Triumph Speed Twin

  Triumph 500cc Speed TwinThree men in a tub: Turner, Page and Kevin

The impact of the 500 cc Triumph Speed Twin is not difficult to measure. Throughout a 28-year production run it was the first commercially successful parallel Twin motorcycle, and almost everyone was influenced.

Around 1927, dealer Edward Turner submitted plans for a four-cylinder motorcycle engine to Ariel Motorcycles owner Jack Sangster. Impressed, Sangster hired Turner to put the machine into production. The result was the 500cc overhead cam Square Four of 1930. Turner became Ariel’s rising design star—a situation that did not sit well with chief designer Valentine Page.
Page left Ariel in 1932 to join Triumph, where he continued work on an idea hatched at Ariel: a 250cc parallel Twin using one of the two crankshafts from Turner’s Square Four. This begat the innovative 646cc OHV parallel Twin 6/1 of 1935 with 360-degree crankshaft, gear primary drive, a single camshaft, semi-unit construction and oil tank cast in the crankcase. Page’s Twin proved powerful and reliable, if overbuilt and expensive to produce.
Triumph, meanwhile had gone bust, and Sangster snapped up the company, installing Turner as chief designer—so he was now Page’s boss. Though many have accused Turner of stealing Page’s parallel Twin concept, Turner fans like to point out that Page also borrowed from Turner’s Square Four. Either way, it was Turner’s genius for what we would now call consumer product design that secured the Speed Twin’s success. (Sangster sold Ariel to the BSA Group in 1940, and Page moved with the company.)
Triumph 500cc Speed TwinTurner brought together a number of important skills. He understood the conservative British motorcyclist, so he designed the Twin to resemble the familiar twin-port single. He had an instinct for what later became finite element analysis—designing parts that were “just” sufficiently strong and durable without being over-engineered. And he was a master stylist. Faster or not, the Speed Twin looked sleeker, speedier and more svelte than its contemporaries, and almost every subsequent British parallel Twin borrowed at least some of its design themes and motifs.
No doubt the Triumph Speed Twin would have stayed in continuous production but for WWII and the destruction of Triumph’s Coventry factory in an air raid, Nov. 14, 1940. Production resumed in 1946 with a new telescopic fork, and in 1947, a sprung rear hub. Instead of being solidly mounted to the frame, the rear wheel spindle was supported on coil springs set inside the large diameter hub, giving a travel of around two inches. There was no damping. The system worked tolerably well when new, but any wear in the hub allowed the spindle to tilt, upsetting the bike’s handling.
In 1950, the Triumph Speed Twin was made over with a headlight nacelle incorporating the instruments, and a new streamline fuel tank design motif featuring four horizontal bars. This Art Deco design was recently reprised by Yamaha’s Roadliner and Stratoliner.
In 1952, a Lucas alternator replaced the dynamo and magneto. Though principally a cost-saving measure, it was a significant technological breakthrough—akin to switching from carburetors to fuel injection. Triumph pioneered this move amid much suspicion from those notoriously conservative British bikers.
Next came a new frame with swingarm rear end in 1955 and full width alloy brake hubs in 1957—but a major development was in the wings. For 1958, unit construction combined the engine and transmission in one casting, and the internal dimensions changed bore and stroke from 63 by 80mm to an oversquare 69 by 65.5mm. With it came revolutionary styling: the “bathtub” rear enclosure, and a deeply valanced front fender.
Unfortunately, the fate of the majority of bathtub Triumphs was to be stripped of their voluminous tinware. This was particularly true in North America, where Triumph was seen as a performance brand. Auntie’s big skirts just didn’t look right on a sportbike.
Triumph was also becoming more attuned to the US market, focusing on the 650cc Bonneville. So when 1967 range was announced in July 1966, the Triumph Speed Twin was missing, as was the 650 Thunderbird and 350 Twenty-One models. With their demise went the famous headlight nacelle, a Triumph feature since 1948.

Triumph 500cc bathtub Speed TwinKEVIN IS A huge fan of Triumph’s bathtub bikes. His Speed Twin left the Meriden factory in 1959 and was sold through a dealer in Canterbury, England. The new owner immigrated to Canada, bringing the bike with him.
About five years ago, a fastidious transmission rebuild specialist by the name of Ken Rotz acquired the Triumph Speed Twin in Victoria and set about restoring it.
Rotz’s meticulous attention to detail and his refusal to accept any sub-standard parts produced an outstanding restoration—and drove local parts suppliers to distraction. Every component was examined by Rotz’s micrometer, and unless the part was within the original manufacturer’s tolerance, he returned it. Rotz was similarly punctilious about tinware, requiring the painter to refinish panels that didn’t meet Rotz’s standard, in spite of looking perfect to everyone else. Needless to say, the painter was less than pleased. But the result has to be seen to be believed. The finish is so smooth, reflections in it are almost distortion-free. Kevin acquired the Speed Twin in a three-way cash-and-swap deal.
Now, a gentle prod on the kickstarter brings the 500 instantly to life, and I quickly discover Rotz’s passion for perfection extended to every aspect of the Speed Twin’s operation as well as appearance. All the controls work smoothly, and the gears shift with a precise click. The engine is unusually quiet for a Triumph twin. There are no oil leaks nor exposed wiring. Progress is reasonably brisk, the Speed Twin’s 27 horsepower propelling a mere 341 pounds. Suspension is taut, steering precise and brakes effective. Kevin says he thinks of the Speed Twin as a “gentleman’s motorcycle,” and I’d have to agree. With a cruising speed of 50-60 mph, the Speed Twin is less comfortable on the freeway. But for a sunny afternoon cruise around the winding back roads of Vancouver Island, it’s close to perfect.

– Robert Smith, April 2010 (issue #260)