Is Your Car’s Speedometer Reading Accurate?
When using a GPS or Sat-Nav, have you ever discovered a major discrepancy between the two? If you have, then there is no need for panic; your speedometer is working perfectly, at least for the time being. Do you think your speedometer is accurate?
To what extent do you trust your GPS more than your speedometer? Your speedometer is probably off by a significant margin, showing a far faster speed than you actually are moving at. But let's examine the internal dynamics of a car's speedometer.
How Does the Speedometer in Your Car Work?
To determine speed, a car's speedometer uses the rotational movement of the wheel, driveshaft, or axle. Through the use of the transmission's speed sensor, the speedometer can determine how quickly the wheels are turning.
You know very well that the definition of speed is the ratio of distance traveled to the amount of time it takes to travel that distance. However, the speed shown by a speedometer is not always the actual speed at which you are driving.
Your car records the number of times the wheels have rotated, performs some very precise math, and then displays the result.
A car's speedometer, however, is highly dependent on the wheels' diameter to be accurate. If you've had the same car for a while, the speed it displays now may not be the same as when you initially drove it home from the dealer.
However, this only holds true if you have not replaced the wheel since you first bought the car. As a result, adjusting the wheels or tires will result in a different reading on the speedometer.
Changing to new tires that are larger in diameter than the previous ones will result in a higher top speed and vice versa.
Problems with Car Speedometers
There are a lot of different parts that go into making up a speedometer's mechanism, which can sometimes lead to problems with the device.
The head of the speedometer might malfunction, rendering the meter useless. When the "Check Engine Light" comes on, it's often because of an issue with the speed indication.
This often occurs when the speed sensors in the car stop relaying data to the car's computer. When this happens, it may be time to change the speed cable.
Does Your Speedometer Give You an Accurate Reading?
In the USA, the margin of error for a car's speedometer is 4%. This means that even at very moderate speeds, you may actually be moving faster than the speedometer shows.
However, at faster speeds, you could be traveling no more than 3 mph slower. You may blame your tires for this since the reading on your speedometer can be significantly altered by either under or over-inflation.
Conclusion
Is the speedometer on your car accurate? Having read this, you should have a good idea of whether or not your speedometer is accurate. That doesn't mean you can't rely on your speedometer, though.
At Euro Car Doctor, we have ASE-certified technicians who can help you to check if your car’s speedometer reading is accurate or not.