Period Modified: Triumph Drag Bike

Launching a triumph drag racing motorcycle down the quarter mile takes a tremendous amount of concentration.

  • Engine: Stock TR6, 649cc air-cooled OHV parallel twin, 71mm x 82mm bore/stroke, 8.5:1 compression ratio, 42hp @ 6,500rpm stock (upgraded to 12:1 compression ratio, power unknown)
  • Carburetion: Dual 30mm Dell’Orto SS1 30 A
  • Transmission: 4-speed, chain drive primary and final
  • Electrics: Lucas Racing magneto
  • Frame/Wheelbase: ca. 1948 TR5 steel cradle type, 53in (1,346mm)
  • Suspension: Triumph telescopic fork front, rigid rear
  • Brakes: Front N/A, Rear 7in (178mm) drum
  • Tires: 3.00 x 21in ribbed Avon front, 4.00 x 18in rear M&H drag slick
  • Weight: unknown
  • Seat height: 24in at the lowest, 28in in at the  highest (609.5mm - 711mm)
  • Fuel capacity: .25gal (0.95ltr)

A competitor needs to focus solely on making it to the end of the run, everything else is just a distraction. But surely, back in the 1950s and 1960s when backyard builds were common at tracks across North America, one would be wondering if all the components of their machine would remain together at maximum velocity while hurtling 440 yards to the finish line.

Decades ago, many ambitious drag bike builders based their racing machines on commonly available motorcycles, such as Triumphs. With some mechanical ingenuity and parts from aftermarket retailers such as Webco and Harman & Collins, the Triumph 650cc parallel twin engines could be hopped up to offer tremendous power in a lightweight package.

Jeff Thompson of British Columbia, Canada, owner of the drag bike featured here, considers Triumphs built between 1955 and 1970 to be the most versatile motorcycles ever constructed.

ownerOwner Jeff Thompson with his drag bike back in the truck. 

“During Triumph’s glory years, their 500 and 650 twins were the ultimate multipurpose bikes,” Jeff explains, and continues, “One of my favorite motorcycles in my garage is a 1970 Triumph T120R. I’ve owned that bike for 25-plus years, and it gets ridden at least weekly. It has been a picture of reliability.

“I love that bike and think 1967 to 1970 Triumph Bonnevilles represent the very best in motorcycle style. But it was my relationship with that 1970 Bonneville that set me on a quest to collect race bikes based upon the Triumph 650 twin platform. A flat tracker, road racer and drag bike.”

12/17/2020 4:19:25 PM

the last line here is used to indicate he: rides it every day; looks at it every day, does not drive it at all; or the thought of it, or...or...Since you have included it I raises the Q. Thnx for the great write up. 40 yrs ago I did a customer's total rewire ona '56 'Thunderbird' (it had "start, off, emergency") but I can not remember anything abt weather it had the unitized construction of motor/transmis.

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