I used various GPS apps on my motorcycle, but they are like 4 to 7 kmph slower than the speedometer. A lot of test studies claim that on test bikes an error of up to 10% is found in the speedometer. Also, there is an ECE regulation that specifies a speedometer can read high by as much as 10 percent plus 4 km/h at a specified test speed, but under no circumstances can the speedometer read low. That may be one of the reasons why motorcycle speedometers show higher speeds than the GPS. According to a
scootyblog research article, new-age motorcycles use sensors that are triggered by gear teeth or slots in ABS wheel ring. The ECU of the motorcycle calculates the speed from the frequency of the square wave signal received from these sensors.