What Speed Does the Car Speedometer Display?
2 Answers
The speed displayed on the car speedometer is the magnitude of the instantaneous speed. There are generally three principles for speed measurement. Pulse Device: There is a pulse device on the tire, which emits a pulse every time the tire completes one rotation. The product of the number of pulses per unit time and the tire circumference gives the speed. Radar: Using pulses, different reflection times indicate different distances, and the ratio of the distance difference to time gives the speed. Radar or Radio: In places without reflection conditions, ground stations and moving objects exchange signals. The distance between them can be determined based on time, and through comprehensive calculation of the signals, the speed can also be obtained.
The car's speedometer displays the vehicle's speed while in motion, measured in kilometers per hour or miles per hour, depending on the car's settings and the region of use. It calculates speed by measuring the rotation rate of the wheels—sensors detect signals for each wheel rotation, which are transmitted to the computer system to compute the real-time speed reading. However, the actual speed may be slightly lower or higher due to factors like tire wear, pressure changes, or switching to wheels of different sizes, which can affect accuracy. For example, smaller tires may cause the speedometer to display a faster speed than actual, potentially leading to unintentional speeding. For safe driving, I recommend occasionally comparing the reading with a GPS on your phone, especially on highways or in speed-monitored zones, to avoid speeding fines or accident risks. Regular maintenance checks on tire condition also help ensure speed accuracy.
