DETROIT - It wasn't all that long ago when it seemed everyone knew that a jack and a tire iron were the tools you needed to change a flat.

Not any more. Experts say a growing number of drivers have no clue how to change a tire, instead relying on cell phones to call for help or high-tech tires that can run while flat.

"We've become much more of a 'do-it-for-me' society," said Michael Calkins, who oversees certification of car repair garages for AAA. "I think more people don't know how to change a tire."

The widespread ability to change a tire could disappear altogether. As automakers try to cut extra pounds to meet stricter government fuel economy standards, more cars are traveling sans spare in favor of sealant canisters and portable air pumps powered by a car's battery. Those gadgets can refill tires, allowing them to keep rolling all the way to a garage.

Here are some questions and answers about the lost art of changing a tire:

Q: Do I still need to know how to fix a flat?

A: Yes. In most cases you can use a cell phone to call and quickly get roadside assistance, but if you drive out of cell phone range, you might get stranded or it could take hours for help to arrive.

"You may be in a position where you have no alternative and you have to take care of it yourself," said Greg Lhommedieu, manager of a Les Schwab Tire Center store in Kirkland, Wash., near Seattle.

Plus, some cars, especially smaller vehicles or performance cars, have specialized tires that might not be in stock at a shop. So you could have to wait a day or two for a new tire to be shipped in if you have no spare.

Q: How often do people get flat tires?

A: Research by General Motors Co. shows that the average driver gets a flat once every four or five years.

Q: Do most cars still come with spare tires?

A: Yes, but that is changing. Some automakers are replacing spares with sealant kits and portable air pumps for convenience or to save weight. For instance, air pumps and sealant are standard equipment on nearly all GM cars and crossover vehicles, although temporary spare tires are optional. Many trucks still carry full-size spares. Most customers still order temporary spares, and only 15 percent to 30 percent take only the compressor and sealant, said Dave Cowger, engineering group manager for tires at GM.

Honda, though, still offers temporary spares standard on all of its models.

Only half of drivers use spare tires when they have a flat, Cowger said, while others call roadside assistance or do something else. For many, using the sealant and reinflating a tire is far easier and faster than jacking up the car and putting on a spare.

Q: Does the sealant work in most cases and does it ruin the tire?

A: If the tread is punctured by a relatively small object, then sealant quickly fills the hole and the tire will hold air. But if the side of the tire is punctured or a larger object has pierced the tread, the sealant may not work.

Whether it ruins the tire is controversial. Some shops won't remove a tire from the rim if its got sealant inside. That's because AAA's Calkins says older sealants were flammable and hardened in the tire, causing safety issues for repair shops and ruining the tire. But newer sealants like those offered by automakers are water soluble and can be safely hosed out of a tire so it can be fixed, he said.

Q: What's the downside to changing a tire yourself?

A: Most flats occur on busy interstate highways where it's dangerous to change a tire near high-speed traffic, so many people opt for towing or roadside assistance, tire store manager Lhommedieu said.

Q: What do I need to know to change a tire?

A: Your car owner's manual has instructions on how to use the tools and where to place the jack, but it's a good idea to go through a test run before you need to do it on a dark, rainy highway, said Jennifer Stockburger, tire test engineer for Consumer Reports magazine.

Make sure you know where the spare and the tools are. They normally are in a well in the trunk, but in some vehicles, tools are in side compartments and spares are bolted to the undercarriage. Stockburger says it's a good idea to oil the bolts regularly to make sure they can be turned if the spare is needed.

Don't try to change a tire on a hill or on a soft surface because the car could slip off the jack. It's better to sacrifice the tire and wheel and keep driving if you get a flat on a busy freeway or in an area where you're uncomfortable getting out of the car, Stockburger said.