Margadonna says this prorating method is similar to how companies reimburse owners under car battery warranties. He uses the example of a tire with an 80,000-mile warranty and a person who was only able to get 70,000 miles of life out of it. "You haven't reached the mileage threshold that we think you should have reached, so we owe you 10,000 miles," he says.
Even so, Tirerack.com notes that consumers have to go on driving with potentially compromised tire performance or safety before they can make a warranty claim: Manufacturers won't consider replacement until the tires are worn down to the 2/32nds tread-wear indicators.
Some notable exceptions to tread-life warranties are winter tires and split-size fitments. Michelin is one of the only manufacturers to have a tread-life warranty on winter tires. Owners must remove the tires during the off-season to ensure proper usage and keep the warranty in good standing. "We want them to be on in the fall, around October 1, and off in the spring, around April 1," says Margadonna. "If not, we reserve the right to void that warranty claim."
Some sports cars have different-size tires that cannot be rotated using the traditional method. In split-size fitments like this, rear tires get half the mileage warranty of the front tires. That's because the rear tires wear out almost twice as fast as the fronts, Margadonna says.