Speedometer Error

Every car on the road has a degree of speedometer error. In a standard setup where the car has not been modified the speedo will always read a speed that is slightly higher than the actual speed that the vehicle is travelling. Manufacturers deliberately design the system in this way to ensure that the speedo never reads a speed lower than what the car is actually travelling. This is done for both safety reasons and so that the manufacturer cannot be liable for speeding fines incurred by the driver.