Triumph Thunderbird

Triumph Thunderbird Background & History

The Triumph Thunderbird was the first Triumph 650. Until its launch in 1950, all other British vertical twins were of 500cc displacement, including Triumph’s own 500cc Speed Twin, launched in 1938, setting off the whole ‘vertical twin race’ with the other manufacturers. But, as usual, as always, Triumph was first. First to build a 500cc vertical twin, and first to punch one out to 650cc.

During the 1920s and 30s, motorcycles developed and improved dramatically. One basic engine layout ruled the era: single-cylinder machines. They started out as side-valve (flathead) designs, but soon graduated on to overhead valves (OHV) as performance steadily improved. By the mid-1930s, displacement and power output had nearly reached their practical limits at around 500cc and 25 horsepower. Adding more displacement, or extracting more power by revving the engines faster only led to horrible engine vibrations that were hard on engines and riders alike. Many solutions were attempted but nothing seemed to work.

The Triumph 498cc vertical twin was bored and stroked to 649cc.

Design Genius

Shortly after Jack Sangster bought Ariel Motorcycles he brought over a promising new designer named Edward Turner, who promptly designed the first Ariel Square Four. When Ariel bought Triumph, Turner was put onto the task of solving the vibration problems the company, and the entire industry, was experiencing.

Turner’s solution took a whole new approach. He split that 500cc of displacement into two parallel cylinders rising and falling together on a 360-degree crankshaft, but firing alternately. The new ‘vertical twin’ as it was dubbed was lighter, made more power, loved to rev, and didn’t have nearly the vibration penalty of the big singles. In 1937, Triumph launched the new engine in a new bike, the 500cc 1938 Triumph 5T Speed Twin. It was an instant hit and changed the entire motorcycle landscape. Suddenly, all the big singles had been outclassed. Most of the British motorcycle industry rushed to bring their own vertical twins to market.

The 1950 Triumph 6T Thunderbird was the first British bike to reach 650cc, and it became the benchmark against which all other British motorcycles were compared.

Triumph Leads the Way

During this era, and beginning with the Speed Twin, Triumph ruled the roost, always setting the pace of innovation, always leading the way with newer, bigger, faster bikes. As quickly as the rest would catch up, Triumph would launch another bike that left them all in the dust. The Speed Twin did it first in 1938. Then, higher compression, hotter cams and a bigger carburetor were added, boosting horsepower, creating the ‘hot rod-version’, with the 1939 Triumph T100 Tiger. World War 2 broke out in 1939 and all civilian production ended until 1946, but when it did, Triumph was back with a vengeance.

The 1956 Triumph 6T 'Blackbird' was styled like the bike Marlon Brando rode in the 1953 movie 'The Wild One'.

Triumph Thunderbird Leads the Way

By 1949 several other British companies began fielding their own 500cc vertical twins, including BSA, Norton, Royal Enfield and Matchless/AJS. But no sooner than they started to catch up Triumph raised the bar again by boring and stroking the 500 out to 649cc thereby creating the 1950 Triumph 6T Thunderbird. And the race was on, the race to build the biggest, baddest bike on the planet. Several of Triumph’s competitors boosted displacement also, Royal Enfield and Norton even passing Triumph’s 650cc displacement. Triumph responded by applying the ‘Tiger-treatment’ to their new 650 and the 1954 Triumph T110 Tiger became just about the fastest bike on the market.

1956 Triumph 6T Thunderbird.

That gave Triumph two 650s in it’s lineup, the 6T Thunderbird and the higher-performance T110 Tiger. This changed the role of the Thunderbird from the biggest, baddest bike Triumph made to being their ‘standard’ version, compared to the hot rod Tiger. The Triumph Thunderbird filled its role well in the marketplace and sold well, both in Britain’s home market and in the all-important US market.

This 1956 Triumph 6T Thunderbird shows the full "Bathtub" look.

Triumph Thunderbird Drops in Status

In 1956 Triumph added a new hot rod to the 650 line with the new Triumph TR6, then three years later, in 1959, the released their ‘top dog’ 650, the legendary Bonneville. It was getting harder for the Triumph Thunderbird to be taken seriously as a performance bike. Throughout this time period, the role and identity of the T-Bird morphed into more of a big commuter bike. In the late 1950s enclosed or partially-enclosed motorcycles were all the rage in Britain, where riding conditions were often rainy, muddy or foggy. British riders were accustomed to wiping down their bikes after each ride to prevent rust. The solution was to enclose the bikes in an outer body. It didn’t work, moisture still got in and now it was hidden inside the shell so rust had its way with the metal parts.

This 1963 Triumph 6T Thunderbird shows how the 'bathtub' shrank more each year until it finally disappeared.

Thriumph Thunderbird Bathtub Bikes

Triumph’s entry was what are now called ‘bathtub bikes’. They had a 2-piece sheetmetal body that wrapped the entire back half of the motorcycle. The first such Triumph as the 350cc Triumph Twenty One launched in 1957. The 500 was next with the 1959 Triumph Speed Twin. Next was the Triumph Thunderbird which donned the ungainly bodywork in 1960. While it may have made some sense in England where bad weather riding was common, it didn’t play well in American, where most people only road in good weather. Americans wanted speed, power and style, and the new bathtub Thunderbird didn’t appeal to them. So, Triumph began downsizing the bathtub with each model year until it disappeared altogether in 1966, its final year in production. The TR6 became Triumph’s entry-level 650.

This 1965 Triumph Thunderbird shows how, in its final year of production, the bathtub was now completely gone.

Triumph Thunderbirds Year-by-Year

Triumph Thunderbird Books

Book: Essential Buyers Guide Triumph TBird/Trophy/Tiger

"Essential Buyer's Guide: Triumph Thunderbird, Trophy & Tiger"

By Peter Henshaw, 64 pages

A straightforward, practical guide to buying a Triumph Trophy, Thunderbird or Tiger. What to look for when buying one – including engine, transmission, frame, brakes, suspension, paint, chrome, and more.

$16.24 paperback

"Triumph 650 & 750 Twins"

By Matthew Vale, 192 pages

A detailed technical analysis of the bikes, and charts the development of the range from its introduction through to its heyday in the late 1960s. It looks at the development of the range, and covers the various models produced including a restoration of probably the best model produced - a 1970 T120R Bonneville.

$10.98 hard cover

"Triumph Speed Twin & Thunderbird Bible"

By Harry Woolridge, 144 pages

A wealth of information, covers the models' year-on-year development history from 1938-1966, engine, frame numbers, model type identification guide, color schemes, complete technical specifications of every model. Details of international sporting achievements attained. In addition, factory photographs show each model in authentic, original detail.

$51.06 paperback

"Factory-Original Triumph Twins"

By Steve Wilson, 160 pages

Detailed color photography of outstandingly original examples of Speed Twins 1938-58, Tiger T100s 1939-58, Thunderbirds 1950-62, Tiger T110s 1953-61, and T120 Bonnevilles 1959-62. Mechanical components, frame, suspension, brakes, electrics, wheels, metalwork, instruments, badging, trim, colors and finishes are all covered, with some 300 specially commissioned photographs pinpointing correct original equipment and specification.

$21.00 hard cover

"Triumph Motorcycles in America"

By Lindsay Brooke, 192 pages Triumph's dominance of the US motorcycle market, lively text, hundreds of historic images.

$24.95

More Triumph Motorcycle Pages

Triumph Motorcycles

Triumph 3T

Triumph Bonneville

Triumph Daytona

Triumph Speed Twin

Triumph Thunderbird

Triumph Tiger

Triumph TR5 Trophy

Triumph TR6

Triumph Trident

Triumph Twenty-One

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