What is the Meaning of the Tire Size Numbers

Installing the correct tires on your car is crucial to its overall performance and safety. Your tire selection should be based on your vehicle’s driving circumstances and handling preferences. Some measurements are written in millimetres on the sidewall, while others are written in inches. The ideal size for your car, truck, or trailer can vary based on where and how you drive. When it’s time to purchase tires, you must grasp how to read tire sizes to make the best-informed choice. Fortunately, calculating the proper tire size for our vehicle is relatively straightforward.

In this article, we will be taking a look at what the meaning of the tire size numbers are and what they indicate so you can have a better understanding of what tires to get for your vehicle.

What is the meaning of the tire size numbers

Many people wonder what is the meaning of tire size, and we are here to help people better understand what the different numbers mean, which can help you in choosing the right tires for your vehicle. The three numbers on a tire’s sidewall denote the tire’s width, height, and diameter, respectively. The width is measured in millimetres and represents the tire’s side-to-side width. The height is calculated as a ratio of height to breadth. The diameter, which is specified in inches, indicates the size of the rim or wheel onto which the tire will fit. Each tire sidewall includes information about the tire’s type, width, aspect ratio, and manufacturing. It also provides information regarding the wheel diameter, load index, speed rating, DOT symbol, TIN, and UTQG. This information must be combined to evaluate whether the tire suits your vehicle.

  1. Tire type

P185 / 75R14  82S

Most automobile tires feature the letter “P” preceding the tire size. This letter indicates that it is a P-Metric tire designed for passenger vehicle specifications. If you see “LT” instead, it indicates Light Trucks. Tire makers develop them to meet the increased inflation requirements of particular trucks. Additional categories include “T” for Temporary, “ST” for Trailer and “C” for Commercial. There is also the possibility that there is no letter on the tire. If so, it may have been manufactured in Europe. Similar to our Passenger tires, Euro-metric tires are available. Consult your vehicle’s owner’s handbook or tire placard for your car’s required tire size and inflation pressure.

  1. Tire Width

P185 / 75R14  82S

The first three numbers to appear in your tire size information is the width, which is measured in millimetres based on how much room there is between each sidewall. For the example we used, the number 185 denotes that this tire measures 185 millimetres from the widest point of its outer sidewall to the widest point when mounted and measured on a wheel with a specified width.

  1. Aspect Ratio

P185 / 75R14  82S

A lot of people wonder “What is the meaning of the second number in tire size?”  The number that appears after the slash mark indicates the tire’s aspect ratio. A tire’s aspect ratio is the ratio between the height of the cross-section and its width. This two-digit number follows the forward slash in the tire size. Aspect ratios are presented as a percentage.

A tire’s aspect ratio is calculated by dividing its height off the rim by its width. A tire with an aspect ratio of 75 has a size that is 75% of its width. In general, tires with a lower aspect ratio, such as a 60 series, provide superior vehicle handling performance than tires with a higher aspect ratio, such as a 75 series. Nonetheless, a common trade-off is a bumpy and very rough driving experience.

  1. Construction

P185 / 75R14  82S

A letter follows the aspect ratio to denote the tire’s construction. “R” relates to the tire’s internal structure and provides a general sense of its stability.

There are three potential styles of internal construction:

  • R -indicates radial structure. The most contemporary kind in which the plies extend radially to the circumference at the correct angle. Additionally, these tires are strengthened with steel belts. The vast majority of tires on the market are of this type.
  • ” or D – diagonal bias-ply structure. The oldest form with diagonally crisscrossing plies.
  • B – indicates a bias-belt construction. This type is identical to bias-ply, except that an additional belt reinforces the tire. 

Until the 1970s, vehicles and light trucks had “bias-ply” tires. However, the great majority of tires on the road nowadays are radial tires. Radial tires have been the industry standard for almost 40 years. Thus, you will most likely find many of the letter “R” on tires. Radial construction indicates that the internal ply cords of the tire are aligned radially (at 90 degrees to the centerline of the tread).

  1. Wheel diameter

P185 / 75R14  82S

It is crucial to know which wheel size the tire is intended for. The last number in the sequence represents the wheel’s diameter or the rim’s diameter. This number indicates which wheel size should be used with the tire. The size is obtained by calculating the distance across the centre from one dimension to the next.

  1. Load rating

P185 / 75R14  82S

The load index of tires might be a complicated topic due to the numerous exceptions, but we will attempt to clarify everything here. The number that follows the rim size in the sequence is the tire’s load index, which indicates how much weight the tire can support when completely inflated in pounds. The load index is the number used to indicate the tire’s maximum load capacity when fully inflated. The higher the load index rating value, the more weight can be placed on the tires. However, based on the above figure, it is difficult to determine the item’s capacity.

We refer to this number as the load “index” because it does not give us the exact number of pounds the tire can bear, at least not by itself. Nonetheless, the number corresponds to a particular load capacity indicated in an index. The load index numbers range from 1 to 150, indicating carrying capacities of 99 to 7385 pounds.

Private vehicle tires have two load types: Standard Load and Extra Load. Standard Load tires have no marks, while Extra Load tires include XL letters following the size and load index. P-Metric and Euro-Type passenger car tires will have a single load index number, while LT-Metric and Euro-Type Commercial (C-Type) tires will have two digits separated by a slash. The first number is the load index for a single-application tire, while the second number is the load index for a dual-application tire. Passenger tires cannot be utilised for multiple applications. The Load Range of light truck tires will also be marked by a letter, such as Load Range E. Load Range is an older word that is still regularly used in the tire industry so you may hear it from your tire dealer. However, the load index figures are the most reliable indicator that you have the correct tire.

The load index figures of standard organisations (P-Metric vs. Euro-Metric) are not necessarily on the same scale, which is a critical but sometimes misunderstood aspect of the load index. Thus, two tires with the same load index number in two different systems may have various maximum load capacities. It is, therefore, essential to examine the load index number and confirm the actual load capacity.

How does metric sizing come into play?

Most passenger cars, SUVs, and light pickups will be equipped with either P-Metric or Euro-Metric tires. The letter “P” appears before the number sequence for P-Metric tires, as in P225/70R16 97H. The Tire and Rim Association has standardised the P-metric classification for “passenger car” tires. There will be no letter preceding the number sequence in Euro-Metric units; 225/70R16 98H. The European Tyre and Rim Technical Organisation have standardised the Euro-Metric designation for “passenger car” tires. P-Metric and Euro-Metric tire sizes are primarily intended for passenger vehicles, such as cars, minivans, SUVs, and other light-duty pickup trucks.

The Tire and Rim Association has standardised the LT-Metric designation for “light truck” tires. Consider that your car is an SUV, truck, or van. In such a circumstance, you may find a distinct size designation on your placard that is particular to heavy-duty light vehicles and vans, especially prevalent on pickup trucks and vans with a gross vehicle weight rating of 34 tons or more. This category comprises two standard size types: LT-Metric and Euro-Metric Commercial (aka C-type). Both sizes are metric and employ the same structure as P-Metric and Euro-Metric; however, they differ from their passenger vehicle cousins in their size designations. LT-Metric tires are denoted by the initials “LT” preceding the size number sequence: LT245/75R17 119/116R Load Range E. Note that there are two load index numbers and a Load Range; refer to the Load Index section for additional information. 

Euro-Metric Commercial or C-Type tires will resemble passenger Euro-Metric sizes with the addition of a “C” immediately following the rim size, as in 23/65R16C 121/119R. The C-type tires have two load index numbers. The European Tyre and Rim Technical Organization have standardised the Euro-Metric Commercial (C-Type) classification for light vehicle tires. Light truck tires are designed for vehicles that can transport oversized freight and are often only mandated by vehicle manufacturers for vehicles that exceed a specific load capacity. Temporary Spares, denoted by the letter “T”, are additional types of tires that adhere to the Metric system. If a size begins with “ST,” it denotes a “special trailer” and is intended for use exclusively on trailers. Whether looking at a P-Metric, Euro-Metric, LT-Metric, Euro-Metric Commercial, T, or ST tire, the size designations are the same.

  1. Speed rating

P185 / 75R14  82S

The speed rating, represented by a letter, is the last figure in a tire size sequence that tells you a tire’s maximum speed capability. In the same way that your load index number refers to a particular load, your speed rating letter corresponds to a specific speed capacity as determined by a standardised laboratory test. Generally, speed ratings correspond to the maximum speed capability of the vehicle. A tire with a speed rating of “S” is rated for up to 112 mph, whereas a tire with a speed rating of “R” is rated for up to 106 mph. Typically, tires with outstanding speed ratings provide superior handling capability. Replacement tires must have the same or a greater speed rating to retain a vehicle’s top speed. 

If a car has tires with varying speed ratings, the “slowest” tire’s speed rating determines the vehicle’s maximum speed. Similar to the load index, the speed rating is not required to be displayed on all tires by law. If your tires do not show the speed rating, the owner’s handbook will include the pertinent information for the stock tire type for your vehicle. Remember that this speed is not advised for cruising. You must always adhere to posted speed restrictions on the streets. To retain the speed capabilities of the vehicle, replacement tires must have the same or a higher speed rating as the original equipment.

  1. DOT symbol

You may notice another set of letters and numbers beginning with “DOT” on the sidewall of your tire. This does not indicate tire size but that the tire meets Federal Motor Vehicle Safety Standards. Following the tire identification number is the abbreviation for the Department of Transportation. After DOT, the first two letters or numbers denote the tire’s manufacturing plant, and the last four digits represent the week and year of production. For instance, the digit 4220 signifies that the tire was manufactured in the 42nd week of 2020.

  1. Tire Identification Symbol (TIN)

Similar to your vehicle’s identifying number, your tire has a serial number. The Tire Identification Number (TIN) provides comprehensive information about the tire. This number appears following the DOT letters. The TIN might have between eight and thirteen letters/numbers to indicate the essential tire characteristics. In addition to displaying where the tire was created, it also shows the manufacturer’s code and the date the tire was produced.

  1. Uniform Tire Quality Grading (UTQG) 

UTQG, or Uniform Tire Quality Grading, is a series of stamps used on certain types of tires. This grade and stamping are necessary for all-season and summer passenger automobile tires (i.e. P-metric and Euro-metric). This regulation does not apply to winter-specific tires, light trucks (LT-Metric, Euro-Metric Commercial, Flotation), or motorcycle tires.

The traction grade indicates the tire’s wet traction performance under controlled testing. The AA-rated tire delivers the most incredible traction on wet surfaces. The temperature rating indicates the tire’s capacity to withstand and distribute heat. The higher the temperature grade, the greater the speed at which it can function. A temperature grade can withstand velocities in excess of 115 mph.

The treadwear grade indicates how the tire performed on government-mandated tests. It’s intended to display the predicted tread wear of the tire. The 6,000-mile government test circuit is sufficiently long to indicate how a tire should wear. A tire with a 150 rating would last 1.5 times longer than one with a 100 rating. Consequently, a tire with a rating of 200 would last twice as long as its 100-grade counterpart. However, tire wear will depend greatly more than this rating. A tire’s performance depends significantly on how a vehicle is driven, the type of road, and other variables. The rating simply indicates the tire’s capabilities.

The purpose of quality grading is to facilitate your tire purchase selection. The method is meant to provide detailed, comparable information so that you may make an informed purchasing decision. However, the scores are based on tests conducted under highly rigorous conditions. This means it is easy to misinterpret the compared data concerning your driving behaviours, situations, etc.

Is it possible to switch tire sizes?

Why not adjust the tire size if you find a great price on tires that are somewhat smaller or larger than what your vehicle’s manufacturer recommends? While it is possible to upgrade the size of your tires, it is typically advisable to remain with the manufacturer-recommended tire size for optimal performance. Increasing the size of your tires may increase your vehicle’s ground clearance, but it may also impair your vehicle’s handling, drivetrain performance, and gas mileage. Remember the changes to crucial data, such as the load index and speed rating, and how they may affect the capabilities of your vehicle if you opt to raise tire size.

Changing the size of a modern car might decrease fuel economy, aberrant handling, friction, alignment problems, and excessive strain on the powertrain. If you own a vehicle manufactured before the early 1980s, changing the tire size is not difficult. Changing the size of an object will typically result in a faulty speedometer. However, the only specifications that can be altered are the width and aspect ratio — never the wheel size unless you purchase replacement wheels — and you should always aim to maintain the same tire height as the manufacturer. Therefore, if the tire is widened, the aspect ratio may need to be decreased, and vice versa.

What is the meaning of tire size in the label of a car?

Before installing new tires on your car, you must select a suitable tire size. There are two ways to refer to a vehicle’s tire size. First, you can examine the current tires on the car. This is a fantastic approach to ensure that the tires on your vehicle are identical. Nevertheless, this approach has a problem.

If someone installed the incorrect tires before you purchased the tires, you might not know. Therefore, inspecting the door jamb on the driver’s side is always advised. There is a sign indicating the proper tire size. It may also be included in the owner’s manual. The automobile manufacturer provides these dimensions directly and very clearly, so you cannot go wrong.

What is important about tire size meaning?

Tires are among the most misunderstood car components. There is a misunderstanding on when they should be replaced, the proper pressure, rotation schedules and formats, and more. To the ordinary driver, though, nothing is more perplexing than all the numbers on the sidewall of your tires. The tires must be an excellent fit for your car to operate correctly. The appearance of incorrectly sized tires is the first issue. When you install tires that are too tiny or too huge for your car, its appearance will be compromised. However, the consequences of using the incorrect tire size are more severe. 

The tires are responsible for supporting the vehicle’s weight and are the only part of the vehicle that touches the road. To ensure your safety on the street, the tires must be rated for your car; otherwise, you put yourself at risk. Using tires that are not intended for your vehicle compromises its handling. You may encounter difficulties when attempting to turn or when driving on slick roads. In addition, improper tires will wear out faster, requiring you to spend more money on replacements. The owner’s manual will specify the suitable tire size for your vehicle. The information is also printed on a placard within the doorjamb of the driver’s side door.

Bottom line

Once you understand how to read the numbers on tires, you can easily filter down your tire options by size. Tire codes are the simplest method to learn about the fundamental aspects of tire selection. If you know the recommended specs for your vehicle and how to read tire codes, you can make a decision much more quickly. 

The correct tire size will fit the rim perfectly and will not be harmed during installation. The appropriate speed rating and load index will boost the vehicle’s best attributes. The age of the tire will indicate how long you will be able to ride it. The majority of tire sidewall numbers are vital for selection. We hope we were able to answer any questions you had regarding the meaning of tire size numbers.


As a user of The Automotive Men (theautomotivemen.com), please note that we participate in the Amazon Associates Program. This means that “As an Amazon Associate, I earn from qualifying purchases.” We are not directly sponsored or endorsed by Amazon, but our website may contain affiliate links that provide us with a commission when you make a purchase through them. Thank you