49 cc), followed by the "Autocycle" with a purpose-built frame incorporating pedals and a two-stroke engine (often a 98 cc Villiers engine), but without a gearbox (e.g. the Malvern Star). Autocycle manufacturers were well established in countries such as Britain and Australia before World War II.

In 1939, the American bolt-on Whizzer gas-engined bicycle kit was introduced, utilizing a 138 cc side-valve