Introduction to Tire Buying Tips

Tires have been a vehicle's most important safety feature for more than 100 years. After all, they are a vehicle's only contact with the road. Even the brawniest engine, strongest brakes, and most advanced anti-skid system are at the mercy of the tire's grip on the road. Every move a driver makes with the steering wheel, brake or gas pedal is transmitted to the road through the four notepad-sized contact patches of the tires.

So, if a consumer has tires that are worn, under-inflated, or not suited to the environment, they put themselves, their vehicle, and others at risk. But most drivers don't know enough about tires to make an educated purchase. For some, the choice comes down to price and availability. Others buy tires based on appearance or reputation. In this article, we'll cover the basic information you should understand to select the right tires for you.

Tire Basics

Simply put, a tire is a flexible container of compressed air. This air container support the vehicle's load; propels a vehicle forward, backward and side-to-side; stops the vehicle; and cushions the load from road imperfections.

Today's tires have between 19 and 25 different components. Tires are built from the inside out rather than the outside in. The heart of every tire is an inner liner. Its job is to give the tire shape and hold in air. Fabric belts are wrapped around the inner liner. The bead is fastened to the bottom of the fabric belts and holds the tire to the wheel.

Tire Image Gallery 


Photo courtesy Bridgestone Firestone
Cutaway of a Bridgestone Potenza. Here you can see the main components: the inner liner, the fabric and steel belts, the bead, the tread, and the sidewall.
See more pictures of  tires.
On top of the fabric belts are steel belts. These belts have two jobs: They give the tire stability and make the tread pattern as flat as possible. (A flatter tread means more contact with the road.) The tire tread is on top of the belts. There are different tread patterns for different types of tires. The sidewell on the side of the tire gives it stiffness and ride characteristics. A taller, softer sidewall will absorb more bumps, while a shorter, stiffer sidewall will provide better cornering ability and sharper steering response.





On the sidewall of every passenger-car and light-truck tire is an alphanumeric code that describes the dimensions of the tire. For most tires, this code will start with a "P" (above, left). Some may start with an "LT" to signify light truck. Some tires may have a "Max. Load" indication (above, right). When selecting new tires, it is important to make sure a tire's load rating is at least a high as the tire you are replacing.

Tire Rotation
Rotating a vehicle's tires is essential to prevent uneven tire wear. If left unchecked, un-rotated tires will cause increased road noise, lower fuel economy, and decreased wet-weather traction. Badly neglected tires will also have to be replaced sooner.

It is generally accepted that on front-drive vehicles, where all tires are the same size, you rotate the front tires to the rear in a straight line and cross the back tires to the front. In a rear-drive vehicle, you rotate the backs in a straight line to the front and cross the front tires to the back.

On all- or four-wheel-drive vehicles, the rotation pattern most often suggested is a simple "X." The left front and right rear swap places, and the right front and left rear swap places.

Many sports cars and some luxury and sport-utility vehicles have unidirectional tires. Unidirectional tires have tread patterns that are designed to perform in the direction denoted on the tire sidewall only. They should always be rotated front to rear (assuming they are the same size). This ensures that the direction of revolution does not change.

If you are rotating a full-size spare into the mix, it is common practice to put that tire in the right rear. Consumers should consult their owner's manual for the correct tire-rotation procedure for their vehicle.

One Size Does Not Fit All

Perhaps the biggest mistake a consumer can make when replacing tires is not using the correct size. On the sidewall of your original-equipment tire (and all tires), you'll find a code that tells the tire's size and capabilities. Here's a sample tire-size code and a description of what that code means:

P195/60R16 63H M+S

  • P - Type of tire
  • 195 - width of the tire across the tread in millimeters
  • 60 - Aspect ratio of the sidewall compared to the width
  • R - Radial construction
  • 16 - Diameter of the rim in inches
  • 63 - Tire's load rating
  • H - Tire's speed rating
  • M+S - Tire is suitable for all-season driving

If the tire-size code starts with LT instead of P, that means the tire is a light-truck tire. Light-truck tires are designed to have higher-load carrying capacities and are usually found on pickups and SUVs. These vehicles are not required to have LT tires, and in many cases, the original-equipment specification calls for passenger-car tires.

The speed rating translates into the tire's ability to dissipate heat, or prevent heat build-up. Heat is a tire's enemy. The more heat, the faster the tire wears, and the faster a tire might break down. A tire with a higher speed rating can dissipate more heat on long highway trips. If a consumer were to spend little time on the highway, the speed rating might not be an important factor in choosing a replacement tire.

Tires are speed rated from 99 to 186 MPH. The most common speed ratings are T (118 MPH) and H (130 MPH). Both of those ratings clearly exceed the nationally posted speed limits and would make excellent long-distance highway tires. If a consumer were to drive only in urban situations at low speeds, a tire with an S (112 MPH) speed rating might be completely acceptable.

Another important factor in choosing a replacement tire is the load rating. The load capacity number on the tire-size code indicates the load-carrying capacity of that single tire. When selecting replacement tires, consumers have to be careful not to select a tire with a lower load-carrying capacity.


Three different tread patterns for three different driving needs. The Bridgestone Turanza is a common touring tire. The large grooves running around the tire help with wet-weather traction.


The Bridgestone Potenza is a performance tire. The larger tread blocks and limited groves increase the contact patch for improved dry performance.

Photos courtesy Bridgestone Firestone
The Bridgestone Blizzak. The open tread design allows for better traction in on snow and ice.

 

Regardless of a tire's speed rating, load-carrying ability, size, and construction, traction are the keys to safety. A common mistake is to select a tire without considering its ability to hold the road. Savvy consumers will balance a tire's traction in dry conditions, in wet conditions, and in the snow. If you desire a high-performance tire but live in northern climates, consider a "winter" tire for driving in the snowy season. If you live where the weather is warm all year, a touring tire may suit your needs just fine.

Most consumers will make the mistake of waiting until spring to get new tires. As a tire wears out, dry traction generally increases and wet and snow traction decrease. So the best time to buy new tires is not in the spring, but in the fall.

Passenger-car and light-truck tires are very different. Pickup and SUV owners will generally select passenger-car tires because they are less costly and offer a smoother ride. However, if a vehicle will consistently be loaded with cargo or will be asked to pull a heavy trailer, then perhaps the higher load-carrying capacity of a light-truck tire would be the better choice.

Tire Inflation
Proper tire inflation is important for many reasons:
  • A properly inflated tire will generate less heat or friction with the road, increasing fuel economy and decreasing tire wear.
  • A tire that's either over- or under-inflated will wear unevenly.
  • A tire that is low in pressure loses cornering ability because the sidewall isn't as stiff.

Perhaps more important for SUV and light-truck owners, a tire's load capacity decreases as it loses air pressure. So, if you were to pack their SUV to the rafters for a family vacation without adjusting tire pressures to handle the increased load, you may be asking for trouble. Those under-inflated tires would quickly heat up under the extra load and possibly have a failure, leading to travel time lost fixing a flat -- or worse.

Regardless of temperature, tires lose between 1-2 psi (pounds per square inch) per month. In addition, for every 10 degree Fahrenheit drop in temperature, a tire will lose another pound of pressure. So a tire left unchecked from the time it was filled to 35 psi on an 80-degree day in May is down by 12 psi on a 30-degree day in November. That under-inflation will affect fuel economy and wet traction, and also increase tire wear.

Replacing Tires

Can you trust your tire store?
According to Bill VandeWater of Bridgestone Firestone North American Tire, a tire dealer should ask a customer shopping for tires the following questions:
  • What did you like about your OE tires?
  • What didn't you like?
  • What are you looking for from a tire?
  • What is important to you?
  • How are you going to use the vehicle?
Based on this information, the dealer can then recommend a tire from his "tire wall" that will meet the needs of the consumer.
When it comes time to get a set of new tires, drivers have a lot of options. Traditionally, the most expensive option is to return to the dealership. Dealers will replace worn tires with original-equipment tires. This option can cost twice as much as going to the local shop down the street.

That local shop, be it a national chain or mom-and-pop establishment, is probably the best place for the average consumer to shop for new tires. Prices can be reasonable and the service manager will help consumers select the correct tire for their vehicle. However, consumers should always shop around for the best prices. Tire and installation prices vary widely from store to store.

A new option is the discount tire retailer. These wholesale tire distributors sell tires at extreme discounts. In addition to low prices, they are often just a phone call or a mouse click away. However, the when consumers purchase tires from the discount retailer, the tires are shipped to the consumer's door. It is up to the consumer to find a local shop to balance and mount the tires. (In some cases, these tire retailers will offer discount mounting and installation at a local tire store.) For some people who want exclusive or hard-to-find tires, this is the only option.

Regardless of where you get new tires, there are a few things you should keep in mind:

  1. Know the size and type of tire recommended by your owner's manual.
  2. Determine your needs and priorities. What type of driving you will be doing? Do you prefer a soft ride, a firm ride, or a mix of the two?
  3. Make sure you purchase a tire that is capable of supporting the load your vehicle might demand. Don't buy a passenger-car tire if you need a light-truck tire.
  4. Don't buy more tire than you need. Consumers often overestimate their tire needs. In most cases, a quality all-season tire will suffice where a touring tire might be suggested.
  5. Keep in mind that any tire selection is a balance between ride quality, noise suppression, fuel economy, wear, load capability, and cost. It's the job of the tire-store expert and the consumer to select a tire that is the right balance of each.
  6. An interesting trend in the automotive aftermarket industry is "plus sizing." It involves mounting bigger wheels and tires on a vehicle to enhance the look or improve handling.

Plus sizing usually increases cornering response and traction. Often these gains come at the expense of increased ride harshness. In addition, these larger wheels and tires are often not as durable as OEM wheels and tires.

A few items of note for consumers considering plus sizing:

  1. Make sure that the tire and wheel are approved for use on your vehicle.
  2. Make sure that the replacement tire has the same load-carrying capacity.
  3. The new wheel and tire combination should be within 3% +/- the original tire diameter.
  4. Make sure that a new tire placard is installed to inform future owners of the correct tire pressure.

The Future of Tire Technology

The biggest change in tire technology is actually a return to the past. Early tires were solid rings of rubber that wrapped around wagon wheels. These tires were hard riding, but also impervious to punctures and very durable -- ideally suited to the rough terrain of the day. Today, tire manufacturers are trying to make the flat tire a distant memory.

Today's run flat tires contain air and are much more complicated in construction than early rubber rings. But, they operate on the same principle: They are tough enough to run without air if necessary.


The above diagram shows the difference in construction between a conventional tire and a stiff-sidewall run-flat tire. In a stiff-sidewall run-flat tire, there is extra sidewall reinforcing rubber that prevents the sidewall of the tire from deflecting. In a inner-liner run-flat, the sidewall is no stiffer than a conventional tire, but a hard rubber or plastic ring inside the tire helps keep the tire's sidewall from deflecting.

There are two different styles of run-flat tires. The first uses very stiff sidewalls that can support the weight of the vehicle in the event of pressure loss. Several tire companies offer this type of run-flat, and they can typically be driven with no air pressure for about 50 miles at speeds up to 55 mph. However, most cannot be repaired after being punctured.

The sidewalls can't be very tall, so most are low-profile designs. Because of this, they are typically used on sports cars such as the Dodge Viper, though they're also available for regular passenger cars and even minivans.


Photo courtesy Michelin
Michelin's PAX system is a tire/wheel package that consists of four components: a tire, a wheel, an inner support ring, and a tire-inflation monitor.
The second style is a new design invented by Michelin dubbed the PAX system. It is currently offered in the United States on Rolls Royces and the 2005 Honda Odyssey minivan, but is expected to be available for other applications in the future.

The PAX system isn't just a tire. It's a tire/wheel package that consists of four components: a tire, a wheel, an inner support ring, and a tire-inflation monitor. If the PAX system tire loses air pressure it only drops about halfway down. At that point, the underside of the tread rests on an inner support ring that runs around the circumference of the wheel. According to Michelin, the vehicle can be driven for 125 miles at up to 55 mph.

The PAX system also incorporates a special bead -- the connection between tire and wheel -- that helps lock the tire onto the wheel even if the tire loses air pressure, something traditional run-flat tires -- and regular tires -- don't usually have. Unlike most run-flat tires, the PAX-system tire can be repaired if the hole is in the tread area and less than 1/4-inch in diameter -- as is the case for regular tires.

Because the sidewalls of an un-inflated PAX tire don't support the weight of the vehicle in the event of pressure loss, the sidewalls can be taller than on run-flat tires. They also don't need to be as stiff, which means that the ride quality is better. This makes the PAX system better suited to SUVs, as well as regular passenger cars and minivans.

There's often little change in driving feel to warn the driver the tire has lost pressure, because the tires don't go "flat." Therefore, run-flat tires must be used with a tire-pressure monitoring system, which illuminates a light on the instrument panel to inform the driver of pressure loss.

In lieu of hard-riding or expensive run flat tires, manufacturers are turning to a less-costly but space saving alternative to spare tires: temporary mobility kits (TMK). Also referred to as "fix-a-flat," TMKs consist of an aerosol can containing compressed air and a liquid rubber. The can is connected to the valve stem of the tire, and the air and rubber are injected. The rubber seals the puncture and the air refills the tire.

In theory, the motorist can then drive to the nearest gas station to get the tire repaired. There are several problems with TMKs, though. First, the tire must have a small puncture and still be roadworthy. In many cases, flat tires are destroyed because drivers travel too far while they are under-inflated. This renders the TMK useless. Second, if the TMK is utilized, it often renders a good tire (with a small hole) irreparable. The liquid rubber in the TMKs can also damage expensive wheels and end up being even more expensive for the driver.

Another trend in the industry is light-truck tires with heavy-duty load ratings and passenger-car-tire comfort levels. In the past, pickup truck drivers had to choose between passenger-car tires (which are soft-riding but can't handle heavy-duty loads) or hard-riding, noisy truck tires. OEM and aftermarket tire suppliers have begun to meld the positive characteristics of passenger-car tires with the load capabilities of truck tires. In most cases these new truck tires cost more than conventional passenger-car tires, but that added expense can be well worth it or consumers asking their truck or SUV to do double duty.

Consumers rarely give tires a second thought. That's too bad, because choosing the right tire can be the difference between and a near miss and an accident. Getting the right tire for a vehicle starts with finding a knowledgeable dealer, one who can help you select the best tire for your needs. Tire retailers should also point out the pros and cons of each brand. The tire retailer should help you find the right tire for your car or truck.

Tires and Fuel Economy
Choosing a tire based solely on fuel economy would be foolish, but according to Bill VandeWater at Bridgestone Firestone North America, "consumers can see a 15-20 percent difference in their fuel economy depending on the tire they select. Some studies have shown that many consumers like high fuel economy, but not at the cost of mileage or performance (especially wet)."

Though many consumers consider fuel economy a high priority, it is typically not the number one priority for the consumer. Therefore replacement tires are not designed for with fuel economy as high a priority. According to VandeWater, "If a consumer wants a good fuel economy tire, the best choice is usually the original equipment tire.

Consumers should also not forget that fuel economy is also dependant on proper air pressure. Monitoring air pressure regularly, and with proper inflation pressures as dictated by the vehicle owner's manual, is the best route to ensure maximum fuel economy.

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