Hyosung GT650R Brake Bulb Size

The Hyosung GT650R uses a P21/5W bulb size for brake applications. Replacement specifications in the chart cover 2010 through 2017 model years.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2010-2017	P21/5W

Description	Bulb Size
ECE standard (Europe & worldwide). Dual-filament signalling bulb with BAY15d bayonet base. 12V, 21W/5W.	P21/5W

The Hyosung GT650R uses the P21/5W bulb across all brake light specifications from 2010-2017, making it the sole bulb type listed for this function.
The P21/5W is a dual-filament bulb, with one filament rated at 21 watts for the brake signal and a second rated at 5 watts for the tail or running light function.
Operating voltage for the P21/5W is 12 volts, which is consistent with standard 12V motorcycle electrical systems.
The P21/5W uses a BAY15d bayonet base, a two-pin offset base design where the two pins are positioned at different heights to prevent incorrect installation orientation.
The P21/5W is classified under ECE (Economic Commission for Europe) standards, indicating it is approved for road use in Europe and a wide range of international markets.
Because the BAY15d base is offset, it is not interchangeable with the BA15d base, which shares a similar bayonet form but features pins at equal heights, making substitution between the two types mechanically incompatible.
The dual-filament design of the P21/5W means a single bulb serves two distinct lighting functions simultaneously, distinguishing it from single-filament alternatives such as the P21W, which shares the same wattage on one filament only.