Understanding Tire Siping

Close-up of a spare wheel

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We hear all the time from tire makers about their superior siping patterns, but what are sipes anyway?

In 1923, a slaughterhouse worker named John F. Sipe grew tired of his rubber-soled shoes slipping on the wet slaughterhouse floor. Using a sharp knife, he cut a series of thin grooves in the rubber of his shoes and found that the grooves provided much better traction. Somewhat later, Goodyear picked up on the idea for use on tires.

The grooves and channels cut into the tire serve to evacuate deep water quickly out from under the tread, but even after most of the water has been evacuated, a very thin and very slick layer of water will still remain. As the tire tread flexes in contact with the pavement, the sipes expand, forming an area of lower air pressure inside the siping cuts, which then sucks that last tiny bit of water into the sipes providing a firm contact between the tire tread and the road. These are generally called rain sipes.

Most snow tires now also use a specialized siping, a zigzagging pattern cut many times through each tread block. This siping pattern was first developed by Nokian and patented as the “Hakka Sipe.” These cuts split the tread block into multiple jagged “fingers.” When the tread makes contact with the pavement, multiple parallel cuts allow the tread block to flex, thus bringing the jagged edges of each “finger” into contact with the snow or ice, greatly increasing the tread's surface area in contact with the ground and allowing the diamond-shaped edges to bite into the snow.

Continuing technological advances in how sipes are formed or cut have allowed the development of what are called 3-dimensional self-locking sipes. These sipes have an internal topological structure beneath the surface of the tread which allows the sipes to flex, but only in certain directions. For example, this video by Goodyear shows how their self-locking sip allow a piece of the tread to flex laterally while the dome-shaped protrusions prevent the tread block from flexing in any direction but the one that the designers intended. Other variations of 3D self-locking sipes only allow the tread to flex so far, or prevent the entire tread block from twisting as with the ones on the WRG2.

Nokian has also developed a brand-new type of siping for the newest version of the Hakka R, which contains small polyhedral chambers under the tire tread, allowing for more room for water to be drawn into the sipes. Nokian calls these “Pump Sipes.”

Many performance tires have very simple and sparse siping patterns designed solely to remove water from the pavement and provide for high-performance grip in wet conditions. In the early days of siping most patterns were cut into already-formed tread using a wire blade or a siping tool, and many tire owners would use a siping tool to cut their own patterns into their tires. Nowadays computer-designed siping patterns are formed directly into the tread when the tire is cured and such experimentation by tire owners is highly discouraged.

Michelin’s Chris Tolbert says factory sipes are superior. “The angle, width and depth are certainly much more precise when originally molded into the tire. Michelin does not recommend aftermarket siping, but rather selecting the appropriate tread for the intended use or application.”

“If we really believed more sipes would help, we would put them in,” says Continental Tire’s Curtis Decker.