Reading your tire's tread: the key to optimal vehicle performance in diverse conditions
This tread thickness examination was first observed in tires manufactured by Nokian. Over time, similar indicators have been adopted by other tire companies, including Continental and Goodyear, and are now found on tires from various manufacturers.
What do the numbers on the tire signify?
The numbers found on the tire are representative of the tread groove depth, measured in millimeters. Each digit corresponds to a unique depth, and as the tread wears down, the corresponding digit eventually disappears.
Typically, the smallest visible digit is '4'. This makes sense because a tread depth of 0.16 inches does not deliver sufficient performance for either winter or summer tires. When only '4' remains on the tire, it signals that while it is still functional, it may soon need replacement. If the number '4' has worn off, it's time to replace the tire.
Why is tread depth crucial?
Tread grooves function as a water reservoir at the tire's contact point with the road. During travel on a wet surface, the tire tread interacts with the road, with the grooves providing space for the water not displaced by the tire. The absence of these grooves would impede water displacement, and as a result, the vehicle's grip would diminish.
The quantity and size of tread grooves at the tire's contact point with the road directly correlate with the space available for water storage. The greater the grooves' number, depth, and width, the more water capacity they offer. This is why winter tires usually feature diagonal tread patterns, also referred to as "fir tree" patterns: it enables more grooves to be generated on the contact surface than a longitudinal tread allows.
The manufacturer determines the nominal width and number of grooves for each tire, making this a non-adjustable factor for consumers following their tire choice. However, depth correlates with wear, offering the users some control over this parameter. Replacing a tire earlier ensures better performance on wet surfaces, while a delayed replacement would significantly compromise its performance.
To fully comprehend the importance of tread groove capacity, consider certain motorsport disciplines where tire notching (i.e., cutting grooves into the tire tread) is employed. In wet conditions, teams often cut grooves into the tire tread in service breaks to adapt them for wet or muddy terrains, albeit with a sacrifice in dry surface grip. This cutting operation always aims to increase groove count or width, thereby boosting the overall water-capacity on the tire's contact surface with the road.