How To Read Tire Size Numbers for 10 Different Parameters

How to read tire size numbers is essential to learn for vehicle owners because tires are an important component of any vehicle. A set of numbers and characters on the sidewall of a tire indicate its size.

Read Tire Size Numbers

But, for individuals who are unfamiliar with these numbers, deciphering them might be difficult. Below, we will explain how to interpret tire size meanings and what each number and letter signifies, so keep reading!

How Can You Read Tire Size Numbers?

To read tire size numbers and understand their meanings, you have to understand different parameters marked on a tire such as metric sizing, aspect ratio, rim diameter, load index, speed rating, flotation sizing, overall diameter, LT type, and maximum inflation.

1. Understanding the Metric Sizing

The width of the car tire is represented by the first digit in the tire size. This figure is significant since it helps define the contact patch of the car tire with the road, which impacts handling and grip. The breadth can vary between 135 and 355 millimeters, with the most frequent widths being 185 to 275 millimeters.

The tire width influences both the overall appearance of the tire and its capacity to handle different road conditions. Selecting the optimum tire width is important for preserving your vehicle’s performance and safety.

Ensure that the tire width you choose is adequate for the brand and model of your car. It’s also worth noting that a wider tire isn’t necessarily preferable, since it might cause issues like rubbing on the wheel well or poor fuel economy.

2. Deciphering the Aspect Ratio

The aspect ratio, expressed as a percentage, is the second number in the tire size. It is the ratio of the tire’s height to width, and it defines the sidewall height. If the aspect ratio is 60, the sidewall height is 60 percent of the width of the tire. A lower aspect ratio results in a shorter sidewall, which can enhance handling and cornering but creates a stiffer ride.

A greater aspect ratio results in a taller sidewall, which improves ride comfort and absorbs road imperfections but reduces handling and cornering abilities. It is important to choose the optimal aspect ratio for your car depending on its suspension, planned use, and personal choice.

A tire with an inappropriate aspect ratio might impair your vehicle’s control and safety. When choosing a tire with a variable aspect ratio, it is important to keep the total tire diameter constant in order to preserve correct speedometer readings and avoid any mechanical concerns.

3. Reading the Rim Diameter

The rim diameter, expressed in inches, is the third number in the tire size and shows the wheel size that the tire is meant to fit. To guarantee perfect fitting and to preserve the accuracy of your vehicle’s speedometer, choose a tire with the right rim diameter.

Checking Rim on a Car

Selecting a tire with a bigger or smaller rim diameter than the vehicle manufacturer recommends can have an impact on the tire’s performance, handling, and overall safety. It is important to match the rim diameter given by the vehicle manufacturer or confer with a tire professional to identify an acceptable alternative size.
Additionally, ensure that the load capacity and the speed rating of the tire is adequate for the planned wheel and vehicle application.

4. Determining the Load Index

The load index is a number that represents the maximum weight that a car tire can support when fully inflated. Load index values generally vary from 71 and 126, with each number representing a specific weight capability in pounds.

A car tire with a load index of 95, for example, can support a maximum weight of 1,521 pounds. Choose a tire with a load index that meets or exceeds your vehicle’s weight requirements, including passengers and baggage. Excessive loading can cause a tire to wear out sooner, handle less well, and perhaps fail altogether.

For the replacement tire to retain the safety and performance of the vehicle, it must have a load index that is equal to or greater than that of the original tire, which is normally found on the sidewall of your vehicle’s tire.

5. Looking at the Speed Rating

The speed rating is a letter designation that shows the top speed that a tire can maintain for a given period. Speed ratings are commonly assigned from Q to Y, with each specific letter representing a different maximum speed. A car tire with a speed rating of V, for example, can handle speeds of up to 149 mph.

Maintaining Car Tires

It is important to pick a tire with a speed rating that meets or exceeds your vehicle’s speed requirements. Choosing a vehicle tire with a lower speed rating might jeopardize the tire’s capacity to handle high speeds. On the other hand, choosing a tire with a higher speed rating than necessary may not give any benefits and may result in increased expenditures.

The speed rating is normally displayed on the tire sidewall, and it is important to verify that the replacement tire’s speed rating equals or surpasses that of the original tire to preserve the vehicle’s safety and performance.

6. Figuring Out the Flotation Sizing

Flotation tires are meant to disperse a vehicle’s weight across a broader surface area, decreasing impact on the ground and offering improved grip on soft conditions like sand or mud. Off-road or agricultural flotation tires are often utilized on light vehicles and SUVs.

Flotation tire sizes are commonly represented by three numerals separated by a dash, for example, 31-10.50-15. The first number in the given sequence represents the tire’s overall diameter in inches, the second number represents the tire’s section width in inches, and the third number represents the rim diameter in inches.

It is important to choose a flotation tire that has the proper size and load rating for the specified purpose and vehicle. Choosing the wrong tire size or load rating can result in poor performance, early wear, and tire failure.

7. Discovering the Overall Diameter

The overall diameter is the distance between the outer border of the tire tread and the opposite edge of the tread as measured through the tire’s center. The total wheel diameter of a tire is significant in determining its fitting on a vehicle, as well as the accuracy of the vehicle’s speedometer and odometer readings.

Reading Wheel Diameter

Choosing a tire with a considerably different overall diameter than the original equipment tire might impact the vehicle’s handling and performance, as well as result in erroneous speedometer and odometer readings.

The overall diameter of a tire is normally specified in inches and may be found on the tire sidewall, along with the tire’s other size characteristics. Ensure that the overall diameter of the replacement tire matches the diameter of the original equipment tire or to visit a tire specialist to establish a suitable alternative size.

8. Confirming the LT Type

LT tires are intended for use on light trucks, SUVs, and vans, and they are distinguished by their enhanced load capacity and durability. Towing or transporting big loads, as well as off-road use, are common applications for LT tires.

The LT designation is usually seen on the tire sidewall, and it is frequently followed by the tire size and aspect ratio. LT tires may also have a load index and speed rating marks, which indicate their load-carrying capability and maximum safe speed.

When selecting LT tires, it is important to pick the suitable size and load-carrying capability for the planned application and vehicle and to consult a tire specialist if there is any doubt regarding the appropriate size or kind.

9. Checking the Uniform Tire Quality Grading

The United States Department of Transportation (DOT) devised the UTQG rating system to offer information on three important performance parameters of a tire: treadwear, traction, and temperature resistance.

The treadwear rating compares the tire’s predicted tread life to that of a control tire, with a higher figure suggesting a longer tread life. The traction rating of a tire reflects its ability to stop on wet pavement, with values ranging from AA (best) to C (worst and lowest).

The temperature resistance grade, which ranges from A (highest) to C (lowest), shows the tire’s capacity to disperse heat (lowest). The UTQG ratings are commonly seen on tire sidewalls and may be used to compare different tire types and manufacturers.

It is crucial to remember that UTQG values are set by the tire manufacturer and may not always reflect real-world performance; thus, when selecting a tire, they should be utilized in conjunction with other sources of information.

10. Verifying the Maximum Inflation

The maximum inflation pressure is the most air pressure that a tire can safely hold. This information, along with the load index and speed rating, is often printed on the tire sidewall. Remember that the maximum inflation pressure is not always the optimum inflation pressure for your tire.

Inflation Pressure on Tire

This can change based on factors including vehicle weight, load, and driving conditions. Tire over- or under-inflation can cause uneven wear, poor performance, and even tire failure. As a result, it is important to frequently check your tire pressure using a dependable tire pressure gauge.

Maximum inflation pressure should only be utilized in emergencies, such as while transporting big items or traveling at high speeds for lengthy periods.

What Do the Tire size Numbers on My Truck Mean?

Understanding the tire size numbers on your truck is crucial for a smooth and safe ride. These numbers provide essential information about the tire’s dimensions, load capacity, and speed rating. By decoding the numbers on your truck’s tire, you can make informed decisions when selecting replacements. Familiarizing yourself with Truck dashboard symbols: meanings and guide will help you navigate through any confusion and ensure optimal tire performance.


Ultimately, understanding tire size definitions are important for maintaining your vehicle’s best performance and safety.

To sum it up, the main ideas we’ve discussed are:

  • Tire size is shown on the tire’s sidewall and contains data including metric sizing, aspect ratio, rim diameter, load index, and speed rating.
  • Metric size refers to the width of the tire in millimeters as well as the aspect ratio, which is the height-to-width ratio of the tire.
  • The term “rim diameter” describes the size of the wheel that the car tire is intended to fit.
  • Speed rating and load index both reflect the highest speed that a tire can safely bear.

From now on, you should be able to understand the numbers on your tire sidewall because of going through our how to read tire size numbers guide.

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