Tire Wear
Every motorist should learn to read tire wear. Tire manufacturers recommend conducting monthly visual inspections of all four tires for cuts, bulges and other irregularities. Tread wear is relatively easy to judge. These days, many tires have wear-indicator bars molded into the tread. As soon as the solid bar becomes visible, the tire should be replaced. For tires that don't have indicators, a penny can be used to gauge tread wear. Stick Lincoln's head into the tread. If the top of his head is visible, the tread is worn out. Special tread-depth tools that serve this same function are available at many auto parts stores.
Uneven tread wear provides clues about other problems. Uneven wear side-to-side and either sawtoothed or feathered shoulders indicate that the car's alignment should be checked. Cupping can indicate that the tires are out of balance or that chassis parts are worn out. Shoulders that wear faster than the centers are signs of underinflation; worn centers with good shoulders signify overinflation.
Correct Pressure
As most of us are now aware, incorrect tire pressure is a serious safety issue. Additionally, improper psi affects the vehicle's handling and fuel economy.
Tire pressure should be checked monthly, before any extended road trip and during extreme temperature fluctuations. Always take a pressure reading while the tires are cold—driving as little as one mile can produce an inaccurate reading. Normal tire deflation is approximately 1 psi per month; cast-aluminum wheels are more porous than steel wheels and allow even faster leak-down. And don't forget to check the spare.
Under-inflation is a serious problem. In fact, the Society of Automotive Engineers (SAE) estimates that under-inflated tires contribute to 26,000 accidents annually. In addition to accelerating shoulder wear, under-inflation generates more friction, which reduces fuel economy and can generate enough heat to potentially cause a blowout. Proper inflation is also necessary for antilock brakes (ABS) to function properly. One industry source estimates that 1/4 of the vehicles on the road at any given time have under-inflated tires.
What's the correct pressure for your tires? Not the number stamped on the sidewall. Close reading will reveal the word MAXIMUM next to the psi number. If the vehicle were loaded to its Gross Vehicle Weight Rating (GVWR), then the maximum psi might be plausible. However, the vehicle manufacturer recommends a specific pressure. This information is normally in the owner's manual or on a sticker on the driver's side door or inside the glovebox door. Always refer to this recommendation first.
Tire pressure should also be adjusted to conditions. When the vehicle is loaded down with gear, most tire manufacturers recommend adding up to 4 psi over the vehicle manufacturer's recommended pressure. However, never exceed the vehicle's maximum load rating or the sidewall's maximum-psi rating. Distribute weight as evenly as possible by sliding loads forward instead of leaving them at the rear.
Rotation
Regular tire rotation promotes even treadwear. The vehicle's owner manual usually recommends the proper interval. Otherwise, every 5,000 miles is the rule of thumb for passenger cars, approximately 4,000 miles for 4x4s, and even every 3,000 miles for aggressive, oversized mud tires. New tires' first rotation is the most critical.
Rotation pattern varies depending on whether the vehicle is front-wheel drive and has a fullsize spare (refer to the owner's manual). Regardless, inflation pressure should be checked and adjusted as necessary at rotation time. Having the tires rebalanced can't hurt either. Clamp-on wheel weights sometimes fall off, and tire imbalance transmits vibration to the suspension and even the steering wheel.
Age/Storage
Over time, rubber degrades, even if the tires aren't being used. Tread and sidewall rubber can crack, and the carcass can deform. Consult a competent tire shop about whether tires that show signs of age are safe.
To maximize tire life on RVs, boat trailers and other often-stored vehicles, jack the weight off the tires to keep them from flat-spotting. Also, cover the tires to protect them from sunlight and airborne contaminants. Spare tires are particularly susceptible to age degradation because they don't get inspected as often as the other four.
Tire Repair
Run-flat tires are starting to appear for more-expensive cars. However, standard tires aren't designed to run without air, and irreparable damage can result from any attempt to do so.
Many tread punctures and gashes less than 1/4-inch large can be repaired, either with external plugs or internal patches. It's illegal to repair a tire's sidewall, and patching tires with less than 1/16-inch of tread depth isn't recommended. A qualified tire professional can assess whether a punctured tire is repairable. Regardless, keeping the spare in good condition and properly inflated is the best remedy for a flat.
Monitoring Systems
As a result of the Firestone/Explorer situation, a new law requires automakers to install tire-pressure monitors on all vehicles within the next three years. (The aftermarket has offered these systems for a few years now.)
Typically, tire monitors have a wheel-mounted sensor and a driver-visible display that shows each tire's pressure and sometimes its temperature. Most existing systems mount the monitor on the dash or visor; in-development setups will include the display on a special rearview mirror.
Shelf Life
Tires' sidewalls have molded-in codes that pertain to their performance and date of manufacture. Uniform Tire Quality Grading System (UTQG) is a DOT program that rates treadwear on a numeric scale (a 400-rated tread theoretically lasts four times longer than a 100), traction (AA, A, B & C in descending order of tractability) and ability to dissipate heat (A, B or C, A being superior, B average and C passable). UTQG ratings are stamped into the sidewall on passenger-car tires.
Sidewalls also have a DOT code that corresponds to their date of manufacture. Because tires harden and crack with age, buying the freshest tires possible makes sense.
Blowout Survival
Unfortunately, knee-jerk driver reactions to a tire blowout make a bad situation worse. Following a blowout, most people instinctively stomp on the brakes—the worst possible technique. This abruptly transfers the vehicle's weight forward, making it nose-dive in addition to pulling toward the blown-out side.
Instead of braking, ease off the gas. Don't panic: The rapidly deflating tire will slow down your car or truck. Then try to steer as straight as possible, avoiding quick maneuvers that can send the vehicle into a rollover. Allow the vehicle to coast to a stop, gingerly steering to a safe stopping place. Remember, driving on a flat tire may damage a wheel, but this is preferable to full-vehicle or bodily damage. Finally, turn on the emergency flashers and exit the vehicle cautiously.
When it comes to tire safety, Bridgestone/Firestone boils it all down to three words: inflate, rotate, evaluate.
Resources
Here are URLs of some of the major tire manufacturers:
