One of the most important checks to perform when doing a tire inspection is the condition of the treads on all four tires. While tread wear is particularly important on the drive wheels, which are the front wheels on most cars, it does matter for all tires because treads are important for both braking and handling as well as drive and steering.
The first thing to check is uneven tread wear. If the tires are wearing more on one side or the other, this is a sign that they are under stress and are more likely to fail. The next thing to look at is tread depth. Most tires have smooth bars that run across the grooves in the tread, which serve as an indicator of when the tire must be changed. If the tread is worn down to the point where it is level with the bar, it is time to replace the tire immediately. One way to check tread depth is with a U.S. Lincoln head penny. If the penny can be inserted far enough into the groove to cover the top of Lincoln's head, the tire is still good. If not, it should be changed. The final thing to check is for foreign objects in the tread. Owners should go through and remove any debris, such as small rocks or bits of glass that might be caught in the tread, as tire wear could force them deeper into the tire, and possibly lead to a puncture.