Question: I recently purchased a new set of tires for my car, and the tire dealer tried to sell me a service called tire siping. I've never heard of it and told him no. What is tire siping, and is it legitimate? --J.M.
Answer: Tire siping is like a lot of aftermarket products and services that claim to improve the performance of your vehicle: Depending on who's talking, it is either a legitimate benefit or a potential detriment.
Siping involves making a series of knife cuts across the width of a tire, creating myriad additional edges in the tread in an effort to improve traction. The process was invented by John Sipe in the 1920s, when he cut slits in the soles of his shoes to improve traction, according to industry legend.
The procedure is done with a so-called siping machine that is designed to closely control the depth of the cuts to avoid damaging the tire body. There is only one known manufacturer of these machines, Saf-tee Siping & Grooving Inc. of Phoenix.
The company's machine makes a series of curved knife cuts ranging in depth from 5/32 to 13/32 of an inch, depending on the depth of the tread. The idea is to leave about 4/32, or an eighth of an inch, of clearance between the bottom of the knife cut and the tire body.
According to the firm's promotional literature, "these slits create thousands of sharp, gripping edges to provide extra traction, safer braking and actually extend the life of the tire as a result of dissipation of heat on highway travel."
But is it true? The Rubber Manufacturers Assn., a trade group representing tire makers, neither endorses nor condemns the procedure. It says, however, that it is critical that siping be done properly to avoid ruining a tire. Individual tire makers are more clearly opposed to the procedure.
Bill Gaudet, director of customer affairs for Goodyear Tire & Rubber Co., said his company does not recommend that passenger tires be siped, because the tread depth and the tire body are not designed for siping. Siping could invalidate the warranty if Goodyear determines that a tire failure was caused by the procedure, Gaudet said.
Similarly, Michelin Tire "does not recommend it, but we realize that it is common in the industry," spokesman Martin Peters said. "It can alter or corrupt the design criteria that were established for that tire. It can cause excess noise, excess heat buildup, and it could ultimately cause damage to the tire."
Siping was more popular years ago, when tire treads were not nearly as sophisticated as today's computer-designed patterns. Nevertheless, a large number of trucking fleets use tire siping in an effort to improve traction and extend tire life in their fleets, Gaudet acknowledged.
Randy Kindel, sales manager for Saf-tee Siping, said the procedure is used across the country by a large number of tire retailers that have siped millions of passenger tires through the years. Discount Tire and Americus Tires, two large chains, still offer the service, he said. A number of Goodyear dealers also offer the service.
"We are not affecting the tread or belting," Kindel said. "We are putting a little more of a footprint on the road, and you are going to get a little better ride."
Saf-tee says that its machines and procedures have been widely tested and that it has won many endorsements. But those endorsement letters, which were provided to The Times, appear in most cases to be many years old.
The National Safety Council and the Iowa Department of Safety, for example, both tested and endorsed tire siping many years ago--particularly for its ability to enhance traction on wet and icy pavement--but spokesmen for the groups said they no longer even know anything about siping.
But that doesn't mean siping is bad. Again, truckers widely perform siping to extend tire life. But truck tires have a more substantial layer of rubber that separates the tire carcass from the tire tread. So knife cuts are less likely to damage cords that give the tire strength.
Siping costs about $10 a tire. Whether any potential improvement in traction is worth the $40 it costs to sipe a new set of tires is ultimately a matter of personal preference.
Times staff writer Ralph Vartabedian cannot answer mail personally but will attempt to respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, 1875 I St. N.W., No. 1100, Washington, DC 20006.
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