You’ve heard about the tire tread and penny depth testing trick, but you don’t know what it is. Almost every state mandates a minimum tire tread depth of 2/32 of an inch for passenger car tires, as measure from the top of a tread wear indicator to the top of the tread. The wear indicator will appear in the tread grooves as a small bump. It just so happens that the lettering over Abe Lincoln’s head on a penny is exactly 2/32 of an inch tall. To make sure you have legal tread depth, grasp a penny with Abe Lincoln upside down, find a wear indicator, and place the penny on top of the indicator. If you can see the letters, you have insufficient tread and should replace your tires.
For more info, see How to Check Your Tire Tread