Traffic regulations around the world are getting stricter and stricter. There's one question that has always puzzled me: while driving, if your speed just exceeds the speed limit, is that considered speeding? When driving on the highway, if the dashboard shows 120 km/h, is your actual speed really 120 km/h?
First, we need to clarify one concept: the speed of a car, which refers to the vehicle’s traveling speed, is the speed displayed on the dashboard for the driver’s observation and control. However, few drivers know that there is a certain difference between the speed shown on the dashboard and the actual speed. In other words, if the dashboard displays 120 km/h, the car’s actual speed is likely between 115–119 km/h.
What causes this discrepancy? It’s because the speed displayed on the dashboard is a simulated speed, calculated through a formula by the wheel speed sensor (other sensors can also be involved, such as the crankshaft position sensor). When the tire diameter changes, the signal from the wheel speed sensor remains the same, but the tire circumference changes, which in turn alters the calculated mileage. Similarly, the car’s speed is calculated based on the wheel speed signal, so there can be a significant gap between the actual speed and the dashboard display. The simulated speed calculated by the wheel speed sensor is not the actual speed.
Many manufacturers play small tricks in this regard: for example, when you floor the accelerator, normally both the RPM and engine should respond simultaneously, but some manufacturers tune it differently. The dashboard RPM responds first, jumping to a high reading instantly to give the driver a false sense of rapid acceleration, and only after 1–2 seconds does the engine gradually catch up. This is quite common and can be attributed to tuning issues or even manufacturer tricks.
Actually, once you understand the above issue of simulated dashboard speed, the problem of speeding becomes clearer. But there are two scenarios: decelerating to 120 km/h, or accelerating to 120 km/h. If you’re decelerating to 120 km/h, and you were already speeding, slamming the brakes when you reach the radar may lower the dashboard speed, but your actual speed could still exceed 120 km/h. Accelerating to 120 km/h shouldn’t be an issue, as no one would recklessly exceed the limit right before a speed trap.
Some drivers have a habit of speeding on highways, and when they see a camera near a speed limit zone, they immediately brake to slow down. But this depends on what kind of speed-limited area you're in. If it’s an average speed check zone, then obviously this won’t help. If it’s a direct speed measurement point, the measurement usually begins about 100–300 meters before the camera. If you haven’t slowed down before that distance, you’ll still be considered speeding — often without even realizing it.
1. Driving a motor vehicle (C1, C2, C3 categories) exceeding the speed limit by more than 50% results in 12 demerit points;
2. Driving a motor vehicle (C1, C2, C3 categories) exceeding the speed limit by 20% to less than 50% results in 6 demerit points;
3. Driving a motor vehicle (C1, C2, C3 categories) exceeding the speed limit by less than 20% results in 3 demerit points;
In fact, there’s one key fact to understand: the speed shown on the dashboard is not equal to the actual speed of the car. That means, if the dashboard shows 120 km/h, your actual speed might be between 115–119 km/h. Is this discrepancy related to the design precision of the vehicle? In reality, according to national regulations, the speed displayed on the dashboard can have an error margin of -10% to +10%, and it doesn’t precisely reflect the actual speed. So, having some error is normal.
When driving on the highway, don’t rely on luck — just follow the rules and drive safely. Of course, you should also be cautious about the following points.
1. Pay attention to tire maintenance, regularly check wear levels, and replace them when needed — all for safety reasons.
2. For those who like to modify their cars, be sure not to change the wheel size arbitrarily, as it can affect driving safety.
3. When driving on the highway, avoid driving right at the speed limit — the risk of speeding is high, since the dashboard speed isn’t the actual speed.
How many speeding tickets have you gotten?