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Tire Myths Dispelled
Everything You've Ever Wanted to Know About Tires

by Denise McCluggage

Tire Shopping 101

"It all depends."

Don't you hate it when that's the answer you get to a question? Unfortunately, that's the correct answer if the question is "What tires should I buy?"

Think of tires as shoes and "It all depends" is understandable. What you wear on your feet depends on whether you are going fly-fishing or ballet dancing, golfing or trailing through museums. And on whether you'll be slogging through snow depths or treading on searing sidewalks. And, of course, on what size you wear. Yes, tires come in sizes and getting the proper fit for your car is important to your safety and the car's performance.

First off, let it be noted it is always safe to replace your tires with duplicates of those with which it was originally equipped. (But if you bought your car used don't go by what it's wearing now. Some sellers throw anything that's round and black on the wheel as long as it looks good. It might not be right.) Original equipment tires, though not wrong, may still not be the best choice for your specific needs or desires. (See All-Purpose, Winter and Summer below.)

A warning important to put way up here at the start — never buy a tire with a lower load index or speed rating than your vehicle's original tire.

The best way to choose your next set of tires is to start now. No matter how deep the tread and pristine the sidewalls it is never the wrong time to learn something about your car's "shoes" so that an emergency won't find you behind the curve and buying something in a rush that you'll regret.

Bob Toth, Goodyear marketing manager for auto tires, notes that his company's research has shown today's tire buyers making hurried decisions far more often than their counterpart of some 15 years earlier. More than half of the 1999 buyers surveyed said they did it all in a day — research, decision and purchase — whereas the same number in 1985 said they spent weeks or months in the process.

Whether you buy your tires the slower way of yesteryear or the faster way of today the first step is to get on your knees and read your existing tire. Imbedded in the rubber on the sidewall is a wealth of information. All you need is a magic decoder to interpret it. And that follows.

On the sidewall you'll find in large letters the manufacturer's name and the tire's model name. Look to the smaller letters for something like this:P215/65R15 89H

- P means passenger car. There might be no letter. Or LT for light truck. Or T, but not for "truck," This T is for "temporary" spare.

- 215 is the measure in millimeters of the width of the tire tread.

- 65 is the aspect ratio meaning the ratio of height of the tire to its width. This legend is for a tire that measures 6.5 inches from tread level to the bead, or where the tire fits on the wheel. (Check out cars in a parking lots. Look for the hot looking roadsters or sports sedans that have very little tire showing. Read the tire and see what that aspect ratio is. Then check a pick-up or van).

- R is for radial, the type of tire construction in nearly every passenger car tire rolling. B and D, should you ever see them, stand for "belted" and "diagonal (bias)" ply tires.

- 15 is the rim diameter in inches.

- 89 is the load index. You'll need a chart to see that this tire's load limit in pounds is 1279, but what's important is that the higher the number the heavier the load the tire is capable of supporting.

- H, the speed rating, means the top safe speed for the tire is 130 mph. But that is in ideal conditions: moderate temperature and proper tire inflation etc. Though you may never drive over 99 (a Q rating) understand that the rating is calculated for the vehicle's capability with a safety margin. That's why you must never go below the rating on the original tire.

Other sidewall information on the sidewall apart from the size designation includes ratings for Treadwear, Traction and Temperature. These numbers and grades are determined by the manufacturer, not the government and thus are best used for comparison within one maker's line.

Treadwear. This is the expected wear index. The higher the number the longer wear to expect but be aware that one maker's 190 may be another's 220. Also be aware that the best wearing tire will most certainly not be ranked the highest in traction. Tires are a story of trade offs. Wearing like iron means cornering like iron, not the greatest attribute in wet weather.

Traction. Ratings are AA (the highest), A, B and C. Super sticky tires, like Goodyear's Aquatread 3, is one of the industry's few AA tires.

Temperature. A (the highest) B and C is a grade for the tire when properly inflated and not overloaded representing its ability to resist and dissipate heat. Understand that the recent failures of Firestone tires were almost exclusively in hot climates with suspected under inflation. Even if overheated tires do not fail catastrophically their useful life is greatly shortened.

Other information on the sidewall might be a graphic symbol of a snowflake within a mountain silhouette or the letters M+S (for mud and snow.) The DOT symbol certifies compliance with the Department of Transportation tire safety standards. Following it will be a serial number and at the end a code to show when the tire was made.

Here's how to crack that code — The numbers 478, say, mean that tire was made in the 47th week of 1998. Since 2000 four numbers are used showing week and year. For instance a vehicle a friend parked in my driveway reads "3801" By my reckoning that's the second week of August, 2001. The tire size designation on that tire reads: P255/70R16 109S

Treadwear, Traction and Temperature on this sidewall are 440, A and B. Think about it: Fairly wide tire and fairly large wheel; ultra high load index; moderate speed rating; very high Treadwear, good Traction, middling Temperature rating. All of this would indicate that the vehicle is a pickup truck (which it is) despite the "P" designation.

Now how can you use this information to choose your tires?

First assess how you use your car and where you drive it. On long straight highways turning up high mileage? In hot, dry conditions? Often in the pelting rain or on icy roads? Around town doing jitney service and household errands? Or, by choice, on twisting sporting roads to appreciate the design and engineering of your car?

Which of the T's? Decide, based on your user profile, if you need to emphasize Traction over Treadwear. And does the heat in your area demand special attention to the Temperature rating?

All-Purpose, Winter and Summer. There is no perfect tire. Tire design is a constant trade off taking into consideration a lot of mutually exclusive traits including noise, ride comfort, economy, wet traction, cornering traction, mud and snow traction, steering ease, price, durability etc. Buyers have to find the best match between what is available (the choice is broad) and what suits their needs and wants.

For that driver grinning through the twisty bits on a back road this next decision could really be costly. Don't compromise, specialize. The latest trend, long common in Europe, is to provide your car with two dedicated sets of "shoes," one for really running on dry pavement in good weather and one for winter conditions.

The All-Season tire has been the standby on American cars for some time now. The All-Season is not too noisy nor does in ride too rough on dry pavement and it is adequate in light snow and not totally impossible when the weather gets really bad. Is that damning with faint praise or what?

By design the All-Season or Multi-Purpose tire is not ideal for any specific condition but it is competent enough for most. And it means avoiding that twice-yearly dance of removing the tires of one season from the wheels; mounting those of the other season and then switching back again months later.

Drivers with the storage space and the money have two sets of wheels to make the change easier. (Drivers with even more space and more money simply have another vehicle.) Europeans have never been satisfied with the compromises implicit in one tire for all seasons. Those with high-performance cars (and driving is generally a greater passion in Europe than it is in the United States) insist on truly high-performance tires for summer and proper snow tires for winter trips to ski areas. At the least that means two sets of wheels and two distinct attitudes.

Compromise or specialty — the decision is yours. But understand this: Really experienced cold-weather drivers say that in serious winter conditions they would rather have a two-wheel drive vehicle with the right tires than a four-wheel-drive one with the wrong tires. That's how great a difference tires can make.
And no one with a truly high-performance car should hobble it with less than high-performance tires specific to the season.

And one last word of wisdom: Shop for value, not low price alone. "Cheap" and "tires" are dangerous in the same sentence. To research your tire purchase check the websites of all the tire manufacturers. To find tires for your car, go to Bridgestone Tires.