Introduction

Aprilia - RX 50 (2003–2004, ZD4STB)

The Aprilia RX 50 with type code ZD4STB belongs to the second generation of the popular RX series and was produced for the 2003 and 2004 model years. With its rugged enduro design, high front fender, and striking upside-down fork, it visually aligns with Aprilia’s larger off-road bikes. As a 50 cc enduro targeted at young beginners with an AM licence or moped permit, it combines sporty looks with practical everyday usability. Thanks to its modular construction, the RX 50 could be easily customised and optimised for road or off-road use.

Model History

The ZD4STB series is based on the technical platform that Aprilia introduced for the RX 50 starting in 2003. The new generation featured a more aggressive design, improved rider ergonomics, and a revised chassis layout. Headlight, fenders, side panels, and taillight were redesigned compared to the previous model. The slim tank and flat seat provided good vehicle control, even when riding standing up off-road. In many countries, the model was factory-limited to 45 km/h, but it was often derestricted or fitted with tuning components.

Technical Data

Air-cooled single-cylinder two-stroke engine with 49 cc displacement and carburettor. Power in unrestricted version: approx. 7.0 hp at 9,000 rpm, high-revving character. 6-speed manual gearbox with chain final drive. CDI ignition, premix or oil injection depending on version. Top speed (unrestricted): ~75 km/h. Fuel tank capacity: approx. 7 litres including reserve.

Chassis and Brakes

Reinforced steel tube frame with bolted rear subframe for easy maintenance. Front suspension via upside-down telescopic fork with long travel. Rear: mono shock absorber with progressive linkage on aluminium swingarm. Tyres in enduro size: 21-inch front, 18-inch rear with knobby tread. Brakes: 260 mm front disc, 180 mm rear disc. Some market versions featured braided brake lines.

Colour Variants

The RX 50 (ZD4STB) was available in sporty colour schemes such as black/red, blue/silver, or yellow/black. Depending on model year and region, sticker sets, type decals, and rim colours varied. Factory equipment sometimes included handguards, side stand, and chain guard. Popular add-ons: sport exhausts, smaller sprockets for more torque, wider handlebars, or modified suspensions for dedicated off-road use.