If you’ve done much shopping for tires – either online or in the store – you know there are lots of styles, types, and designs. Some are easy to understand, such as winter tires compared to all-terrain styles. Others can be more difficult.
There are many types of groupings within tire categories that are conveyed with tire symbols. Unless you are an expert in how to read tire codes, chances are that you’ve got some questions about what these symbols mean.
It is essential to understand all of the markings on a tire before you purchase new ones – especially if you are ordering them online. Tires can be a pretty big investment; plus, the safety and performance of your vehicle depend on the tires you install. A great set of tires will ensure that your car, truck, or SUV can safely drive through inclement weather conditions or even improve its fuel efficiency.
So, let’s dive in to explain what the numbers and tire symbols mean so you can find the exact model your vehicle needs.
The Basics of Tire Symbols
First, let’s break down the most common tire symbols you will see displayed. These are usually listed in the tire sidewall in the following order to make it easy to understand the details about the tire at a glance.
After the brand name of the tire, there will be a long line containing some numbers and letters. The very first letter listed is the vehicle tire type.
This states what type of vehicle the tire is designed for. Here are what the letters mean:
• P – Passenger
• LT – Light truck
• T – Temporary (spare)
• ST – Special trailer
Next, there will be a three-digit number that indicates the tire width. This measurement is given in millimeters and covers the width from the front-facing sidewall to the back sidewall.
After the three-digit tire width, you will notice a front slash (/) symbol followed by another set of numbers. This digit is the aspect ratio, which is the comparison of the width of the tire to sidewall height. So, say that a tire has the symbol: 215/65. This means that the width of the tire is 215 millimeters and the aspect ratio is 65% of 215. Mathematically, this equates to 139.75 millimeters.
Now, doing that kind of math can be kind of tricky. What’s important to remember is that the ratio impacts the driving experience of the tire. Lower ratios generally have higher performance ratings, meaning that the tires have fantastic handling and are great for high speeds. A higher aspect ratio results in a quieter, smoother ride.
After the aspect ratio, there will be a single letter listed which represents the tire construction. There are various construction styles for tires that help to improve their performance for specific vehicles.
Most passenger vehicles use radial tires, which is represented by the letter R. – this marking is mandated. Radial construction uses layers of cords made from polyester, steel, and fabric coated with rubber which is laid perpendicular (or radially) on the tire.
Bias tired can be represented with a B or a D. Bias tires are made with belts that have a slant forming an X pattern across the tire. The B stands for bias, and the D stands for diagonal. Unlike radial tires, the letter marketing is not mandated for bias tires.
Run-flat tires use a combination of diagonal piles, which are designed to protect the interior from any punctures. Run-flat tires can be identified by the letters RF, RFT, SSR, EMT or ZP. The variation is due to different manufacturers using different markings.
Trailer tires are commonly marked with an ST – for Special Trailer.
The next number states the diameter of the wheel that the tire should be mounted on. This is typically a two-digit number that represents the number of inches between the part of the wheel where the tire will be sealed, known as the bead seat areas. This number ranges from 13” to 24”.
Next up is the load index number, which will be either two or three digits long. This number tells you the maximum weight that the tire can support, which is based on a loading chart. We will cover this chart in detail later in the post.
Next up will be the tire’s speed rating, which once again is based on a chart. This is represented by a letter that correlates to a maximum speed capability of the tire.
Most vehicle tires have a speed rating that is far higher than the average driver will ever go. This ensures that you can still keep safe control of your vehicle at typical highway speeds – you don’t really want to get too close to the maximum speed rating for too long. No need to push your luck!
Next is the Department of Transportation (DOT) number code, which proves that this tire model meets the National Highway Traffic Safety Administration’s safety standards.
This code begins with DOT and then is followed by three sets of 4 digits, which are a combination of letters and numbers. The first two numbers represent the week the tire was manufactured. The second two represent the year. So if the DOT number is 3620, it means the tire was manufactured in the 36th week of 2020.
Tire Identification Number (TIN)
The numbers following DOT on the tire are part of the tire identification numbers. The first step of 4 numbers and letters represents the manufacturer and factory where the tires were constructed. Next is the manufacturer-specific coding which is used for tracking. This number is important if there is ever a recall listed.
Finally, the last four numbers are the date the tire was produced – as discussed.
UTQG (Uniform Tire Quality Grading)
The Uniform Tire Quality Grading System is used by the US DOT to measure the tire’s performance in specific performance categories. The grading rates include:
- Treadwear – This number grades the tire’s wear based on a 7,200-mile vehicle test. The higher the number, the longer the tire will last. This number can be anywhere between 100 to 1000.
- Traction – This is based on a letter grading scale and it rates the tire’s braking ability on wet surfaces on a test track. The traction grades are similar to school grading, as they can be AA (the highest), A, B, or C (the lowest).
- Temperature – Next, the tire is rated for its resistance to heat that is generated when it is driven at high speeds. The grade ranges from A to C, with A being the best at dispersing heat.
These values are determined by the manufacturer’s testing facilities – or independent testing agencies hired by the manufacturer.
What Do Tire Size Numbers Mean?
Now, let’s go back to the tire size numbers and review them so you know exactly how to read tire size symbols. These will be the first set of numbers on the tire sidewall after the letter representing the tire type (P, T, LT, etc.)
Next, will be the set of three numbers measuring the width of the tire in millimeters.
The 2rd set of numbers is the aspect ratio, which compares the height of the tire to the width.
Next, there will be a letter representing the construction of the tire with a letter, such as R or B.
The next numbers state the diameter of the tire in inches.
These letters and numbers are how you tell tire size quickly and compare it to the requirements for your vehicle. Most tire models offer a range of sizes to fit the most common passenger, truck, and SUV models.
What Are Tire Codes?
After the size markings, you will run into the load index and speed index rating codes. These can be a bit more confusing since they require additional charts.
How to Read Tire Codes
The load index code is a number ranging from 60 to 139, which indicates the chart rating of the weight in kilograms and pounds the tire can handle when inflated. It’s important to keep in mind that this number is the weight load limit for one tire – so if you’re buying a set of 4, the maximum load limit should be multiplied by 4.
To determine this number, simply look up the code correlation on a load index chart. For example, if the tire has the number “85” on it, then the weight load limit is 1,135 lbs. per tire. For a set of four, the weight load limit would be 4,450 lbs.
Next is the speed rating, which is indicated by a letter. Some low-speed tires are rated as A1 – A8 – but these have very lower speed ratings. Most passenger, truck, and SUV tires are rated as T, H, V, W, or Z, which is a range of 118 to 149 mph.
Again, to determine the speed rating of the tire, you can simply refer to a speed rating index chart.
Understanding Tire Symbols When Buying Tires Online
When you are going to buy a tire online, it’s important to have at least a basic understanding of all these tire symbols so you can find the right type. Giga Tires offers a handy feature that lets you narrow down the selection based on these important factors. You can enter in the criteria for the tires you need, such as the section width and aspect ratio. This is to make sure you get the right tires. The best way to begin your tire shopping is to get the size of your current tires, and input that size to see your available options.
You can further filter the results by optional features, such as the brand type and style, category, and season.
Winter Tire Symbols
Winter tires have their own unique set of tire symbols which indicate their capabilities and ratings for snowy or icy roads. It’s important to note these features when buying winter tires so you can find a model that will keep you safe in extreme driving conditions.
Many winter tires have the M+S rating symbol on the sidewall. This stands for Mud and Snow, meaning that the tires are constructed to improve grip on muddy and snowy roads. These tires have a specific block tread pattern which helps to improve traction.
Now, just because a winter tire has an M+S rating does not necessarily mean it is safe to use in inclement weather. The M+S test is not very in-depth by today’s standards (like freezing temperatures and ice. It only measures a tire’s performance in packed snow and mud. It does not indicate how well the tire performs in thick, freshly fallen snow, dry frozen roads, ice or loose snow and mud.
You may also see a unique tire symbol that looks like a three-peaked mountain with a snowflake inside.
The Three Peak Mountain Snowflake symbol indicates that the tire is rated for “severe snow service”, which is a far more reliable way to determine a winter tire’s safety rating.
These tires go through a far more rigorous test to measure the traction performance on many types of roads, including slippery, low temperatures, and freezing surfaces.
Have More Questions?
Finding the exact style, type, and size of tire for your vehicle can be overwhelming. There are a lot of tire symbols to consider here! But if you know how to read tire codes and have a general understanding of what the numbers and symbols mean, it will make it far easier to narrow down your options.
Our team at Giga Tires is on-hand to answer any questions you may have regarding tire codes, sizes, and styles. Please reach out to our team today for help finding the exact fit for your vehicle!