Auto Repair For Dummies, 2nd Edition
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You should check your tires for wear at least once a month and before and after long trips. You check them to determine whether you need to buy new tires, have your wheels balanced, have your wheels aligned, or change your driving habits.

Underinflated tires wear out faster, create excessive heat, increase fuel consumption, and make your car harder to handle. Overinflated tires can “blow out” more easily, wear out faster, and make the vehicle unstable and unsafe to handle. And a new set of tires on wheels that are out of alignment can wear out completely in as little as one day of hard driving!

What the signs of poor treadwear mean.

What the signs of poor treadwear mean.
To determine what’s causing problems with your tires, try the following:
  • Look for things embedded in each tire. Do you see nails, stones, or other debris embedded in the treads? Remove them. If you hear a hissing sound when you pull a nail, push the nail back in quickly and take the tire to be fixed. Tires with leaks should be patched by a professional.

  • Look at the sidewalls. Check for deeply scuffed or worn areas, bulges or bubbles, small slits, or holes. Do the tires fit evenly and snugly around the wheel rims?

  • Look at the treads. Most tires have built-in treadwear indicators. These bars of hard rubber are normally invisible but appear across treads that have been worn down to one-sixteenth of an inch of the surface of the tire (the legal limit in most states). If these indicators appear in two or three different places less than 120 degrees apart on the circumference of the tire, replace the tire.

    It’s time for new tires when treadwear indicators appear.

    It’s time for new tires when treadwear indicators appear.

    If your tires don’t show these indicators and you think that they may be worn below legal tolerances, place a Lincoln penny head-down in the groove between the treads. If you can see the top of Lincoln’s head, your tire probably needs to be replaced.

    To measure treadwear more precisely, place a thin ruler into the tread and measure the distance from the base of the tread to the surface. It should be more than one-sixteenth of an inch deep. (If your front tires are more worn than your rear ones and show abnormal wear patterns, you probably need to have your wheels aligned.)

    Sometimes one-sixteenth inch of tread isn’t enough to keep you safe. If you live in a rainy area, measure the depth of your treads with a quarter rather than a penny, using Washington’s hair to see if your tires have at least two-sixteenths of an inch of tread remaining.

  • Pay attention to leaks. If you keep losing air in your tires, have your local service station check them for leaks. Sometimes an ill-fitting rim causes a leak. The service facility has a machine that can fix this problem easily.

The following table summarizes tread wear and what it means.
How to Read Your Tire Treads
Clue Culprit Remedy
Both edges worn Underinflation Add more air and check for leaks
Center treads worn Overinflation Let air out to manufacturer’s specifications
One-sided wear Poor alignment Have wheels aligned
Treads worn unevenly, with bald spots, cups, or scallops Wheel imbalance and/or poor alignment Have wheels balanced and aligned
Erratically spaced bald spots Wheel imbalance or worn shocks Have wheels balanced or replace shocks
Only edges of front tires worn Taking curves too fast Slow down!
Saw-toothed wear pattern Poor alignment Have wheels aligned
Whining, thumping, and other weird noises Poor alignment or worn tires or shocks Have wheels aligned or buy new tires or shocks
Squealing on curves Poor alignment or underinflation Check wear on treads and act accordingly

How to add air to your tires

If your tires appear to be low, check the pressure and note the amount that they’re underinflated. Then drive to a local gas station and add air. It’s easy, but be sure to bring some change (usually quarters) with you for the air dispenser. (Forget about things being “as free as air” — at many stations it isn’t!)

Follow these steps to add air to your tires:
  1. Park your vehicle by the air dispenser.

    You will need to reach all four tires with the air hose.

  2. Remove the cap from the tire valve on the first tire.

  3. Use your tire gauge to check the air pressure in the tire.

    Air hose gauges at many gas stations are inaccurate.

    Checking your tire pressure.

    Checking your tire pressure

    The pressure will have increased because driving causes the tires to heat up and the air inside them to expand. To avoid overinflating the tire, no matter what the second reading indicates, you should only add the same amount of air that the tire lacked before you drove it to the station.

  4. Use the air hose to add air in short bursts.

    Check the pressure after each time with your tire gauge.

    If you add too much air, let some out by pressing the pin on the tire valve with the back of the air hose nozzle or with the little knob on the back of the rounded end of the tire gauge.

  5. Keep checking the pressure until you get it right.

    Don’t get discouraged if you have to keep adjusting the air pressure. No one hits it on the head the first time!

About This Article

This article is from the book:

About the book author:

Deanna Sclar is an acclaimed auto repair expert. She has appeared on hundreds of radio and TV shows, including NBC's Today show and the NBCNightly News. Sclar lectures internationally on the ecological impact of vehicles and is active in promoting residential solar energy programs. Sclar is also the author of Buying a Car For Dummies.

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