TIRE WEAR AND DAMAGE

Wear bars, also called tread wear indicators or TWI, are raised rubber ridges moulded into the bottom of the main tread grooves at 1.6 mm. When they were new they sat well below the tread surface. When the tread wears down level with them, the tire has reached its legal wear limit and must be replaced.

Inside the main circumferential grooves, running across the groove floor. Many tires mark their location with a small triangle, the letters TWI, or a brand symbol on the shoulder or lower sidewall so you know which groove to look into. Check them in several places around the tire, because wear is rarely even.

It maps wear patterns to causes. Both shoulders worn means underinflation. Centre worn means overinflation. One shoulder worn means a camber or toe alignment issue. A cupped or scalloped surface means imbalance or worn shock absorbers. Feathering across the tread blocks means a toe problem. Each pattern points at a specific fix.

Chronic underinflation. With too little pressure the tire flexes excessively and the shoulders carry more load than the centre. Underinflated tires also build heat, hurt fuel economy, and in severe cases fail structurally at speed. Cold Canadian weather drops pressure naturally, which is why monthly winter checks matter.

An uneven wavy pattern around the circumference of the tread where high and low spots alternate. It usually indicates wheel imbalance or worn shock absorbers letting the tire bounce rather than maintaining steady road contact. Cupping generates noise and vibration and it is not reversible once it develops.

A bulge or bubble in the sidewall means internal cords have broken and the tire can fail without warning. Any cut deep enough to expose cord material. Any separation between tread and casing. Any tire driven while flat. Tread level with the wear bars. In each of these cases, replace rather than repair.