Feature Article: Siping Strides

John Baxter | December 01, 2009

Tire makers take tread to new levels through advanced siping, improving traction and longevity.

Cover-story-1Modern tread designs are complicated affairs. Ribs, intervals between tread blocks, and hairline slits called sipes are interconnected to deliver higher levels of performance.

Computer modeling has enabled exhaustive virtual and demonstration-type testing where the tread’s behavior can be watched through glass. In due course, major tire manufacturers have figured out how to use siping to improve wet traction, prevent irregular wear and even help tires run cooler.

The evolution of siping suggests that when purchasing new tires or picking the tread pattern for a retread, you should ask the company how any model’s sipe design works with the rest of the tread pattern and how it affects the tire’s lifespan. If you do off-road or severe service work, ask if the siping is compatible, as some sipes can trap small stones and cause damage. You might also want to talk about rotating a tire from its original position and how its siping is likely to affect operation on another type of axle. And, if you do your own siping, be sure to ask about how the manufacturer’s warranty might be affected.

Two major benefits of siping advances are improved heat dispersion and traction.

“Part of the energy that wears a tire comes from heat,” says Weir Schankel, manager of Van Alstine Manufacturing, which makes an aftermarket siping tool. “When a siped tire warms up, the sipes open up and this means more surface for dispersion of heat.” He notes that in car racing, where tires sometimes blister from heat, drivers have found their tires run cooler after siping.

The main function of sipes is enhancing traction. When driving in snow, for example, “anything that can’t be evacuated gets pushed into the sipes so there is more tread block touching the road,” says Walt Weller of CMA LLC, the maker of Double Coin tires.

Sipes have their drawbacks, too. Chris Tolbert, business segment manager, Michelin Americas Truck Tires, says that siping reduces tread life and fuel efficiency. “The more sipes a tire has and the deeper the sipes are, the more unstable the tread is, which can lead to blocks chunking out and use of extra fuel,” he says.

Michelin designed a sipe pattern to help compensate for these factors. “Our Matrix Siping molds zig-zag grooves into the walls of our sipes,” Tolbert says. “When the tread design rolls through the contact patch, the sipe walls lock together. By doing this, the technology resists unnecessary horizontal and vertical movement, offering longer life than traditionally siped tread.”

Bridgestone's R195F trailer uses cross-rip sipes to evacuate the water into the grooves for a solid grip on wet roads.
Bridgestone's R195F trailer uses cross-rip sipes to evacuate the water into the grooves for a solid grip on wet roads.

Continental has a unique sipe called a Visual Alignment Indicator that helps users recognize irregular “river” wear typical of tires that cruise on the highway for long hours and rarely scrub. If the tire’s wear is irregular, the sipe’s thin lines will disappear in a non-uniform manner with as little as 3⁄32-5⁄32 of wear, alerting the owner to the problem before the tread is ruined.

Bridgestone/Firestone sometimes uses shallow sipes primarily to control irregular wear, says Guy Walenga, director of engineering. They disappear with wear, but open up to “control stretch and distortion” while the tread blocks are deep and therefore more flexible and vulnerable.

Many sipes like this R287 steer radial are built with club-shaped ends to help combat tearing by small stones and gravel.
Many sipes like this R287 steer radial are built with club-shaped ends to help combat tearing by small stones and gravel.

Apart from these advanced designs, there are different varieties of sipe because of differing purposes. Goodyear’s Rick Harden, senior tire engineer, says, “Siping may be considered for treadwear optimization in one location in the tread pattern, while different siping may be included at another location within the same tread pattern in order to enhance and balance treadwear and traction requirements.”

“A sipe that is molded into the edge of a rib,” says Matt Tharp of Toyo Tires, “is used to dissipate the friction energy that can cause irregular wear conditions such as river wear or punch wear. A sipe that is molded into the center of a rib or block is placed there to increase traction and braking. The sipe used to increase traction is most effective during wet or icy conditions.”

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