For many people, the topic of tire sizes is a very confusing one. Learn to read a tire size and to get a better understanding of what is written on the side of the tire.
In order for your vehicle to operate properly, it is crucial that the right size tires are installed on it. There are, however, some people who are not familiar with how to read a tire’s size. On the sidewall of the tire, you will find that there are a lot of numbers and letters listed, making it difficult to interpret their meaning.
Choosing the right tires for your vehicle can make a huge difference in how your vehicle performs and how safe it is. When choosing your tires, you need to consider the conditions in which you drive as well as your preferences for how you want your vehicle to respond and handle. The most important thing you need to know when it comes to buying tires, however, is how to read the tire size information so you can make the most informed decision.
As a matter of fact, determining the correct tire size for your vehicle is relatively easy if you know where to look. In addition to your owner’s manual, there are several places on the vehicle itself where you will find all the information that you need.
We will take a closer look at all of the information that is listed on the sidewall of the tire in this article. The tire size and all the information that it contains will be clear to you once you have finished reading it.
Table of Contents
Tire Size Meanings
A tire’s sidewall will have three numbers printed on it, one for the width of the tire, one for the height of the tire, and the other for the diameter of the tire. In terms of width, this measurement is expressed in millimeters. The width tells us how wide a tire is from side to side. There is a ratio that is used to measure the height of a building based on its width and height. The diameter of a tire is measured in inches, and the size of the rim or wheel that the tire can be mounted on will be determined by its diameter.
As an example, a tire with a width of 225, a height of 50, and a diameter of 17 would be called a 225/50/17 tire if the dimensions of the tire were in this order.
Each tire sidewall contains information on the type of tire, the width of the tire, the aspect ratio, and the construction of the tire. This document also contains information about the wheel diameters, load indices, speed ratings, DOT symbols, TINs, and UTQGs. For you to know if a tire is right for your vehicle, you must combine these data to determine if they are the right ones.
1. Tire Type
The letter “P” is usually found at the front of the tire size of most car tires. As you can see the letter P, indicates that it is a P-Metric tire designed for passenger vehicles according to the American Standard.
The letters “LT” instead represent Light Trucks when you see them on a sign. These tires are designed by tire manufacturers to meet the higher inflation requirements of some trucks.
As well to this, there are also other types of trailers that are used, such as “T” for Temporary, “ST” for Trailer, and “C” for Commercial. There is also a possibility that the tire does not have any lettering at all. In this case, it might have been made in Europe if this is the case. It is similar to our Passenger tires in terms of the Euro-metric metric system.
2. Tire Width
The width of a tire is used to measure its size. Usually, this measurement is given in millimeters and it is based on the amount of space that exists between each sidewall. There is also a term that can be used to refer to this as the section width.
When it comes to the tire size, the first three numbers refer to the tire’s width. An example of this would be if the tire size of your vehicle is P225/65R17, which means that the width of your tire is 225 millimeters.
3. Aspect Ratio
The next number you will find after the slash mark is the aspect ratio of the tire, which can be found below it. In the case of tires, the aspect ratio refers to the ratio between the height of the cross-section and the width of the tire. The two-digit number that follows the slash symbol in the tire size is a two-digit number.
In the example above, the aspect ratio is 65 in the example of P225/65R17, since it is the P225/65R17. A tire’s height equals 65% of its width, which means that the height of the tire is the same as the tire’s width. Based on this figure, you can determine how well your tires will be handled by the vehicle. If there is a higher number, it means that the turn will take longer to respond to a command, while a lower number indicates a faster response time.
The aspect ratio is usually indicated by an “R” after the tire’s aspect ratio on most passenger tires. A radial tire is identified by a letter that indicates it is radial. Tires of this type are the most common type of tires on the road and they are made by assembling piles of fabric, steel, polyester, and coated rubber, lying in an angled pattern perpendicular to the direction in which the tire travels. It is designed in such a way that it provides the smoothest ride and the longest tread life.
Additionally, some tires have a “D” in their name, which stands for Diagonal Piles. In other words, these types of tires are also known as Bias-Constructed Tires, Bias Ply Tires, Cross Ply Tires, and Conventional Tires. As a general rule, you will find this type of tire to be used most commonly with trailer tires or motorcycle tires.
Some tires come with an “F” before the construction letter on the sidewall. Run-flat tires are the only ones that are marked with this letter.
5. Wheel Diameter
You should know what size of the wheel the tire is meant for before you purchase it. A wheel’s or rim’s diameter is the last number in the sequence, and it represents the diameter of the wheel or rim. As can be seen in this figure, the right size wheel should be used with the right size tire.
As a rule of thumb, the measurement is determined by figuring out the space across the center of a product, from one size to another. This figure is usually written in inches, for example, 17 inches from our example of P225/65R17 would be listed as 17 inches.
6. Load Index
The load index is a figure used to show how much weight the tire is capable of handling under full inflation when it is inflated to its maximum air pressure. It is possible to put more weight on the tires when the load index rating of the tire is higher than the number of the tire. The simple fact is that if you just look at the figure, you won’t be able to tell how much weight it holds.
The best way to understand what a load index rating means would be to refer to a chart that shows you how it’s calculated. It is important to understand that, for example, a load capacity of 117 indicates that the tire can handle a load of 2,833 pounds. There is a range of load indexes from 70 to 125 that are used by most passenger vehicles. Please see the chart below for more information about load indexes
7. Speed Rating
There is also a figure that needs to be referenced using a chart to help you understand what the speed rating is or the maximum speed rating. You can use this figure to determine the maximum speed that you can achieve with the tire. A tire with a higher speed rating will provide you with greater control at higher speeds as well as better heat handling capabilities.
For a family sedan, an SUV, and a van, the most common speed ratings for the tires are the S and T, which are translated as 112 mph and 118 mph respectively. The H (130 mph) speed limit is usually used for passenger cars, SUVs, light pickup trucks, coupes and sports cars, regardless of the size. Other light trucks use one of the following codes (87, 93, 99, 106 mph): N, P, Q, or R.
Driving a high-performance vehicle may result in you seeing a V, W or Y (149, 168, or 186 mph) on your dashboard. I would say that almost all winter tires are rated either Q, S, or T according to their speed. There is no doubt that this is just a tire’s maximum speed capability, and it is your responsibility to always adhere to the legal speed limits at all times.
8. DOT Symbol
Every tire sidewall must have a DOT symbol on it for the tire to be used in the United States. The DOT stands for the Department of Transportation.
It is important to know that this symbol signifies that the tire complies with the Federal Motor Vehicle Safety Standards. When you are buying a high-quality brand, you can be assured that the DOT symbol is used by any reliable manufacturer, so you don’t have to worry about it.
A tire is also equipped with a serial number, which is similar to the identification number on the side of your car. This is what the Tire Identification Number (TIN) tells you about the tire. It contains all the information that you need about the tire. Following the DOT letters, you will find this number located on the left side of the document.
The TIN can be eight to 13 letters or numbers to identify the most important aspects of a tire. This will not only reveal where the tire was made, but it will also provide the manufacturer’s code along with the date the tire was manufactured along with the manufacturer’s code.
A Uniform Tire Quality Grading system is what is known as the UTQG. Based on the data provided by this rating system, which was developed by the Department of Transportation, you will be able to make an informed decision regarding the type of tire and whether it will be suitable for your climate, traction, and treadwear.
As a result of controlled testing, the traction grade indicates how well the tire performs in terms of wet traction capability. When driving on wet roads, it is best to use the AA-rated tire because it provides the best traction.
Temperature grade indicates how well a tire will be able to handle and dissipate the heat it generates. There is a connection between the higher the temperature grade, and the faster the device is capable of operating. Temperature grades of A are capable of handling speeds of over 115 miles per hour.
As a result of government testing, the treadwear grade is an indication of how the tire performed. To reveal the expected wear of the tread of the tire, this device has been designed. It is a government test course that runs 6,000 miles, so it is long enough to offer a good idea of how the tire should wear over time. There would be a 1.5-time increase in the life of the tire with a 150 grade compared to the same tire with a 100 grade. The outcome is that a tire with a rating of 200 will last twice as long as the same tire with a rating of 100.
Nonetheless, the wearing of a tire is going to be influenced by much more than just the rating that it has. Several factors contribute to the tire’s performance, including the type of road on which it is driven, the type of weather that is present, and other factors. A tire’s rating shows only what it is capable of, and not what it is capable of doing.
Is it important to have the right size of tires?
For proper operation of your vehicle, the tires must fit perfectly to the vehicle. When you have improperly sized tires, the first issue you will encounter is the appearance of the tire. You won’t be able to make a car look right when you put on tires that are too large or too small for your vehicle.
Despite this, if the wrong size tires are used, there can be more serious consequences than you may think. It is the tires that bear the brunt of the weight of your vehicle, and they are the only part of it that comes in contact with the ground. For the tires to be safe on the road, they must be rated for the type of vehicle you have, otherwise, you are putting your life at risk.
Using tires that are not intended for your vehicle will hurt the handling of your vehicle. When you attempt to turn or you are driving on slick roads, you may notice that you have issues. Additionally, when the tires aren’t set up correctly, they will wear out sooner, which will cost you more money to replace them if you don’t take care of them.
There is a specific tire size recommended for your car in the owner’s manual that you should refer to. The information can also be found on a placard located on the inside jamb of the front driver’s side door.
An explanation of tire size examples
The purpose of this article is to show you how to read a tire based on the factors we discussed above by evaluating two popular types of tires. It should be clear to you after looking at these examples that you will be able to figure out your own tire sizes by following the same formula we have used.
As an example, let’s take a look at P225/65R17 100T as our first example. If your tire says this, you should evaluate it based on the following criteria.
- Tire Type: Having a P before the number indicates that it is a passenger tire since it has a P before the number. There are several types of cars on the road, but this is by far the most common.
- Tire Width: There are 225 millimeters in the diameter of this tire. It is estimated that this measurement will be slightly more than 10 inches when taken from sidewall to sidewall. Section width is also known as a section width.
- Aspect Ratio: There is 65% of the width of the tire is taken up by the sidewall. As a result, the sidewall of the tire is about 146 millimeters (about 5.75 inches) long.
- Construction: It stands for Radial Tires in the abbreviation R. There are many different types of tires on the market, but this is the most common type.
- Wheel Diameter: Approximately 17 inches is the diameter of the wheel. The size of the wheel should be determined by measuring the width from the edge of the tire to the edge of the wheel.
- Load Index: Considering that this tire has a load index of 100, the tire can carry up to 1,604 pounds if the load index of the tire is 100.
- Speed Rating: A tire like this one has a speed rating of T. In other words, it means the tire is built to be able to handle speeds of up to 118 mph.
- As a review, this P225/65R17 100T tire is considered a passenger tire that contains a width of 225 millimeters. It features an aspect ratio of 65% with radial construction. Plus, it features a 17-inch diameter that can carry up to 1,604 pounds and travel up to 118 mph.
Let’s look through one more example to ensure you get the point. For this example, we will use P275/55R20 111S.
- Tire Type: Because it has a P before the numbers, you know that it is a passenger tire. This is the most common found on the road.
- Tire Width: This tire measures 275 millimeters. This measurement is taken from sidewall to sidewall, estimated to be slightly smaller than 11 inches.
- Aspect Ratio: The tire’s sidewall is 55% of the tire’s width. Knowing this, the sidewall is about 151 millimeters or about 6 inches.
- Construction: The R stands for Radial Tire. This is the most common tire type on the road.
- Wheel Diameter: The diameter measures 20 inches. This is measured from edge to edge, showing what size wheel you should put the tire on.
- Load Index: If the load index of this tire was rated at 111, that tire can carry up to 2,403 pounds.
- Speed Rating: This tire has a speed rating of S. That would mean it is built for speeds up to 112 mph.
- It would be fair to say that this P275/55R20 111S tire has a width of 275 millimeters, and could be considered a passenger tire because of its size. With a 55% aspect ratio, it has a radial construction to give it a 55% aspect ratio. In addition, it has a diameter of 20 inches, which allows it to carry up to 2,403 pounds and travel at speeds of up to 112 miles per hour.
Where to Find Tire Size
As soon as you decide to replace your vehicle’s tires, you want to be sure you are selecting the right size for the tires you will be using. Your vehicle’s tire size can be determined in two ways depending on how you reference it.
In case you are unable to locate the manual, don’t worry. You may also be able to find a tire fit guide in the following places:
- The driver’s side door jamb
- Inside your glove box door
- Within your gas tank hatch
It would be a good idea to first take a look at the tires that are currently attached to the car. The easiest way to get the same tires on your vehicle is to match this information with your vehicle’s information. This method does indeed have a flaw, but there is also a benefit to it. There is a possibility that when you buy a car, the wrong tires may have been put on by someone before you bought it.
Therefore, if you have a car with a jammed door, it is always recommended that you check the jamb inside the driver’s side door jamb. Appropriate tire size is shown on a placard that is attached to the vehicle. A copy of the owners manual might also be able to help you find it. As these measurements have been provided directly from the car manufacturer, you know you won’t be able to go wrong if you use them.
Tire Size Charts
Load Index Chart
Speed Rating Chart
Frequently Asked Questions
There are three numbers on tire sizes, which represent the width of the tire, the height of the tire, and the diameter of the tire. The width of a tire is measured in millimeters, which is a measurement that indicates the width of the tire from side to side. A height-to-width ratio is used when measuring the height of a building. The diameter of the tire is measured in inches and it is the measurement that tells you what size rim or wheel the tire will fit on.
In the example above, the height of 225, the width of 225, and the diameter of 17 would make 225/50/17 a tire with a diameter of 17 and a width of 225.
In general, trucks and cars use the same tire sizing system when it comes to their tires. When it comes to truck tire sizes, the first number in the size is the width of the tire in millimeters. As a result, the second number is the height, which is also referred to as the aspect ratio. Thirdly, there is a measurement of the diameter of the wheel in inches, which is the third number. Additionally, you will be able to find truck tire sizes in inches as well, which we will explain in more detail below.
There can be some slight differences in tire sizes between tires measured in millimeters and tires measured in inches. As an example, (35X12 50R18) is a tire with a width of 35 inches and a height of 12 inches, while 50 (the proportion of the sidewall height to the width) specifies the aspect ratio (the percentage of the sidewall height to the width). The last R18 indicates the rim diameter in inches, so if a tire is 35X12 50R18, that means it has a 35-inch wide sidewall and an 18-inch rim diameter. That would mean it has a 35-inch wide rim and an 18-inch rim diameter.
There are usually no differences in tire sizes between motorcycles and cars. A tire’s width can be measured in millimeters (mm) in the first three digits of its model number. There are two digits following the slash mark that represent the aspect ratio of the tire, which is the ratio of the width of the tire’s cross-section to the height of its cross-section. In addition, the last two digits after the dash of the motorcycle wheel’s number represent its diameter, in terms of inches, at the center of the wheel.
Although it is certainly possible to upgrade the size of your tires, it’s best to stick with the size recommended by your vehicle’s manufacturer in order to ensure optimal performance. In addition to giving your car a higher ground clearance, increasing the size of your tires may also benefit your car’s handling, drivetrain performance, and fuel economy as well. Should you decide to increase the size of your tires, bear in mind the changes you may have to make to key figures, such as your vehicle’s load index and speed rating, as well as how these changes could have an impact on your vehicle’s capabilities.