Automobile speedometer - ERROR!

Automobile speedometer



Possible error automobile speedometer readings depends on the characteristics of its design, and a number of other reasons. Instruments with mechanical drive (with rope) - the least accurate, with the electric - a little better, but their testimony has some error. According to requirements of normative documents of the EU, to underestimate mileage in any case should not, and an increase in their permitted a maximum of 10% plus 4 km / h. The higher the speed, the greater the difference between the speedometer and the actual speed. This explains the results of separate "drivers", showing their cars at the maximum speed is higher than those specified in the technical characteristics of their car.

The accuracy of the speedometer and depends on the size installed on vehicle tires and even the pressure in them. For the principle of work of any speedometer is based on the translation of the number of wheel revolutions in the position of the arrow on the scale. If you set the wheels of greater diameter than those used to determine the gear ratio, the speedometer will understate the testimony. For example, instead of tires in size 175/70 R13 set tire 185/70 R13. Its outer diameter of more than 14 mm. Absolutely accurate speedometer will show a 90 km / h, and the real rate would be 92.19 km / h. If instead of the prescribed construction tires 185/70 R13 set the smaller the diameter 175/70 R13, with the same mileage actual speed will be 87.86 km / h, ie, the smaller wheel unit overstated testimony.

Check the speedometer on your car can be as follows: for the city to detect by the time it moves with constant velocity between kilometer posts, to calculate the true speed and compare it with the speedometer. The more traveled with constant velocity distance, the more accurate result. For example, the speedometer shows 90 km / h. You drive through 5 km (5000 m) for 3 min 28 sec (208). Your average speed will be 5000:208 = 24 m / sec. We translate meters per second to kilometers per hour: 24h3, 6 = 86,4 km / h.