How Does a Speedometer Work?

A speedometer is a device that measures the speed of a vehicle. It is an essential instrument on a car’s dashboard, and its accuracy is critical for safe driving. The speedometer works by measuring the rotation of the wheels and converting that information into a numerical value. In this article, we will explore in detail how a speedometer works.

Mechanical Speedometers

Mechanical speedometers were used in older cars and motorcycles. They consist of a speedometer cable that connects to the transmission of the vehicle. As the wheels turn, the transmission turns the cable, which in turn rotates the magnet inside the speedometer head. The magnet then pulls a pointer on the gauge, indicating the speed of the vehicle.

Electronic Speedometers

Electronic speedometers are used in modern cars and motorcycles. They work by using a speed sensor, which is usually located on the transmission. The sensor sends a signal to the car’s computer, which then calculates the speed and displays it on the dashboard. Electronic speedometers are more accurate than mechanical speedometers, and they are not affected by cable wear or breakage.

GPS Speedometers

GPS speedometers are becoming increasingly popular in modern vehicles. They work by using satellite signals to calculate the speed of the vehicle. GPS speedometers are the most accurate type of speedometer and are not affected by factors that can affect other types of speedometers, such as tire size or gear ratio.


Regardless of the type of speedometer, it is important to calibrate it regularly to ensure accuracy. Calibration involves comparing the speedometer reading to a known speed and adjusting it if necessary. Inaccurate speedometer readings can lead to speeding tickets or accidents, so it is important to ensure that the speedometer is always calibrated correctly.


In conclusion, a speedometer is an essential instrument in a vehicle, and its accuracy is critical for safe driving. There are three types of speedometers: mechanical, electronic, and GPS. Each type works differently but serves the same purpose. It is important to calibrate the speedometer regularly to ensure accuracy.