1959 Triumph 5TA Speed Twin


Brand new in 1959, the Triumph 5TA Speed Twin was Triumph’s first “unit construction” 500cc design. Like the 350cc 3TA which preceded it by one year, the engine and transmission shared a common case. The new model also shared its little brother’s bulbous and heavy steel bodywork, designed for rainy Britain; it was often removed and discarded by American customers.

The 5TA served as the basis for dirt track and road racing machines where its high-revving “oversquare” bore and stroke made it an immediate success. Some would argue the 500cc bike ran at a decided handicap; AMA rules for Class C racing limited overhead valve motors to 500ccs, where the Harley-Davidson purpose built KR750 and the Indian Scout ran 750ccs as they were flathead designs. Numerous road race and dirt track AMA pros made their marks with the 500cc Triumph.

The ancestor 1938 Speed Twin was the brilliant work of Edward Turner who came to Triumph from Ariel about 1936. Both the styling of the original motorcycle and its general mechanical design are Turner’s and were revolutionary and lasting; modern Triumphs still reflect the styling down to the primary cover, the fuel tank and mufflers. As we look back, the Speed Twin’s trademark Amaranth Red with hand painted pinstripes on the chrome plated tank look so right.

The unit 500 engine continued development in the Tiger 100 and Trophy 500 model ranges that were offered through 1973. Triumph ceased manufacture of the 500cc twins to concentrate on its 750 twins and triples, while AMA racing classes leaned toward the full 750cc formula regardless of number of cylinders.

There are numerous stock, custom and racing Triumphs on display at the National Motorcycle Museum. Other fine examples are the original 1938 Speed Twin and the 1959 Triumph Thunderbird constructed by Bud Ekins and customized by Von Dutch. In a totally different direction is the late Dave Mungenast’s Triumph TR5T ISDE enduro bike on display in the DIRT RIDING USA exhibition area.


  • Engine: OHV Parallel Twin
  • Bore & Stroke: 69mm x 65.5mm
  • Displacement: 490cc / 29.9 Cubic Inches
  • Electrics/Ignition: Alternator, Battery & Coil
  • Carburetion: 7/8-in. Amal Monobloc
  • Compression Ratio: 7.0:1
  • Clutch: Multi-Plate
  • Starting: Kick Only
  • Horsepower: 27HP
  • Transmission: 4-Speed, Foot Shift
  • Primary: Roller Chain
  • Final Drive: Roller Chain
  • Frame: Lugged Steel, Single Down Tube
  • Suspension: Hydraulic Fork / Twin Shocks, Swingarm
  • Wheels: 17” Front, 17” Rear
  • Brakes: 7” Drum, Front & Rear
  • Wheelbase: 58 Inches
  • Top Speed: Approximately 92
  • Weight: 350 Pounds


  1. Thomas Morrison

    My dad bought a basket case Tiger in ’71. Most Triumphs in our area were NOT 500′s, and being rather new to motorcycle engine repairs(only worked on Honda’s before then) had to learn a few things on this bike, like the DRY SUMP system…I had the bike up and running, FINALLY, but only in the garage; and when my dad rode it for the first time out on the highway, we found the return piston oil pump wasn’t doing it’s job, and all the oil was leaking out the transfer case. At the time, the local Triumph dealer (Detroit, MI) had no pumps available, so I was directed to a motorcycle junkyard guy named Cowboy, who had a coffee can of pumps, and NONE of them with a guarantee they would work…Guess I was lucky, because it worked. My dad didn’t keep the bike for long; the previous owner had set it up as a hardtail, and he didn’t like the harsh ride. I later worked on a BSA, so at least I knew a LITTLE bit about British bikes.

  2. Paul

    One of the first real bikes I rode (other than mopeds) was a Triumph 500…it was owned by a friend, and built from a basket case…not too long after that, I rode an 80″Harley flathead…what a difference!

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