Have you ever looked at the numbers on the side wall of a tire? You’ve probably been left scratching your head wondering what this jumble of numbers and letters means. Well, it’s a code that tells you everything you need to know about the product and its origins. Today, I’ll give you a complete answer to the question, what do the numbers on a tire mean?
By the end of this article, you’ll be a bona fide tire number reader. I’ll explain each component of the numbers and explain what the numbers on a tire mean.
How to Read Tire Numbers (the basics)
For the purpose of this article, we will look at a Firestone All-Season Touring Tire with the number P255/55R20 107 H.
These numbers represent every metric regarding the composition and functionality of the tire, including:
- the type of rubber
- tire type
- its size
- how it was constructed
- how much load it takes
- what speeds it can handle
- specific ratings for U.S. regulators
- the product identity
The numbers on every tire will be a little different. Keep reading to find out how to decipher the numbers on your tire.
Full Explanation of What Every Number on a Tire Means
On most tires, you’ll have a series of letters and numbers on the sidewall which provide information about the tire. This information can help you understand your tire size, which can save you time when ordering a new set of tires.
These tire numbers and codes refer to the following:
Additionally, you may also see the following on your tire’s sidewall:
- DOT Symbol
- Tire Identification Number
- UTQG (Uniform Tire Quality Grading) Scores for Traction and Temperature
Let’s take a closer look at each of these:
How to Read Tire Type on a Tire
Using our example (P255/55R20 107 H), the letter “P” means this is a P-Metric tire. This is a fancy way of saying the tire meets regulatory requirements in the United States for Passenger vehicles.
So, a P-Metric is for any vehicle that is for personal use and is not a commercial vehicle.
If you do not live in the United States, your tire will have no letter at the beginning. This is known as the Euro-Metric terminology, and tires under this metric may have different load capabilities.
Sometimes you will see the letters “LT” starting the tire number, which means the tire is specifically for Light Trucks.
One of the core differences between LT and P-Metric tires is light truck tires usually need high inflation pressure. You can find information about which tire your vehicle should have in the owner’s documentation.
Importantly, the Metric letter/s can appear at the start or end of the tire numbers.
Which Number on a Tire Refers to Tire Width?
If you want to know how wide your tire is, you can look at your tire wall number. All tire widths are measured from sidewall to sidewall.
Width is always shown within the first three digits of the tire number and is in millimeters. So, in our example (P255/55R20 107 H) the width is 255mm.
Tire Aspect Ratio (definition & where to find the number)
Aspect ratio is the technical term for what most people call the “profile” of a tire. If you run a Ford F150, you will have a wider profile, while a Corvette will have a low profile.
Regular passenger cars have something in between.
On the tire, the aspect ratio is visible on the sidewall as a percentage number. This is because it is a percentage of the width of the tire taken by measuring from where the rim and sidewall meet to the top of the tread.
The aspect ratio is the number that follows the tire width on the tire number.
So, in the example Firestone tire we are using in this guide (P255/55R20 107 H), the aspect ratio is 55 (or 55 percent of the tire width). In other words, the tire sidewall is 55% as high as the tire is wide. Or 55 percent of 255mm, which is 140.25mm.
Tire Construction Method Letter
There is a letter in your tire number that tells you your tire’s construction method. This will be either an R or a D.
R: If you see an R, that means you have a radial tire. This is the most common type of tire available on the market.
As you can see by our example, the Firestone All-Season Touring is a radial tire (P255/55R20 107 H). This type of construction provides better grip on road surfaces by limiting rolling.
You will also find R tires offer superior comfort, mileage capabilities, and durability. In terms of construction, radial tires have layers of strings made from a mixture of steel, fabric, and polyester, which are coated in rubber and laid straight facing forwards.
D: If the letter is D, that means your tire was built with crisscrossing piles. Sometimes D tires are known as cross-ply tires or conventional tires.
Tire Wheel Diameter / Rim Size
Next up is the diameter of the wheel, which essentially tells you the rim size the tire was made for.
Our P255/55R20tire is for a wheel that is 20” in diameter. Needless to say, you will need to select a tire size to match the rims on your vehicles.
Of course, you can buy the same model tire across a range of wheel diameters.
What is a Tire’s Load Index Number (and where is it on the tire)
Now you will see a gap in the tire number, leading to the next section (P255/55R20 107 H) that shows a three-digit number. This is the load index and details how much weight the tire can support.
There are dozens of different load capabilities available depending on your tire. The tire we are looking at has a load index of 107, which means its capacity weight is 2,149 pounds (based on maximum air pressure).
Tire Speed Rating Letter
And finally, on the main tire number, you will see the final letter (P255/55R20 107 H), which is the speed rating.
As the name suggests, this highlights the top speed the tire can handle for a sustained amount of time. This is a rather archaic inclusion because no driver will run at the speed limit of their tire for long enough for it to be important.
Still, each letter represents a specific feed, as the table below shows with our example highlighted:
| TIRE SPEED RATING SYMBOLS | ||
|---|---|---|
| Symbol Speed | Speed (km/h) | Speed (mph) |
| A1 | 5 | 3 |
| A2 | 10 | 6 |
| A3 | 15 | 9 |
| A4 | 20 | 12 |
| A5 | 25 | 16 |
| A6 | 30 | 19 |
| A8 | 40 | 25 |
| B | 50 | 31 |
| C | 60 | 37 |
| D | 65 | 40 |
| E | 70 | 43 |
| F | 80 | 50 |
| G | 90 | 56 |
| J | 100 | 62 |
| K | 110 | 68 |
| L | 120 | 75 |
| M | 130 | 81 |
| N | 140 | 87 |
| P | 150 | 94 |
| Q | 160 | 100 |
| R | 170 | 106 |
| S | 180 | 112 |
| T | 190 | 118 |
| U | 200 | 124 |
| H | 210 | 130 |
| V | 240 | 149 |
| W | 270 | 168 |
| Y | 300 | 186 |
Why Do Some Tires Have the DOT Symbol?
Depending on your tire and where you are from, you may see a DOT symbol on the sidewall.
This number will be separate from the standard tire number and simply shows that the product complies with Vehicle Safety Standards set by regulatory bodies in the United States.
About the Tire Identification Number (where it is, how to read it)
The tire identification number (TIN) is also located separately from the main number.
It is comprised of 12 numbers and letters. It identifies the week and year the tire was made, as well as in which factory it was manufactured.
Tire companies in the United States are legally required to include the TIN on their products.
Uniform Tire Quality Grading Codes on a Tire
UTQG (Uniform Tire Quality Grading) is a system where the U.S. Department of Transportation gives tires a rating based on quality. This gives consumers an idea of whether the tire is good or not before making a purchase.
UTQG ratings cover three important components of a tire: traction, temperature, and treadwear.
Traction
Traction grades highlight how well a tire has been shown to function in wet road conditions, albeit in controlled test scenarios.
The system assigns grades of AA, A, B, or C to tires. AA is the best and indicates a tire likely to be excellent in wet driving conditions.
Temperature
Temperature grades show how well the tire dampens and dissipates heat that would otherwise damage the rubber compound.
The higher the grade the better the tire will function at high speeds.
An A grade means the tire performs well at speeds over 115mph for a prolonged length of time, B is for between 100mph and 115mp, followed by a C grade for speeds between 85mph and 100mph.
Treadwear
Treadwear grades provide insight into how the tread on a tire is likely to hold up over time. If the grade is 180, it will last twice as long as a tire with a treadwear grade of 90, at least on average.
Which Numbers on Your Tire Are Most Important?
While I could argue all numbers on the tire sidewall are important, I think some provide more essential information than others. For example, the grading system is too vague to be really helpful beyond offering a buying guide.
Similarly, the DOT symbol tells you that the tire passes regulatory standards, but it’s not specific enough to tell you anything more than that.
So, I think the two most important numbers on the tire are the Tire Identification Number (TIN) and the main number that shows dimensions, speed, and construction. All this information is necessary when it comes time to replace your tires.
Knowing the TIN will allow you to buy the same tire should you have an issue with just one, while the main tire number will allow you to get the rim size and tire dimensions right.
How to Use the Numbers on Your Current Tire to Order New Tires
If you need to order and buy new tires, the numbers on the sidewall can help you choose the right ones. For example, if you’re purchasing a new single tire, you should try to match it with the other three tires on your vehicle.
All the information on the tire sidewall, including the brand, identification number, and construction process will help you find your model.
Maybe you are changing all your tires and are less concerned about buying the same model. Well, the information on your existing set can still be useful.
For example, the numbers tell you the size of wheel on your vehicle, as well as the load and speed capacities you will need for your new tires.
Of course, you can ensure the best results by taking your vehicle to the shop for a professional to determine the tire size range that suits your car.
It is worth noting, that while you can change the size of your tires, the load limit on your vehicle will still be the same.
Final Thoughts: What Do the Numbers on a Tire Mean?
What do the numbers on a tire mean? They actually tell you a lot about your vehicle’s tires, their size, construction, and how you can expect them to perform.
Now that you understand this, it will be easy to shop for new tires and to understand how the tires on your car or truck stack up (and where they may fall short).