A tire's tread is designed to provide traction in a typical range of driving conditions. While racing tires are designed solid and smooth to maximize contact on perfectly flat, dry surfaces, the average driver requires practical tires that can handle everyday factors such as wet weather, varying degrees of road wear, and heat buildup at high speeds. The ribs, grooves, sipes, and other elements that make up a tread pattern are each designed to improve particular handling characteristics in the tire.
Blocks: Also sometimes called tread lugs, tread blocks are the parts of the tread area that come in contact with the road, separated by wide grooves. Depending on their size and shape, tread blocks determine a tire's performance and grip capabilities. Wider tread blocks put more rubber in contact with the road, improving driver input feedback and handling response on highways. On the other hand, blocks with jagged shapes are ideal for rugged off-road traction. Tread blocks also affect the tire's harmonics and pitch noise generation while driving.
Ribs: Tires today often have tread rib patterns formed by wide main grooves that run circumferentially around the tire, dividing the tread area into long, circumferential sections or ribs. These rib blocks run parallel with the tire's line of travel, providing a consistent contact patch for stable traction and reduced rolling resistance. Each rib may be designed as a solid, continuous block for increased tread rigidity, or divided by lateral grooves into smaller blocks for improved cooling.
Each rib is designed to fulfill a particular role. The center rib, or the rib closest to the tire's centerline, is primarily responsible for the tire's linear performance characteristics. It provides contact and traction during braking and accelerating, and stabilizes the tire's directional input. The shoulder ribs, or the ribs closest to each sidewall, are responsible for the tire's lateral handling capabilities. They support the tire and provide grip during cornering, and are generally the thickest parts of the tread.
Grooves: Also called tread voids or slots, the wide grooves between each rib and block are vital to safe wet driving. When driving on wet roads at high speeds, a thin film of water may form under the tires and separate the tread from the road, causing the vehicle to lose traction and hydroplane. Circumferential and lateral grooves provide channels that allow water to escape from under the treads, preventing hydroplaning and maintaining control on wet roads.
Additionally, grooves create "biting" edges that sink into loose terrain such as mud or snow for increased traction. Grooves also allow air to flow between tread blocks, cooling down the tire's heat buildup. However, increased grooves also decrease the tire's road contact area and reduce block stiffness, which can interfere with braking and steering response.
Notches: Notches are short lateral grooves that only extend partway across a tread rib or block. They assist in water evacuation by draining water from the middle of tread elements, while still linking the rib or block together to preserve tread integrity. Like full-length grooves, notches provide biting grip on mud and snow. Notches also assist in dissipating the tire's heat buildup.
Sipes: Sipes are extremely thin slits in a tread block, similar to grooves or notches, but much narrower. Like grooves, sipes make the tread more flexible, increasing traction in wet or icy conditions at the cost of some dry handling precision. They often have wavy or zigzag shapes for extra biting grip. Many all-season tires are designed with 3-dimensional sipes that are designed to flex on wet or snowy roads for increased wet traction, but lock together on dry surfaces to prevent tread squirm.
Depending on how its blocks, sipes, and grooves are arranged, a tire's overall tread pattern can be categorized as one of three types: symmetrical, asymmetric, or directional. Each pattern offers different performance characteristics for different driving needs.
Symmetrical: Symmetrical treads are the most common type of tire pattern. A symmetrical tire features the same arrangement of ribs, blocks, grooves, notches, and sipes on each half of its tread. This allows the tire to be mounted and rotated in either direction for ease of installation. Symmetrical tires offer decent value for day-to-day driving, and are commonly used on standard passenger and highway tires.
Whether it features continuous ribs or rows of repeating blocks, a symmetrical tire has roughly the same void-to-contact ratio on both tread halves. This helps to uniformly distribute road pressure across the contact patch, boosting the tire's straight-line stability and improving linear tracking. A symmetrical tread design helps to maintain the tire's direction of travel, promoting smoother ride quality and encouraging even treadwear for a longer-lasting tire.
Asymmetric: An asymmetric tire has a different pattern on each half of its tread, with one side designed to face inward and one side designed to face outward. This allows each half to incorporate different tread elements that improve both wet and dry handling characteristics. Due to their versatility, asymmetric tread patterns are often used on high performance and premium all-season tires. Asymmetric tires may only be mounted or rotated in one direction.
Usually, the inner tread is optimized for wet and snow handling. They typically feature smaller blocks with increased lateral grooves for enhanced water evacuation and dense siping for biting snow grip, increasing traction on slippery roads. On the other hand, the outer tread is optimized for stabilized dry handling. They generally have large, wide shoulder blocks for increased road contact and lateral grip during high-speed turns. This allows for sharper turns and increases cornering traction on dry surfaces.
Directional: On a directional tire, the two halves of the tread are designed to mirror each other, with angled lateral grooves forming a repeating V-shaped pattern all around the tire. These V-shaped grooves excel at channeling water, slush, or snow away from the contact patch as the tire rolls. For this reason, directional tread patterns are frequently used on both summer performance tires and dedicated winter tires. A directional tire may only be mounted and rotated in one direction, indicated by an arrow on its sidewall.
A directional tire offers exceptional hydroplane resistance even at high speeds. The angle of its grooves are highly effective at redirecting water drainage and flow, especially when combined with open shoulder slots, while the shape of its blocks are ideal for cutting through rainwater in the tire's path. Many high-performance tires feature directional tread elements for extreme wet handling and road grip. Some directional tires are designed with a solid center rib for centering stability, while others feature a main center groove for efficient water evacuation.