The Bonneville T120 was Edward Turner\’s last production design at Triumph (in retirement Turner designed the Triumph Bandit/BSA Fury which did not pass the prototype stage before BSA went under).
The new motorcycle was conceived and developed so quickly that it was not included in the 1959 Triumph catalogue. With a 649 cc (39.6 in3) parallel-twin (two-cylinder) engine the T120 was based on the Triumph Tiger T110 and was fitted with the Tiger\’s optional twin 1 3/16 in Amal monobloc carburettors as standard, along with that model\’s high-performance inlet camshaft. Launched in 1959 by Triumph as \The Best Motorcycle in the World\, the Bonneville T120 was aimed mainly at the lucrative US market where enthusiasts were demanding extra performance.
Initially produced with a pre-unit construction engine which enabled the bike to achieve 115 mph (185 km/h) without further modification, the power tended to induce high speed wobbles from the single downtube frame, so in 1963 a stiffer and more compact unit construction model was introduced, with additional bracing at the steering head and swinging arm. The steering angle was altered and improved forks were fitted a couple of years later, which, together with the increased stiffness enabled overall performance to match that of the Bonneville\’s rivals.
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