Racing? That is my answer before because someone told me it stands for “Racing”. But as we came across their official website Q&A page. “R” really stands for Resistive and not Racing.
NGK “R” or resistive type sparkplugs has a 5Kohms ceramic resistor. This ceramic resistor inside the sparkplug minimizes the electrical noise cause by ignition. NGK “R” are a must on motorcycles with a lot of electronics like Fuel injection systems, Sensors, Engine Control Unit(ECU), GPS, electronic gauges etc. Electrical noise can affect electronic components functions. Just like in the aircraft wherein they want you to turn off your cellphone because your cellphone creates electrical noise which can affect the computers on the aircraft.