It is generally true that vehicle speedometers can display a slightly higher speed than the actual speed. This intentional adjustment is known as speedometer calibration or speedometer error.
The reason behind this intentional adjustment is primarily for legal and safety considerations. Manufacturers typically calibrate speedometers to ensure that they do not display a speed lower than the actual speed to prevent drivers from unknowingly exceeding the speed limit. It provides a margin of error to account for variations in tire size, tire wear, and other factors that may affect the accuracy of speed measurements.
The amount of calibration or error can vary between vehicles and manufacturers, but it is typically within a small range, usually around 1-5 miles per hour. This means that when your speedometer displays a speed of, for example, 60 miles per hour, your actual speed might be slightly lower, such as 57-59 miles per hour.
It's important to note that speedometers can still have some level of inaccuracy, and for precise speed measurements, it is recommended to use GPS-based speedometers or other external devices that provide more accurate readings.