Monkey bike is a motorcycle term used to refer specifically to a line of small, low-powered motorcycles by that name manufactured by Honda, but can also refer in general to similar motorcycles made by other companies. The term monkey bike is more commonly used in the United Kingdom than in North America, where similar type motorcycles are often called minibikes. Commonly, a monkey bike is defined as a motorcycle with a single-cylinder, four-stroke engine that can vary in size between 50cc and 90cc, and that has a seat height of less than 22 inches (55 cm). This type of motorcycle is named for the crouching, supposedly monkey-like, position the rider has to assume when sitting on such a small motorcycle. Honda's first monkey bike, the Z100, was launched in 1961, but other small, compact motorcycles had preceded it, for example the welbike used by the British Armed Forces in the Second World War.
The immediate origin of Honda's line of monkey bikes was a miniature motorcycle developed for use in a Japanese amusement park. The popularity of this ride spurred the company to make road-worthy miniature motorcycles. The first monkey bikes made by Honda in the 1960s, such as the CZ100 and Z50M, had no suspension, 5 inch (12.7 cm) wheels, and many could be folded and fitted into the trunk of a car for transport. Later Honda monkey bike models, such as the Z50A from 1969 and the Z50J from 1974, featured suspension and 8 inch (20.3 cm) wheels. Additional features on later Honda monkey bikes also included separately folding handlebars, larger fuel tanks, and front and rear racks.
Since the 1970s, Honda has released several types of monkey bikes for the Japanese market, such as the Honda Gorilla, Honda Monkey, and Honda Ape. Other companies, like Kawasaki, Zhen Hua and Jinchang, also manufacture motorcycle models similar to Honda's monkey bikes. Many of these motorcycles are produced for the local Japanese or Chinese market, and have to be specially imported in the rest of the world.
Some monkey bikes are made to drive on regular roads, while others are specifically designed for track racing, or off-road use. Many monkey bike riders and enthusiasts customize their motorcycles, tuning and styling their monkey bike to make the engine more powerful, or to add new features such as front or rear suspension, or a different exhaust system. Monkey bike organizations and clubs often organize special runs and races to showcase these miniature motorcycles.