A drive assembly for a two-wheeled vehicle, wherein a closed chain is guided around a drive pinion and a sprocket for output. The chain is formed by pins, on each a bush rotatable about the center longitudinal axis of the pin, a roller provided on each bushing, for rotation around the bushing and has play, and the pins being connected to each other at two opposite ends by means of plates. The outer surface of the bushings and the rollers is coated with pure ta-C, having no further chemical elements except for unavoidable trace elements resulting from production in a PVD method. An R.sub.a roughness between 0.03 μm and 0.2 μm and/or an R.sub.z roughness between 0.3 μm and 2 μm is adhered to the surface of the coatings. The surfaces of the pinion and the sprocket in contact with the rollers do not have a coating of diamond-like carbon.

A drive assembly for a two-wheeled vehicle, wherein a closed chain is guided around a drive pinion and a sprocket for output. The chain is formed by pins, on each a bush rotatable about the center longitudinal axis of the pin, a roller provided on each bushing, for rotation around the bushing and has play, and the pins being connected to each other at two opposite ends by means of plates. The outer surface of the bushings and the rollers is coated with pure ta-C, having no further chemical elements except for unavoidable trace elements resulting from production in a PVD method. An R.sub.a roughness between 0.03 μm and 0.2 μm and/or an R.sub.z roughness between 0.3 μm and 2 μm is adhered to the surface of the coatings. The surfaces of the pinion and the sprocket in contact with the rollers do not have a coating of diamond-like carbon.

A system and method for simple transmission of a multi-speed bicycle is provided. A bicycle can have a transmission that can be toggled by a kickback shifting mechanism. A rear wheel hub can support a freewheel having a high speed gear sprocket and a low speed gear sprocket with dedicated chains to create dedicated gear-shifting. Rotating the pedal shaft in the non-drive direction approximately one-quarter rotation can toggle the transmission between the first gear ratio and the second gear ratio with a shifting surface that alternately allows driving engagement of the high speed gear sprocket with the rear wheel driver.

A system and method for simple transmission of a multi-speed bicycle is provided. A bicycle can have a transmission that can be toggled by a kickback shifting mechanism. A rear wheel hub can support a freewheel having a high speed gear sprocket and a low speed gear sprocket with dedicated chains to create dedicated gear-shifting. Rotating the pedal shaft in the non-drive direction approximately one-quarter rotation can toggle the transmission between the first gear ratio and the second gear ratio with a shifting surface that alternately allows driving engagement of the high speed gear sprocket with the rear wheel driver.

The present invention relates to an auxiliary drive arrangement for a pedal-powered vehicle having a drivetrain comprising a pedal- driven sprocket and chain (15B) for connecting pedals (34) to a driven wheel. The auxiliary drive arrangement comprises: an electric motor (6) arranged to be mounted to the vehicle; a power source (14) for the electric motor; and a sprocket member (24) comprising first and second sprockets (24A, 24B). The sprocket member is configured to be selectively attachable via an attachment formation to the drive train of the vehicle. The sprocket member is configured to be mounted on an existing pedal sprocket and operatively connected to the electric motor to provide a drive path from the electric motor to the pedal-driven sprocket via the sprocket member.

A sprocket having a gear tooth valley radius which varies around the sprocket perimeter provides additional gear torque multiplication to a rider, which is especially beneficial when climbing hills. In some embodiments, the sprocket is a bicycle chainring with reduced gear tooth valley radius over at least a portion of the chainring. In other embodiments, the sprocket is a bicycle rear wheel cassette cog with increased gear tooth valley radius over at least a portion of the cassette cog. Regions of both reduced and increased gear tooth valley radius may be present on a given sprocket. The sprocket valley floor surface may be rounded or may include N segments adjoined by N vertices. The segments of the valley floor surface may be curved or straight. The vertices of the valley floor surface may be curved or angled. Embodiments for bicycles and motorcycles are presented.

A crank assembly comprises a crank arm, a front sprocket unit, and at least one chain-drop control protrusion. The at least one chain-drop control protrusion is configured to inhibit a drive chain from getting into a space provided radially inwardly from the at least one control protrusion and between the crank arm and the front sprocket unit in the axial direction. The at least one chain-drop control protrusion is configured to be provided to at least one of an axially inwardly facing crank-surface of the crank arm and an axially outwardly facing sprocket-surface of the front sprocket unit. The at least one chain-drop control protrusion has a through bore.

A bicycle chain ring having a plurality of teeth extending radially about an axis of the chain ring, the plurality of teeth including a first group of teeth and a second group of teeth. The first group of teeth has a first width at a tooth base that is sized to be received within a chain cavity defined between parallel links of a bicycle chain. The second group of teeth has a second width at the tooth base, the second width being different from the first width. Further, the first group of teeth have a tooth tip that is substantially centered on a plane defined between an inner surface and an outer surface of the chain ring and the second group of teeth is at least partially offset from the plane.

A bicycle chain ring having a plurality of teeth extending radially about an axis of the chain ring, the plurality of teeth including a first group of teeth and a second group of teeth. The first group of teeth has a first width at a tooth base that is sized to be received within a chain cavity defined between parallel links of a bicycle chain. The second group of teeth has a second width at the tooth base, the second width being different from the first width. Further, the first group of teeth have a tooth tip that is substantially centered on a plane defined between an inner surface and an outer surface of the chain ring and the second group of teeth is at least partially offset from the plane.

A drive device (1) for a bicycle (100), includes a sensor for detecting a crank angle and a rotational speed of the pedal crankshaft and generating appropriate sensor data, a sensor for detecting a rotational speed of the driven shaft and generating appropriate sensor data, a sensor for detecting a rotational speed of the rotor shaft and generating appropriate sensor data, and a control device (10), which is configured to process the sensor data and control, by way of an open-loop system, a downshift from a currently engaged gear into a next-smaller gear as a function of the sensor data by energizing the electric machine (7).