BMW Motorcycle R90 front and rear turn signal bulbs use P21W size specifications. The replacement chart covers 1973 to 1976 production years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21W is the sole bulb type specified for the BMW Motorcycle R90, covering both front and rear turn signals across all listed model years from 1973-1976.
The P21W operates at 12 volts with a 21-watt output, classifying it as a single-filament incandescent bulb intended for signalling functions rather than illumination.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet fitting. The "s" designation indicates a single offset pin, distinguishing it from the dual-contact BA15d variant, which is not interchangeable.
The P21W is governed by ECE (Economic Commission for Europe) standards, meaning it is designed for compliance with European and international vehicle lighting regulations rather than SAE standards used in North American markets.
Because the BA15s base is a single-contact design, any replacement bulb must match this contact configuration precisely. A BA15d bulb physically resembles the BA15s but carries two contacts and is not a compatible substitute.
The front and rear turn signals on the BMW Motorcycle R90 share an identical bulb specification across all listed years, meaning the same P21W bulb serves all four turn signal positions on the motorcycle.
The 21-watt rating of the P21W is a standard wattage for turn signal applications in ECE-regulated vehicles, as this wattage level is associated with the flash rate requirements defined under ECE regulations.