improving appearance is provided. A front swing arm includes a left and right arm portions, and a bridge portion integrally connecting the left and right arm portions, a first lightening hole, a second lightening hole and a third lightening hole are provided in the arm portion, the first lightening hole, the second lightening hole and the third lightening hole are covered with a reflector provided to be exposed to an outer side surface of the arm portion from outside.

A bicycle can include a forward frame triangle that can include a top tube, a bottom tube, a bottom bracket, a structural seat tube, a compliant seat tube, and a pair of seat stays. The top tube can have a first end connected to a head tube and a second end. The bottom tube can have a first end connected to the head tube. The bottom bracket can be connected to the bottom tube. The structural seat tube can be connected to the bottom bracket and the top tube. The compliant seat tube can extend in an upward direction from the bottom bracket to the top tube and within the structural seat tube. The compliant seat tube can be coupled to the forward frame triangle such that the compliant seat post can bend within the structural seat tube.