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Triumph Speed Twin

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Title: Triumph Speed Twin  
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Subject: Triumph Engineering, Edward Turner, Norton Dominator, Cheney Racing, BSA Golden Flash
Collection: Standard Motorcycles, Triumph Motorcycles
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Triumph Speed Twin

Triumph Speed Twin 5T
Manufacturer Triumph
Production 1938-1940 1947-1959
Engine 498 cc 360 degree parallel twin OHV four-stroke
Power 27 bhp @ 6,300 rpm
Transmission 4 speed / chain
Wheelbase 55 inches (140 cm)

The Speed Twin 5T is a motorcycle that was made by Triumph at their Coventry factory. Edward Turner, Triumph’s Chief Designer and Managing Director, launched the Triumph Speed Twin at the 1937 National Motorcycle Show. It was a 500 cc OHV vertical twin in a lightweight frame and the first truly successful British twin, setting the standard for many twins to follow. After World War II the Speed Twin was responsible for the survival of Triumph - and every major British marque offered a 500 cc twin designed on similar lines to the Speed Twin.[1]


  • History 1
  • Development 2
  • References 3
  • External links 4


The timing side of 1937 Speed Twin engine

Edward Turner’s Triumph twin was a major turning point for the British motorcycle industry, as although a 500 cc parallel twin of medium capacity was not revolutionary, the 5T Speed Twin model was lighter than many contemporary singles with significantly more power and torque. Early models were only available in 'Amaranth red' with hand painted gold pinstripes to set off the chrome. Initially the one piece iron cylinder was secured with six studs which led to weakness, so these were replaced by eight studs.[2] The two cylinders were fed by a single Amal Type 6 carburettor and many features such as the transmission and clutch were straight from the Triumph single.[3] Originally with girder forks, the sprung saddle was the only rear suspension as the Speed Twin had a rigid frame - also from the single cylinder production line.[4] On the night of 14 November 1940 the majority of the city-centre of Coventry was destroyed by German bombs and the Triumph factory (which was working on an order of thousands of military specification 5T's) was completely wiped out, and all of Triumph's technical records, drawings and designs were destroyed.[5]


The drive side of 1958 Speed Twin engine

After the war the recovery of Triumph at Meriden was largely due to the Speed Twin, which was developed in 1946 with telescopic forks and optional sprung hub rear suspension. The headlamp and instrument area was tidied up in 1949 with the Turner-designed nacelle, a feature retained until the end of the model line. In 1953, the Speed Twin caused controversy among traditional British riders as the generator and magneto were replaced with a Lucas alternator and battery/coil ignition system.[6]

The 1959 5TA Speed Twin-note rear 'bathtub' fairing and headlamp nacelle.

Further development led to the 1959 model 5TA with a unit engine and gearbox construction and styling changes including the unpopular 'Bathtub' fairing which became more and more abbreviated as the model developed before disappearing altogether for the last year of production in 1966.[7]

The unit 500 engine continued development in the parallel Tiger 100 range ending with the Tiger Daytona models which ceased production in 1973.


  1. ^ "Triumph Speed Twin. 1937". Retrieved 2008-07-12. 
  2. ^ Kemp, Andrew (2001). Classic British Bikes. Bookmart Ltd. pp. 90–91.  
  3. ^ Remus, Tim (1997). Triumph Motorcycles Twins & Triples. Motorbooks. pp. 9–12.  
  4. ^ "Triumph Speed Twin". Retrieved 2008-07-12. 
  5. ^ "Triumph Motorcycles timeline". Retrieved 2008-07-13. 
  6. ^ Robert Smith (March–April 2009). "1959 Speed Twin". Motorcycle Classics. Archived from the original on 2009-11-29. Retrieved 2009-08-05. 
  7. ^ "Speed Twin" (PDF). Archived from the original on 2011-07-21. Retrieved 2008-07-12. 

External links

  • Triumph Speed Twin review
  • 1939 factory manual
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