A Brit bike as American as apple pie, this Bonnie wears a mix of home market features.

by Dain Gingerelli

By the time the 1950s played out, Great Britain’s Triumph Motorcycles had established itself among the top-selling brands in North America. Other leading marques included Harley-Davidson, Norton and Royal Enfield, among others, plus BSA, which as a company had actually acquired Triumph Motorcycles earlier that decade.

It wasn’t by accident that Triumphs were so popular among American riders, either. Shortly after World War II’s merciful conclusion, Edward Turner and Jack Sangster, who shared the company’s managerial duties, realized that if Triumph was to sustain and grow it needed a majority of its sales to originate in North America. Clearly, Triumph’s initial postwar success was owed to the Speed Twin engine, itself a half-liter bundle of addictive horsepower. Models such as Triumph’s 5T Speed Twin and TR5 Trophy sold well, especially in North America where the United States and Canadian markets were sizzling due to postwar economies bullish on luxury and consumer items that had been denied citizens during the second war to end all wars.



But Turner, especially, understood that Triumph’s existing line of 500cc vertical twins wasn’t going to be enough. The Yanks and Canucks would eventually step up and demand more … more powerful engines, that is. Turner and Sangster searched for a solution, and by 1949 they both realized that models with larger-displacement engines were the answer.

Welcome to the era of British 650cc vertical twins, and the first entry to roll out of the Meridian factory became known as the 6T Thunderbird for the 1950 model year. Fittingly, that first model to carry the new 650cc engine got its name from Native North American mythology, perhaps a positive omen for Triumph’s new chapter in its remarkable history.


Image by Dain Gingerelli

The recently-restored bike showed zero miles on its Smiths gauges.


  • Engine: 649cc OHV air-cooled 4-stroke vertical twin, 70.9mm x 82mm bore and stroke, 8.5:1 compression ratio, 50hp @ 6,500rpm (claimed)
  • Top speed: 110mph (period test)
  • Carburetion: Twin 1-1/16in Amal Monobloc
  • Ignition: Lucas magneto
  • Transmission: 4-speed
  • Frame/wheelbase: Double-cradle, tubular steel/55.2in (1,402mm)
  • Suspension: Telescopic fork front, dual shocks rear
  • Tires: 3.25 x 19in front, 4.00 x 18in rear
  • Brakes: 8in (203.2mm) SLS drum front, 7in (178mm) SLS drum rear
  • Weight: 410lb (182kg)
  • Seat height: 31.5in (800mm)
  • Price (then/now): $1,139/$7,000-$18,000

Bigger is better

Delivering the larger engine into the production cycle proved surprisingly easy, basing much of its design on the existing 500cc vertical twin that Turner, in his engineering capacity, had gifted to the motorcycling community more than 10 years previously. Stretching the Speed Twin’s bore and stroke from the half-liter engine’s 63mm x 80mm specs to 71mm x 82mm dimensions, the new 6T checked in displacing 649cc, good for 34 horsepower at 6,300rpm. Compression ratio for the domestic market was kept at a sedate 7:1, more than likely due to inconsistencies in the spotty quality of England’s postwar gasoline, but North American variants included optional 8.5:1-spec engines for its customers.


A single Amal 276 carburetor with a 1-inch mouth — basically the same fuel mixer equipped on most Speed Twin 500s at the time — fed fuel to the 650’s two combustion chambers, and therein lied the new engine’s first problem; the one-inch Amal didn’t deliver the promised performance that Turner had assured the motorcycling press, America’s two importers (Johnson Motors, aka JoMo, in the western half of the United States, Triumph Corporation, aka TriCor, in the east), and above all, Thunderbird customers for the new bike. Initially Turner felt that the Amal 276 was sufficient for the larger engine.

But when JoMo took delivery of their first batch of Thunderbirds in California, parts manager Pete Coleman soon realized something was missing to the puzzle. Years later when interviewed by author Lindsay Brooke for his book, Triumph Motorcycles (A Century of Passion and Power), Coleman claimed that the Thunderbird “would barely touch 90 miles per hour.” The solution, Coleman determined, was a replacement Amal carburetor sporting a 1-1/16-inch opening. The bigger carb proved its worth, leading Brooke to conclude in his book, “Given proper breathing the T-bird became a favorite all-rounder for the solo rider, two-up tourers, sidecarists, and police forces.” Proof again that bigger can be better, and with that in mind Triumph Motorcycles moved forward in its journey for bigger engines to feed the performance-hungry, and rather lucrative, American market.


A sidebar at this point is in order: The Thunderbird wasn’t necessarily Triumph’s first 650cc vertical twin, nor was the Speed Twin the marque’s first-ever vertical twin of any capacity. Those honors go to a rather rare and obscure package, the 1935 6/1, which was designed by engineer Valentine Page. However, the world was locked in a global economic depression at the time, and wasn’t ready for the 6/1, which Triumph discontinued before production figures reached 500 units.

But years later there was no cause to cease production of the 6T Thunderbird as sales of the new and bigger Triumph continued to please the bean counters and customers alike. The smaller 500cc models continued their popularity, too, and soon enough racers competing in California’s desert Hare & Hound events, not to forget Bud Ekins’ win at the Catalina GP, further cemented the TR5 Trophy 500’s popularity among competitors. Eventually a variation of the Thunderbird, the TR6 Trophy-Bird, joined the racing stable, this one catering to desert racers in California. Triumph was building its reputation as a motorcycle company offering equipment for any competent rider to win with. In these and other ways, Triumph Motorcycles was inching its way toward creating perhaps its most popular and famous model ever — the T120 Bonneville, such as the 1962 model featured here that belongs to Tim McIntyre of Lake Elsinore, California.

Just add salt

As most Triumph aficionados will tell you, the Triumph Bonneville was named after what is considered America’s largest and fastest race track, the naturally-occurring Bonneville Salt Flats, located about 100 miles west of Salt Lake City, Utah. The Salt Flats are named after Benjamin Bonneville, a U.S. Army officer who participated in various exploratory missions of the Great Basin (where the Salt Flats lie) and portions of the Northwest Territory. The Salt Flats themselves are the remnants of an expansive lake that dominated the region during the Pleistocene epoch. Today the remaining salt beds — nearly 6 feet thick in places — cover an area of about 12 miles by 5 miles, and it was on those flat, wide-open spaces that a Triumph-powered motorcycle set two world speed records in 1955 and 1956. (Later Triumph-powered streamliners set subsequent land speed records, but it was the two marks set in 1955-1956 that prompted the Triumph Bonneville model name.)


How those first two records were set is quite a story, which actually begins early summer of 1955 in New Zealand, where Russell Wright rode his Vincent to a new land speed record of 185mph.

But even before Wright’s speed was officially logged into the world record books, and as summer 1955 came to a close, a self-sponsored team from Texas brought their homebuilt Triumph-powered streamliner to pursue the land speed record. The Texans’ bike had a semi-enclosed body shell for streamlining, designed by career airline pilot J.H “Stormy” Mangham, who possessed a deep understanding about aeronautical engineering. The handcrafted body concealed a special tube frame holding a single modified TR6 Thunderbird engine, built by Jack Wilson, whose day job was service manager at Dailo’s Triumph in Ft. Worth. The 15-foot, 8-inch long cigar-shaped racer would be piloted by flat track racer Johnny Allen. The team had, for the most part, no major financial backing to speak of from Triumph of England. As Coleman told Brooke in his book Triumph Motorcycles in America, “The whole feat was basically sponsored by American Triumph dealers, JoMo and our suppliers,” which included Dunlop, Amal, Lucas, Renold Chain and Mobil-Oil.

The racer was initially referred to as the Mangham Streamliner before the name later officially became The Devil’s Arrow; over the course of time that name morphed into The Texas Cigar (or Cee-gar), depending on what source you reference. What never changed was the team’s goal to break the 185mph speed record. In the end the Texans raised the mark to 193.3mph, although the FIM (Federation International Motorcycliste), the world’s leading motorcycle organization, didn’t recognize the privateer team’s accomplishment due to time-keeping technicalities that FIM rules required; only the AMA (American Motorcyclist Association) allowed the world record to stick.

The Texans’ AMA record stood for a year, until late in the summer of 1956, when a small contingent of LSR motorcycles built and sponsored by NSU (a leading German motorcycle brand) went to Bonneville to chase down land speed records for several displacement categories, ranging from 50cc to the Open Class (500cc and up). Wilhelm Herz was chosen to pilot the Open Class bike for the grand prize, the absolute motorcycle land speed record. After the small-displacement NSU bikes set their respective speed records, Herz squeezed into his wind tunnel-tested streamliner to break the Texans’ 193mph record. He succeeded, in the process guiding the first-ever motorcycle to surpass 200mph. Herz’s two-way average was 211.4mph.


Image by Dain Gingerelli

Owner Tim McIntyre aboard his Bonneville. Tim recently restored the 1962 model, the last year for pre-unit Triumphs.

And with that, the Germans packed up and went home, confident in their performance. Then came the gritty Texans once again, answering the challenge to regain their record, ultimately setting the record at 214.4mph. Nuff said, and the Texas speed rangers triumphantly rode off into the sunset one more time.

It began in England

In a round-about way, Triumph’s race for the record actually had its origins in England when the lads in the engineering department, searching for better air/fuel delivery for the factory-sponsored ISDT riders’ off-road bikes, tried to adapt a larger air filter to the single-carb Tiger engines. It turned out that the bike frame’s rear center post miffed their plans. One solution was to create a dual-carb cylinder head that pointed two smaller carburetors to either side of the frame tube. Equipping them with individual, and rather compact, air filters solved the problem. Called the Delta head, the design proved efficient and accommodating for even more horsepower, too, and the whole kit eventually found its way into Triumph’s American importers’ parts catalogs as well, making it an official factory-certified item. And one of those units found its way onto the Texas Cee-gar’s TR6 engine that Jack Wilson built to smoke across the Salt Flats.

In fact, Wilson’s modified TR6 engine was based primarily on factory-spec speed equipment available to all Triumph owners. Soon enough TR6 owners began lining up for their Delta cylinder head kits; single-carb heads were no longer the ticket for top speed, and dealers let that fact be known to JoMo and TriCor, who promptly forwarded that information to the lads in England. The ball was now in Triumph management’s court regarding a future dual-carb street bike.

parcel rack

Image by Dain Gingerelli

The stylish parcel rack lets you use a tank bag without fear of scratching the paint.

At this point we’ll let Lindsay Brooke throw cold water on the party, as he wrote in his Triumph Motorcycles In America book: “By all accounts Edward Turner was hesitant about offering a twin-carb 650, and his reluctance then was not as difficult to understand as it may seem today.” Brooke cited several reasons for Turner’s pessimism, foremost that increasing the 650 twin’s power put additional stress on an engine originally designed to support 500cc power. There was more: Turner was infatuated with some rather grandiose styling treatments found on Triumph’s new Twenty-One model that included enclosed body parts (“streamliners” as American dealers called them). Turner also pushed for Triumph scooters (including the Tigress) being added into the lineup. Those models might have suited international targets, but as history proves, they didn’t hold water for America’s thriving motorcycle market that placed performance above all other features. And … Triumph was preparing to introduce its new unit-construction engines for the half-liter lineup, plus it already offered the twin-carb TR5AD (the “D” standing for Delta), which, even though a 500cc model, happened to be the most expensive model in Triumph’s entire 1958 lineup.

The wrong stuff

Despite all that, Triumph launched the T120 Bonneville for 1959, but practically with little fanfare; the new model wasn’t even listed in the 1959 lineup or included in sales brochures. “Instead,” wrote Brooke, “it [the Bonneville] was announced by a separate leaflet later inserted into the [dealer’s] brochure.” So Triumph introduced its most iconic U.S. model ever, not with a bang, but a whimper. Added Brooke: “In fact, Meriden’s publicity department was uncharacteristically silent, treating its new twin-carb 650 rather like an illegitimate child.”


As for the Bonneville name, Turner had previously met with TriCor’s management, and both parties agreed that, with Johnny Allen’s two land speed records still fresh in people’s minds, they would go with Bonneville.
In fact, to cope with the additional horsepower engineers had given concessions to the engine’s lower end, replacing the three-piece crankshaft with a new forged one-piece unit. However, the frame still favored the T110’s, which led to other problems, foremost excessive vibration and unsatisfactory handling. There was more — the Bonneville’s styling was the least bit sporty by American standards. Start with the front fender’s flared ends, matched by an excessive rear fender that drooped forlornly behind the rear tire — both visual turnoffs to customers. The headlight sported Turner’s beloved, and whimsically fancy, nacelle, and the rider’s seat was obtrusively flat and wide. Even the two-tone paint — Tangerine and Gray — was non-inspiring. Compared to the Trophy, the Bonneville came across as bland and stodgy, a complete disappointment by most standards. No surprise, sales were lackluster.

In response U.S. dealers began equipping TR6s with Delta head conversions, in essence making a sportier-looking pseudo-Bonneville for customers. TriCor went so far as to send a memo to its dealers February 27, 1959, encouraging them to equip a TR6/A with a Delta head, creating what the distributor termed a “TR6/A-style T120” for customers.

A major face-lift was due for 1960, and Triumph responded with a Bonneville looking much like those dual-carb TR6/A conversions. A more rigid duplex frame improved handling and gave cause to alter steering geometry for improved stability. Despite the changes, vibration remained an issue, and the brazed-lug frame was susceptible to fracturing around the headstock. Blue became the dominant color for the sleeker Bonneville’s gas tank, and customers responded positively to what was becoming Triumph’s alpha male model.

The following year the steering rake and trail were altered again, and to isolate vibration from the gas tank, three rubber blocks were incorporated into the design. Indeed, by 1962 rubber isolators had found their way to various other points, such as the instruments, handlebars and such, for a more enjoyable ride. As Cycle World magazine stated in its January 1962 issue’s Bonneville road test, “Vibration-damping rubber mounts are used extensively. Most noticeable of the mountings was the fuel tank.”

Elsewhere on the racing front, a Bonneville, ridden by John Holder, won the 1961 Thruxton 500, perhaps the most followed production-class road race in the Queen’s Empire at the time. Win there on Sunday and your dealers win sales all across the Isles on Monday.

A Yank in Europe

The 1962 Bonneville featured here was recently spotted by Tim McIntyre. It was in need of restoration, and Tim liked its composition so he bought it. He also suspected that it had not found its way into the U.S. via importers Johnson Motors or Triumph Corporation. Its VIN numbers indicated it to be a domestic (European) model, which proved correct. Oddly, though, the bike had some interesting features otherwise found on U.S. models.


Image by Dain Gingerelli

The 649cc overhead-valve twin makes 50 horsepower at 6,500rpm, fed by twin 1-1/16-inch Amal Monoblocs.

“Bonnevilles made for export to the U.S. were stamped with T120R,” explains Tim about their VINs. “My bike is a numbers-matching T120, intended for the home market.” Oddly, too, it had a tachometer (an option for domestic models) and it wore the high-rise flat-track (or TT) handlebar that was standard on export models. “European models,” says Tim, “usually had very low-rise handlebars.” Another subtly set this Bonneville from other domestic models — Tim spotted remnants of what appeared to be Flame Orange and Silver Sheen paint on the 4-gallon gas tank — itself a domestic-market component; yet the color combo was for an export model (European-market Bonneville tanks were Blue over Silver Sheen). Also, export Bonnevilles had slightly smaller 3.5-gallon gas tanks. Based on these items, Tim feels that the original owner might have been a member of the U.S. military who bought the bike while stationed in England, and created his own mix-and-match styling treatment for the bike.

All of those items made for a rather interesting restoration by Tim, resulting in what qualifies as an Anglo-American Bonneville. Regardless, the bike remains a shining example of what turned out to be the final year for “pre-unit” Triumphs. The following year Triumph completed its transition to unit-construction 650s, solidifying further the British company’s grip on the U.S. market until another landmark model hit these shores to close out the 1960s. That bike, of course, is Honda’s legendary CB750. MC

Updated on Feb 4, 2022  |  Originally Published on Feb 3, 2022

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