How can tire tread depth be measured?

Tire tread depth can be effectively measured using a tread depth gauge or the "penny test." A tread depth gauge is a specialized tool designed to provide an accurate measurement of the remaining tread depth on a tire. This ensures that the readings are precise and reliable, allowing one to determine whether the tires are safe for use.

The "penny test" is a simple method that involves inserting a penny into the tread grooves with Lincoln's head facing down. If the top of his head is visible, the tread is too shallow and the tire should be replaced. This method offers a quick visual indication of tread wear, but it's worth noting that using a dedicated tread depth gauge gives a more accurate measurement.

The other methods mentioned have limitations. Using a ruler may not provide the precision needed, particularly in the narrow grooves of modern tire treads. Visual inspection alone can be misleading, as it relies on subjective judgment and may not accurately reflect tread depth. Using a digital caliper could work for measurement, but it's not commonly used for tire tread depth due to the design of tire grooves which can make measurement difficult without proper adaptation.