The only thing between a car or truck and the road are tires, but surveys show too many people neglect them -- sometimes with dire results.

One in three passenger vehicles -- or about 65 million -- has at least one tire that is significantly underinflated, according to the National Highway Traffic Safety Administration.

Driving a vehicle with underinflated tires increases the chance of tire failure, shortens tire life and decreases fuel economy. It doesn't take much: Tires underinflated by only 6 psi can lead to tire failure, and tread life can be reduced by as much as 25 percent. Tires overinflated by 6 psi can be damaged more easily when running over potholes or road debris. Higher inflated tires can't isolate road irregularities well, causing a harsher ride.

It makes no difference if it's a Ferrari or a Chevrolet -- a car won't deliver its best steering, handling and braking without correct tire pressures.

Long gone are the good old days when attendants at full-service gasoline stations checked a car's engine coolant and oil levels -- and tire pressures. Filling stations now sell items such as bread and milk, along with gasoline.

Motorists thus often have tires inflated at quick-oil-change outfits, where they don't stop nearly as often as drivers did at the old full-service stations, said John Rastetter, tire information director at the Tire Rack, based in South Bend, Ind. It sells all brands of tires and ships them to a network of 3,200 local installers. Its 80 tire experts test tires at its facilities and provide buying information.

"People don't take time to inflate tires because it's just not something they think about during their busy daily lives. They feel they have more important things to do," said Jerry Pekow, president of veteran Chicago area Goodyear tire retailer Acorn Tire & Supply.

"Neglecting pressures is especially dangerous in winter because cold weather lowers tire pressure and slow leaks can develop with the aluminum tire rims used on many vehicles."

Most motorists don't use tire pressure gauges, and the low-tire-pressure situation has gotten so bad that the government is mandating low-tire-pressure warning systems for vehicles, starting with the 2004 model year, Rastetter said.

Pekow said such systems will go a long way toward making tires safer and will help consumers save money "because underinflated tires wear out faster, fail sooner and don't deliver the best fuel economy."

The Tire Rack long has provided car buffs with specialized tire information, but has expanded services to help average car and truck owners.

Many auto buffs want tires with extremely good traction on snow and ice for high-performance cars. Tires have become so sophisticated that some specialized winter tires provide more traction than even noisy, road-damaging studded ts once did. However, Rastetter said good all-season tires do fine during most driving.

Car buffs know that tires have complicated construction with often markedly different materials and tread designs -- and thus have different performance characteristics. To the average person, tires just look like chunks of rubber. However, even economy car tires have far more durability and provide much better performance than tires of the 1950s, '60s and even '70s.

"People who took long vacation drives once took it for granted that they'd have at least one flat tire on the trip," said Matt Edmonds, vice president of marketing for the Tire Rack.

If you want to buy tires in your neighborhood, go to a tire store rather than a chain store that sells tires -- preferably with an owner present. Being specialized, tire stores know more about tires.

Look for knowledgeable tire sales people. Check a few tire sellers to get a feel for the sincerity and expertise of sales people.

Also, tires with name brands are more consistent in quality than private label tires.

"People usually only buy replacement tires every two to four years and thus feel intimidated when shopping at a tire store," Edmonds said. "That's why motorists ask car buffs which are the best tires."

"Get tires that suit your driving style and geographic area and buy the most expensive tires you can afford," said Tire Rack spokesman Russell Datz. "Putting aside super-cheap tires in come-on advertisements that really don't fit many vehicles, tires generally cost about $49 to several hundred dollars apiece. You get what you pay for."

Consumers should check wear, temperature and traction ratings on tire sidewalls, Edmonds said. "People often ask about the wear rating, but seldom about important traction or temperature ratings."

The better the traction rating, the better a tire grips the road.

The better the temperature rating, the more able a tire can dissipate tire-destroying heat buildup. (See sidebar) Generally, the higher the wear rating, the lower the traction and temperature ratings -- it's always a compromise between those factors. For instance, tires with very high wear ratings are too hard to provide traction sometimes needed to avoid a collision or to grip the road securely on slippery pavement.

"Excessive emphasis is put on long mileage warranties," Pekow said. "It's a gimmick. Nobody pays off on them. Generally a radial tire will last a long time if properly inflated and the car is mechanically OK. Tires almost always wear out prematurely due to mechanical failure, and that voids the warranty. A high mileage warranty doesn't necessarily mean the tire is better."

With higher-speed summer driving ahead, early spring is a good time to check tires for such things as low tread wear, cuts and bruises, partly because of damage caused by such winter road hazards as potholes, Pekow said. But he added that tires should be checked at least monthly for low pressure.

"Drivers of a vehicle that hits a bad pothole hear and feel the impact, hold their breath for a moment, and give thanks that the impact didn't cause a flat tire," Rastetter said. "But that impact may have internally damaged the tire. It generally rolls 800 times every mile and may fail in a few months. It's like hitting your leg hard on a table -- it hurts, but the bruise doesn't appear until the next morning."

Proper tire pressures when hitting that pothole might prevent internal damage. Follow the vehicle manufacturer's recommended tire pressures, which are put in a vehicle in such places as the driver-side door jamb.

"You don't want too much pressure, or too little. It's best to put a few more pounds of air in a tire, than leave it a few pounds under the recommended pressure," Edmonds said. "A tire has more stability and responsiveness with slightly higher pressures. Also, every 10-degree drop in temperature causes a tire to lose one pound of air pressure. And tires lose about one psi every month because of air escaping through the rubber as it stretches."

GRADING TIRES

The Transportation Department requires tiremakers to grade passenger car tires on three performance factors: tread wear, traction and temperature resistance.

Here's what to look for on a tire's sidewalls:

Tread Wear

More than 100: Better

100: Baseline

Less than 100: Poorer

Traction

A -- Best

B -- Intermediate

C -- Acceptable

Temperature

A -- Best

B -- Intermediate

C -- Acceptable