Layout: Two cylinders next to one another, connected to a common crankshaft. Benefits: Narrow layout, strong torque, good economy.
The parallel twin was to form the backbone of the British motorcycle industry for the best part of 40 years. There are many stories to its creation, but a popular history is related to Ariel’s chief engineer Val Page, who experimented with two cylinders from the firm’s square-four motor.
He saw the potential in the configuration and, switching jobs to work for Triumph, went on to produce the ‘6/1’ 650cc twin in the early 1930s for use in powering sidecars. Triumph’s Edward Turner took up where Val left off and was accountable for the Speed Twin in 1937, which proved such an impressive configuration that everyone from BSA to Norton adopted the engine-type.
The Japanese also saw the potential in the twin design and famously put it to the British in the 60s with Honda releasing the 450cc twin Black Bomber in ’64, while Yamaha overwhelmed the twin market in 1968 when it released the XS650. Nowadays, twins are favoured for their mild nature and good economy.