The tread wear indicator is a narrow elevated strip running across the tire's longitudinal tread grooves. The letters TWI (Tread Wear Indicator) are visible on the side of the tire. When approximately 1.6 mm (1/16 inch) is left on the tread, the tread will be at the same height as the tread wear indicator. Replace the tire as soon as possible. Tires with low tread offer very poor traction in rain or snow.