How to Read Tire Sizes: A Complete Guide |
Learn how to read tire sizes and understand tire width, aspect ratio, construction, wheel diameter, load index, and speed rating. Get expert help today!
How to Read Tire Sizes: Understanding the Numbers on Your Tires
The numbers and letters printed on your tire’s sidewall may look confusing at first, but they provide important information about the tire’s size, construction, load capacity, and speed rating. Understanding how to read tire sizes can help you replace your tires correctly, compare different options, and make more informed decisions when upgrading your wheels.
Whether you’re replacing the factory tires on your car, upgrading the wheels on your truck, or looking for a more aggressive tire setup for your SUV, knowing what the numbers mean is an important part of the process.
At Automotive Expressions, we help drivers understand wheel and tire fitment so they can choose combinations that match their vehicles, driving needs, and style preferences. This guide explains how to read tire sizes and what each number and letter means.
Where to Find Your Tire Size
The easiest place to find your current tire size is on the sidewall of your tire. A typical tire size may look like:
265/70R17 115T
Each part of this sequence provides specific information about the tire. The first portion describes the tire’s physical dimensions and construction, while the final numbers and letters provide information about its load capacity and speed rating.
Let’s break down each component.
What Does the First Number in a Tire Size Mean?
The first number represents the tire width.
In the example 265/70R17, the number 265 means the tire is approximately 265 millimeters wide from sidewall to sidewall.
Tire width can influence the appearance and driving characteristics of your vehicle. Wider tires may provide a more aggressive appearance and can affect handling and traction. However, wider isn’t automatically better for every vehicle.
When changing tire width, you need to consider the width of the wheel, wheel offset, suspension clearance, and fender clearance. A tire that is wider than the original equipment size may potentially rub against suspension components or the vehicle’s body.
This is why tire width should always be considered as part of the complete wheel and tire package.
What Does the Second Number Mean?
The second number represents the tire’s aspect ratio.
In 265/70R17, the 70 means the sidewall height is approximately 70% of the tire’s width.
The aspect ratio affects the height of the tire’s sidewall. A higher aspect ratio generally means a taller sidewall, while a lower aspect ratio means a shorter sidewall.
For example, a low-profile tire may have a shorter sidewall and provide a sportier appearance. A tire with a taller sidewall may offer a different ride feel and can be common on trucks, SUVs, and vehicles designed for certain off-road applications.
When changing wheel sizes, drivers often adjust the aspect ratio to help maintain a similar overall tire diameter.
What Does the “R” Mean?
The letter R stands for radial construction.
Radial tires are the standard type of tire used on most modern passenger vehicles. The term refers to how the tire’s internal cords are arranged.
You may occasionally see other construction markings on specialized tires, but radial tires are by far the most common for everyday cars, trucks, and SUVs.
What Does the Last Number Mean?
The final number in the first part of the tire size indicates the wheel diameter.
In 265/70R17, the number 17 means the tire is designed to fit a 17-inch wheel.
This measurement is expressed in inches, unlike the tire width, which is expressed in millimeters.
This number is particularly important when upgrading your wheels. A tire designed for a 17-inch wheel cannot be mounted onto an 18-inch wheel, for example.
If you’re moving to a larger wheel, you’ll need to select a tire with the appropriate diameter to match your new wheels.
What Is the Load Index?
After the tire size, you may see another number. In our example, the complete marking is:
265/70R17 115T
The 115 is the tire’s load index.
The load index represents the maximum weight the tire is designed to support under specified conditions. The exact weight associated with each load index is determined using a standardized load index chart.
Load capacity is especially important for trucks and SUVs, as well as vehicles used for towing or carrying heavy loads.
When selecting replacement tires, you should choose a load rating appropriate for your vehicle and intended use. A tire’s physical size alone doesn’t tell you whether it is suitable for the vehicle’s weight requirements.
What Is the Speed Rating?
The final letter in the tire marking represents the tire’s speed rating.
In 265/70R17 115T, the letter T indicates the tire’s speed rating category.
Speed ratings are assigned based on standardized testing and indicate the tire’s rated ability to perform at certain sustained speeds under specified test conditions. Speed ratings vary by tire and are represented by different letters.
While drivers aren’t typically choosing tires based on maximum speed alone, the rating is an important part of selecting an appropriate replacement tire.
Your replacement tires should have a speed rating suitable for your vehicle and driving needs.
How to Read a Tire Size Example
Let’s take a closer look at a common tire size:
225/55R18 98V
Here’s what each part means:
- 225 – The tire is approximately 225 millimeters wide.
- 55 – The sidewall height is approximately 55% of the tire’s width.
- R – The tire uses radial construction.
- 18 – The tire fits an 18-inch wheel.
- 98 – The tire’s load index.
- V – The tire’s speed rating.
Once you understand the basic format, reading tire sizes becomes much easier.
Why Tire Size Matters When Buying New Wheels
If you’re replacing your tires with the same factory size, the process is relatively straightforward. However, choosing tires becomes more complicated when you’re upgrading your wheels.
For example, you may want to replace your factory 17-inch wheels with larger 20-inch wheels. Because the new wheels have a larger diameter, you’ll typically need a tire with a shorter sidewall to maintain a comparable overall tire diameter.
This is commonly referred to as plus sizing.
However, maintaining a similar overall diameter isn’t the only consideration. The new setup must also be evaluated for:
- Tire width
- Wheel width
- Wheel offset
- Bolt pattern
- Hub bore
- Brake clearance
- Suspension clearance
- Fender clearance
- Load capacity
- Speed rating
- Overall vehicle use
A wheel and tire combination that looks good on paper may not be appropriate for every vehicle.
Does Changing Tire Size Affect Your Vehicle?
Yes. Changing tire size can affect several aspects of your vehicle.
Handling
Changing tire width and sidewall height can alter steering response and handling characteristics.
Ride Comfort
Lower-profile tires generally have less sidewall to absorb impacts. Depending on the setup, this can create a firmer ride.
Speedometer Readings
Changing the overall tire diameter can affect the relationship between tire rotation and vehicle speed. Significant changes may affect speedometer accuracy.
Ground Clearance
Larger overall tire diameters can increase ground clearance, while smaller tires can reduce it.
Vehicle Clearance
A wider or taller tire may create clearance issues when turning or when the suspension moves through its range of travel.
For these reasons, changing tire size should be approached as a complete fitment decision rather than simply selecting a different number from a tire size chart.
How to Find the Right Tire Size for Your Vehicle
If you’re replacing your existing tires with the factory size, start by checking the driver’s-side door jamb label, owner’s manual, or current tire sidewall.
If you’re considering a different size, however, it’s important to evaluate the entire wheel and tire combination.
At Automotive Expressions, our fitment-focused approach considers your vehicle’s specifications along with your goals for appearance, performance, comfort, and intended use.
For example, the ideal setup for a daily-driven sedan may be very different from the right setup for a lifted truck or an SUV used for off-road driving.
Don’t Choose Your Tire Size Based on Numbers Alone
Knowing how to read tire sizes is an excellent starting point, but the numbers don’t tell the entire story.
Two tires with the same size designation can have different tread designs, construction characteristics, load capabilities, and intended applications. Similarly, two wheels with the same diameter may have different widths or offsets that affect how they fit your vehicle.
If you’re planning a wheel upgrade or changing your tire size, it’s important to consider the entire combination.
Automotive Expressions can help you understand your options and identify wheel and tire packages designed around your specific vehicle and goals. From everyday replacement tires to custom truck and SUV setups, professional fitment guidance can help you avoid costly mistakes and achieve the look and performance you want.
Get Help Choosing the Right Tire and Wheel Combination
Understanding how to read tire sizes gives you a better foundation for making decisions about your vehicle. Once you know what the numbers and letters mean, you can more easily compare tire options and understand how changes may affect your vehicle.
However, selecting the right tire size is only one part of proper fitment. Wheel diameter, width, offset, tire dimensions, load requirements, and vehicle clearance all need to work together.
If you’re ready to replace your tires or upgrade your wheels, contact Automotive Expressions for help finding a wheel and tire combination that fits your vehicle and matches your goals.
Frequently Asked Questions About Reading Tire Sizes
What does 265/70R17 mean?
A 265/70R17 tire is approximately 265 millimeters wide, has a sidewall height equal to 70% of its width, uses radial construction, and is designed to fit a 17-inch wheel.
Where can I find my vehicle’s recommended tire size?
You can typically find the recommended tire size on the driver’s-side door jamb label, inside the owner’s manual, or on the sidewall of your current tires. Your vehicle may have more than one approved tire size depending on the model and factory equipment.
Can I put a larger tire on my vehicle?
Possibly. Whether you can safely install a larger tire depends on the vehicle, wheel dimensions, suspension, tire width, wheel offset, and available clearance. Larger tires may require additional modifications depending on the application.
What is the difference between tire width and wheel diameter?
Tire width is typically measured in millimeters and describes the approximate width of the tire from sidewall to sidewall. Wheel diameter is measured in inches and indicates the size of the wheel the tire is designed to fit.
Do I need different tires when I buy larger wheels?
Yes. If you change to a larger-diameter wheel, you will need tires designed to fit the new wheel diameter. The tire’s width and aspect ratio may also need to change to achieve the desired overall diameter and proper vehicle fitment.