Written by Mike Manges.
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.