Wednesday, January 30, 2008

Tires: Everything You Wanted to Know (But Were Afraid to Ask)

Do your tires sag a bit, as if they could benefit from a gym membership? Do your tires bring to mind Montel Williams, Captain Picard, or Yul Brynner? Do you own a tire pressure gauge? (And if so, do you know where it is?)

If you’re like me, you take your tires for granted. You’re not sure what condition they’re in, whether you need new ones, or even how to shop for tires. And if you’re like me, this uncertainty makes you a little nervous, because we all know that bad tires can lead to bad accidents.

What Is a Tire, Anyway?

Oh my--a tire is so many things. Historically, it’s a descendant of the wheel, mankind’s first step toward industrial progress. Philosophically, it is a circle, a symbol of eternity, of that which never ends, of freedom. Scientifically, a tire is the device that acts against the inertia of your car, moving it, stopping it, and fighting centrifugal force at every turn.

But most importantly, a tire is what keeps you from being plastered to the roadway like an unfortunate opossum.

To learn more about tires, I visited a local tire store and beleaguered my anonymous source–we’ll call him Deep Tread (what else?)–with questions. He kindly showed me a slice from a real tire. It looked something like the letter U.

Body: The body of a tire (also tastefully called "the carcass") is made of synthetic or natural rubber. It includes chemicals to reinforce the rubber, keep it from degrading, and help it adhere to the road.

Bead: See those little flaps at the top of the U? Those represent the tire’s beads, the steel-cable-reinforced inner edges of the tire that seal against the tire’s rim.

Cords: Running through the body of a tire from bead to bead are strong polyester cords that help smooth your ride. Most car tires today are radial tires, which means that the polyester cords run straight across the tire from bead to bead. This particular formation decreases rolling resistance and increases tread life and gas mileage.

Sidewalls: The sides of the U represent the sidewalls. All sorts of information about the tire is molded into the outside sidewall, and several cosmetic options are available (including whitewalls, solid white letters, outline white letters, etc.).

Treads: At the bottom of the U is an extra pad of rubber forming the treads, the part of the tire that makes contact with the road. The channels between the treads, which siphon away water and allow air circulation, are called sipes.

Steel belts: Between the treads and the polyester cording you will find one or two steel belts (hence the term "steel-belted radials") that protect against punctures and keep the tread area firm, increasing your gas mileage.

Tire Maintenance

Before I started on this article, I’d gone out and bought a spankin’ new set of tires. The tires that came with my car (the original equipment, or "OE" in auto lingo) had exceeded their life expectancy by so many miles that I considered them among the living dead.

I worried that my tires had worn to fragile membranes that would rupture on the highway. I feared I would spiral out of control, gore chunks from nearby cars, perform a sloppy double tuck over the highway median, and (if I was lucky) barely escape the massive explosion that would launch me and my hunky male protagonist through the air only to land–singed, breathless, and wildly attracted to each other–on the gravel shoulder. Lucky indeed.

I went to the tire shop, told them the make, model, and year of my car, and said I wanted tires that would last for 80,000 miles. Their computer told them what size tires to use, and they chose the particular tires from their stock (based, I believe, on whether they had a matching set of four). The price they quoted seemed reasonable, and a few hours later, I was feeling much better with my new tires.

I may have bought myself peace of mind, but did I buy good tires? Did I even need new tires?

Here is what I should have done before I replaced my tires (and what I should have been doing once a month). These maintenance steps will keep your tires safe and happy, which in turn keeps you safe and happy. You’ll get more miles out of your tires, and you may even improve your gas mileage.

Check Your Tread Depth

Got a penny? (If not, check between your sofa cushions.) Stick Mr. Lincoln headfirst into the channels between your tire treads. If you can see all of his head, your treads are too shallow (they should be at least 1/16" deep) and you need new tires. Some tires are made to show flat bands across the treads when it’s time to replace the tire. Chances are, Mr. Lincoln’s head will be partially hidden by the treads, indicating your tires are safe. But while you’re down there, remove any embedded pebbles or other debris; these can work their way into your tire, causing a leak. If you see no treads at all and you’re not the owner of an Indy race car, walk–don’t drive–to the tire store.

Check Your Air Pressure

My anonymous source, Deep Tread, confided that most of his customers arrive at the shop with under-inflated tires. As it turns out, under-inflation is the leading cause of tire failure, not punctures.

You know all those pieces of tire you see on the highway? They’re known as road alligators. Most people think road gators are the detached treads from retreaded tires (see the links below), but most road gators are actually from new tires that were under-inflated.

If your tire treads are more worn on the outside edges than in the middle, under-inflation is probably the culprit. On the other hand, over-inflation decreases a tire’s traction and causes excessive wear in the middle of the tread. Proper inflation maximizes traction, minimizes tread wear, increases gas mileage, and keeps you safe.

If you have a tire-pressure gauge and you know where it is, good for you. You’re doing better than I am. (Don’t have a pressure gauge? You can buy one for cheap from the Tire Industry Safety Council.)

Now check your air pressure. (See Car Care Basics for instructions.)

Is your air pressure correct?

Sorry, that was a trick question! You have no way of knowing what the correct pressure is for your tires until you look in one of 3 places:

1. Your trusty but neglected owner’s manual (which may refer you to #2 below);

2. The tire placard, a sticker located somewhere on your car (probably on a doorpost, on the edge of a door, or behind the gas panel);

3. The tire itself. (Molded right into the sidewall of your tires is the maximum pressure to which the tires can be inflated. Never exceed that amount.)

Now do you know whether your air pressure is correct? Not necessarily. Measuring tire pressure can be tricky. Because air expands when it warms, a tire with the same amount of air in it will have a higher psi (pounds per square inch) measurement in the summer than in the winter.

The same thing happens when you drive: the tire heats up, and air pressure increases 2-6 psi as a result. Remember that you should always measure the pressure when your tire is cold–after the car has been parked for at least three hours. If you need to drive to a service station to check your air pressure, drive no more than one mile.

If you’ve read your owner’s manual or tire placard and measured your air pressure, you now know whether your tires need more air. Service stations usually have an air compressor you can use for free to fill your tires. If the machine has a pressure gauge, don’t trust it–exposure or abuse (even psychos with crowbars need properly inflated tires) can make it inaccurate. Double-check with your own pressure gauge.

A tire can lose 1-2 pounds of pressure every month in cold weather, more in warm weather. Check all your tires (ideally) once a week or (at least) once a month–and that means your spare, too. After all, what good is your spare if it is as flat as the tire you’re replacing? If you have a compact temporary spare, refer to your owner’s manual for its proper inflation pressure.

Rotation, Balancing, and Alignment

Rotation means moving your wheels from one axle to another and from one side of your car to another. Have your tires rotated regularly, at least every 6,000 miles. (Check your tire warranty to see how often you must rotate your tires to keep the warranty valid.) Rotation will make your tires wear more evenly and last longer. Deep Tread recommends that you have your tires rotated every other oil change. (You are changing your oil every 3,000 miles, right?)

Balancing your wheels fixes uneven weight distribution around your tire. After your tire specialist places the tire on the rim, he uses a machine to determine the heaviest point on each side of the tire. He will then place a weight opposite these points. Balancing keeps your car from shuddering at high speeds.

Your wheels should be aligned any time you buy new tires. According to Deep Tread, improper alignment can cause your car to pull to one side and can create uneven wear on your tires.

How to Buy New Tires

Before you plunk down your hard-earned nickels, make sure you understand what you’re buying.

Read Your Tire

If you’re in the market for new tires, start with the fine print. The Federal Motor Vehicle Safety Standards (FMVSS) not only set the safety requirements for tire manufacture, but also stipulate that the manufacturer must mold all sorts of useful information right onto the tire itself. (Click here for a good visual guide from Goodyear.) Your tire will tell you how it’s constructed, how big it is, and what load it can carry, just for starters. All of this information will also appear on a sticker placed on the treads of the tire.

Among the most useful information on the sidewall of a tire is the Uniform Tire Quality Grading System (UTQG) rating for treadwear, traction, and temperature resistance. On your tire, the rating looks like this: "TREADWEAR 400 TRACTION A TEMPERATURE B," or simply "400 A B." The UTQG was established by the federal government to help buyers compare tires. (Since the tire manufacturers grade their own tires, keep in mind that the UTQG rating may be more useful when comparing tires from the same manufacturer.)


The treadwear grade is not based on the actual mileage you will get out of your tire, but on the life expectancy of your tire relative to that of a tire graded 100. A tire graded 200 will last twice as long as a 100 tire. My tire is graded 560, so it will last 5.6 times longer than a tire graded 100 by this manufacturer.


The traction grading is very important. What else is your tire for but to provide traction? As you may have heard, your brakes don’t stop your car–the tires do. The best traction grade is AA, followed by A, B, and C. Tires graded C meet the minimum FMVSS standards.

Temperature Resistance

Simply put, temperature resistance is your tire’s ability to resist heat buildup and to dissipate heat. If your tires get too hot, the rubber can start to break down. Extremely high temperatures can even cause your tire to blow. If you ever plan to drive for more than an hour at highway speeds, it’s best to get tires with a higher temperature grade. The highest is A, followed by B, then C. As with traction, a tire graded C meets the minimum FMVSS standards. My tires are graded B, which is less than I would have chosen had I done my research, since I often drive at highway speeds for prolonged periods.

Types of Tires

Now that you understand how tires are rated, you’ll need to choose the type of tire that best suits your car and your driving habits.

All-Season Tires

Your basic tire is the all-season tire, designed to handle a certain amount of rain, mud, and snow. If you have an all-season tire, your sidewall will carry the designation M+S for "mud and snow." Your basic tire is also interchangeable–the same tire can go in any position on your car.

Performance Tires

High-performance cars, especially those with rear-wheel drive, may come with performance tires instead of all-season tires. Performance tires are made of a softer rubber designed to stick snugly to the road, and therefore don’t last as long as all-season tires. Their treads also don’t handle snow very well.

Snow Tires and Tire Chains

Deep Tread informs me that snow tires, all but abandoned in favor of the all-season tire, are making a comeback with owners of high-performance cars. Snow tires can handle winter better than performance tires, so some car owners are storing their performance tires in the winter. If you’re thinking about getting studded snow tires or chains for your regular tires, check to see if your community allows their use, and when.

Directional Tires

Some brands of tires are directional, meaning that the tread pattern must face the same direction on all four tires. Tires designed to handle a lot of water on the road are often directional, with the direction of rotation indicated on the tire’s sidewall. As many Corvette owners know, tires can also come in pairs: a left tire and a right tire. If you own or buy this kind of tire, remember to point them out to the service technician when you have them rotated.

Get the Biggest Bang for Your Buck

Okay, perhaps "bang" isn’t the best word to use when discussing tires, but you know what I mean. When you buy tires, know what you’re paying for. Wheel balancing and alignment should be included, and many dealers offer lifetime tire-rotation service.

Your invoice may also include a tire disposal fee, as mine did. Ask your dealer what will happen to your old tires. Deep Tread informed me that his old tires are recycled, which gave me a warm glow. Then I asked how they were recycled. I was disappointed to hear that in my area, the primary recycling options seem to be shredding the tires for use on landfill roadbeds and burning the tires for fuel. (That must be where my warm glow came from.)

If recycling tires is important to you, call around and try to find a dealer who sends tires to be retreaded. If you’re really into recycling, you may even consider buying retreads yourself, rather than new tires.

Rubber manufacturers are also researching ways to reclaim the raw materials from tires for other uses. Make sure your tires aren’t going to be dumped in a big pile with 10,000 other used tires–such tire dumps are fire hazards and prime mosquito breeding grounds. (Mosquitoes lay their eggs in water that has collected in the tires.)

Tire Dos and Don’ts

Do be aware that the use of aerosol tire inflators and sealants–handy as they may be when you have a flat–can void your tire warranty.

Do make sure to tell your tire repair person if you used an aerosol inflator or sealant. The gases forced into your tire are flammable, and a metal-on-metal spark could cause a movie-worthy explosion. Plus, in the words of my tire-store sources, spray inflators also make the inside of a tire "goopy and icky."

Don’t judge your tire pressure by how your tire looks. Hint: squinting one eye and kicking the tire won’t help. Radial tires are notorious for looking low on pressure when they’re not.

Do, if you are changing your own flat tire (or directing the poor schlep who is), put your compact temporary spare on your rear axle if you have front-wheel drive and on your front axle if you have rear-wheel drive. Your best tires should be on the drive axle.

Don’t, if you are stuck in mud, ice, or snow, spin your tires madly in an effort to escape. This can cause severe heat buildup and can make your tire explode like beans in a microwave.

Do, if you are stuck in mud, ice, or snow, rock your vehicle gently back and forth by shifting from drive or second gear to reverse. It may not get you unstuck, but your tires won’t explode. If you can’t get out, call a tow truck.

Don't drive with less than the recommended air pressure in your tires during the winter. Many people allow their tire pressure to dip 5 psi below recommendations under the misconception that doing so will improve traction on ice and snow. It won't, and you may damage your tires.

Do check your winter tire pressure: as the weather gets colder, the air pressure in your tire will naturally drop as the air cools and compresses. Add the necessary amount of air to keep your tires inflated properly.

Tire Terminology

bead: the cable reinforced edge of a tire that forms the seal with the rim.

bias-ply: a tire with cording running diagonally across the tire from bead to bead.

carcass: the rubber body of a tire.

cording: polyester cord that reinforces the rubber body of the tire.

FMVSS: Federal Motor Vehicle Safety Standards.

psi: pounds per square inch, a measurement of air pressure.

radial: a tire with polyester cording running straight across the width of the tire from bead to bead.

retread: a used tire that has had the original tread buffed off and replaced with a new tread.

rim: the metal "center" of the wheel that holds the tire.

sipe: the channels or grooves between the raised treads.

steel belt: a strong woven steel mesh that makes the tread area stronger and firmer.

tread: the part of the tire that makes contact with the ground.

UTQG: Uniform Tire Quality Grading System.

wheel: the rubber tire and the metal rim together.

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