Speedometer: Did you know how this device works?

Publié le Traduit avec l'aide de l'IA à partir de notre article original (source :

A speedometer is a device that measures the speed of a vehicle in miles per hour (mph) or kilometers per hour (km/h). It is a critical component of the dashboard and provides the driver with real-time information about the vehicle's speed.

In this article, we will look into the function of speedometers and their types.

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How Does a Speedometer Work?


The speedometer is linked to the vehicle's transmission system through a cable or an electronic sensor. As the vehicle moves, the transmission system rotates a magnet, which creates a magnetic field.

This magnetic field interacts with a metal disc or a needle in the speedometer gauge, causing it to move proportionally to the vehicle's speed.

Speedometer History in a Nutshell

The invention of the speedometer can be traced back to the late 19th century. In 1895, a Croatian engineer named Josip Belušić built one of the first known speedometers, called the velocimeter, to measure the speed of vehicles. A mechanical device operated using a rotating wheel and a pointer to indicate speed.

However, the American engineer Arthur P. Warner created the first patented speedometer in 1902. Warner's speedometer used a flexible cable connected to the vehicle's transmission, which drove a rotating magnet inside the device, causing the speedometer needle to move in response.

Later in 1916, Nikola Tesla developed a speedometer based on a rotating shaft-speed indicator and received a patent. The rights to the first invention of the speedometer, however, remained in hands of Arthur P. Warner.

Is Speedometer Lying to You?


The majority of speedometers possess a margin of error of around 10%, primarily resulting from differences in tire diameter. Factors contributing to these tire diameter variations include wear, temperature, pressure, vehicle load, and standard tire size.

To prevent liability for drivers exceeding speed limits, vehicle manufacturers typically calibrate speedometers to display a higher speed than the actual vehicle speed, equal to the average error. This ensures that the speedometer never underestimates the vehicle's true speed.

If you want to know the exact margin of error of the speedometer in your car, simply compare the speed that the speedometer is showing with the speed shown by the GPS on your phone. The difference between these two values is the speedometer deviation, and you can then calculate the percentage.

Speedometer Types

  1. Mechanical Speedometers

  2. Electronic Speedometers

  3. GPS Speedometers

  4. Heads-Up Display (HUD) Speedometers

1. Mechanical Speedometers

Mechanical speedometers are the oldest type of speed measurement device, dating back to the early days of the automobile industry. They function using a flexible cable driven by the vehicle's transmission, which connects to a rotating magnet inside the speedometer.

The magnet generates a magnetic field that exerts a force on a metal cup connected to the speedometer needle. The needle moves proportionally as the magnet spins faster, indicating the vehicle's speed. While electronic models have mostly replaced mechanical speedometers, they are still used in some classic and vintage vehicles.

2. Electronic Speedometers

The advent of modern electronics has given rise to electronic speedometers, which have become the standard for most vehicles today. These devices utilize a speed sensor, typically mounted on the transmission or wheel, that generates electrical pulses corresponding to the rotation of a gear or wheel.

The speedometer's microprocessor calculates the vehicle's speed by counting the pulses and converts it into an electrical signal to move the needle or display the numerical value digitally.

3. GPS Speedometers

Global Positioning System (GPS) speedometers represent a more recent development in speed measurement technology. These devices rely on satellite signals to calculate the vehicle's speed. A GPS receiver in the speedometer tracks the vehicle's position and movement by triangulating satellite data.

The device then calculates the speed based on the change in position over time. GPS speedometers are particularly useful for off-road vehicles, boats, and other applications where traditional speed-sensing methods may be less accurate or impractical.

4. Heads-Up Display (HUD) Speedometers

Heads-Up Display speedometers are a modern innovation designed to improve driver focus and safety. These devices project speed and other relevant information onto the vehicle's windshield, allowing drivers to view the information without taking their eyes off the road.

HUD speedometers can be standalone units or integrated into a vehicle's existing speedometer system. While these devices typically rely on electronic or GPS speed sensing, their unique display method sets them apart from other speedometer types.

Speedometer Issues

The chance that your speedometer will malfunction is quite low, but if that happens, it can be caused by inaccurate readings, a stuck needle, or a completely dead gauge. If you encounter any problems with your speedometer, we recommend having it checked and fixing the issue.


In conclusion, a speedometer is critical to your vehicle's dashboard, providing real-time information about your vehicle's speed. There's a low risk that this component will become faulty, but if it is, it's good to fix it asap.

A short video demonstration of how the speedometer works: