Tire Tread Test Tips
It used to be that to check tire tread wear, a driver inserted a penny into the tread gap. If you couldn't see the top of Lincoln's head, the tire tread was adequate. These days it is recommended that a quarter be used for the test, and Lincoln has been swapped out for Washington. This is to allow for less time between tire changes and a safer amount of tire tread. If the top of Washington's head can be seen, that means there is one-eighth of an inch of tread left, and ample time to get those tires replaced.