The 1800 Roadster, model number 18TR, was designed in the closing days of World War II. Triumph had been bought by the Standard Motor Company in 1944, and the managing director of Standard, Sir John Black, wanted a sports car to take on Jaguar, who had used Standard engines in the pre-war period. Frank Callaby was selected to style the new car. After getting Black's approval for the general shape, Callaby worked with Arthur Ballard to design the details of the body. Design of the rolling chassis was by Ray Turner. Walter Belgrove, who had styled the pre-war Triumphs and was employed as Chief Body Engineer, had no part in the design.
The only significant update in the Roadster's production came in September 1948 for the 1949 models, when the 2088 Vanguard engine, transmission, and rear axle were fitted. A retrograde step was the fitting of a three-speed gearbox even though it now had synchromesh on bottom gear. Apart from minor modifications to the mounting points, the chassis, suspension and steering were unaltered. This later version of the Roadster was given the model designation TRA.
On test the changes resulted in the top speed increasing marginally to 77 mph (124 km/h) but the 0-60 mph time was much better at 27.9 seconds. The car was never made in large numbers and was mainly hand built. 2501 examples of the 1800 and 2000 of the larger-engined version were made. Production ended in October 1949.