The Truth About Motorcycle Speedometers: Accuracy and Calibration
The accuracy of a motorcycle speedometer can vary based on several factors, including the make and model of the motorcycle, tire size, and any modifications made to the bike. This guide explores these factors and offers practical advice on how to ensure the accuracy of your motorcycle's speedometer.
Understanding Manufacturing Tolerances
Most motorcycle speedometers are designed to be accurate within a certain percentage, often around ±5%. This means that if your speedometer reads 60 mph, your actual speed could be anywhere from 57 to 63 mph. This tolerance is a general guideline and can vary depending on the specific manufacturer and model.
The Impact of Tire Size
Changing the tire size can significantly affect the accuracy of the speedometer. If you choose a larger tire than what the speedometer was calibrated for, it will under-read your speed. Conversely, a smaller tire will cause the speedometer to over-read. This is because the speedometer is based on the circumference of the tire, and a change in size alters this measurement.
Wear and Tear
Over time, components such as the speedometer cable or electronic sensors can wear out, leading to inaccuracies in the speedometer reading. Regular maintenance and periodic checks can help maintain the accuracy of your speedometer.
Calibration and Adjustments
Some motorcycles allow for speedometer calibration, especially if modifications have been made. It's important to consult the owner's manual or contact a dealer for specific guidance on how to calibrate your speedometer. This process can help ensure that your speedometer readings match your actual speed more closely.
Comparing with GPS
A common method to check the accuracy of your speedometer is to compare it with a GPS device. GPS units typically provide a more accurate reading of speed, making them a reliable reference. You can compare your speedometer reading with the GPS speedometer to determine if your speedometer is off, and by how much.
Personal Experiences with Speedometer Accuracy
Many motorcycle enthusiasts have reported that the speedometer on their motorcycles is often on the optimistic side. I was not happy with the gearing of my Kawasaki Ninja 300, as I was constantly looking for a non-existent 7th gear to shift to on the open road. After replacing the transmission output chain sprocket from the stock 14 tooth to an aftermarket 15 tooth sprocket, not only did 6th gear feel like an overdrive, but my speedometer now reads accurately.
Whenever I ride past one of those “your speed” radar signs, the speed displayed agrees very closely with my speedometer reading. My Kawasaki Ninja 300's speedometer was replaced, and now it reads accurately.
Common Trends Among Japanese Manufacturers
It seems to be a long manufacturer's tradition to make motorcycle speedometers that are slightly optimistic. I have observed that on my R1, the ECU is set at 6. My friend with a Gixxer also advises the same. My guess is that it's the same for all Japanese manufacturers. This pattern suggests that speedometer accuracy might be a point of consideration when choosing a motorcycle.
Conclusion
Ensuring the accuracy of your motorcycle speedometer is crucial for safe and legal riding. By understanding the factors that affect speedometer accuracy and taking steps to calibrate and maintain your speedometer, you can trust the readings you see on your speedometer. Regular comparison with a GPS device can help you verify the accuracy of your speedometer and make necessary adjustments to ensure safe and accurate readings.