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How Do You Read Tire Sizes: Reading the Sidewall

How To Save on Your Next Purchase Of Tires

Your tires support the weight of the vehicle and are the only parts that make contact with the road. Ensuring you have the proper tire size when it’s time to shop for new tires is critical for your vehicle. Without properly fitting tires, your safety is at risk.

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Reading the sidewall of a tire is a life skill too many of us lack. Not many people know how to read this and it can easily be misinterpreted.

Looking at the tires for the first time may seem like you are reading a foreign language, but once it is broken down, it is not too complicated. If, after reading this blog, it still seems like a mystery, you can always ask a tire professional to help walk you through the process.

Knowing how to read the tire wall may not seem like a talent you would use everyday unless you work in a garage; however, if you buy tires for your car, replace the tires on your car, or require roadside assistance for a blown-out tire, you may be thankful to know what’s what when looking at the wheels.

This blog outlines what the numbers and letters mean on tire sizes and provides brief recommendations on how to purchase tires in the future. It also presents the average cost of tire replacement these days.

What Do the Numbers Mean on Tire Sizes?

With some explanation, it’s easy to understand what all of the letters and numbers mean on your tire’s sidewall so that you can read the tire size properly. These numbers are indicators of the size, type, and performance of the tire.

How to Determine Tire Size

Reading the tire size is a fairly straightforward process that begins by looking at the numbers and indications on the side of the tire. It should be visible to the naked eye without having to use any tools or equipment to find the information.

The most common time people concern themselves about tire sizes is when replacing tires on their ride.

Once you have decided it’s time to buy new tires, you need to know what size tires are correct for your vehicle, meaning you need to know how to read the tire size. Luckily, this information is usually inside the car door or in the owner’s manual. 

To ensure your current tire or replacement tire matches your vehicle’s requirements, it is important to understand how tire sizing works. If you want to substitute a new size or tire type, it’s important to have a professional advise you on what will help your car run efficiently.

What is Metric Sizing on Tires?

Reading tire sizes means understanding that most vehicles come with tires that are either P-Metric or Euro-Metric. Both P-Metric and Euro-Metric tires are designed for passenger vehicles which include cars, minivans, SUVs, and other light-duty pickup trucks.

P-Metric tires contain the letter “P” before the sequence of numbers from the tire walls. P-Metric tires are standardized by the Tire and Rim Association. Euro-Metric tires don’t contain any letter before the sequence number begins and are standardized by the “European Tyre and Rim Technical Organization.”

If you have an SUV, pickup truck, or van, you may see a different type of size designation specific for heavy-duty light trucks and vans. There are two common size types in this category: LT-Metric and Euro-Metric Commercial (C-Type).

LT-Metric tires contain the letters “LT” before the sequence of numbers and are standardized by the Tire and Rim Association. C-Type tires look similar to a passenger Euro-Metric size except there is a “C” after the rim size. C-Type tires are standardized by the “European Tyre and Rim Technical Organization.”

Other types of tires that fall into the Metric size type are Temporary Spares that start with the letter “T”. Sometimes you may see “ST” meaning “special trailer”.

How to find the Width on a Tire

When reading tire sizes, the first number to appear on the tire wall is your tire size width in millimeters. This width refers to the measurement from one sidewall to another. For example, a tire with the measurement “P225” is for a passenger vehicle with a width of 225 millimeters.

What is Aspect Ratio?

The next number on a tire is for the tire’s aspect ratio, which, when reading tire sizes, tells you how tall your tire’s profile is. 

The aspect ratio is a percentage calculated by dividing a tire’s height off the rim by its width. For example, if a tire has an aspect ratio of 60, it means the tire’s height is 60% of its width.

Tire Construction

Continuing to read the tire size, after the aspect ratio, a letter follows that indicates the type of internal construction maintaining your tire’s stability: either R for radial or D or B for Diagonal or Bias Ply respectively. 

Fun fact: radial tires are the most common tires on the road in the United States.

Reading the Rim Diameter

After reading the construction type, the next number is the diameter code, in inches, of the rim size on which the tire can be mounted.

What is a Load Index?

One of the most confusing numbers when reading tire sizes is the load index. The load index tells the consumer how much weight, in pounds, the tire can support when fully inflated. However, this number doesn’t tell us the precise number by itself; it corresponds to a specific load capacity listed in an index.

The load index begins with 1 and ends with 150. The numbers in the load index represent carrying capacities from 99 to 7,385 pounds.

There are two types of load types for passenger tires: Standard Load and Extra Load. Standard Load tires have no markings, but if the tires are Extra Load, they will contain the letters “XL” after the size and load index.

Passenger car tires, P-Metric and Euro-Metric, only have one load index number whereas LT-Metric and C-Type tires have two numbers separated by a slash. The first number indicates if the tire is used in a single application and the second number indicates if the tire is used in a dual application.

It is important to note that there are different load index standards between organizations. Two tires in two different systems may have the same load index number but could have different maximum load capacities. Double check with a tire specialist at your local garage should you have additional concerns.

What is a Speed Rating for a Tire?

The final number in reading tire sizes is the speed rating which is indicated by a letter. The speed rating letter corresponds to a particular speed capability based on a laboratory test. Replacement tires must have the same or higher speed rating as the vehicle’s original equipment to maintain speed capability.

Off-Road Tires: Flotation Sizing

Off-road tires for a light truck or SUV use flotation sizing, which is different from reading tire sizing from the Metric formats. These tires cannot be used in dual applications and a tire may have a different load capacity from the same size as its LT-Metric counterpart. The tire sequence is as follows:

  • Overall diameter
  • Section width
  • Construction
  • Rim diameter
  • LT type

Uniform Tire Quality Grading

Another group that affects reading tire sizes is the Uniform Tire Quality Grading or UTQG. This grading is required for passenger car tires in the all-season and summer categories. Some winter tires, light trucks, and motorcycle tires are excluded from this requirement.

Quality grading is intended to provide simple data so you can make an intelligent decision in which tire to purchase, but the ratings are based on test results in special conditions meaning it’s possible to misinterpret the data as it relates to your driving style.

Quality grading designates performance levels into three categories:

  • Treadwear
  • Traction
  • Temperature

The treadwear grade rates the wear rate of the tire on a special course of 6,000 miles. For example, a tire graded 150 would wear one and a half times better on the course with the same tire that received a grade of 100.

The traction grades from lowest to highest are C, B, A, and AA. They represent how well the tire stop on wet pavement.

The temperature grades of A, B, and C represent the tire’s resistance to the generation of heat and its ability to dissolve heat. Sustained high temperatures can cause the tire to degenerate and fail. The grade C represents a performance level all passenger car tires must meet. A and B represent higher levels.

Tire Sizes: Now that I Know How to Read Them, Which Do I Buy?

Tire sizes can be very confusing. Some numbers on the sidewall are listed in metric and some in inches. You can see your original equipment tire size in the owner’s manual and even though it is the tire size recommended by the manufacturer, your driving habits also dictate which tire you should purchase.

Knowing how to read a tire is a good place to start, but it’s best to have a tire professional help you determine a tire size range that will best fit your vehicle and your driving habits. Even using a tire size calculator will just give you a quick estimate.

Ask the tire expert about how the tire will fit your vehicle’s suspension, any differences in tire speed, load index, and speed rating so your ride quality and vehicle performance are maintained.

Insider Secret: A Tire Size Shortcut

Many tire experts realize that reading tire sizes quickly is like speaking a foreign language, it takes plenty of practice, especially if you’re not to use to it.

In some cases, you might get away with being able to just find all of these codes and take a quick picture of the information with a smartphone. If you are able to send the picture to an expert, or show the mechanic the information on your phone screen, you could let them do the dirty work.

Another easy hack is to see if the information is present in your car owner’s manual. It might save you some time.

The Average Cost of Tire Replacement

If you’re curious about reading tire sizes, you are likely to be buying or replacing tires. Sometimes only one tire is replaced, usually it is two or four. Either way, you’ll have to know what tire size to mention to the mechanic when getting an estimate on the work.

The average cost of tire replacement depends on many factors. For example, tires designed for winter driving have a different price than those designed for off roading. It is often more expensive to outfit a SUV with new tires than it is a car. Even where you live could impact the price of tire replacement.

Consumers can buy “economy” tires, or even used tires, which are often cheaper. However, many customers end up paying for this choice down the line. They get a flat or require tire replacement more often. Sometimes it pays to go toward mid or elite levels just for the reassurance and durability.

On average, one new tire is about $100. For an SUV, it’s about $175. Pickup trucks cost a little more.

A set of four tires runs anywhere from $400 to $2,000. The variables influence the final price a lot, so look for coupons and promotions. Be aware that smart shoppers call up a few different places to get an estimate. If you have a handy mechanic in your family, you might run the job by them.

Tire replacement is a chore, and it’s one that requires being able to identify tire size information. Relying on resources helps get the job done in no time flat.

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