To sipe or not to sipe? Dealers say yes, tiremakers say no
Wes Sprunk doesn't take cutting remarks sitting down. Last winter, a Minneapolis, Minn., TV station aired a negative segment on siping that grabbed his attention. The station claimed to have tested several siped passenger tires and declared that the process was worthless. It even implied that siping was a scam perpetrated by tire dealers to make a few extra bucks at the expense of gullible customers.
An upset Sprunk, who owns Phoenix, Ariz.-based siping machine manufacturer Saf-Tee Siping & Grooving Inc., tried to get in touch with the TV station, but officials there refused to return his calls. He even contacted the person who donated the tires that were supposedly evaluated by the station but was told they had been discarded.
Sprunk discussed the situation with a Minneapolis lawyer, who agreed that he had a case. However, there was one problem: The most recent available test data on siping was nearly 20 years old! "He said, 'You'll have to contact a national testing agency and get new tests done,'" recalls Sprunk. And that's exactly what he did with the help of Mobility Research, a Greenville, S.C.-based independent tire testing firm with facilities in upper Michigan. It wasn't cheap, according to Sprunk, but he says the results validated his claim that siping improves tire performance.
To the test
Mobility Research tested the performance of size P205/55R16 siped and non-siped all-season tires and size P205/50ZR16 siped and non-siped high performance tires. The P-metric tires were mounted on the drive axle of a test vehicle -- a modified pickup truck -- that was driven on stretches of medium-packed snow until the vehicle's test position (right rear) wheel broke traction. Ten runs were performed each day for three consecutive days.
Results showed that siped all-season tires achieved 33% more traction than their non-siped counterparts, while siped performance tires achieved at least twice as much traction as non-siped performance tires, according to Mobility Research President Paul Schultz.
"The differences were so significant that it's easy to validate (Sprunk's) claims that siping improves snow traction," says Schultz.
"Siping works well for those who need it," says Sprunk, especially drivers in snowy regions.
Proper siping "can make a fair tire into a good tire," he says, adding that sipes also improve stopping distances. In addition, the presence of sipes may extend a passenger tire's life since they "cool" the tire by letting air into the tread, which reduces harmful heat build-up, he claims.
Sprunk adds that siping doesn't compromise a tire's structural integrity because "you're not taking any rubber out when you sipe. You're just cutting into it." However, excessive or inaccurate siping can hurt tire performance. Saf-Tee Siping tells customers never to sipe deeper than 13/36-inch. "If you cut too deep, you'll get tread squirm." Narrow cuts are recommended ("the more narrow you cut, the more traction you'll get") and the space between cuts should measure less than a half-inch. "Otherwise, you defeat the purpose."
Major tire manufacturers Bridgestone/Firestone North American Tire LLC (BFNT), Cooper Tire & Rubber Co., Goodyear Tire & Rubber Co. and Michelin North America Inc. discourage siping passenger tires. "We don't recommend altering a tire in any way," says a Michelin spokesperson, who adds that if a Michelin-made tire "becomes unserviceable due to siping," its warranty would be voided.
BFNT officials say that siping also invalidates its tires' warranties, "because you've altered the tires. Our tires are designed a certain way with certain tread patterns. Any alteration, in our minds, just doesn't make sense."
Goodyear's official policy states that "any tire, after leaving a factory producing Goodyear tires, (that) has been intentionally altered to change its appearance (e.g., white inlay on a black tire, regrooving or siping)" will not be covered under warranty.
That doesn't surprise Sprunk. "Most (tiremakers) say, 'We already make a good enough tire," he says.
Jeff Schroeder, director of product development for Cooper Tire & Rubber Co., also cites other reasons to discourage siping. Sipes "loosen up tread elements," he says. "As you put cuts into (a tread), suddenly you have blocks that are moving more independently," which leads to increased wear.
While Schroeder admits that sipes might be beneficial in severe winter conditions, a siped tire "won't perform as well in the dry. When you put a sipe in, you create a biting edge," which is not needed on dry surfaces, he says. "On a dry (surface), the texture of the tread is interacting with the road." Cooper and other manufacturers offer dedicated snow tires that have been siped at the manufacturing level via the mold process. "The need to sipe isn't that great," says Schroeder.
Sprunk says independent tire dealerships throughout the country, including major names like Discount Tire Co., Les Schwab Tire Centers and Peerless Tyre Co., routinely sipe tires for customers. Denver, Colo.-based Peerless began siping passenger and light truck tires at select locations less than a year ago "We haven't encountered any problems" with or because of siping, says Peerless Tyre President Sam Forbes. "We've never had negative (feedback) on siping. Everything I've seen is positive or in the worst case, neutral."
Forbes calls siping profitable. "You go through blades very quickly but the real cost is the machine and the training that goes with the employees."
Les Schwab Tire Centers has been siping passenger and light truck tires for more than 20 years, according to Brian Capp, the Prineville, Ore.-based dealership's director of sales and marketing. "Like any service, your people have to believe in it," he says. "And the way your people believe in it is by your customers believing in it. In general, we've gotten lots of compliments on the performance of siped products."
Capp says in many established Les Schwab outlets, customers specifically request siping. In newer stores, employees spend more time promoting the service's features and benefits. "We wouldn't be doing that if (siping was) destroying tires and making customers unhappy."
"If it's not a value to the customer, we're not going to offer it," says Mike Metz, vice president of purchasing for Discount Tire Co. Inc., North America's largest independent tire dealership. Discount offers passenger and light truck tire siping "where it's applicable. For example, we don't have siping machines in Phoenix, Ariz., but we do in Colorado."
Metz has never heard of a tire failing due to siping. "When you sipe a tire, you sipe the tread block itself. It doesn't affect the structural integrity of a tire."
While dealerships like Peerless, Schwab and Discount continue to push siping at their outlets, Sprunk is continuing his one-man crusade to get a retraction from the Minneapolis station that denigrated the service. He has sent a copy of his test results to station officials and is planning to meet with them this month.