New tire technology: The numbers that can save your grip
A tire's tread depth is crucial for its performance on wet surfaces and snow. As a result, tires have a TWI (Tread Wear Indicator) that shows when a tire is worn out. Some manufacturers have introduced new, simpler, and more precise indicators.
The TWI is a long-used solution involving low blocks between the tread elements. When the tread wears down to its height, the tire is due for replacement. This system works well for summer tires. Many drivers, quite sensibly, choose to replace winter tires at lower wear levels than summer ones. This is where the numbers placed on the tire tread become helpful.
The first numbers of this kind appeared on Nokian tires, but they are also found with manufacturers like Continental and Goodyear. Other producers are starting to use them, too. These numbers are the tread groove depth markings in millimetres. The numbers on the tire indicate the groove depth and disappear as the tread wears away.
The smallest visible number is 4, which is intentional. A tread depth of 4 millimetres (about 0.16 inches) stops providing adequate grip for tires, especially winter ones and summer ones. Seeing only the "four" signals that the tire is still usable, you should consider replacing it. When the last number disappears, the tire only qualifies for replacement.
Why is tread depth so important?
Tread grooves act like reservoirs for water at the road contact point. When a car drives on a wet surface, these grooves create space for the water that would otherwise remain under the tire. If the tire were completely smooth, the water wouldn't be removed, leading to a loss of traction.
The more grooves a tire has, the more water it can store, increasing driving safety. Grooves are more efficient the deeper and wider they are and the more numerous they are on the tire. That's why winter tires often have a "herringbone" pattern, allowing for more grooves at the road contact point than a longitudinal pattern.
This is similar to understanding that the diagonal is always longer than any side in a rectangle. It contacts the asphalt surface in a rectangle-like form.
The width and number of grooves are determined by the tire manufacturer, and we cannot change them by choosing a model. For users, the key aspect is the depth of the grooves, which changes as the tire wears. Replacing tires earlier means better performance on wet roads; delaying can have negative effects.
To better understand the importance of tread grooves, consider motorsports, where tread cutting adapts tires to wet or dirty conditions. During rainy races, teams use tread cutting, even though it involves a worse grip on dry surfaces. This increases the number of grooves or their width to enhance the overall capacity at the road contact point.
