The speedometer helps drivers to determine the speed of movement at the moment, as over time, the eyes of car owners get used to it and a sufficiently high speed can seem very slow. Next, we will talk about what kind of device it is and why it can display incorrect information.
A speedometer is one of the on-board instruments in a car, located on the dashboard, it is necessary to instantly determine at what speed the car is moving. Its data is measured in kilometers (km / h), and in some foreign countries - in miles (m / h). This device is of analog (mechanical) type and digital.
How does he work?
In a car with rear-wheel drive, this device reads information from the secondary shaft of the gearbox and, starting from it, calculates the speed of movement. Thus, the accuracy of its data is influenced by the size of the tires, the gear ratio of the rear axle gearbox and the accuracy of the speedometer itself.
On many modern cars, instead of the usual analog speedometer, a digital one is installed. It is convenient to read information with such a device, but it has inertia. For example, when driving on a highway at a speed of 120 km / h, it is quite difficult to quickly reduce it to 79 km / h.
On a front-wheel drive car, the speedometer calculates the driving speed by reading the data from the left wheel drive. This suggests that to the inaccuracy of the device and the dependence on the size of the tire, it is necessary to add the effect of rounding the roadway: when turning to the left, the readings of the device are slightly less than on a straight road, and when turning to the right, the readings will be slightly higher.
Why can a speedometer lie?
In the case of this device, it is easy to understand its inaccuracy upward. First of all, this reduces the risk of the driver breaking the speed of movement and receiving a fine. In the background, the fact that with low speed readings, car owners would sue car manufacturers and prove that accidents and fines are the fault of the meter's malfunctioning.
The whole problem is that it is much more difficult for him to show accurate data than the rest of the measuring instruments in the car. This depends on the fact that driving speed is most often measured by the speed of rotation of the wheels. In turn, this speed is influenced by the size of the wheel, which is a variable figure.
Now devices are being produced that have an inaccuracy of 10%, but the speed should be 200 km / h. This is usually a variable parameter, that is, when driving at a speed of 110 km / h, the deviation will be 5-10 km / h, and if you drive 60 km / h or less, then the inaccuracy is quite insignificant.
How does the replacement of standard tires affect the accuracy of the device?
When 185 / 60R14 tires are replaced with 195 / 55R15, the accuracy of the device will change by 2.5%. It seems to be a little, but how it will develop with the accuracy of the device, with tire wear and pressure in them is unknown. It is worth noting that low pressure also affects the accuracy of the data.
What are the malfunctions of the speedometer?
The main malfunctions are as follows:
- worm gears are destroyed, they are often plastic;
- the cable breaks off at the point of engagement with the high-speed unit screwed into the gearbox;
- the sensor contacts are oxidized, the power supply wires break off (for self-checking the power, you will need to use a multimeter);
- there are problems in the electrics located inside the instrument panel.
The speedometer is calculated for miles, but how can this data be calculated in kilometers?
This applies to American cars. Everything is simple here: 1 mile equals 1.6 km. This means that when the meter reads 90 mph, it will be 144 km / h. That is, you need to multiply 90 by 1, 6. When counting down, you need to divide by 1, 6.
