Probably the most studied dial on a vehicle’s dashboard is the speedo clock. Speedo clocks, which are normally driven electro-magnetically, are a dashboard instrument that advise the driver of the velocity at which the vehicle is travelling. This is obviously a vital component which not only enables the driver to maintain a safe driving speed but also ensures that the speed of the vehicle is kept within legal limits.
The way in which most speedo clocks work is quite straightforward. Basically, they operate through the transfer of information from the wheels of the vehicle to the speedo clock itself. This is achieved by means of the speedometer cable, which makes the connection between the turning wheels and the speedo clock. In simple terms, the faster the wheels turn the faster the cable rotates. This rotation creates an electro-magnetic reaction in a speed cup that is located inside the speedometer. This magnetic reaction is responsible for the creation of force, which pushes the needle of the speedometer. The faster the speedometer cable spins the greater are the magnetic forces that are created, causing more force and more movement of the speedo dial.
Speedo clocks are an essential component and it is illegal to drive without a working speedometer. If a speedo clock is faulty it should be repaired or replaced immediately.