The speedometer is one of the key instruments on the car panel, which shows the current speed. However, not all drivers know the correct name of this device from the point of view of science and technology. In everyday speech we use the word “speedometer”, but in technical documentation, standards and textbooks on the automotive industry other terms are used. Let's figure out what the scientific name of this device is, how it works and why it is important to understand its operating principles.
The question of the correct name of the speedometer arises not only among beginners, but also among experienced car owners, especially when it comes to legal aspects (for example, when checking the accuracy of the readings) or maintenance. In addition, knowledge of terminology helps to better navigate instructions for repair, diagnostics and calibration of the device. In this article we will look at official definitions, the history of the speedometer, its types, and even little-known facts that will be useful to every motorist.
Scientific name of speedometer: terminology and standards
From the point of view of metrology (the science of measurement) and automotive engineering, the speedometer has several official names, which are used depending on the context:
- 🔬 Driving speed meter — the general name of the device in the technical documentation. This term is universal and applies to both mechanical and electronic devices.
- 📏 Speed indicator - a term that is often found in GOST and standards for automotive devices (for example, GOST R 41.39-99regulating the requirements for speedometers).
- 🚗 Speed tachometer - an outdated name that is sometimes found in old textbooks. It is important not to confuse it with tachometer (a device for measuring engine speed).
- 📊 Speedometer is a term used in railway transport, but is sometimes applied to automotive instruments, especially in the context of precision measurements.
In international standards (for example, ISO 3918:1985 or ECE R39) speedometer is designated as speedometer or vehicle speed indicator. In Russian regulatory documents the wording most often used is "speed indicator", since it reflects the main function of the device - indication, not measurement (the latter implies high accuracy, which speedometers often do not possess).
Interestingly, in some countries, for example in Germany, the speedometer is called Tachometer, which can be misleading. However, in German-language technical literature under Tachometer is understood precisely speed indicator, not a tachometer (the term used for engine speed is Drehzahlmesser).
Speedometer design: from mechanics to electronics
To understand why the speedometer has several names, let’s look at its structure. The instrument has evolved from simple mechanical designs to complex electronic systems, and the terminology may differ in each case.
B mechanical speedometers, which were installed on cars until the 1990s, the main element was flexible shaft (cable) connected to the gearbox. The rotation of the shaft was transmitted to a magnetic disk, which interacted with a metal cup connected to the arrow. The higher the rotation speed, the more the needle deviated. Such devices were called induction speedometers.
B electronic speedometers modern cars use a cable instead speed sensor (for example, based on the Hall effect), which sends pulses to the electronic control unit (ECU). The data is processed by a microcontroller, and the result is displayed on a digital or analog display. In this case, the device is often called electronic speed indicator or digital speedometer.
| Speedometer type | Scientific name | Operating principle | Accuracy |
|---|---|---|---|
| Mechanical | Induction speed indicator | Flexible shaft + magnetic disk | ±5–10% |
| Electromechanical | Electronic-mechanical speedometer | Hall sensor + arrow stepper motor | ±3–5% |
| Digital | Electronic speed indicator | Pulse sensor + microcontroller | ±1–2% |
| GPS speedometer | Satellite speed meter | Data from GPS/GLONASS satellites | ±0,1–0,5% |
Why the speedometer is inaccurate: errors and standards
One of the most common questions among car owners: “Why is the speedometer lying?” The fact is that almost all speedometers overestimate readings - this is not an accident, but a safety requirement. According to international standards (eg ECE R39 or SAE J1226), the speedometer should not underestimate real speed, but maybe it overstate within the permissible error.
Main reasons for inaccuracy:
- 🔄 Design features: Mechanical speedometers have a large inertia, while electronic ones depend on the calibration of the sensor.
- 🚛 Wheel size: If you installed wheels with a larger or smaller diameter than those specified by the factory, the speedometer readings will change.
- ⚙️ Gear ratio: in some cars (eg Toyota Land Cruiser or Nissan Patrol) the speedometer is calibrated for a standard transmission, and after its modification, reconfiguration is required.
- 📡 Interference: electronic systems may experience failures due to electromagnetic interference or sensor malfunction.
According to GOST R 41.39-99, the permissible error of a passenger car speedometer is +10% of the actual speed when driving at a speed of more than 40 km/h. For example, if you are driving at 100 km/h, the speedometer may show up to 110 km/h. This is done to ensure that the driver does not exceed the speed limit, focusing on the device.
⚠️ Attention: If the speedometer underestimates speed (shows less than it actually is), this is a violation of safety requirements. Such a device must be replaced or recalibrated.
How to Check Speedometer Accuracy: Practical Methods
If you are in doubt about the accuracy of your speedometer, there are several ways to check it. The simplest one is to use GPS navigator or mobile application (for example, Speedometer GPS or Waze). Compare the speedometer and GPS readings on a flat stretch of road at a stable speed (for example, 60 or 90 km/h). A difference of 3–5 km/h is considered normal, but if it exceeds 10%, you should contact a service center.
A more accurate method is bench check in a car service. The master connects the speedometer to special equipment that simulates the rotation of the wheels at a given speed. This method is suitable for mechanical and electromechanical devices. Digital speedometers may require diagnostics via OBD-II scanner.
Check tire pressure (must be correct)
Make sure the wheels are standard size (no lift or spacers)
Use a flat section of road without slopes
Record speedometer and GPS readings for comparison
-->
If a significant error is detected, the reasons may be as follows:
- 🔧 Flexible shaft wear (in mechanical speedometers).
- 📉 Speed sensor malfunction (in electronic systems).
- 🖥️ Firmware failure (in digital devices).
- 🔄 Incorrect calibration after replacing the gearbox or wheels.
⚠️ Attention: In some vehicles (eg Volkswagen or Audi with the system CAN-bus) the speedometer receives data not directly from the sensor, but through the control unit. In this case, specialized equipment is required for diagnosis, for example, VCDS or ODIS.
History of the speedometer: from the first prototypes to modern systems
The first speedometer was invented in 1902 by a German engineer Otto Schule (Otto Schulze). Its device was based on the centrifugal principle: a rotating disk lifted weights, which moved the arrow through a system of levers. This device was installed on cars Benz and Mercedes beginning of the 20th century.
In the 1910s there were magnetic induction speedometers, which became the standard for the next 70 years. Their main advantage is the absence of a direct mechanical connection between the pointer and the rotating shaft, which reduced wear. In the 1960s the company VDO (today part of the concern Continental) released the first electronic speedometer with a stepper motor, which was used in cars BMW and Porsche.
Modern speedometers are integrated into combined instrument panels (for example, Virtual Cockpit from Audi or i-Cockpit from Peugeot), where the speed is displayed on a digital screen. Some models (eg Tesla or NIO) completely abandoned the traditional arrow, replacing it with a completely digital display.
Why do speedometers in some countries show speed in miles instead of km/h?
In the USA, Great Britain and some other countries, the imperial measurement system is used, where speed is indicated in miles per hour (mph). For example, car speedometers Ford Mustang or Chevrolet Camaro, officially supplied to these countries, are graduated in mph. However, most modern machines support switching units of measurement through the settings menu.
Legal aspects: what the law says about speedometers
In Russia, the requirements for speedometers are regulated by several documents:
- 📜 GOST R 41.39-99 (“Uniform provisions concerning the approval of vehicles with regard to the speedometer”)
- 📄 Technical Regulations of the Customs Union TR CU 018/2011 (“On the safety of wheeled vehicles”)
- ⚖️ Code of Administrative Offenses (CAO), Article 12.9 (speeding)
According to these documents:
- The speedometer should be OK and calibrated in accordance with factory parameters.
- Permissible error - no more than +10% of actual speed (but not less than 4 km/h at speeds up to 40 km/h).
- Replacing the speedometer or modifying it (for example, reflashing) must be carried out at certified centers.
- If the speedometer does not work, operating the vehicle prohibited (clause 7.4 of the List of malfunctions in which the operation of the vehicle is prohibited).
It is important to understand that when legal disputes (for example, when challenging a speeding fine) speedometer readings are not evidence. To record violations, certified radars or cameras are used, which undergo regular verification. However, if the speedometer underestimates speed, this may be a reason to check its serviceability.
If you plan to participate in court proceedings regarding a speeding fine, request radar verification data from the traffic police. According to the Resolution of the Plenum of the Armed Forces of the Russian Federation No. 20 of June 25, 2019, evidence obtained using unverified equipment may be declared invalid.
The future of speedometers: digital technologies and alternative solutions
With the development of unmanned vehicles and systems ADAS (advanced driver-assistance systems) traditional speedometers may be a thing of the past. Already today, some manufacturers are experimenting with alternative ways to display speed:
- 🌐 Head-Up Displays (HUD): speed is projected onto the windshield to help the driver stay focused on the road (e.g. BMW 7 Series or Mercedes-Benz S-Class).
- 🤖 Voice assistants: in some concept cars (e.g. Mercedes-Benz Vision AVTR) speed is announced by voice.
- 📱 Mobile applications: instead of a standard speedometer, you can use a smartphone connected to
OBD-II(for example, via an adapter ELM327). - 🛰️ GPS monitoring: commercial vehicles often have tracking systems that record speed using satellite data (e.g. Wialon or Navtelecom).
One of the most promising areas is integration of speedometer with navigation systems. For example, in cars Tesla the speed is displayed on the central screen along with the restrictions for the current section of the road. And in Volvo testing a system that automatically reduces speed when approaching a school or pedestrian crossing.
However, it is not yet possible to completely abandon the traditional speedometer. According to international standards, a car must have analogue or digital speed indicator, visible to the driver without the need for distraction. Therefore, even in the most modern cars, the speedometer remains an essential element of the dashboard.
Digital speedometers are more accurate than mechanical ones, but are more vulnerable to software glitches. Update your dashboard firmware regularly to avoid errors in readings.
FAQ: Frequently asked questions about speedometers
Is it possible to drive if the speedometer does not work?
No, this is prohibited by clause 7.4 of the List of malfunctions for which operation of the vehicle is not permitted. If the speedometer is broken, you face a fine Part 1 Art. 12.5 Code of Administrative Offenses (500 rubles) or warning. In addition, without a speedometer, you risk getting a fine for speeding, since you will not be able to control it yourself.
Which speedometer is more accurate: mechanical or electronic?
Electronic speedometers are more accurate than mechanical ones, as they do not have inertial errors. However, the most accurate way to measure speed is GPS speedometer, since it does not depend on wheel size or transmission ratios. The error of GPS measurements usually does not exceed 0.5 km/h.
Is it possible to calibrate the speedometer yourself?
In most cases, no. Calibration requires special equipment and access to ECU service settings. For example, in cars Volkswagen or Skoda For this you need a diagnostic scanner VCDS, and in Toyota — Techstream. Incorrect calibration may cause the instrument panel to malfunction.
Why does the speedometer show speed when the car is stationary?
This is possible in two cases:
- Defective speed sensor (for example, closing contacts).
- The car has a system installed start-stop, and the speedometer reads data from the gearbox, and not from the wheels (in this case, the needle may twitch in place).
If the problem persists, contact the service for diagnostics.
Can the speedometer show speed higher than actual speed?
Yes, and that's okay. As mentioned earlier, the standards allow speedometers overstate speed, but do not underestimate. For example, if the actual speed is 100 km/h, the speedometer may show up to 110 km/h. This is done to ensure that the driver does not exceed the speed limit.