The Tread Pattern includes multiple ribs, blocks and lugs or a combination of all three. The most common passenger and light truck tyres feature 5-rib designs, where 5 tread ribs are separated by 4 circumferential grooves. The ribs include the outboard shoulder, outboard intermediate, center, inboard intermediate and inboard shoulder.
- Outboard Shoulder: the outer edge of the tread between the tyre’s footprint and its sidewall. The outboard shoulder encounters the highest lateral stresses as it holds a vehicle in a corner.
- Outboard Intermediate: the tread rib adjacent to the outboard shoulder. The outboard edge of outboard intermediate ribs experience the second highest lateral stresses and wear when cornering.
- Center: contributes to straight-line acceleration and braking traction, as well as highway cruising stability and tracking.
- Inboard Intermediate: the tread rib adjacent to the inboard shoulder. Prone to faster wear if the vehicle’s alignment specifies negative camber.
- Inboard Shoulder: the inward edge of the tread between the tyre’s footprint and its sidewall. The inboard shoulder encounters the lowest stresses in a corner. Prone to faster wear if the vehicle’s alignment specifies negative camber.
RibA continuous strip of tread rubber around a tyre’s circumference. Multiple side-by-side ribs are typically molded across a tyre’s tread.
BlockFreestanding, independent tread blocks are positioned around the tyre’s circumference. Multiple side-by-side rows of tread blocks are typically molded across a tyre’s tread.
Extra large, freestanding, independent lugs positioned around the tyre’s circumference. Commonly used to describe design elements of mud-terrain tyre tread patterns.
- Circumferential Grooves
- Lateral Grooves
Tie BarsShort rubber links molded across lateral grooves between adjacent tread blocks. Often used between independent shoulder tread blocks, tie bars connect tread elements circumferentially to reduce tread squirm when rolling, as well as during acceleration and braking. By opposing block movement, tie bars promote stability that help resist irregular wear. However as the tyre wears down to the tie bars, the tie bar portion of the lateral groove will disappear and it will be reduced into a lateral notch.
Typically featured in all-season and all-terrain tyres, sipes are thin slits molded into an otherwise smooth tread surface to improve traction in wet, snowy or icy road conditions. Sipes essentially subdivide tread blocks into smaller elements to provide additional biting edges for foul-weather traction.
Straight sipes simplify the manufacturing process and make it easier to remove a tyre from its mold, however many of today’s sipes feature zigzag shapes or 3-dimensional designs that help lock the elements of the tread block together to enhance handling while increasing foul-weather traction.
The quantity, location and design of sipes are carefully engineered into a tyre’s tread design to balance traction, handling and wear. Engineers strategically locate sipes in tread blocks to reduce the possibility of squirmy handling in dry, hot conditions.
Sipes can be molded with a v-shaped blade of less depth than the tread circumferential grooves. While its overall depth will remain the same, sipes designed this way will shorten in length as the tyre wears. Additionally some sipes will often virtually disappear as the tyre wear reaches the tread-wear indicators. This evolution in a tread design as the tyre wears typically sacrifices the tyre’s wet and wintertime traction, reducing the vehicle’s ability to accelerate, brake and corner in foul-weather conditions. Fortunately this evolution in tread design is visually apparent as the design elements disappear and the tyre approaches a slick, unadorned tread pattern.
2/32” (1.6mm) tall raised bars molded across the bottom of each circumferential tread groove from shoulder to shoulder. Tread-wear indicators will appear as a solid strip across the tread design to enable a person visually inspecting a tyre to easily determine whether any of the circumferential grooves have worn to 2/32” (1.6mm) of remaining tread depth. Tyre warranties expire when the remaining tread depth matches the height of the tread-wear indicator and tyres are considered worn out.
- Tyres with 12-inch or smaller wheel (rim) diameters are required to have a minimum of three sets of treadwear indicators.
- Tyre tread depth should never be measured at the tread-wear indicators.