In other words, conventional roller chain drives suffer the potential for vibration, as the effective radius of action in a chain and sprocket combination constantly changes during revolution ("Chordal action"2.2.1 Chordal Action: You will find that the position in which the chain and the sprockets engage fluctuates, and the chain vibrates along with this fluctuation. ). If the chain moves at constant speed, then the shafts must accelerate and decelerate constantly. If one sprocket rotates at a constant speed, then the chain (and probably all other sprockets that it drives) must accelerate and decelerate constantly. This is usually not an issue with many drive systems; however, most motorcycles are fitted with a rubber bushed rear wheel hub to virtually eliminate this vibration issue. Toothed belt drives are designed to limit this issue by operating at a constant pitch radiusBut in toothed-belt systems, chordal action occurs by circle and chord, the same as chains. Generally this effect is less than 0.6 percent, but when combined with the deflection of the pulley center and errors of belt pitch or pulley pitch, it can amount to 2 to 3 percent. ).
