Triumph TR6 and TR7
Triumph TR6 Background & History
The Triumph TR6 was the hottest bike Triumph made when it was introduced in 1956. It was the next step in the evolution of Triumph’s big vertical twin, with each step faster and more powerful than the last.
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.
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.
The seminal 500cc 1938 Triumph Speed Twin started it all.
The Vertical Twin
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 500cc Triumph T100 Tiger and the later 650cc T110 Tiger were the hot rod models...until the TR6 arrived.
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.
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 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. Several boosted displacement, 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. Faster than most fast cars, too. Again, the market rushed to catch up. Just when some of them started to gain a little ground Triumph did it again. They developed a new alloy cylinder head dubbed the “Delta Head”. It was not only lighter and offered better cooling but it flowed better and so made even more power. They introduced it in a whole new bike, the 1956 Triumph TR6. Once again, Triumph reigned in performance. But, in the motorcycle business, “too much is never enough”.
The 1956 Triumph TR6/B.
Triumph Bonneville is Born
In 1959, Triumph took their feisty 650 twin to the next level. They reworked the Delta Head to accommodate two carburetors and the 1959 Triumph Bonneville was born. Until then, nearly every twin on the market, Triumph’s included, ran only one carburetor, made possible by the even firing pattern of the 360-degree cranks on vertical twins. Adding a second carb seems obvious today, but it was a revelation in 1959. Running two carbs on the Triumph 650 added some top end power, but at the sacrifice at low-RPM torque and driveability. And two carbs were much harder to tune than one. But, the fame and reputation of the Bonneville probably benefitted more from the two carbs than did the horsepower. At the time, The Bonneville was one of the fastest machines you could buy, on two wheels or four. They were also incredibly handsome machines, and the flew off the shelves in the US.
This 1956 Triumph TR6 is replica of the famous Big Bear desert racing bike of that era. It shows what people were doing with the TR6.
Triumph TR6 for Road & Off-Road
The Triumph TR6 was available both in it’s street version, the TR6A, and the off-road version, the TR6B that had, among other changes, an easily-removable headlight for motocross. Both versions sold well and quickly gained the respect of the motorcycle buying public. The Triumph TR6 would remain the hottest bike in Triumph’s growing lineup for just 3 years before the next shoe dropped: The 1959 Triumph Bonneville. It’s big improvement over the TR6 was it’s twin carburetors. Until then, all vertical twins came with one carb, which worked great. But, as is the saying in motorcycle business “too much is never enough”. If one carb is good, two is better. In actuality, the twin-carb Bonneville made slightly more power, but at a higher RPM point. However, at normal engine speeds, like in traffic, they didn’t run as well as the single-carb bikes. And of course, one carb is always easier to tune than two.
This 1964 Triumph TR6 shows the styling of a typical unit-construction 1960s-vintage TR6. Note the single leading show front brake, replaced by the TLS in 1968.
The Triumph TR6 was a huge hit, remained one of Triumph’s best sellers, and remained in production through the 1972 year when it was replaced with the 750cc Triumph TR7. The TR6 followed the same design path of the Bonneville, sharing all bodywork (other than in the Bonneville’s first year, 1959) and components, but each model was painted differently in a color scheme that changed every model year. The TR7 variant was produced until 1980, leaving the Bonneville as the Meriden Co-Ops’s only model.
This 1973 Triumph TR7 Tiger was the first year for some major upgrades: a bump in displacement to 750cc, a much-needed 5-speed gearbox and a front disc brake.
Triumph TR6 Motorcycle Books
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