What Is a Speedometer?In some vehicles, the speedometer is a circular gauge located on the dashboard, with the smallest numbers at the bottom of the gauge, and increasing steadily as the numbers climb the circle. A needle radiates out from the center of the gauge and points to the number that matches your current speed. Most speedometers have two rows of numbers, indicating the speed in both miles per hour and kilometers per hour. In other vehicles, the speedometer shows your speed digitally, with the number changing as you increase or decrease speed.
A Short History of the SpeedometerThe earliest cars didn’t have speedometers, which wasn’t a problem as most early cars topped out at relatively low speeds and it was easy for drivers to keep their speed under control. By the turn of the 20th century, however, top speeds had increased to around 30 mph, leading to an increase in serious accidents. In response, Otto Schulze invented the first speedometer in 1902. These first speedometers were expensive and difficult to find, but by 1910 carmakers began to offer speedometers as standard equipment.
DID YOU KNOW: Early speedometers had two gauges: one for the driver, which was located on the dashboard, and a larger, exterior gauge on the front side of the vehicle so the police could read your travelling speed.
Types of Speedometers: Mechanical and Electronic SpeedometersBroadly speaking, there are two types of speedometers: mechanical and electronic. Mechanical speedometers have been around since 1902 and are based on the designs of Otto Schulze. Electronic speedometers are a relatively recent invention and appeared during the 90s.
Mechanical SpeedometersMechanical speedometers are often called eddy-current speedometers because they use magnetic eddy currents to display the speed of your car. Mechanical speedometers are analog devices that attach directly to the transmission shaft of the vehicle. They gave drivers a reliable way to measure their speed at a time when electronic sensors didn’t exist. They consist of several parts:
- the drive cable
- the mandrel
- a spiral gear
- permanent magnet
DID YOU KNOW:Because speed, distance traveled and engine rotation can all be derived from the rotation of the transmission shaft, the drive cable is also linked to the odometer and the tachometer.