The first choppers were built in America, and were an outgrowth of the milder customization trend that had originated after WW2 when returning soldiers and others began modifying cars and motorcycles, frequently to improve performance in top-speed races on dry lake beds in Southern California and similar desolate spaces such as unused airstrips in other parts of the country, or on the street for street racing. These early modified motorcycles were known as “bobbers”, and there are many common features between bobbers and choppers, with choppers differentiated by more radical modifications, especially frame tube and geometry modifications (“chopped” by welding) intended to make the bike longer.
The earliest choppers tended to be based on Harley-Davidson motorcycles, at first making use of the Flathead, Knucklehead and Panhead engines—many of which could be found in surplus military and police motorcycles bought cheaply at auction. As new engines became available they were soon utilized in choppers. British bikes, particularly Triumphs, were also a popular motor for choppers early on. As the Japanese manufacturers began offering larger engines in the late 1960s these motors were also quickly put to use by chopper builders. The Honda 750-4 was the most widely used Japanese motor for early chopper builders. Choppers have been created using almost every available engine, but builders have always shown a preference for older air cooled designs. It is rare to see a chopper with a radiator.
