The tread's center rib has the words "Replacement Tire Monitor" on it multiple times. With the tread wear the words wear out and, when just "Replace Tire" is visible on the tread, the tire needs to be replaced as it no longer has good road gripping ability. The Visual Alignment Indicators are placed on either side of the tire's shoulders. They also wear with the tread and indicate whether the vehicle's alignment is good or not. If the two parallel indicators wear in the same manner, the alignment is good. However, if they are not identical, it means that the alignment is off and the tire is wearing in an irregular manner. This allows the driver to recognize irregular wear across the tread area, which prevents uneven wear patterns from forming across the tread surface.