The Aprilia Sportcity 50 inner brake bulb uses a P21/5W size while the outer brake bulb uses a 921 size. The replacement chart covers vehicle production years spanning 2009 to 2011 with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Aprilia Sportcity 50 uses two distinct brake bulb types across its inner and outer brake positions for the 2009-2011 model years.
The P21/5W is a dual-filament bulb operating at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. Its dual-filament design allows it to serve both a running light function and a brighter brake light function within a single unit.
The P21/5W follows the ECE standard, which is the regulatory framework used across Europe and much of the world, and it fills the inner brake position on the Sportcity 50 across all three listed model years.
The 921 is a single-filament wedge-type bulb in a T15 form factor, rated at 12V and 16W. Wedge bulbs rely on the tension of their wire leads against the socket contacts rather than a twist-lock or bayonet mechanism for retention.
The 921 follows the ANSI standard, the North American classification system used in the United States and Canada, and it occupies the outer brake position on the Sportcity 50 across all three listed model years.
The inner and outer brake positions on the Aprilia Sportcity 50 require different bulb types, and the two are not interchangeable. The P21/5W uses a BAY15d bayonet base, while the 921 uses a wedge base, making the socket interfaces physically incompatible.
Beyond the base type difference, the wattage ratings also differ between the two positions. The P21/5W carries a 21W brake filament, while the 921 is rated at 16W, reflecting a difference in light output between the inner and outer brake functions.