BOSTON (MainStreet) — A recent test of more than 3,000 Americans' cars found that less than 10% had all four tires properly inflated, but here's pre-Labor Day look at how you can avoid the problems that high or low tire pressure can cause.

"Tires are the Rodney Dangerfield of cars — they get no respect. They always look round and black no matter what shape they're in, so people say: 'Oh, they look OK," says Dan Zielinski of the Rubber Manufacturers Association, which sponsored the test.

Tire shops working with the RMA in 26 U.S. cities recently checked the air pressure on some 3,300 customers' vehicles and discovered that:

  • only 9% had all four tires properly inflated;
  • 69% had at least one tire underinflated;
  • 22% had at least one tire overinflated;
  • 18% had at least one tire underinflated by at least 8 pounds per square inch, which is enough on many cars to trigger dashboard warning lights (which the RMA figures drivers simply ignored).

A 2013 RMA survey also found that just one car owner in six properly tests their vehicle's tire pressure, while only one in three checks the spare and half don't know how to recognize a bald tire.

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All of that's bad because poorly maintained tires can cause a wide range of problems.

For instance, low tire pressure can worsen fuel efficiency by making a car's engine have to work harder to push the vehicle around. Underinflation also creates extra friction that heats a tire's interior up, degrading the rubber and leading to a shorter lifespan and higher blowout risk.

Conversely, high air pressure means less of a tire's tread will touch the pavement, reducing your car's grip on the road. Overinflation also increases wear on the tread's center area and boosts the odds of a flat tire or blowout if you hit a bump, curb or other road hazard.

Lastly, bald tires have insufficient tread to stop quickly enough if you get into a skid or are about to hit something.

"If you neglect your car's tires and they fail at highway speeds, that can lead to a crash — and a serious one at that," Zielinski says.

To prevent such problems, the RMA advises drivers to check their cars' tires before any Labor Day trips or other long drives, as well as at least once a month throughout the year.

Zielinski says you shouldn't just "eyeball" tires, as they can be as much as 50% underinflated and not look low. Similarly, a car's "Low Tire Pressure" warning light will come on generally only when a tire has dropped to 25% below its recommended air pressure.

Other tips from the RMA:

Know your tires' correct psi. You'll find your tires' correct pressure listed in terms of psi (pounds per square inch) on a sticker attached to the driver's side door jam or the glove-box door's interior. Don't use the psi listed on the tire's sidewall — that's the maximum pressure a tire can safely handle, not the correct everyday setting.

Check "cold" tire pressure. Always check your car's "cold" tire pressure, the reading you'll get after the vehicle has been parked for a few hours. Driving the car around first will create friction that expands the air in the tires, leading to incorrect readings.

Remember to check the spare. You don't want to find out when you've got a flat tire that the spare is flat, too. So check the spare's tire pressure when you test the regular tires. You'll find the spare's correct pressure level on the same sticker that shows your other tires' psi settings.

Check the tread using the "penny" test. You can check your car's tread level by grasping a U.S. penny between your thumb and forefinger and slipping it into the treadwell at a few spots with Abraham Lincoln's head facing downward.

If you can see the top of Lincoln's head at any point, the tire has less than 1/16th of an inch of tread remaining and needs replacement. Some experts recommend doing this test with a quarter, which has 1/8 of an inch of space between the top of George Washington's head and the coin's edge.

— By Jerry Kronenberg