DETROIT — Tire inflation used to mean something else.

Now, thanks to soaring prices for oil and rubber, it refers to tire prices as well as air pressure. Consumers shopping for a new set are finding the tab up 5 percent to 10 percent this year and likely to head higher.

Keith Price, a spokesman for Goodyear Tire & Rubber, says the price of oil, now at all-time highs, makes up 60 percent of the raw materials cost for a tire. Natural rubber, a commodity nearing 28-year price highs, makes up another 25 percent.

Many car owners, already feeling pinched by inflation at the gas pump and supermarket — and deflation in the their home value — are responding by driving on tires until the tread is practically bare, a worrisome trend.

"We're seeing more and more customers every day deferring their tire purchases," says William Bainbridge, director of brand communications for Hankook Tire America. "Consumers are shocked by tire prices. ... Buying a tire isn't something people want to do."

Hankook dealers are seeing drivers come with treads that fail the penny test, he says. (Place a penny with Lincoln upside-down in the tread. If the tread covers the top of his head, you have at least 2/32 inch of tread, the bare minimum safe tread depth.)

"If this trend continues, I think we could start seeing more accidents" caused by bald tires, Bainbridge says.

Scott Webb, vice president of merchandising and marketing for Pep Boys, an auto parts retailer that sells its own private-label tires, says cost is the reason. "The customer is very, very sensitive to price right now. People are waiting until the last minute to replace their tires."

Barbara McMullen, an Ann Arbor, Mich., resident, put off buying tires for her Ford Freestyle crossover, even though she was having traction-control problems last winter. She is turning in the car at the end of its lease in a few weeks and thought she could make it until the car was back at the dealer's.

No such luck. Upon visiting the dealer, she was told she'll have to replace the tires before handing the vehicle in or pay for tires the dealer will install.

"It was actually really bad timing," she said. "We're paying for summer camps now, and with gas and everything else, it was just one more thing."

Goodyear has been backing out of the lower-price end of the tire market and focusing on selling more tires that are highly engineered, says Price, because buyers interested in the more sophisticated tires have not pulled back.

"We do not see consumers trading down in either performance characteristics or in brand," Price says. "And the newer advanced products we have in the market are actually doing very well so far this year."