How to Find Out Tire Size

Wondering how to find out tire size? You’ve come to the right place.

In this guide, we’ll cover how to find out tire size, as well as how to determine which tire size is right for your vehicle and how to choose the right wheels for your car.

Where Do I Find the Size of My Tires?

The size is listed on the side of the tire, in the area known as the sidewall. However, there are several other sources you can check to find out the appropriate size.

Tire Sizes Explained

The information you find on the sidewall indicates what kind of vehicle the tires are designed for, their dimensions, and the load they can bear. Always make sure you read the information from left to right. 

Type

how do i find my tire size

There will probably be a letter at the start of the sequence you find on the sidewall:

  • P: this means that the wheel is approved for use in the US on a passenger vehicle. This is the most common code you’ll find on wheels unless you drive a truck.
  • LT: this stands for a light truck. It means that the wheels can be used to tow a trailer weighing up to a ton.
  • T: this indicates that the tire is a spare and is only being used temporarily.
  • ST: this type of wheel is designed for special trailers. You shouldn’t ever use a wheel with this code on a standard car.

Simple enough so far. Let’s move onto the numbers.

Width

The first number you’ll find on the sidewall describes the width of the tire in millimeters. You’ll need to know this information to know if the wheel will fit your automobile properly.

Aspect Ratio

This is the third measurement you’ll find on a wheel. It describes the ratio between the tire’s width (the second number) and the cross-section height.

What is a tire’s cross-section? You can find this at any point on the tire by measuring from the base of the sidewall to the top. The aspect ratio describes the height of this section as a percentage of the width of the tire. So if the second number (width) is 200 and the third number (aspect ratio) is 60, this means the height is 60% of the width — 120mm.

Construction

how do i know my tire size

The fourth part of the display will usually be a letter followed by a number, e.g., R14. This letter will be either R or B.

  • R: this stands for radial. Radial models are the most common type. Unless you drive a very certain type of car, your wheels are likely radial. These models provide a good grip on the road and are the standard issue for most US automobiles.
  • B: this stands for bias. The bias model indicates a cross-ply design that provides less grip than radial wheels but has a longer footprint.

Diameter

The number immediately following this letter indicates the diameter of the wheel. It is measured in inches and useful for calculating whether a spare tire will fit on your wheel. For example, if your wheel measures 14 inches and the number on the spare tire is 14, this means that your spare will fit the rim of the wheel.

 how do you size tires

Load Index

The next number you’ll find is the load index. If you’re using a passenger-style wheel, there’ll probably only be 1 number. 

However, if you’re using an LT model, there will likely be 2 numbers: the first is for capacity when only using 1, and the second one is for if you’re driving with 2 LT tires.

The number in this section corresponds to a value denoting the maximum load the wheel can bear. Refer to a load index values guide to get the exact specifications of your tire.

Speed Index

The final number is the speed index. This indicates the maximum speed the tire can tolerate. 

The speed rating or index of a tire is the tire’s nominal maximum speed at which the heat dissipation is optimum. A higher speed rating means that the tire can withstand more heat, resulting in less wear over time. 

In our example, the symbol “S” indicates that the tire’s maximum speed rating is 180 km/h or 112 mph. 

Here’s a quick overview of all the standard speed index symbols and what they mean:  

  • L: 120 km/h – 75 mph
  • M: 130 km/h – 81 mph
  • N: 140 km/h – 87 mph
  • P: 150 km/h – 94 mph
  • Q: 160 km/h – 100 mph
  • R: 170 km/h – 106 mph
  • S: 180 km/h – 112 mph
  • T: 190 km/h – 118 mph
  • U: 200 km/h – 124 mph
  • H: 210 km/h – 130 mph
  • V: 240 km/h – 149 mph
  • W: 270 km/h – 168 mph
  • Y: 300 km/h – 186 mph

What Size Wheel Fits My Car?

Consult your vehicle’s manual to find this information. Then, match the instructions to the information on the sidewall.

 how to check size of tire

Does VIN Number Tell Tire Size?

Yes, for the most part, and as long as you enter the right information. By entering your VIN on VIN Decoder, you should be able to pull up accurate information about what tire size your vehicle needs.

How Do I Find Out My Rim Size?

You can find this information by either:

  1. Checking the sticker plate information on your vehicle, or
  2. Looking up the exact make & model of your automobile.

You then match this information to the tire’s diameter.

Conclusion

Wondering how to find out tire size isn’t too mysterious. As long as you know what the letters and numbers mean, you’ll be fine. If you’re worried, print out this guide and keep it in your glove compartment!

Did you find our guide helpful? Then consider checking others:

How Do You Measure Tire Size
How To Measure Tire Rim Size
How To Read Trailer Tire Sizes
How To Convert Tire Size To Inches
How To Find Tire Diameter