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1972 BSA B50MX

The BSA B50MX is a 500cc, single cylinder, four stroke, motocross motorcycle manufactured by BSA.

The B50MX was based on and looks similar to the BSA B50T Victor Trail. It had high mount fenders, adequate fork travel, racing plates, cross-braced handlebars, knobby tires, and two angled exhaust pipes mounted on the right side. Ground clearance was adequate for a vertical four stroke engine.


The bike was born as an exotic magnesium and titanium racing machine, handcrafted for the BSA works motocross team. Later, the BSA management decided to manufacture the MX in steel and aluminum as a production motocross racer. While a good racer, it had a very difficult time against Husqvarna Desert Masters, WR400s, Maico 501s, Maico Radials and CZ 380s.


  • Price, suggested retail 1972: U.S.A., POE $1300
  • Tire, front: 3.00 in. x 20 in. Rear: 4 00 in. x 18 in.
  • Brake, front .875 in. x 6.00 in. Rear 1.125 in. x 7.00 in.
  • Brake swept area: 41.21 sq. in.
  • Specific brake loading: 10.2 lb/sq. in., at test weight
  • Engine type: Four-stroke ohv single
  • Bore and stroke: 3.30 in. x 3.54 in., 84mm x 90mm
  • Piston displacement: 30.5 cu. in., 499cc
  • Compression ratio: 10.0:1
  • Carburetion: 1; 32mm; Amal
  • Air filtration: Pleated paper
  • Ignition: E T. Magneto
  • Bhp @ rpm: 38 @ 6200 rpm
  • Mph/1000 rpm, top gear: 11.2
  • Fuel capacity: 1.25 gal.
  • Oil capacity: 4.75 pints
  • Gear ratios, overall: (1) 15.04 (2) 11.30 (3) 8.59 (4) 6.90
  • Wheelbase: 56 in.
  • Seat height: 33 in., with rider
  • Ground clearance: 9.5 in., with rider
  • Curb weight: 263 lbs., with 1/2-tank of gas
  • Test weight: 428 lbs., with rider
  • Instruments: None
  • Top speed: 75-80 mph


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