how do speedometers work?
In: Technology
The wheels spin a flexible shaft that looks like a cable. This shaft has a magnet on the other end that sits inside another circular magnet that, via a spring and a couple of gears, is attached to the needle in the speedometer. When the shaft spins, the other magnet wants to spin and twist the spring/gears, but it’s designed with some resistance to stop it from spinning; spinning the shaft faster lets the other magnet overcome that resistance. Because the resistance has been specifically designed, the speed the shaft and, therefore, the wheels, need to spin at correlates directly with the numbers written on the speedometer, giving you your speed.
Note that because of this, the wheel is effectively a gear, giving the reason why you need to put the right sized wheels on your car; if you change the size of the wheels, the original speedometer gives the wrong reading.
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