Motorcycles are motorized vehicles that carry one or two riders. They are different from cars in that they only have 2 wheels and are designed to travel with fewer than four wheels in contact with the road (this excludes three-wheeled vehicles such as the hack and motortrike).
Like bicycles, motorcycles have a center of gravity located over their engine. This results in a lateral acceleration and centrifugal force that makes the vehicle lean into turns, but also requires the rider to keep a balance of lean and weight.
In a typical design, the gasoline engine converts reciprocating motion into rotary motion, and this is transmitted to the rear-wheel sprocket by a drive system. The front-wheel sprocket is driven by the crankshaft of the engine, while the rear-wheel sprocket is usually driven by a chain or belt. The rider controls the engine speed and clutch using twist-type levers located near the handgrips, while the brakes are controlled by foot pedals or a combination of front-wheel and rear-wheel pedals.
Most modern motorcycles have an analog dashboard with a simple readout or a digital display showing information such as fuel, speed and rpm. Some models also have a trip computer to track distances, fuel consumption and other information. A tachometer is an optional feature that tells the rider how fast the motorcycle is going. The majority of motorcycles are single-rider machines, but a passenger seat is available on some models. A variety of aftermarket seats are also available for most motorcycles.