DETROIT -- Sandy Gossett was getting into her black 2000 Isuzu Trooper LS when she noticed the rear right tire was leaking air.
Gossett, 48, of Whitmore Lake, Mich., despises changing flat tires. She left the SUV in her driveway for five days until she had time to drive it to a tire shop.
If she had been stranded roadside with a flat tire, "I'd call AAA, or my husband," she said.
Similar sentiments from an increasing number of customers are persuading automakers to phase out spare tires, much as they did cassette tape decks. Fewer motorists are changing their own flats, and automakers say eliminating spares saves money, creates space, and reduces vehicle weight, which ultimately helps gas mileage.
Only about 40 percent of new vehicles in the United States and Canada are equipped with a full-size spare tire, and that number will drop to 36 percent by 2011, said Bruce Harrison, senior consultant with automotive research firm Global Insight Inc. in Lexington, Mass.
Today's popular larger rims are heavier and come equipped with more lug nuts, making it more difficult for average motorists to change their tires. While 15-inch rims were the norm in the 1960s and 1970s, rims edging past 20 inches in diameter are more frequent. By 2011, Harrison predicted, only 9 percent of vehicles will have 15-inch rims.
Improved cellphone reception, services like AAA or GM's OnStar system, and advanced tires called run-flats, which are drivable when flat, are giving travelers more and safer options.
"If you can push a blue button or dial your cellphone and have someone there in about 30 minutes, it's certainly better than the aggravation of changing it yourself," said Phil Trent, of Discount Tire Co. "I told my wife, before I bought her run-flat tires, just get somewhere safe -- I can always replace the wheel and tire."
Government regulation also has reduced the need for spares. In 2002, the National Highway Traffic and Safety Administration mandated tire pressure monitoring systems, which signal the driver when there's a significant decrease in air pressure.
About 45 percent of 2006 vehicles were equipped with the monitors, and that figure will rise to 70 percent by September, according to the Alliance of Automobile Manufacturers. By model year 2008, all new vehicles must be equipped with the monitoring systems.
Blowouts, which can occur when under inflated tires heat up, happen less frequently because drivers are notified before a possible accident.
"People are paying closer attention to their tires, knowing they don't have a spare," Trent said.
GM, Ford, and Chrysler already have swapped spares for run-flats on their sports cars: the Corvette, Shelby GT, and Viper.
Using spare tires on the Viper, for instance, would be an extra hassle because the front and back tires are different sizes. Two spares would be needed.
"It makes more sense to carry a quick repair kit or extra service with the vehicle," Chrysler spokesman Nick Cappa said.
Experts say there will be no immediate rush to eliminate spare tires because traditional truck owners prefer to keep a full-size spare handy.
And for now, run-flats generally are more expensive than spares. Discount Tire sells 16-inch Goodyear EMT run-flats for $226 per tire; larger sizes cost more than $300. A typical spare tire, in a range of sizes, can cost less than $100.