Speedometer Accuracy in Motorcycles – Does It Really Matter?
Many people don’t know that the speedometer on their motorcycle only displays approximate values. It is an estimated value that varies from model to model and even depends on riding conditions. Is it really possible to tell how fast you’re going just by using a motorcycle speedometer?
There’s a lot of information about the difference between speedometers on motorcycles. Some believe that a digital speedometer will provide more accurate readings, whereas others swear by mechanical speedometers. To get the low down on speedometer accuracy, let’s talk about that in this article.
Speedometer Accuracy
Some riders argue about the accuracy of speedometers. But does the accuracy really matter? The answer to that question is not so simple. If the speedometer is too low, you’ll have a problem. But if it’s too high, you might find yourself speeding down and at risk of an accident. In other words, the accuracy of the speedometer can be a genuine concern, but in the end, it may not be a huge issue.
When we’re driving on the road, we often find ourselves confused by a number indicated on the YOUR SPEED sign – it’s different from the one on your speedometer. Why is there a discrepancy?
If there is one accurate statement about the accuracy of a motorcycle speedometer, it is this: it is fraught with errors, and it’s unreliable.
This is not to say that all motorcycle speedometers are inaccurate. There are a few reliable ones, and most of them are American-made bikes.
Motorcycle Speedometers – Mechanical and Electronic
Speedometers are either mechanical or electronic. A mechanical speedometer consists of a drive cable, magnets, a speed cup, a hairspring, and the terminal pointer needle on the dash.
Mechanical Speedometer
Drive Cable
A drive cable is a collection of small coiled springs that connects to a vehicle’s transmission. A small gear connects the drive cable to the transmission’s gear wheel on the output shaft. The wheels are connected to the output shaft to increase the vehicle’s speed.
By connecting the speedometer’s drive cable to the output shaft, a reasonably accurate estimate of the vehicle’s speed can be obtained. The motion of the output shaft is carried to the central mandrel of the drive cable. As the drive cable begins to spin, the output shaft rotates at the same rate as the bike’s wheels.
Magnets and Speed Cup
There is a magnet inside the speed cup. The magnet and the interior of the speed cup are separated by an air gap. The air gap between the speed cup and the magnet is kept, so the magnet does not actually touch the speed cup’s interior.
The motion of the drive cable is transmitted to the magnet. The magnet’s rotating magnetic field revolves around itself. The rotation of the magnetic field causes the small eddy currents in the speed cup. The speed cup is forced to rotate in the same direction as the magnet due to the torque of these eddy currents.
Hairspring and Pointer Needle
The stronger the magnetic field, the faster the output shaft rotates, causing the speed cup and pointer needle to move along the speed dial. When the vehicle is not in use, the hairspring resists the torque on the speed cup and keeps the pointer at zero. The hairspring will stop turning when the opposing torque of the hairspring equals the torque of the pointer needle. A correct speed value on the dial is indicated.
Electronic Speedometer
An electronic speedometer is much simpler than its mechanical counterpart. The construction of an electronic speedometer consists of only four parts. A magnet, a magnetic field sensor, a small circuit to interpret the readings, and an analog or digital display unit are required.
The apparatus is made up of a metal disk with tiny teeth. When the shaft spins, the magnetic field is picked up by the magnetic field sensor. The total number of wheel turns determines the car’s speed.
Whether mechanical or electronic, speedometers only show the motorcycle’s estimated speed and are not indicators of the vehicle’s actual speed.
GPS
GPS is a satellite navigation system that enables your phone or tracker to tell you where you are. It does this by calculating your location based on the satellites in space and their information. GPS is the most common navigation tool used today. It is available on almost every device, from smartphones to tablets and even cars and some motorcycle models.
The distance traveled is calculated by dividing the time it takes the vehicle to travel from one point to another. The number indicates how fast the vehicle traveled between the two points. If a vehicle’s position is used to calculate its speed, it is also called a positional speedometer. Source
Speedometers are usually composed of many mechanical parts and are prone to mechanical errors. Speedometers measure speed by indirectly being in contact with the tires. A tire change can change the reading, making it inaccurate. A typical example is a change in the tire’s dimension, then tire pressure, everyday wear and tear, temperature, and load.
If a customer puts on new tires or chooses to drive with a different set of tires than the manufacturer recommends, the speedometer must be recalibrated. Otherwise, the speed reading will be off. Most speedometers are calibrated to read higher than the actual speed. However, this could lead to accidents if drivers are unaware of the discrepancy.
The only difference between the two is that GPS uses a purely mathematical technique to measure the vehicle’s speed and is thus more accurate than a speedometer. That being said, there is a catch as well. When the motorcycle is traveling in a straight line and has a clear view of the sky, it is the best time to use a GPS device.
A clear line of sight is required because the GPS receiver must interact with satellites. GPS has no way of knowing how tight a turn is when the vehicle travels on the road with numerous twists and turns. Even though GPS readings can be relied on, they are not always reliable.
The instantaneous speed of the vehicle is one of the things that is missing from a GPS device. It only gives the average speed with a slight delay.
Conclusion
One thing is for sure: mechanical ones can be wrong. Even though GPS systems give more accurate data, the end result is only average and not real-time. The rider needs to be careful when he is on the road.
