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Buying Car Tires: When, Where, and How

Everything you need to know about replacing your tires in one place – how should you know your tires need to be replaced? Do you need to buy four tires at once? What are the benefits of rotating? What do the markings on the tires actually mean? Learn the answers to these questions and more!

When do you need tires?

Tires are considered legally worn out when the tread depth reaches 2/32 of an inch. Sure, you can purchase an inexpensive tread depth gauge to help you measure your tires, but there are also two easy ways to inspect your tread depth.

First, most tires have “wear bars” on them. These bars are spaced periodically into the grooves of the tire. They are raised to 2/32" so that when the bars become level with the remaining tread, you know it’s time to replace your tires.

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Second, you can use a regular United States penny to get an idea of how much tread you have left. First, take a penny and pinch Lincoln’s body between your fingers. Find a spot on the tire where the tread seems the lowest and put Lincoln’s head down into the groove. If any part of Lincoln’s head is obscured by the tread, you’re okay. If you can see the top of Lincoln’s hair, or where it says “In God We Trust,” it’s time for you to get new tires.

You should also replace tires when they approach five years old. As tires age, they become susceptible to dry rot and cracking, which increases their risk for failure. You can determine the age of your tires by seeking out the DOT number stamped into the tire sidewall, near the rim and bead of the tire, on either the inside or outside of the tire. The DOT number consists of various digits, usually nine to ten in length, that denote the manufacturer, the plant, and other manufacturer identifying digits. The last four digits of the code identify the date of manufacture. The first two digits indicate the week the tire was made and the last two digits are the last two digits of the year. So, for example: 4808 indicates the tire was manufactured in the 48th week of 2008.

To be safe, you should consider replacing your tires as they reach about 4/32"–5/32" of tread. You really start to sacrifice wet traction at those levels and increase your risk of hydroplaning and maintaining contact with the road in inclement weather conditions.

Where is the best place to buy tires?

Tires are marketed very aggressively and competitively throughout the automotive retail repair industry. Marketing tires aggressively is seen as a way to develop a relationship with a potential customer, with the intent of gaining confidence and future business.

With that in mind, there are often very good deals offered for tires. Pay attention to special offers and rebates at all retailers, from the national chains to a discount tire retailer featured on the Internet or in magazines. In the last ten years, even automotive dealership repair facilities are boasting low prices on tires for most cars. Look for offers like “Buy 3, Get 1 Free” or “$100 rebate with the purchase of four tires.” Depending on the tire you are buying, you can find a great deal. 

When determining the cost of your new tires, make sure that you are figuring in not only the cost of the tire, but the labor to install it, the labor and materials to balance the tire, and the valve stems your rims need to support your new tires. Consider also that there is often a state tire tax and disposal fee to contend with.

How many tires do you need?

In ideal circumstances, any time you buy tires, you should replace the entire set. This guarantees optimum matching of brand, type, size, and uniform tread thickness. Some cars and trucks mandate replacement of all four tires at the same time when outfitting your four-wheel-drive (4WD) or all-wheel-drive (AWD) vehicle with fresh rubber.

If you do not replace all four tires at once on an AWD vehicle, you risk damage to components in your AWD system, such as your transfer case. These parts are very sensitive to the overall outside diameter of your tires. Any fluctuation whatsoever can cause damage. Some snow tires should also be replaced with all four at once. This is because the type of tire being installed differs significantly from the construction of your conventional tires and can cause significant handling challenges if mismatched.

For the majority of cars and trucks on the road, it is satisfactory to replace tires at least two at a time. You should replace your worst two tires and keep your newest tires up front. This helps keep the steering accurate, which is important in varying weather and road conditions. Sure, in snowy areas, you may want to put two new tires in the rear if you only replace two because it will aid in severe weather traction. However, this is the exception to the rule. Placing your new tires in the front helps prevent hydroplaning and loss of vehicle control.

When you have a single tire fail, usually by a puncture that is not repairable, there are occasions where it acceptable to replace just one tire. Keep in mind that you want to match both left and right as close as possible, if not identical, in make and model of tire. If your tread thickness or style varies too much, it can cause handling issues with your car and affect vehicle safety.

If you have a full-size spare that has never been used, you can use it with a matching sibling on the other side. In these cases, just make sure the age of the tire is not older than five years, as described earlier.

What should you know about your tires?

There is a ton to learn and know about tires, and many specialists spend a significant amount of time acquiring knowledge and keeping up with new advances in the industry. However, there are some key points to know that will help you feel more confident when it comes to purchasing tires.

The place to start is on the tire placard for your vehicle. This is usually located either on the driver’s door jam or the fuel door. This placard tells you the requirements for the tires on your vehicle. It will tell you the size of the tire for all positions, the air inflation pressure required, plus the load rating and speed rating your tires need to have.

Size of tire

When you start shopping for tires, first know the size. Today’s tires have a size indicated first by tread width in millimeters—this is three digits. Then there is the “aspect ratio,” which indicates the size of the tire's sidewall. This is a two-digit number that indicates percentage of the tread width. The final number is the rim size, in inches. So, for example, the size P215-60 R16 indicates that the tread width is 215 millimeters, the sidewall of the tire measures 60 percent of 215 millimeters (or 129 millimeters), and the rim opening is 16 inches.

For the vast majority of tire purchases, you will be maintaining the identical size of your tire when purchasing a new set. Sure, when adding custom wheels or modifying your vehicle in other ways, you may consider changing your tire size. But for the purposes of this discussion, you should maintain your tire size. Changing even one of the numbers in your tire size can cause serious issues. Some of your vehicle's electronic components (e.g. the anti-lock brake system) rely on the size of the tire for accurate system functioning. Further, if you benefit in one aspect by successfully changing your tire size, you may sacrifice something else. For example, by changing a tire size, you may improve the way your car handles, but you may also make the ride uncomfortable and harsh.

Uniform Tire Quality Grading ratings (UTQG)

Treadwear
The treadwear is a number that each tire manufacturer uses to rate their tires for longevity of wear. Each manufacturer is required to show a rating, but the ratings are not very strictly regulated. For example, one Michelin tire may rate 300 treadwear and another may rate 600. From this, you can ascertain that the tire with 600 treadwear should last at least twice as long as the 300 treadwear.

But, there is a problem. Since tire manufacturers do not have to show a maximum treadwear, they can legally understate a treadwear rating for the purpose of posturing various models for marketing. Besides that, you cannot compare the number across brands, such as comparing the Michelin 300 rating with a Goodyear 3for treadwear. Therefore, while knowing the treadwear value is a good thing, it is best only to use that number as a minor factor when deciding what tires to purchase.

Traction
The traction of a tire is rated AA, A, B, or C for the expected ability of the tire to cope with wet weather. Keep in mind that this means water—not ice and snow. This rating is assigned by testing the tire under controlled conditions as mandated by the United States government. A tire rated AA has the best possible traction. Most tires have AA or A. The B rating is less common and is usually found on economical tire lines.

Temperature
The temperature is rated A, B, or C for the ability of the tire to dissipate heat. A tire that keeps cool lasts longer and is less likely to exhibit failure under extreme conditions. Look for an A or B here.

Tire speed rating and load rating
A third important designation on the tire is the speed rating (also referred to as a “handling rating”). Nearly all tires today have a speed rating—from S to Y.

If you take the basic interpretation of the speed rating “S,” for example, the tires should be capable of performing up to 112 miles per hour. If you have an economy car, you may wonder—do I really need a tire rated to 112 miles per hour? The answer is yes—if the vehicle manufacturer lists it as a requirement. This is because the higher the speed rating, the better is the tire will handle. They progressively get far more stiff and firm on the sidewalls up to the (Y) rating.

The following are common speed ratings on tires:

S = 112 mph
T = 118 mph
H = 130 mph
V = 149 mph
Z = beyond 149 mph
W = 168 mph
Y = 186 mph

There are two things you should know about speed ratings. First, your new tires should be rated to match the car's required rating, located on a sticker, usually located in the driver’s door jam. Second, all four tires on the car must match in speed rating. For example, you should not mix an “S” with a “V.” Having tires with mismatched speed ratings can cause handling issues and unpredictable steering response.

Finally, the “load rating” of the tire is something you should be aware of, especially for trucks. All tires have a load rating, usually listed as the number before the letter of the speed rating (for example, a 89S would be a load rating of 89 and a speed rating of S). Truck tires, however, also use a letter rating system (C, D, E, F, G, and so on). You must use the correct load rating for your vehicle, as denoted on your vehicle's tire placard.

What kind of tires should you buy?

The easiest tire swap is with the identical tires. Your car was engineered with a specific size and type of tire in mind for optimum performance. To maintain this suggested level of performance, simply replace the tires with the same make and model.

There are endless available brands and models of tires for you to choose from. They will vary by quality—economical choices may use lesser expensive materials and tread compounds, and brand name—some lesser-known tire brands such as Hankook perform very well and are comparable to dominant brands such as Goodyear or Firestone. The tires will also have different features and benefits to cater to various needs. For example, a tire that may have exemplary tread life may sacrifice some wet traction quality. Or, a lower price tire that is superb in wet traction may be noisier than most tires due to the tread design.

The best situation you can put yourself in is to determine what is important to you about your driving and the conditions you operate in. Then, see a reputable tire retailer for a solid explanation of the features and benefits of the tires you can choose from.

Conclusion

Purchasing tires can be a daunting task—and an expensive one. However, by educating yourself with a few basics, you can make a solid and informed choice.

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