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Understanding tire terminology

Tires 101
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What size, type, and rating do you need?

Tire sizes are a combination of many different variables: the actual size in width, height and diameter as well as the ratings related to load-carrying capacity and speed-handling ability. Look in your vehicle's owner's manual to find the correct tire size, or check the metal tag often found inside the driver's door jamb, glove-compartment door or fuel hatch. If you find more than one size listed, you should look on the sidewall of your tire instead.

 

How to read the sidewall of a tire

The "P" designates passenger tires . "LT" designates light-truck tires. Here's what the numbers indicate:

Aspect ratio

This number tells you how tall your tire is. The bigger the number, the taller the tire. And typically, the lower the aspect ratio, the higher performance the tire. An all-season passenger tire will usually have an aspect ratio between 65 and 80. It is expressed as a percentage of the height divided by the width (75%, 70%, 65%) and is commonly referred to as the tire series (75, 70, 65).

Load index

The load index refers to how much weight a tire can carry. If your tire has a load index of 82, locate that number on the chart below,  and look to the right of it under load (lbs.) to see that it can support 1,047 lbs. at maximum air pressure. Multiply that by four to get your maximum load-carrying capacity. It is not a good idea to install tires with a lower load index than the factory tires that came on your vehicle.

load index 

Speed rating

The U.S. government issues a speed rating for each tire based on how well it reaches and sustains a specific speed. A higher speed rating generally means that the tire will provide better handling.

Things to think about when looking at speed ratings:

  • Downgrading the speed rating of your tires may result in poor handling and unpredictable steering. If you're looking for better cornering response, install a higher speed-rated tire on your vehicle.
  • Never mix and match tires with different speed ratings. This will cause serious handling problems.
Speed rating

 Temperature grade

This represents a tire's resistance to heat when tested under controlled test conditions. The grades from highest to lowest are "A," "B" and "C." All three grades pass the federal safety standard. "A" is the coolest running tire, "B" runs warmer and "C" just meets the minimum performance requirements (but is by no means unsafe).

Traction grade

This represents the tire's ability to stop on wet pavement as measured under controlled conditions on asphalt and concrete test services. The grades from highest to lowest are "AA," "A," "B" and "C." These grades do not take into consideration the cornering or turning performance of a tire.

Treadwear grade

This is a comparative rating based on the wear of a tire when tested carefully under controlled conditions. This tire grade is useful only when comparing tires made by the same manufacturer. For example, a tire graded 300 should have its useful tread last twice as long as a tire graded 150.

Another manufacturer may have a different number system, so a different brand tire graded 500 isn't necessarily better than the 300 of a different brand.

 

Uniform Tire Quality Grading System (UTQGS)

The U.S. government has established the Uniform Tire Quality Grading System (UTQGS) to help you in deciding which tires you want to purchase. Understand that it is a relative comparison system—not a safety rating and not a guarantee that a tire will last for a prescribed number of miles. Under UTQGS, tires are graded by manufacturers in three areas: treadwear, traction and temperature. When purchasing tires, this information can be found on the paper label on the tread as well as on the tire's sidewall.

Ready to buy some tires? You can search our Tire Finder by vehicle or by tire size. To search by vehicle, simply enter the make, model and year of your vehicle. To search by size, enter your vehicle's current tire size or the size you're looking for.

 

Used with permission. © 2014 Walmart. All Rights Reserved. See full legal.

Used with permission. © 2014 Walmart. All Rights Reserved. See full legal.

 

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