Sticker shock replacement tires can be costly.(up front: News / Trends / Advice)

Tire-industry professionals have a new name for some customers: accidental performance buyers. Wide, low-profile performance tires are increasingly common as original equipment on new cars. That can lead to sticker shock when it's time to buy new tires. And that time can come sooner than buyers expect: Besides being more expensive, performance tires, which include many run-flat tires, often don't last as long as regular tires.

"It's where the industry is heading," says Phil Romba, a spokesman for the tire maker Michelin, which works with carmakers for up to two years to match a tire to a new model. "Carmakers are using tires to make the cars perform better." Performance tires can yield better handling and grip.

But consumers are often unaware that they're buying a car with performance tires. "Drivers really have no idea," Romba says. A new Scion tC sports coupe, for example, carries a sticker price of $16,740, which appeals to budget-minded buyers, but the tC we tested came equipped with Bridgestone Potenza RE92 P215/45ZR17 performance tires. On the Web site of Tire Rack, a retailer, they cost $170 each.

Z-rated tires such as those Potenzas are designed to perform at speeds of 150 mph or more--speeds the Scion can't attain. Passenger tires without such high-speed capability often carry warranties of 40,000 to 100,000 miles. Many performance tires, including the Z-rated Potenzas, carry no such ...