Like any concerned grandfather, Anaheim resident John Bradley was alarmed when he learned that his granddaughter’s car had suffered a punctured sidewall at a shopping center.

But what alarmed him more was that the trunk of his granddaughter’s spankin’ new 2012 Hyundai Elantra held nothing more than a “tire mobility kit” consisting of a can of sealant and a 12-volt air compressor about the size of a hefty novel. There was no spare tire in sight.

The mobility kit proved to be about as useful as a politician’s campaign promise. The sealant works only on tread punctures, not on sidewall damage. Bradley’s granddaughter called the Auto Club and had her car towed to an auto repair shop for a replacement tire. “If the problem had occurred at 2 a.m.—where would you find a shop open at that hour?” asks Bradley. “The window sticker said nothing about the car not having a spare tire, and the salespeople never told us.”

The traditional full-size spare tire that resides in a trunk well with a jack and lug wrench seems to be going the way of three-buck-a-gallon gasoline. Although pickups and larger SUVs usually still come with full-size spares, they’ve already disappeared from most passenger cars. And AAA research shows that 13 percent of 2011 model cars had no spare tire at all. Here’s why the trend is likely to accelerate:

Weight is the enemy of fuel economy.
To meet increasingly stringent government-mandated fuel-economy standards—an average of 34.1 mpg by 2016—automaker engineers sweat over removing mere ounces from vehicles. Losing 40 pounds of tire, wheel, and tools is a godsend toward that effort.

Cargo space is limited in smaller cars, and in hybrids, which carry battery packs.
Eliminating the full-size spare frees up real estate in the trunk for other stuff, such as your golf clubs.

Flat tires have become less common in recent years, most likely as a result of advances in tire technology.
Last year, 12 percent of the calls to the Auto Club for roadside assistance were for tire-related problems, a 3 percent drop compared to 2005.

“Unfortunately, many vehicle owners may be unaware that their vehicle has no spare tire until they get a flat,” says John Nielsen, AAA National Director of Auto Buying and Consumer Information.

Of course, it’s better to find out what may or may not be in your trunk before you have a problem. The Auto Club’s Automotive Research Center (ARC) has evaluated the alternatives to full-size spare tires and “found no safety concerns as long as they’re used properly,” says ARC manager Steve Mazor. Still, each has its pluses and minuses.

Temporary Spare
It’s smaller and lighter than the vehicle’s regular tires. But like a full-size spare, it’ll get you on your way if you have a flat.

• Disadvantage: In general, it’s not meant to be driven for more than about 70 miles or at high speeds (above 55 mph).
• New vehicles that use them: Most Ford, Honda, and Volkswagen cars and crossovers.
• If you get a flat: Using the jack and lug wrench, re-place the flat with the temporary spare just as you would a full-size spare—or call the Auto Club and have Roadside Assistance safely perform the chore for you.

Mobility Kit
The kit’s sealant and compressor let you reinflate the tire in about five minutes, and you don’t need to jack up the car.

• Disadvantage: It’s only a temporary fix—a tire shop still needs to inspect the tire (and pressure-monitoring sensors in later model cars) and make a permanent repair. Although the kits are useful for most flats—90 percent, says Hyundai spokesman Derek Joyce—they won’t work if the tire separates from the wheel, if the puncture is large (more than a quarter-inch in diameter), or if the sidewall is damaged, as happened with Bradley’s granddaughter’s car.
• New vehicles that use them: Many Hyundai, Cadillac, and Porsche cars.
• If you get a flat: If the tire isn’t badly damaged, plug the compressor into the car’s 12-volt power outlet, insert the sealant, and inflate the tire. Drive slowly (under 50 mph) for a couple of miles, then recheck the tire’s pressure with the compressor’s built-in gauge. Auto Club Roadside Assistance can help you with this process.  

Run-flat Tires
Some automakers have come up with an alternative to the conventional spare tire—no spare tire at all. Run-flat tires have reinforced sidewalls that allow you to drive with no air in them at all if they’re punctured.

• Disadvantage: In run-flat mode, they can be driven at speeds under 50 mph and for no more than about 50 miles. Run-flats are usually more expensive to buy and mount than conventional tires. They often produce more road noise and give a harsher ride, although improvements are being made.
• New vehicles that use them: Most BMWs and many Corvettes.
• If you get a flat: Continue to drive the car until you can have the tire repaired or replaced, keeping speed and mileage limits in mind.

From the motorist’s perspective, it’s tough to beat a full-size or temporary spare tire. If your car has a mobility kit, an automaker may offer a spare tire as an extra-cost option.

But no matter what your car has, be sure to check your tire pressures frequently with a pressure gauge, even if you drive a newer-model car with a built-in tire–pressure–monitoring system. Properly inflated tires are less likely to fail from overheating and are more resistant to punctures, making them your best defense against a flat in the first place.

Peter Bohr writes Westways’ DriveSmart column.

Read more information about spare tires, including an equipment list by make and model

Offers, prices, event particulars, contact information, and other details mentioned in this article are time sensitive and subject to change without notice. AAA does not endorse the opinions of the magazine’s columnists or reviewers, nor any products, activities, or companies mentioned unless otherwise explicitly stated.