The importance of proper tire inflation cannot be overemphasized. A tire employs air as part of its structure. It is designed around the supporting strength of the air at a specified pressure. For this reason, improper inflation drastically reduces the tire's ability to perform as intended. A tire will lose some air in day-to-day use; having to add a few pounds of air periodically is not necessarily a sign of a leaking tire.
Two items should be a permanent fixture in every glove compartment: an accurate tire pressure gauge and a tread depth gauge. Check the tire pressure (including the spare) regularly with a pocket type gauge. Too often, the gauge on the end of the air hose at your corner garage is not accurate because it suffers too much abuse. Always check tire pressure when the tires are cold, as pressure increases with temperature. If you must move the vehicle to check the tire inflation, do not drive more than a mile before checking. A cold tire is generally one that has not been driven for more than three hours.
| Fig. 1: Tires with deep cuts, or cuts which bulge,
should be replaced immediately
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| Fig. 2: Radial tires have a characteristic sidewall
bulge; don't try to measure pressure by looking at the tire. Use a quality
air pressure gauge
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| Fig. 3: Common tire wear patterns and causes
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A plate or sticker is normally provided somewhere in the vehicle (door post, hood, tailgate or trunk lid) which shows the proper pressure for the tires. Never counteract excessive pressure build-up by bleeding off air pressure (letting some air out). This will cause the tire to run hotter and wear quicker.
CAUTION
Never exceed the maximum tire pressure embossed on the tire! This is the pressure
to be used when the tire is at maximum loading, but it is rarely the correct
pressure for everyday driving. Consult the owner's manual or the tire pressure
sticker for the correct tire pressure.
Once you've maintained the correct tire pressures for several weeks, you'll be familiar with the vehicle's braking and handling personality. Slight adjustments in tire pressures can fine-tune these characteristics, but never change the cold pressure specification by more than 2 psi. A slightly softer tire pressure will give a softer ride but also yield lower fuel mileage. A slightly harder tire will give crisper dry road handling but can cause skidding on wet surfaces. Unless you're fully attuned to the vehicle, stick to the recommended inflation pressures.
All automotive tires have built-in tread wear indicator bars that show up as 1⁄2 in. (13mm) wide smooth bands across the tire when 1⁄16 in. (1.5mm) of tread remains. The appearance of tread wear indicators means that the tires should be replaced. In fact, many states have laws prohibiting the use of tires with less than this amount of tread.
| Fig. 4: Tread wear indicators will appear when the
tire is worn
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| Fig. 5: Accurate tread depth indicators are inexpensive
and handy
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You can check your own tread depth with an inexpensive gauge or by using a Lincoln head penny. Slip the Lincoln penny (with Lincoln's head upside-down) into several tread grooves. If you can see the top of Lincoln's head in 2 adjacent grooves, the tire has less than 1⁄16 in. (1.5mm) tread left and should be replaced. You can measure snow tires in the same manner by using the "tails'' side of the Lincoln penny. If you can see the top of the Lincoln memorial, it's time to replace the snow tire(s).
| Fig. 6: A penny works well for a quick check of tread
depth
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