Triumph’s Speed Twin transformed postwar motorcycling

Parallel-twin-powered bikes are currently motorcycling’s dominant force. Honda’s new Hornet and Transalp are earning rave reviews. Aprilia, BMW, Husqvarna, Kawasaki, KTM, and Royal Enfield have popular families. Fantic’s first-ever twin borrows its engine from Yamaha’s MT-07 and Ténéré, which sell by the boatload. Even the engine in Suzuki’s latest V-Strom is a parallel, not a vee.

And then there’s Triumph, which has a thriving family of parallel-twin models: Bonneville, Scrambler, and Thruxton. The brand, having just changed its Street Twin’s name to Speed Twin 900, now also has a pair of retro roadsters named after the 498cc machine that appeared through the post–Second World War gloom to begin motorcycling’s first parallel-twin era.

The Speed Twin was actually launched in 1937. It made an immediate impact, but the war’s outbreak two years later halted production. When the Triumph returned—in subtly updated form—as of 1946, it proved that two cylinders could be better than one. Triumph inspired rival firms to follow suit, thus triggering a period of parallel-twin dominance that would last for decades.

The Speed Twin’s designer, Triumph’s charismatic boss Edward Turner, outlined the advantages of the bike’s engine in typically forthright fashion. “It will run at higher revolutions than a single [cylinder] of similar capacity without unduly stressing major components,” he said. “The engine gives faster acceleration, is more durable, easier to silence, and better cooled. In every way it is a more agreeable engine to handle.”

Few disagreed after riding the Speed Twin. Its top speed, just over 90 mph, was matched by some singles, but none could match the effortless way the Speed Twin could cruise at 70 mph. The pushrod-operated engine, which had a 360-degree firing arrangement (pistons rising and falling together), was softly tuned, with a maximum output of 28 hp at 6000 rpm. Although there was some vibration, by single-pot standards the engine was smooth.

Turner had recently arrived from Ariel, where he had designed the glamorous Square Four, after that firm had taken over Triumph. He announced himself by revamping Triumph’s single-cylinder range of 500-, 350-, and 250cc models with fresh styling and catchy new names: Tiger 90, 80, and 70.

Turner’s rare talents for marketing and styling were again evident in the Speed Twin’s evocative name and handsome lines. The Twin’s lean, simple look was not misleading. It used essentially the same frame and forks as the Tiger 90, was actually slightly lighter than the 500 single, and its engine was slightly narrower.

It was the Speed Twin’s performance, though, that sent the testers of the day into rapture. “On the open road the machine was utterly delightful,” reported The Motor Cycle. “Ample power was always available at a turn of the twist-grip, and the lack of noise when the machine was cruising in the seventies was almost uncanny.” The magazine managed a two-way average of 93.7 mph and a “truly amazing” one-way best of 107.

The journalist from rival magazine Motor Cycling was similarly enthusiastic in a January 1946 review. After collecting a Speed Twin from Triumph’s base at Meriden, near Coventry, where the factory had been rebuilt since being damaged by German bombs, he headed southwest, towards Cheltenham, searching out twisty roads where the bike’s handling could be tested.

The Speed Twin did not disappoint, judging from the glowing report: “How can mere writing express that sense of mastery, that sympathy with the machine, that exhilarating impression of complete control which a healthy engine, hair-fine steering and super-adequate braking can combine to inspire?” He then took the Triumph for an off-road ride, where it again impressed.

My own Speed Twin test ride kept to the road and was distinctly brief in comparison, but I found it easy to appreciate the Triumph’s performance and light, easy handling.

This bike was standard, apart from handlebars that curved back slightly more than the originals. As a 1946 model it featured the telescopic forks that had been fitted that year, in place of the original girder design. Other post-WWII upgrades included a larger, four-gallon fuel tank and new magneto ignition.

The Triumph felt like a period piece: I heaved it off the tricky rear-wheel-mounted center-stand, tickled the tiny, unfiltered Amal carburetor to get the petrol flowing, and gave a light kick to fire up the motor. The sound from the twin pipes was a lovely, mellow purr as I blipped the throttle. First gear went in with a graunch, but the controls were light, and once I was under way the right-foot gearchange was precise.

It didn’t take long to discover why so many riders had taken to the Speed Twin. Its half-liter motor was impressively smooth almost all the way through its rev range. The Triumph was enjoyably eager for such an old bike, its effortless low-rev response helped make it easy to ride, and vibration was not an issue at up to 60 mph.

The Twin also handled well, at least for a bike with a hard-tail (read: unsuspended) rear end. At 368 pounds with fuel, the Triumph was light even by modern middleweight standards, and its ultra-low and sprung saddle helped make control effortless. Its brakes were reasonably efficient, too, despite being simple drums.

The Triumph’s telescopic forks were hydraulically damped, intended to give extra rear-wheel grip on bumpy road surfaces, compared to the girders, and to improve feel of the front end. Despite the lack of rear suspension, the Twin handled fine on reasonably smooth surfaces.

Even comfort was reasonable, thanks to the sprung saddle. Triumph introduced an optional sprung-hub rear suspension system two years later, in 1948, but it was disliked by many riders: It tended to make the bike weave.

The Speed Twin, by contrast, remained hugely popular for years, as did its sportier Tiger 100 derivative, whose extra power raised top speed to 100 mph. In 1950 Triumph added the Thunderbird, with its bigger, 650cc engine, in an attempt to stay ahead of rival firms who by now had twins of their own. The format would continue to dominate until the ’70s, when Japanese firms took over with their more powerful, smoother, and better engineered fours.

And now parallel twins are back at the top of the sales charts. These engines cost less to produce than fours, triples, V-twins, or boxers. Many power fine bikes, offering adequate performance and balancer-shaft smoothness, plus added character from irregular firing orders. But they’ll never match the impact of Triumph’s original, which transformed motorcycling in a way that only a select handful of bikes have done.

1946 Triumph Speed Twin

Highs: Sweet power delivery, easy handling

Lows: Easy to drop, when trying to use the center stand

Summary: An all-time great that still rides beautifully.

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Price: Project: $8800; nice ride, $12,300; showing off, $15,800

Engine: Air-cooled parallel twin

Capacity: 498 cc

Maximum power: 28 hp @ 6000 rpm

Weight: 368 pounds with fluids

Top speed: 95 mph

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Via Hagerty UK