How accurate are modern speedometers

Auto-Tacho: Tolerance for speed display

With everyone Car ride the gaze falls on the again and again Speedometer. That way, drivers keep that speedin the eye. If it shows too high a speed, you have to Reduce the pace. If the speed is below the permissible Top speed, you can step on the gas again if the road, visibility and weather conditions permit.

The view of the Speedometerafter a vehicle driver flashedhas been. Because the speedometer can Tempo sinnerquickly find out at how much km / h the Speed ​​limithas been exceeded. If this is known, it can already be guessed at this point in time which sanctions for the Tempo violation become due.

But the speedometer always shows exactly that driven speed at? How does a Speedometer actually? What if the speed displayed under or over the speed actually driven? Why is a tolerance spoken? These questions are clarified below.

What is a speedometer and how accurate is a speedometer display?

A Speedometer in the car measures the driven speed. According to § 57 of the Road Traffic Licensing Regulations (StVZO) every vehicle must be equipped with such a device:

Motor vehicles must be equipped with a speedometer that is in the immediate field of vision of the driver.

The Speedometer should also use the Regulations the EU Directive 75/443 / EEC correspond. Here it is also specified that the speedometer display illuminated must be so that the measured value is not only at Day, but also at night can be clearly recognized. The Display area has speeds up to that specified by the manufacturer Top speed to include.

Many drivers are surprised when the Speed ​​camera measured speed on the Penalty noticediffers from the one on the Speedometer on the car seen at the time of measurement. What many do not know: A speedometer never shows the actual speed. However, EU Directive 75/443 / EEC regulates the extent to which the Speedometer measured speed of the actually driven differ can:

The displayed speed must never be lower than the actual speed.

The Display value on the Speedometer may therefore above the actual pace, however never under. How much tolerance may the speedometer have? There are guidelines as to how much of that Speedometer of the actual speed differ may:

  • At Vehicles registered before 1991 the displayed value may be up to 7 percent differ from the real one.
  • At approved after 1991Vehicles the displayed value may be up to 10 percent differ from the real one. (+ 4 km / h)

An example: A newer vehicle drives 100 km / h. The speedometer can thus show a value of up to 114 km / h. If the speedometer display shows a value less than 100 km / h, this is not permitted.

These tolerance at the Speedometer can Manufacturer at the Car manufacturing exhaust. In order for the built-in speedometer to be permitted, the Tolerance not exceeded and the actual speed not fallen below become. As a rule, however, the deviation is with the car speedometer not quite as pronounced. Most speedometers give way only a few km / h on the actual value.

By the way, it is different with Navigation devices: Here is usually almost the actual speed displayed. This is done with the navigation system using GPS determined. Usually the displayed value deviates only at one km / h from the real one.

Conclusion on the tachometer accuracy: A speedometer usually shows Not exactly that actual speed driven at. It will be a certain Tolerance limit granted that Measurement inaccuracies should compensate. So if your speedometer is inaccurate, don't worry. However, the deviation on the Speedometer a distinction can be made between:

  • The speedometer shows too much: This is permissible up to a certain tolerance limit.
  • The speedometer shows too little: This is not allowed.

How does a speedometer measure and how does the deviation come about?

That the Car speedometer Some tolerance is granted because that way Inaccuracies should be compensated for during the measurement. The driven speed is namely about the Wheel revolutions and the one needed for it Time determined. On the basis of previously determined Averages, as Comparative values serve, then the speed certainly.

That I tiresand their nature Change over time, the speedometer must have a certain amount tolerance be granted. The following Factors have a influence on the properties of tires and thus on the measured speed:

  • Tread depth of the tires
  • Tire pressure
  • Tire model
  • Condition of the tires (summer or winter tires)

Worn tires: Already a few millimeters can keep the speedometer 1 percent the speed driven deviates.

When is a speedometer adjustment necessary?

Suspect that from the speedometer displayed value too far above the actual speed driven or even below real value you should get the Car speedometer on Check accuracy to let. You can do this with a Car workshop to do.

For example, will the tires through a new model replaced, it can happen that a car mechatronics technician is checking the speedometer recalibrate got to. Is that problem on the other hand with the speedometer itself, this must be carried out by an experienced specialist readjusted become. Note that for that costs incurred - usually between 100 and 500 euros.

By the way, won't only with the speedometer a tolerance deducted. Even with one Speed ​​measurementwith the speed camera can it to Measurement inaccuracies come. That is why it is here with most Measuring devices from Measurement result a tolerance of 3 km / h (up to 100 km / h) or 3 percent (from 100 km / h) deducted.

FAQ: Speedometer tolerance

How accurate is a car speedometer?

A speedometer on the car never shows the actual speed, but always deviates from the real value.

How big can the difference in the speedometer on the car be?

In newer vehicles, the speedometer may deviate up to ten percent plus 4 km / h from the actual speed.

Can the speedometer also show less?

No, a downward deviation in the speed indicated on the speedometer is not permitted.