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.[7] 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.[4]
Early post-war steel shortages meant that most of the body was built from aluminium over an ash frame, using rubber press tools that had been used making panels[7] for the largely wooden bodied Mosquito bomber that had been built by Standard during the war. Only the front wings were made of steel.[citation needed] The frame was hand welded up from steel tube.[4] The engine was a version of Standard's 1.5-litre, four-cylinder side-valve design that had been converted to overhead valves by Harry Weslake and built by Standard exclusively for SS-Jaguar before World War II.[8] The Triumph version featured a downdraught Solex carburettor instead of the Jaguar's side-draught SU, and a 6.7:1 compression ratio instead of 7.6:1.[4] A four-speed gearbox[4] with synchromesh on the top three ratios was used.[9]
The tubular steel chassis was a short-wheelbase version of the 1800 saloon, featuring transverse leaf sprung independent suspension at the front and a live axle with semi-elliptic springs at the rear.[4] The rear track was wider than the front by some 4 inches. Brakes were hydraulic.
The body design was anachronistic. A journalist old enough to remember the pre-war Dolomite Roadster that had inspired the car felt that the elegant proportions of the earlier model had been abandoned in favour of a committee-based compromise, "a plump Christmas turkey to set against that dainty peacock ... [more] Toadster [than Roadster]".[3] The front had large separate headlamps and the radiator was well back from the front between large "coal scuttle" wings. Passenger accommodation was on a bench seat that was claimed to seat three: the car's 64 inch width helped make a reality of the three-abreast seating, and the approach meant a column gear change was required. The car's unusual width also made it necessary to fit three screen wipers in a row, an example followed by early shallow windscreen Jaguar E Types.[3] Additional room for two was provided at the rear in a dickey seat with its own folding windscreen: this was outside the hood that could be erected to cover the front seat.[7] Entry and exit to the dickey seat was never easy and a step was provided on the rear bumper.[10] The Roadster was the last production car with a dickey seat.[1][7][10]
On test by Autocar magazine in 1947 top speed was found to be 75 mph (121 km/h) and 0–60 mph (0–96 km/h) took 34.4 seconds. Evidently keen to be positive without misleading their readers, the magazine described the maximum speed as "satisfying but not startlingly high".[3]
