Motorcycles are two-wheeled motor vehicles steered by a handlebar from a saddle-style seat. They use an internal combustion engine for propulsion and most have a clutch and throttle that must be manually operated by the rider, though some newer models have automatic transmissions. The engine drives a shaft connected to the rear wheel through a series of sprockets, with the drive usually augmented by a belt or chain on smaller bikes. Motorcycles may be powered by single- or multiple-cylinder engines of various displacements. The most common are inline fours with a crankshaft positioned in the front of the machine and driven by an overhead cam. The cylinder heads are often shaped to provide for leaning the machine at low speeds, which improves handling and allows the rider to control the vehicle by turning the steering wheel.
Riders must be alert to the presence of other vehicles and pedestrians, and to the road layout and surface conditions. They must wear protective clothing, including gloves and a helmet. They must also be free of alcohol and drugs, which impair judgment, coordination, balance, throttle control, and the ability to shift gears.
When motorcycling was first introduced, its creators could not have imagined how popular the sport would become or the close-knit brotherhood and sisterhood that the lifestyle cultivates. But they did know that riding a motorcycle gives a sense of freedom and adventure that other modes of transport simply cannot match.