Editing Triumph Engineering (section)

==Post-war era==
The [[Triumph Speed Twin]] designed by [[Edward Turner (motorcycle designer)|Edward Turner]] before the war was produced in large numbers after the war. Efforts to settle the [[Lend-Lease]] debts caused nearly 70% of Triumph's post-war production to be shipped to the United States. Post war, the Speed Twin and [[Triumph Tiger 100]] were available with a [[Triumph sprung hub|sprung rear hub]], Triumph's first attempt at a rear suspension.

Privateers put wartime surplus aluminium alloy barrels on their Tiger 100 racers, and won races, inspiring the Triumph GP model. By 1950 the supply of barrels was exhausted, and the GP model was ended. The American market applied considerable demand to reverse this action, and a die-cast close finned aluminium alloy barrel was made available. The aluminium alloy head made the valve noise more obvious, so ramp type cams were introduced for aluminium alloy head models to reduce the noise.

Another motorcycle based on the wartime generator engine was the 498&nbsp;cc TR5 Trophy Twin, also introduced at the 1948 Motor Cycle Show. It used a single carburettor, low compression version of the Grand Prix engine. Britain won the prestigious 1948 International Six Days Trial. The Triumph works team had finished unpenalised. One team member, Allan Jefferies, had been riding what amounted to a prototype version.<ref name="veloce">[http://www.veloce.co.uk/shop/graphics/pdf/V4065.pdf Veloce.co.uk V4065.pdf] {{Webarchive|url=https://web.archive.org/web/20090927132024/http://www.veloce.co.uk/shop/graphics/pdf/V4065.pdf |date=27 September 2009 }}. Retrieved 26 December 2006.</ref>

To satisfy the American demand for motorcycles suited to long-distance riding, Turner built a 650&nbsp;cc version of the Speed Twin design. The new bike was named the [[Triumph Thunderbird|Thunderbird]] (a name Triumph would later license to the [[Ford Motor Company]] for use for a car model). Only one year after the Thunderbird was introduced, a motorcyclist in [[Southern California]] mated the 650 Thunderbird with a twin carb head intended originally for GP racing and named the new creation the Wonderbird. That 650&nbsp;cc motor, designed in 1939, had the world's absolute speed record for motorcycles from 1955 until 1970.

The Triumph brand received considerable publicity in the United States when [[Marlon Brando]] rode a 1950 Thunderbird 6T in the 1953 [[film]], ''[[The Wild One]]''.

The Triumph Motorcycle concern was sold to their rivals [[Birmingham Small Arms Company|BSA]] by Sangster in 1951. This sale included Sangster becoming a member of the BSA board. Sangster was to become Chairman of the BSA Group in 1956.

The production 650&nbsp;cc Thunderbird (6T) was a low-compression tourer, and the 500&nbsp;cc Tiger 100 was the performance motorcycle. That changed in 1954, with the change to swing arm frames, and the release of the aluminium alloy head 650&nbsp;cc Tiger 110, eclipsing the 500&nbsp;cc Tiger 100 as the performance model.

In 1959, the T120, a tuned double carburettor version of the [[Triumph Tiger T110]], came to be known as the ''[[Triumph Bonneville|Bonneville]]''. As Triumph and other marques gained market share, Harley became aware that their 1-litre-plus motorcycles were not as sporty as modern riders would like, resulting in a decreasing share of the market. The Triumphs were models for a new, "small" Harley-Davidson as a result: the now-fabled [[Harley-Davidson Sportster]], which started as Harley's version of a Triumph Bonneville. With its anachronistic V-twin, the Sportster was no match for the Bonneville, but it proved a solid competitor in US sales and eventually also in longevity.

During the 1960s, despite internal opposition from those who believed that it would reduce the macho image of the brand, Triumph produced two scooters; the ''[[Triumph Tina]]'', a small and low-performance 2-stroke scooter of about 100&nbsp;cc with automatic clutch and a handlebar carry basket, and the ''[[Triumph Tigress]]'', a more powerful scooter available with either a 175&nbsp;cc 2-stroke single or a 250&nbsp;cc 4-stroke twin engine for the enthusiast.

In 1962, the last year of the "pre-unit" models, Triumph used a frame with twin front down-tubes, but returned to a traditional Triumph single front downtube for the unit construction models that ensued. The twin down tube, or duplex frame, was used for the 650 twins, as a result of frame fractures on the Bonneville. Introduced in 1959, for the 1960 model year, it soon needed strengthening, and was ended in 1962, with the advent of the unit engines for the 650 range. The 3TA (21) was the first unit construction twin, soon followed by the short-stroke, 490&nbsp;cc "500" range.

From 1963 all Triumph engines were of [[unit construction]].

In 1969 Malcolm Uphill, riding a Bonneville, won the Isle of Man Production TT race with a race average of {{convert|99.99|mph|km/h}} per lap, and recorded the first ever more than {{convert|100|mph|km/h|0}} lap by a production motorcycle at {{convert|100.37|mph|km/h|2}}. For many Triumph fans, the 1969 Bonneville was the best Triumph model ever.

American sales had already maximised, in 1967. In truth, the demand for motorcycles was increasing, but Triumph could not supply the demand.

During the 1960s, 60% of all Triumph production was exported, which, along with the BSA's 80% exports, made the group susceptible to the Japanese expansion. By 1969 fully 50% of the US market for motorcycles more than 500&nbsp;cc belonged to Triumph, but technological advances at Triumph had failed to match those of the foreign companies. Triumphs lacked electric start mechanisms, relied on push-rods rather than overhead cams, vibrated noticeably, often leaked oil and had antiquated electrical systems; while Japanese marques such as Honda were building more advanced features into attractive new motorcycles that sold for less than their British competitors. Triumph motorcycles, as a result, were nearly obsolete even when they were new. Further, Triumph's manufacturing processes were very labour-intensive and largely inefficient. Also disastrous, during the early 1970s the US government mandated that all motorcycle imports must have their gearshift and brake pedals in the Japanese configuration, which required expensive retooling of all the motorcycles for US sale.

Triumph and BSA were well aware of [[Honda]]'s ability, with Honda winning motorcycle world championships since 1961, racing in Formula One, and offering the [[Honda CB450]] twin since 1965, but while the Japanese were only making smaller engined models, the large engine market was considered safe. When the first [[Honda CB750]]&nbsp;cc four cylinder was released for sale to the public in 1969, Triumph and BSA had trouble. Despite developing and releasing a 3-cylinder 750 cc engined motorcycle prior to the Japanese fours—the [[BSA Rocket 3/Triumph Trident]]—the Japanese bikes were praised in the press for their modernity (disc brakes, 4-cylinder engines, leak-free engine casings, etc.). The British triples outperformed the Japanese fours (top speed, acceleration and handling) but the Japanese fours required less maintenance and they did not leak.

The 1970 Tiger/Bonneville re-design and taller twin front downtube oil tank frame had a mixed reception from Triumph enthusiasts at the time, and was insufficient to win back those already riding the Japanese bikes that had been sold since 1969—the Honda 750 Four, and the Kawasaki 500 Mach 3. The Triumph 350&nbsp;cc Bandit received pre-publicity, but its development was quietly brought to an end. Triumph was still making motorcycles, but they no longer looked like the motorcycles Triumph fans expected. The Trident attracted its own market, but the Japanese motorcycles were improving more rapidly.

The parent BSA group had losses of £8.5&nbsp;million in 1971, £3&nbsp;million for BSA motorcycles alone. The British government became involved. The company was sold to [[Manganese Bronze Holdings]], which also owned [[Norton Motorcycle Company|Norton]], [[AJS]], [[Matchless]], [[Francis-Barnett]], [[Velocette|James-Velocette]] and [[Villiers Engineering|Villiers]].

<gallery>
Image:Triumph 3T motorcycle.jpg|Triumph 3T. This short-lived post-war economy 350cc twin proved unnecessary with the Speed Twins and Thunderbirds selling so well.
Image:Triumph Speed Twin.jpg|Triumph Speed Twin with telescopic front fork
Image:Triumph Thunderbird.JPG|1964 Triumph Thunderbird with "bathtub" rear fairing and siamesed exhaust.
Image:Triumph Tiger 100.jpg|Triumph Tiger 100
Image:1971 Triumph Daytona.JPG|1971 Triumph Daytona
</gallery>