Why does the speedometer show the speed with a deviation??
At any car ride the eye always falls on the speedometer. This is how drivers keep speed in the eye. If the speedometer indicates that the speed is too high, you must reduce speed. If the speed is below the permissible maximum speed, you can step on the gas again if the road, visibility and weather conditions permit.
Particularly important is the view of the speedometer, after a vehicle driver speed camera was. Because the speedometer can be used to speedometer quickly determine by how much km/h the speed limit exceeded was. If this is known, it can already be guessed at this point which sanctions will be imposed on the speeding violation due.
But the speedometer always shows the exact speed driven at? How does a speedometer actually? What if the displayed speed under or over the speed actually driven? Why does the speedometer show a tolerance spoken? These questions are clarified in the following.
What is a tachometer and how accurate is a tachometer display??
A speedometer in 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 in the driver’s direct field of vision.
The tacho should exceed the regulations the EU Directive 75/443/EEC corresponding. Here it is further specified that the tacho display illuminated must be accurate, so that the measured value is not only at tag, but also with night is clearly recognizable. The display area has speeds up to that specified by the manufacturer maximum speed to include.
Tolerance: with the speedometer, accuracy is not mandatory – a deviation is allowed up to a certain limit.
Many car drivers are surprised when the speed limit speed camera measured speed on the penalty notice from the deviation you see on the speedometer on the car have 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 speed limit set by the speedometer measured speed from the actual speed being driven deviate can:
the displayed speed must never be below the actual speed.
The display value on the speedometer therefore via the actual speed, but never below. How much tolerance the speedometer may have? There are guidelines for how much the speedometer from the deviate from the actual speed may:
- At vehicles registered before 1991 the displayed value may be changed up to 7 percent from the actual.
- At permitted after 1991vehicles the displayed value may deviate up to 10 percent deviate from the actual. (+ 4 km/h)
An example: a newer vehicle goes 100 km/h. The speedometer may thus display a value of up to 114 km/h. If the speedometer display shows a value lower than 100 km/h, this is not allowed.
This tolerance at speedometer can manufacturer at autobuild exhaust. In order for the installed speedometer to be permissible, the tolerance not exceeded and the actual speed does not fall below will be. As a rule, however, the deviation in the car speedometer is not quite so pronounced. Most speedometers differ only by a few km/h from the actual value from.
By the way, it is different with navigation devices: here, as a rule, almost the actual speed displayed. This is calculated at the navi by means of GPS determined. Normally the displayed value deviates only by one km/h from the real one.
Conclusion on speedometer accuracy: a speedometer usually shows not exactly the actual speed at. There will be a certain tolerance limit granted measurement inaccuracies should be compensated. If your speedometer is inaccurate, this is no reason to worry. However, at the deviation on the speedometer can be distinguished:
- The speedometer shows too much: up to a certain tolerance limit this is permissible.
- The speedometer shows too little: this is not allowed.
How does a speedometer measure and how does it deviate?
Insufficient accuracy: readjusting the speedometer may be necessary in some circumstances.
That the car speedometer a certain tolerance is granted, is due to the fact that in this way inaccuracies should be compensated during measurement. The driven speed is in fact over the wheel revolutions and the required time determined. On the basis of previously determined average value, that as comparative values then the speed determined.
Since tires and their condition change the speedometer over time, it must be tolerance be granted. The following factors have a influence on the characteristics of tire and thus on the measured speed:
- Tire tread depth
- Tire pressure
- tire model
- Condition of the tires (summer or winter tires)
worn tires: already few millimeters can ensure that the tachometer 1 percent from the driven speed deviates.
When is a speedometer adjustment necessary?
Do you suspect that the speedometer displayed value too far above the actual speed driven or even below the real value you should check the auto-tacho at check accuracy let. This can automotive workshop do.
If, for example, the tires by a new model replaced, an automotive mechatronics technician may have to change the speedometer recalibrate must. If the problem on the other hand at the speedometer itself, this must be done by an experienced specialist readjusted become. Note that for this costs incurred – usually between 100 and 500 euro.
By the way only at the speedometer a tolerance subtracted. Also with a speed measurement with the speed camera it can lead to measurement inaccuracies come. Therefore here with the most measuring devices from the measuring result a tolerance from 3 km/h (up to 100 km/h) or 3 percent (from 100 km/h) subtracted.
FAQ: speedometer tolerance
A speedometer on a car never shows the actual speed driven, but always deviates from the real value.
For newer vehicles, the speedometer may deviate upwards by ten percent plus 4 km/h from the actual speed driven.
No, a downward deviation in the displayed speed on the speedometer is not permitted.