What is the actual speed when the odometer shows 120 miles?
3 Answers
It is approximately 120 mph. Below are the specific details regarding this topic: Error: There is a certain discrepancy between the value displayed on the car's dashboard and the actual value. This is to ensure travel safety. Before the car leaves the factory, the manufacturer stipulates that the speed displayed on the dashboard must be greater than the actual speed, but the error between the two should not be too large, generally maintained at around 3%. Note: Miles and kilometers are not the same. In fact, what is now referred to as 120 miles actually means 120 km/h. However, strictly speaking, 120 miles is close to 200 kilometers per hour, which is why in many racing competitions, commentators often mention speeds in miles rather than kilometers.
In my first year of driving, I truly believed the speedometer's 120 mph was the maximum speed. It wasn't until I installed a GPS that I realized the actual speed was only between 112 and 115 mph—quite a difference. This discrepancy is mainly due to manufacturers intentionally setting an error buffer, typically 5% to 10% higher, to subconsciously encourage us to drive slower and avoid speeding traps. My experience as a novice taught me not to rely entirely on the dashboard, as speed cameras don’t account for such errors. I always keep a GPS device in my car for comparison, especially on long highway trips, as it’s more accurate. If tires are worn or the wrong size is installed (e.g., mismatched aspect ratios), the error can increase. That’s why I regularly maintain tire pressure to ensure safety and avoid misjudgments that could lead to fines. Remember, this design is fundamentally for safety, not a vehicle malfunction.
After driving for most of my life, I've observed that when the speedometer shows 120 mph, the actual speed is usually only around 114 to 117 mph. Manufacturers generally calibrate this error, as regulations require the displayed speed not to be lower than the actual value, so they set it slightly higher to account for speeding risks. Different car models have varying deviations, and older vehicles or those with worn tires can be even more inaccurate. I remember a road trip where the GPS showed an actual speed of 115 mph while the dashboard read 120, which saved me from a speeding ticket. My advice is not to chase the highest number on the dial—it's often exaggerated. In reality, having it slightly lower is safer. Using GPS devices or smartphone apps to measure speed is a reliable way to avoid being misled by the dashboard and risking your safety. Developing good high-speed driving habits and maintaining your tires properly are crucial to minimizing unexpected deviations.
