Always a step ahead of their rivals, Triumph followed up the trend-setting Speed Twin 500 of pre-war days by being first in the field with a 650cc parallel twin. Announced in September 1949 and displayed at the Earls Court Show in October, the Thunderbird was Triumph's response to demands for more power emanating from American racers and British sidecarists alike. The model remained in production in fundamentally its original form, though with progressively updated cycle parts, until the arrival of the unit-construction 650 range in 1962.

This matching-numbers Thunderbird is offered together with an aluminium-bodied single-seater sports 'chair' of unidentified make, complete with chassis and wheel. Accompanying documentation consists of an expired MoT (1978), old/current Swansea V5/V5C documents and the machine's original buff logbook listing the current vendor's father as '3rd Change'.