Triumph T120 Bonneville
Handling was less of a Bonneville strong point than engine performance, but a 1961-model TI20R was well suited to rapid cornering.
Few Triumph enthusiasts agree on which Bonneville model is best or most attractive, but this 1961 model would get plenty of votes.
The Bonneville remains Triumph’s most famous model of all, and for very good reason. Launched in 1959 as a hotted-up, twin-carb version of the Meriden firm’s existing 650cc vertical twin, the T120 Bonneville was advertised as offering 'the highest performance available today from a standard production motorcycle’ - and the Bonnie lived up to its billing.
For much of the following decade the T120 was as fast as any production bike on the road, and it was a long-lasting hit for Triumph. Bonneville- based bikes were also raced successfully all around the world, from the Isle of Man TT to American dirt tracks. The Bonnie was repeatedly updated, enlarged to 750cc, and survived into the 1980s. No wonder John Bloor’s reborn Triumph concern chose the famous name for its new generation parallel twin, launched in 2001.
Back in 1959, the name Bonneville was evocative of speed and excitement for a different reason. Triumph’s legendary boss Edward Turner chose it in honour of the record-breaking run by Johnny Allen, who in 1956 had taken a streamlined, Triumph twin-engined machine to 214mph (344km/h) at the Bonneville salt flats in Utah,USA. The American market was Triumph’s biggest, and the name fitted the new bike perfectly.
The original T120 was relatively simple for Triumph to develop. Its format of 649cc parallel twin, with pushrod valve operation, four-speed gearbox and 360-degree crankshaft was that of the Tiger 110. In 1958 the Tiger had been available with an optional cylinder head with splayed inlet ports, for fitment of twin carburettors, plus a list of optional tuning parts including high-performance camshafts and Amal racing carbs. Following demand from its US distributors for a high-performance model. Triumph incorporated hot cams and twin, filterless Amal Monobloc carbs in the new T120, increasing peak output by 4bhp to 46bhp. Initially the Bonneville, which was conceived in such a hurry that it wasn't even included in the firm’s 1959 catalogue, retained the Tiger’s headlamp nacelle and touring handlebars. For I960 it gained a separate headlamp shell and sportier mudguards, plus a redesigned twin-cradle frame that gave steeper steering geometry and a shorter wheelbase.
The frame was strengthened for 1961, by which time the Bonneville had become firmly established as a stylish and fast road-burner. British magazine Motor Cycling wrote in June 1961 of the 'outstanding acceleration and high top speed -without temperament’ of a bike that lapped a banked test-track at an impressive average of I08mph (I74km/h). Three months later the magazine tripped the timing lights at l I7mph (I88km/h) on the same bike, now revving higher after being fitted with Triumph’s high-performance option of ‘chopped’ Amal Monobloc carburettors sharing a single float bowl.
Easy handling and good looks
The Bonneville was regularly updated over the next decade, notably with the adoption of a unit-construction engine and gearbox in 1963. Chassis stability did not always match engine performance, but the Bonnie remained much loved for its light weight, easy handling and good looks. In 1971 the twin gained a new ‘oil-in-frame’ chassis, which was much criticized until lowered a year later. In 1973 Triumph increased capacity to 744cc to produce the T140 Bonneville, which was more flexible, if no faster and less smooth. Bonnevilles were raced with great success, notably in the Isle of Man, where John Hartle won the production TT in 1967, and Malcolm Uphill set the first production lOOmph (I6lkm/h) lap on the way to victory in 1969. During the 1960s the T120 took four wins in the annual 500-mile (805km) production race at Thruxton and Brands Hatch, with riders including Triumph tester Percy Tait. The Bonnie was still competitive on the track in 1978, when Steve Trasler’s T140 beat the Japanese fours to win the British production championship.
The Silver Jubilee Bonneville of 1977 was a special edition of the 750cc TI40, built by Triumph to celebrate Queen Elizabeth II’s 25 years on the British throne. The Bonnie was old-fashioned compared to Japanese rivals, though not witho
Above right: The
Bonneville made a return in 2001, when John Bloor’s reborn Triumph firm introduced a roadster twin, styled afier a 1968-model TI20 but with a modern 790cc, dohc eight-valve engine. Ironically the new 61bhp Bonnie was no faster than many old models.
Specification Triumph T120 Bonneville
(1961)
- Engine Air-cooled four-valve ohv pushrod parallel twin
- Capacity 649cc (71 x 82mm)
- Maximum power 46bhp @ 6500rpm
- Transmission Four-speed, chain final drive
- Frame Steel twin downtube
- Suspension Telescopic front; twin shocks rear
- Brakes Drum front and rear
- Weight 403lb (183kg) wet
- Top speed 110mph (177km/h)
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