How Changing Tire Size Affects Speedometer Accuracy

Many car owners do not realize the importance of maintaining the overall diameter (OD) of the original tire when upgrading to larger tires and wheels. This measurement is crucial for the proper functioning of the vehicle and accurate speedometer readings.

If the new tire has a lower profile, it must be mounted on a larger wheel so that the overall diameter of the new tire closely matches that of the original tire. A difference of more than 5% in overall diameter can affect the vehicle's transmission system and cause the speedometer to display incorrect readings.

Why is this important?

The speedometer is calibrated at the factory based on the exact size of the original tires. If you switch to taller tires, the circumference of the tire increases. This means that one rotation of the tire covers a longer distance. Since the speedometer is calibrated to the old tire size, it will show a lower speed than your actual speed.

For example, if your new tire is 3% taller, when your speedometer shows 60 km/h, you are actually traveling at 63.3 km/h. This can create safety issues and result in fines.

How to check speedometer accuracy?

The easiest way to check accuracy is by performing a road test. Take a friend or passenger with a stopwatch. Set the cruise control to 60 km/h and start the stopwatch as you pass a kilometer marker. It should take 60 seconds to reach the next kilometer marker. Repeat this test 3-4 times and calculate the average time. If the average time differs by more than 3 seconds, your speedometer likely needs recalibration.

Conclusion:

Be careful when changing your tire and wheel sizes. Choosing the correct tire diameter ensures proper operation of the transmission system and accurate speedometer readings. At ASKO stores, you can find high-quality tires suitable for your vehicle. To learn more about ASKO, please fill out the form below.