Led motorcycle speedometer displays the speed of the motorcycle through the swing of the pointer. Simply put, there is a system (turntable with pointer shaft, shaft with a permanent magnet, bearing, hairspring, and other parts) in the speedometer to control the swing of the pointer. The swing range of the pointer is ultimately determined by the speed of the transmission output (that is, the shaft of the speedometer is driven by a flexible shaft, and the flexible shaft is connected with the worm gear in the output shaft of the motorcycle transmission or transfer case-the worm gear in the worm drive pair ). Due to the manufacturing process and assembly errors of these parts, the natural wear during use, and the magnetic changes of the magnetic components will cause the indication error of the speedometer.
Another important reason for the error is related to motorcycle tires because the display number of the speedometer is only related to the speed output by the transmission, but the actual speed is not only related to the speed but also related to the rolling radius of the tire. Motorcycle tires gradually wear out as the mileage increases during use, and their rolling radius gradually decreases. The tire pressure also affects the size of the rolling radius. Therefore, the indicated value of the speedometer and the actual vehicle speed will form an error. According to regulations, the allowable error range of the speedometer is +20% to -5%. That is, when the actual vehicle speed is 40km/h, the speedometer indication value should be between 38～48km/h, or when the speedometer indication value is 40km/h, the actual vehicle speed should be between 33.3～42.1km/h.
At present, there are two main methods for checking the speedometer: the road experiment method and the indoor bench experiment method. The road test method is that the motorcycle passes through a predetermined length of test road at the same speed on the speedometer, determines the time to pass the road section, and then calculates the actual speed, and then compares it with the speedometer to obtain the different speeds. The indication error of the speedometer. The indoor bench test method is mainly to test through a drum speedometer test bench.