A question that not many people want to hear is how fast they were going. Everyone knows to follow the speed limits, but occasionally they feel rushed or impatient and start driving a little bit faster. This isn’t very safe, for them or others, so the police patrol the roads trying to keep speeding to a minimum. What’s more dangerous however is when people are unaware they are speeding because of a speedometer malfunction, or because it is off because of modifications to a vehicle. This is why speedometer calibration and speedometer repair is important, because it can be dangerous to go faster than the posted limit, but especially so if you don’t know you are doing it.

How do Speedometers Work?

This is a good question, and helps understand why speedometer calibration is important. They rely on electromagnetic fields to let you know how fast your wheels are turning, and thus how fast you are going at any given time. The science behind speedometers is pretty cool, but in the most basic terms, there is a long flexible cable attached to the wheel. This spins in time with the wheel, and on the other side is attached to a small magnet that rotates inside a metal cup. The magnetic and electrical force this generates try to spin the cup as well. The cup has a hairspring on it that stops it from rotating very far, but lets it move a little bit, pushing the dial on your car up just a little bit. The faster the wheels turn, the harder the magnetic forces from the cable push on the cup, and by extension the dial, pushing it up and showing that you are going faster.


Actually knowing how fast you are going depends on the calibration of the spring and parts within the speedometer, and that whoever calibrated them had their math right. This is why Speedometer repair and calibration is important, because they are delicately balanced, and a broken one can look fine, and have all working parts, but still give you a wrong speed when you drive. In fact, no speedometer is 100% accurate, and companies aim for a range between 1%-5% too fast or too slow.

Potential Issues

Speedometer calibration can get thrown off when parts of a car are modified, most significantly the wheel size. When the wheel or tires are changed then the math was done to get the speedometer to turn right, and portray an accurate speed gets thrown off and the dial will no longer accurately give your speed. After you have an accident, or change your tires to a different size you should go in to get your speedometer recalibrated, because it could be off, making every drive you make dangerous.

High Speeds

Speedometers are a very important and often overlooked part of every car that helps everyone drive more safely and efficiently. IF you think yours might be off you should get it checked out, and recalibrated or repaired. It is important to be safe while driving, and a speedometer is a big part of staying safe.