A cush drive is part of the drive train of many powered two-wheeled vehicles, such as motorcycles or scooters. Short for cushion drive, the cush drive uses springs, rubber gear teeth or a combination of the two to absorb the shocks or jerks that occur when changing gears or accelerating suddenly. When one of these conditions occur, the flexible parts of the drive absorb some of the shock, cushioning the impact between the teeth of the gears in the drive train and allowing for a smoother acceleration.
The cush drive is typically located between the drive train, which generates and applies mechanical power, and the drive wheel, which applies the power to the road, moving the vehicle. Standard designs of cush drives either include an assembly of two matching sprockets with springs, rubber pads or both between them. When a change in speed occurs at the first sprocket, the springs or rubber pads are met by the teeth of the first sprocket and absorb some of the force before transferring it to the second sprocket, thus cushioning the blow that would have otherwise occurred.
Another design of cush drive uses two metal plates lying one on top of the other that are connected together by a series of springs. When the drive train accelerates, one of the plates suddenly rotates faster. The initial shock is absorbed by the springs and then transferred to the second plate, which transfers the additional power to the drive wheel. As the two plates reach equal speeds, the force is reduced and the springs expand again ready to react to another shift in gears or sudden acceleration.
The actions of cush drives do more than simply make for a smother ride. They reduce the force of the impact between gears or the drive train, reducing wear. They also provide cushioning between the sections of the drive train that, under severe conditions, could literally snap the teeth off of gears or throw a drive shaft or chain, which can not only cause mechanical damage, but also could injure the rider.
Cush drives themselves are necessarily made of flexible components, such as rubber blocks and springs, which tend to wear more rapidly than other drive train components. In the case of rubber blocks, they will harden over time losing the ability to absorb shock. Springs will lose flexibility and then snap, putting additional stress on other springs and causing them to snap until none remain. As a result, cush drives are the parts of drive trains most subject to wear and requiring repair; the additional life they give to the vehicle in general, as well as the added safety, make them well worth the trouble, however.