How do I check my Tire Tread for Wear?

“The best way to keep children at home is to make the home a pleasant atmosphere and let the air out of the tires.”
- Dorothy Parker

During the winter it's especially important that your car's tires have a good grip on the road. I've already experienced black ice and curves slick with pouring rain this season. Are my tires in good shape? How can I tell?

 Coin Test

Use the coins in your pocket for a quick tread check.

• Place a penny upside down in a tire groove with Lincoln facing you. If the tread reaches the top of Lincoln's head then you have 2/32" or more of tread.
• Turn the penny around and upside down again. If the tread reaches the top of the Lincoln Memorial, then you have 6/32" of tread.

If you are between 2/32 and 6/32 inches, try this test...

• Place a quarter upside down with Washington facing you. If the tread reaches the top of Washington's head then you have 4/32" or more of tread.

Be sure to check both inner, outer and middle grooves of each tire, because tires can wear differently on each side, due to improper wheel alignment or low inflation.

Wear Bar Test

Tires sold in North America are required to have "wear bars" which run across the tire from the outside shoulder to the inside. When the tread is worn down to the "wear bar" then it's time to get new tires.

Bottom Line

New tires typically begin with 8/32 to 12/32 of tread depth (deeper for snow tires).

According to most states' laws, tires are legally worn out when they have worn down to 2/32" of remaining tread depth (i.e. top of Lincoln's head).

If wet roads are a problem, consider replacing your tires with 4/32" of remaining tread depth (i.e. top of Washington's head). New tires aren't cheap but cost less than an accident.

If snow is a problem, put on new tires or snow tires when the tread depth falls before 6/32". But don't toss the old tires away. You could put the old tires back on in the spring and wear them down to 4/32 or more when the snow is gone.

Tip

To prolong the life of your tires' tread, make sure your tires are properly inflated at all times. Over or under-inflated tires can put extra wear on the rubber, decreasing your car's fuel efficiency and even making it more hazardous to drive during bad weather. Consult your car's instruction manual or driver-side door panel for advice on the right air-pressure levels for your tires 

Tire Pressure

"A suburban mother's role is to deliver children obstetrically once, and by car forever after."~Peter De Vries

Last night as I was driving home I thought, “I should really check my tire pressure.” My wife’s car is newer and the dashboard has a warning light for low tire pressure. My car is not so smart and it’s been awhile since the pressure was checked.

Next to the brakes, the tires are the most important safety devices on a car. Incorrect tire pressure will compromise cornering, braking and stability, and lead to tire failure (i.e. a blow-out). Incorrect tire pressure also will affect your comfort, fuel economy and tire life.

If tire pressure is too high, then less of the tire touches the ground and your car will have more road bounce, have less traction and a longer stopping distance. If tire pressure is too low, then too much of the tire touches the ground, which increases friction, lowers your gas mileage, wears tires prematurely, and overheats tires leading to tread separation.

Tire pressure should be checked at least monthly (some say weekly). It’s not unusual to lose 1 psi per month. Even if there is no leak, the pressure will change with air temperature. Tire pressure decreases by about 1 pound per square inch (psi) for every 10-degree drop in outside air temperature. If your tire was just right in July at 80 degrees outside, it could be dangerously 10 pounds under inflated in January at minus 20 degrees.

The psi number listed on the tire itself is the maximum allowable air pressure. Don’t use this! Instead look on the edge of the driver’s door for the recommended pressure for your car. If there’s no sticker on the door, you can usually find the specs in the owner’s manual. Most passenger cars will recommend 32 to 35 psi.

Bottom Line

Check your tire pressure monthly. Check all four tires and your spare while the tires are cool, that means after driving only a few miles to reach a gas station, not after hours of driving.

Web Resources

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1
http://www.michelinman.com/tire-care/tire-saving-tips/air-pressure-tips/
http://cars.cartalk.com/content/advice/tirepressure.html