1959 Triumph Bonneville

1959 Triumph Bonneville Background & History

The 1959 Triumph Bonneville was the first in a long line of these great sport bikes, but it was also the top of the totem pole, preceded by a long line of high-performance machines that led the market for two decades by 1959. The ‘Bonnie’ was the hottest bike Triumph made when it was introduced in 1959. It was the final step in the evolution of Triumph’s big vertical twin, with each step faster and more powerful than the last.

It all started with the 500cc 1938 Triumph Speed Twin, the world’s first ‘modern’ vertical twin. Triumph caught the rest of the British motorcycle industry flat-footed, but when the success of the Speed Twin became known, all the other brands (except Velocette who couldn’t afford to do it) rushed to bring their own vertical twins to market. Before they could even catch their breaths, Triumph did it again. They ‘hopped up’ the Speed Twin to create the hot rod version, the 1939 Triumph T100 Tiger. World War 2 put a lid on things until 1946, but when civilian production ramped up again, within just 3 years, five of Triumph’s competitors all fielded their own 500cc vertical twins. By 1949, BSA, Ariel, Norton, Royal Enfield and Matchless/AJS had all joined the ‘vertical twin club’, just in time for Triumph to do it again.

The 1959 Triumph Bonneville was a handsome brute for sure.  In the UK that placard on the front fender would have had the license plate on it.

The 1959 Triumph 6T Thunderbird was the first of a seemingly endless stream of 650cc twins and once again Triumph was first. Within a few years, the others upped their displacements as well, some up to 600cc, some to 650cc. Royal Enfield even trumped Triumph with their 700cc Super Meteor. But Triumph was resting on its laurels. In 1953 Triumph introduced swing arm rear suspension to its lineup. In 1964, they gave the new 650 the ‘Tiger-treatment’ with higher compression, hotter cams and a bigger carburetor for the new Triumph T110 Tiger. Again the market struggled to keep up. In 1956 Triumph introduced a new alloy cylinder head called the ‘Delta Head’, which not only offered more power but improved cooling as well. With it they created yet a hotter version of the 650, the 1956 TR6.

1959 Triumph Bonneville engine, timing side.

1959 Triumph Bonneville Styling

In 1959, Triumph reworked the single-carb Delta Head from the TR6 to accommodate twin carbs for even more power, thus creating the 1959 Triumph Bonneville. At this time, there were two distinctly different styling languages in Triumph’s twin-cylinder line. On the commuter/touring side (ie: the Triumph 5T Speed Twin, Thunderbird, T100 and T110 Tigers) these bikes got bigger fuel tanks, contoured seats, full-valance, painted mudguards (we Yanks call them fenders) and an old-fashioned headlight nacelle. The sporting bikes (ie: the TR6) was smaller, shapelier teardrop tanks, slim polished fenders and an exposed headlight. In fact, the off-road versions of the TR6 featured a clever system of quickly detaching the headlight when racing. Triumph, like most of their contemporaries, were accustomed to the British home market being their biggest market, hence the stodgy styling. This home market was riding a motorcycle primarily as an inexpensive means of basic transportation, which meant they were going to work every day, rain or shine. After all the riding weather in the UK is horrible by American standards, and bikes with humungous fenders and headlight nacelles make sense in a set environment like that. However, in America, most motorcycle buyers rode for recreation and almost always in good weather, what Americans cared about was speed, power and good looks. Triumph was learning quickly and adjusting smartly.

1959 Triumph Bonneville engine, primary-drive side.  This photo shows how the carbs are splayed outward.  Note the small megaphone on the carb inlet.  The '59 Bonnie didn't have air cleaners.

When the 1959 Triumph Bonneville was introduced to the world, it wore the stodgy, ‘old man’-bodywork of the Speed Twin and Thunderbird, big fenders, headlight nacelle and all.  And it was painted in pastel sort of color scheme of cream and orange.  The 1959 Triumph Bonneville as probably one of, if not the fastest motorcycles you could buy at the time and it looks like a fuddy-duddy.  Many buyers of new 1959 Triumph Bonnevilles had the dealers change out the bodywork for the sleeker TR6 components.  It didn’t take long for Triumph to get the message however, because by the 1960 model year, the Bonneville carried the same slim bodywork as the TR6 line, and would continue to do so throughout its entire existence.  The only difference between them, besides the number of carbs, was the two-tone paint schemes different on the Bonneville that the TR6 each year, and those colors changed with each model year.  Each year of each model was offered in only one color combo for the year.  In other words there were no optional colors.

This shot shows the full-valance fenders, the headlight nacelle, contoured seat and the fully-enclosed battery box that the 1959 Triumph Bonneville inherited from the Speed Twin and Thunderbird.

1959 Triumph Bonneville Engine

The 1959 Triumph Bonneville has a non-unit construction engine, which means the crankcase, the primary chain case and the gearbox are all separate components held together by a system of brackets.  This was superseded in the 1963 model year with the 650cc twins by a new ‘unit-construction’ engine incorporating all three components into one common, unitized case, hence the name.  But, for 1959 Triumph used the same engine as they did in the TR6, with the reworked Delta Head, the 8.5:1 compression ratio, a bore and stroke of 71mm X 82mm for a displacement of 649cc.  The only real difference is that the intake ports on the Bonneville’s Delta Head are splayed outwards, away from each other, while the TR6’s intake ports are closer together and both pointing straight back, and parallel.  The 1959 Triumph Bonneville used a set of Amal Monobloc 1-1/16” carbs over the TR6’s single carb.  The net effect was that the Bonneville made 46 hp at 6700 rpm, while the TR6 made 42 hp @ 6500 rpm.  The TR6, with its single carb pulling more manifold vacuum, ran better at low speeds, and ran out of air quicker at higher rpms.  On the Bonneville its twin carbs were each pulling not half of the manifold vacuum of the TR6, whose single carb was being shared by both cylinders.  As such, the 1959 Triumph Bonneville didn’t run quite as smoothly at lower speeds and especially under heavy loads at low speed, such as climbing a hill in too high a gear.  But, they were designed to make big power up on top of the rev range, and that they did.  Until the 750cc Norton Atlas came along in 1962, the ‘Bonnie’ was probably the fastest bike on the street.

1959 Triumph Bonneville Frame & Running Gear

The 1959 Triumph Bonneville launched with the same frame as the 1959 TR6 used, with a single front down tube and a swing arm rear suspension.  Triumphs have always been known as fine handling bikes but their twin down tube frames gained a reputation for flexing under heavy cornering loads.  The new single down tube frames cured that problem.  The front forks were Triumph’s own hydraulically dampened telescopic units supporting a 19-inch front wheel with an 8-inch single-leading shoe (SLS) front drum brake.  The rear mounted an 18-inch rim with a 7-inch SLS rear drum brake cast in common with the final drive sprocket on the left side of the bike.  This made manufacture simpler certainly, but it made gear ratio changes exceedingly difficult.

1959 Triumph Bonneville Leads the Market

Despite the stuffy bodywork the 1959 Triumph Bonneville was a handsome machine and it captivated the imagination of legions of buyers, mostly in America.  At the time, the market the market was flooded with British vertical twins of varying sizes from 350 to 750cc and all of them ran a single carburetor.  Today it seems like an obvious improvement to add a second carb, but at the time it was revolutionary.  But the second carb added more than just horsepower, it enhanced the reputation of the new Bonneville, which became one of Triumph’s top sellers.  And once again, Triumph has left the competition in the dust, but as always they struggled to catch up.  Suddenly new twin-carb bikes began to appear.  Triumph, and now the 1959 Triumph Bonneville closed the 1950s at the top of their form, and things were only going to get better…for awhile.

1959 Triumph Bonneville Specifications

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Triumph Bonneville Books

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Other Triumph Bonneville Pages

1959 T120 Bonneville

1960 T120 Bonneville

1961 T120 Bonneville

1962 T120 Bonneville

1963 T120 Bonneville

1964 T120 Bonneville

1965 T120 Bonneville

1966 T120 Bonneville

1967 T120 Bonneville

1968 T120 Bonneville

1969 T120 Bonneville

1970 T120 Bonneville

1971 T120 Bonneville

1972 T120 Bonneville

1973 T140 Bonneville

1974 T140 Bonneville

1975 T140 Bonneville

1976 T140 Bonneville

1977 T140 Bonneville

1977 T140J Silver Jubilee

1978 T140 Bonneville

1979 T140 Bonneville

1980 T140 Bonneville

1981 T140 Bonneville

1982 T140 Bonneville

1983 T140 Bonneville

1983 TSS Bonneville

1983 TSX Bonneville

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