2. Use your Tread Wear Indicator (TWI) – premium tyre manufacturers such as Bridgestone mould TWI’s into the design of the tyres’ tread pattern. It’s easily identifiable; it’s made up of six or more small rubs across the bottom of the main tread grooves, which are usually 1.6mm to 2mm above the base of the groove. The legal limit of 1.6mm is reached when the tyre is worn to the level of the tread wear indicators in the main groove – as soon as this happens, the tyre should be replaced.