Do larger tires affect speedometer accuracy?

The speedometer of a vehicle determines speed based on the revolutions of the factory sized wheels and, as such, mounting larger tires will affect its accuracy. Fortunately, there are online conversion tools that help determine what speed a vehicle is traveling with larger mounted tires.

A standard speedometer is calibrated to the revolutions of a standard tire size. When larger or smaller tires are installed onto the said vehicle, the calibration of the speedometer will be inaccurate.

1. Larger tires
Large tires have bigger diameters, and so when a larger tire completes a revolution, a longer distance is traveled. This means that the speed of the distance traveled has also increased. After mounting larger tires, it is recommended to have the speedometer calibrated to avoid any accidental speeding violations.
2. Smaller tires
Smaller tires have less of a diameter as opposed to standard tires, which actually slows down the vehicle.
3. Calibration of a speedometer
An electronic speedometer is relatively simple to calibrate using and dynamometer. The vehicle hooks up to the machine and the operator configures it. On newer vehicles, there is also an auto-calibration mode. This allows the vehicle to use the distance traveled, when approximately equal to 1 mile, to calculate its speed. The auto-calibration method can also be used on a dynamometer.