Check your tire's tread at least once a month when you're checking their pressure. Tires have built-in "treadwear indicators," which are raised sections that run in between the tire's tread. When the tread is worn down so that it's level with the tread indicator, it's time to replace your tires.
tread remaining at three pints in the center two grooves and average the three measurements. Where the averaged tread depth remaining line meets the appropriate original tread depth column, the percent of tread worn off the tire will be found. Using this percentage to calculate the customer's replacement price.