June 3, 2010 -- As reported today on "Good Morning America," checking your tires is important for the safety of you and your family. But 64 percent of drivers do not know how to check their tires' tread depth, according to a tire trade association, and 85 percent do not know how to check their tire pressure.
Indeed, 11 percent of vehicles have at least one bald tire and 49 percent have at least one underinflated tire, according to the Rubber Manufacturer's Association. When "Good Morning America" tested 100 cars in a Virginia parking lot, our own results were much the same. Eleven percent of the cars failed our tread depth test and 45 percent failed our tire pressure test.
Under-inflation and tire tread may not seem like a big deal but as Dave Craig of Cooper Tire explained, your tires are "really the only piece of the vehicle that touches the road , and keeps them on the road. … Maintenance level and time put into that is very important."
Here are some tips to help get you started on checking your tires.
Tire Inflation Tips:
Tire pressure is measured in PSI or pounds per square inch.
Overinflation causes the center of the tire to bulge out and rub the road unevenly, wearing your tires our prematurely.
Underinflated tires can cause handling problems, or even a blowout.
Always check the pressure when the tires are cold for an accurate reading.
Tire Inflation Tips
The Rubber Manufacturers Association recommends you check your tire pressure once a month.
It's especially important to check your tire pressure when the seasons change because outdoor air temperature affects tire pressure. Typically, for every 10 degree change in outdoor temperature, your tires' pressure will go up (in summer) or down (in winter) by one PSI.
Some service centers charge extra to inflate your tires with nitrogen instead of regular air, claiming they will hold their inflation level better. While it won't void your warranty, studies have shown nitrogen does not make a dramatic difference, so there's no need to spend the extra money.
"Your tire is designed to function … at the specified air pressure," former race car driver and Cooper Tire adviser Johnny Unser said. So if your tires are underinflated, "you're going to sacrifice a little bit on safety, you're going to sacrifice a little bit on mileage and you're going to sacrifice a little bit on performance."
Bald tires are the biggest safety threat of all. Tread is crucial for absorbing water as you drive through it, providing the best handling during wet conditions. On a slick test track, a car with a healthy amount of tread will perform fine, but one with bald tires typically spins out.
Tire Tread Tips:
Try the penny test on your tires. Take a penny and insert it into your tire tread with Lincoln's head facing down. If Lincoln's head is totally exposed, you need new tires. If your tire tread touches the tip of Lincoln's head, you have a 16th of an inch of tread depth, which is the minimum.
More tread is better. Some industry groups now suggest using a quarter for your tire test instead. If the tread comes up to the edge of Washington's head that means you have an 8th of an inch of tread depth.
Also look for the "wear bars" on your tires. These are little pieces of rubber, usually set at a diagonal to the rest of the tread. When your tread is even with these bars, it's time for new tires.
It's best to replace all four tires when any one is bald. But if you absolutely cannot afford to do that, experts say, you should put the new tires on the back of your vehicle to help prevent fishtailing.
Rotating your tires as often as your owner's manual or mechanic recommends will also help preserve your tread. The frequency varies, but many manufacturers recommend tire rotation every 6 thousand miles.
Safety Tips for Tires
Nicks in the sidewalls of your tires are a hazard, too, because they subtly degrade the strength of this vital part that carries your heavy vehicle. And even missing air caps are not ideal, because they will very slowly let air out and dirt in. Proper tire maintenance can be achieved with a few simple tools. You will need a penny or a quarter as well as a tire pressure gauge, which can be purchased at any vehicle service center, tire retailer or the automotive section of your local warehouse store.
Finally, it's a good idea to scrutinize the tires of any used car you are looking to buy.
"Tires are one of the windows into the car's past," said Chris Basso of Carfax, the vehicle history report company.
For example, if a used car has low mileage but the tires are not the original tires, it's possible the mileage is inaccurate because the odometer has been rolled back.
"The tires are a great way to tell if the seller's being up front and honest," Basso said.
Additionally, many Carfax reports contain service information that reveals whether the car's tires have been properly maintained.