According to Yamaha’s records, the YSR50 was designed to be a scaled-down micro-racer version of the YZR500, something intended to appeal “to the spirit of race enthusiasts in a playful way.”
“Playful” is a good choice of words, as it looks like a toy. The original English magazine advertisement (PDF) echoed this playful vibe, stating “Just about everybody could end up riding one, provided they’re small-minded enough.”
However, the YSR50 is no toy, and you definitely shouldn’t put your kids on it. This little wonder is equipped with a two-stroke single-cylinder engine rated at 49cc, plus a return type 5-speed transmission, front disc brakes, and several other bells and whistles that you’d find on a professional-grade racing motorcycle. If you really crank it up, you can get a maximum performance of 7 horsepower at 8,800 rotations per minute.
The YSR50 had a standard cruising speed of around 37 miles per hour, but if you put the pedal down, you could see top speeds of around 40 to 50 miles per hour. It’s maybe a little low for a high-speed highway, but that’s more than enough to be street legal, and fearsome besides.
During the YSR50’s heyday in the late 80s, early 90s, it was the king of the mini-bike racing scene, as it was small enough to pass amongst its contemporaries, yet powerful enough to outrace all of them. If you can find a YSR50 nowadays, they’re an absolute blast to zoom around on the open road. Just make sure to wear a helmet.