2009 Derbi Dirt Boy 50 Technical Analysis & Specification Breakdown
Built around Derbi's minibike, cross motorcycle platform, the 2009 Derbi Dirt Boy 50 pairs a 49.9 cc (3 cu in) air-cooled single cylinder, four-stroke architecture with road-focused gearing. Internal engine geometry specifies a bore and stroke of 39.0 x 41.8 mm (1.5 x 1.6 inches) with a 12.0:1 compression ratio.
On the scales, the Dirt Boy 50 measures 47 kg (104 lbs) dry. Rider ergonomics and chassis geometry center around a 610 mm (24 in) seat height — giving shorter riders and urban commuters confident flat-foot reach at traffic stops, combined with a 905 mm (35.6 in) wheelbase engineered for quick, flickable steering geometry. The 2.3-liter (0.6 US gal) fuel tank supports practical everyday commuting and weekend road stints.
Within MotoLibrary's Derbi archive, this model family spans 2 indexed model years from 2008 to 2009, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.
Standover Height
610 mm (24 in)
Engine
Displacement49.9 ccm (3.04 cubic inches)
Engine TypeSingle cylinder, four-stroke
Engine DetailsSingle cylinder, four-stroke
Compression12.0:1
Bore x Stroke39.0 x 41.8 mm (1.5 x 1.6 inches)
Fuel SystemCarburettor. 14 mm
IgnitionCDI
LubricationOil pump
CoolingAir
Transmission
Gearbox1-speed
Chassis
Front SuspensionHydraulic fork.
Front Travel120 mm (4.7 inches)
Rear SuspensionMonoshock.
Rear Travel140 mm (5.5 inches)
Wheelbase905 mm (35.6 inches)
Wheels & Brakes
Front Tyre2.50-12
Rear Tyre2.75-10
Front BrakesSingle disc
Front Brake Ø160 mm (6.3 inches)
Rear BrakesExpanding brake (drum brake)
Rear Brake Ø90 mm (3.5 inches)
Dimensions & Weight
Dry Weight47.0 kg (103.6 pounds)
Seat Height610 mm (24.0 inches) If adjustable, lowest setting.
Use this page to compare this motorcycle by its real specifications, not only by model name. Focus on the details that affect fit, comfort, handling, range and ownership.
Seat Height
Check the seat height against your inseam and riding posture before choosing a motorcycle.
Weight
Compare weight carefully because it affects low-speed handling, parking and confidence.
Fuel Capacity
Fuel capacity helps estimate touring range and how often you may need to stop.
Brakes
Brake setup is worth comparing if you ride in traffic, mountains or with a passenger.
Suspension
Suspension details can matter for comfort, road feel and long-distance riding.
Transmission
Transmission and final drive affect maintenance, smoothness and everyday usability.
