Most people don't realize that their speedometer is calibrated for their specific vehicle. This means that if you change the size of your tires, you will need to recalibrate your speedometer so it is accurate. Many people don't do this and they end up driving too fast or slow because they are relying on an inaccurate speedometer.
It's actually not that difficult to calibrate your speedometer and there are a few different ways that you can do it. One way is to use a GPS unit. You can drive at a constant speed for a mile and then check the GPS to see how fast you were going. If your speedometer was off, then you know by how much and you can adjust it accordingly.
Another way to calibrate your speedometer is with a radar detector. You can drive at a constant speed and then have someone else measure your speed with a radar detector from behind. Again, if your speedometer is off, then you'll know by how much and can adjust it as needed.
The best way to ensure accuracy, however, is to take your car into the dealership or service center and have them recalibrate it for you using their own tools and equipment. This way, you'll know for sure that your car'sspeedometer is reading correctly before hitting the road again