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The Ultimate Tire Size Guide

Understanding tire sizes is crucial for every driver, but the numbers can get confusing. Without knowing the correct tire size for your vehicle, buying new tires may become unnecessarily difficult.

However, to explain tire size numbers, we should take into account the different tires that brands manufacture. The versatile tire size format of metric and numeric tires can cause additional headaches. But, no matter if a passenger or an LT tire size is looked at, a tire size guide can greatly help with that.

From the placement of the tire size to “How to read a tire size?”, today we will discuss everything in detail.

Where to Find the Tire Size?

Identifying the tire size of your vehicle is not difficult and there are multiple ways to go about it. Car manufacturers make sure the tire size is easy to find. Due to this, they place the recommended tire size stickers in different locations.

These are the most common tire size locations:

  • Owner’s Manual - The vehicle's owner's manual has the recommended tire sizes noted in it. Sometimes it even mentions suitable alternative tire sizes.
  • Driver-side Door (Jamb) - Car brands place a sticker on the driver-side door or on the door jamb that showcases the OE tire size.
  • Glove Box Door - Opening the glove box can show another tire size sticker on the inside.
  • Gas Tank Hatch - The gas tank hatch contains a smaller sticker that shows the OE tire size of the vehicle.
  • Current Tires - Probably the safest way to check the tire size is to look at the current tires. If the original equipment tires and wheels were changed in any way previously, the OEM tire size will no longer work.

How to Read Tire Size Numbers?

Finding the recommended tire size placement is just the first step. Before buying a new tire set, you need to know how to read a tire size correctly.

Reading tire size numbers can get tricky. Not everything is straightforward and not knowing how to determine tire size can leave you in a bind.

What does tire size mean for metric and flotation numeric tires? Let's walk through them.

Metric Tire Size

Whether you need a passenger or an LT tire set, metric tire sizes can work for your vehicle. Most performance categories, including touring, performance, highway, and even some off-road tires, use metric tire sizes to identify models. Due to this, they are the most widespread tire size found on the roads.

This is the metric tire size explained:

tire size meaning - metric tire sizes

Letters

Before the actual tire size, metric tires indicate what type of vehicles they are for. Manufacturers place “P”, “LT", or “ST” in front of the tire size.

If there is a “P” in the tire size, the tire is built for passenger cars, SUVs, crossovers, and electric vehicles. However, an LT tire size will have the letters “LT” ahead of the tread width and these tires are meant for light trucks. When the tire size starts with “ST” it means that the tires are for Specialty Trailers.

Some tires will have the letter “C” at the end of the tire size, which signifies a commercial van tire.

Tire Width

The tire width is the first number in the tire size, which consists of three digits. The tire width size is measured from sidewall to sidewall, across the tire's footprint in millimeters.

For example, if the tire size is 205/55R16, the tire footprint is 205 mm wide.

Aspect Ratio

The middle number in the tire size is the aspect ratio, also known as the tire sidewall size. This two-digit number is the ratio of the height of the tire's cross-section to its width and it is shown in percentages. The bigger that number is, the taller the sidewall will be for tires of the same width

Therefore, looking at the same 205/55R16 size, the aspect ratio will be 55% of its width.

Construction

Between the second and third numbers, you will find the letter that explains the tire's construction. This second letter is placed after the aspect ratio and it can be “R”, “D”, or just a hyphen (-).

“R” indicates a radial construction, “D” represents a diagonal structure, and the hyphen means a bias-ply one. These internal structures make the tires perform in different manners and which one you choose depends on their applications.

When there is “ZR” in a tire size, it is a high performance tire. ZR tires are radial models that can safely perform at the speed of 150 mph or faster.
Don't forget to check out our Radial vs. Bias Tires blog if you wish to know more about the topic.

Diameter

The tire size diameter, simply known as the rim diameter or the rim size, is the last number of the tire size. It tells drivers the size of the rim they need for the specific tires.

While drivers can tweak the first two numbers to certain degrees, this last number cannot be changed without buying new rims.


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Flotation or Numeric Tire Sizing

While flotation tires are more often used for specialty vehicles like ATVs or tractors, tire brands also manufacture off-road truck tires and commercial truck tires with this sizing type. Such tires feature a wider footprint, which creates a need for wider wheels. However, this also helps them conquer various off-road terrains with ease.

Flotation tires measure tire size in inches.

tire size meaning - flotation tire sizes

Tire Height

The first number of the tire size is the overall tire height or tire diameter. To determine the tire size, check the tire height from the ground to the center of the tire's top.

If the tire is 35x12.50R17 that means the tire is 35 inches tall.

Tire Width

With flotation sizes, the tire size's middle number is not the sidewall height. Rather, it is the section width from one sidewall to the other. This does not measure the tread or footprint width like metric tire sizes do.

With the 35x12.50R17 tire size, the tire is 12.50 inches wide.

Construction

Brands manufacture off-road flotation tires with radial or bias constructions. If the letter R is placed after the width, the second number of the tire size, the tire features a radial structure. But if there is only a hyphen (-) between the last two numbers, it sports a bias-ply one.

For example, 35x12.50R17 tires are radial while 35x12.50-17 tires are bias-plied.

Rim Diameter

The last tire size number notes the rim diameter, showing what rim size the tires need to properly function. These tire size markings stay the same even if we convert a tire size to metric.

Tire Size Comparison Chart: Flotation Vs. Metric Tire Size Conversion

Changing the tire size from metric to flotation, or vice versa, is often necessary as the difference between them is not just in their tire size format.

Here's a list of the most common sizes that you can use to convert a tire size to metric:

tire size chart: metric and flotation sizes

Load and Speed Ratings

The tire size markings also include the speed and load ratings. These indexes are found after the tire size on the tire's sidewall and indicate the maximum load and speed durability of the specific tire.

The load index is the number located right after the tire size and it is the maximum load capacity of one tire. This is a numerical scale that starts with 1 and goes up to 150. Typical passenger cars will have a load index between 75 and 100, and SUVs and trucks are above 100. Metric LT tire sizes will have two load ratings.

On the other hand, the speed rating is a letter situated after the load index. It represents the maximum speed durability of each tire. The letters range from A1 to ZR and are alphabetically arranged - except for H. Manufacturers determine a specific tire's speed rating based on its performance category and capabilities.

Frequently Asked Questions

What Do the Tire Size Numbers Mean?


Each tire size number represents a part of the tire size. The first number of the tire size is the footprint width in millimeters. The second number is the sidewall height presented as a percentage of the tire width. The last number is the rim diameter which determines what sized rim the tire needs.

How to Check the Tire Size?


The tire size can be checked in multiple ways. If the OEM tire size has previously been switched to a different size, the owner's manual and the stickers located on the car can give you false information. For this reason, the best starting point is checking the tire's sidewall to see the current tire size.

Where to Find the Tire Size?


You can find the tire size in the owner’s manual of the vehicle or on the stickers placed inside the car. Manufacturers place these tire size stickers in convenient places, such as the driver-side door or door jamb, inside the glove box, or the gas tank hatch.

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