What Do the Numbers on a Tire Mean? (Full Guide)

If you've ever wondered what the numbers on a tire mean, it's actually easier to understand than it sounds. Those numbers and letters tell you everything from the tire type (like P for passenger or LT for light truck), the width in millimeters, the aspect ratio, the construction type, wheel diameter in inches, load index, and the speed rating. By knowing what each part of the code means, you can choose the right tires for your vehicle with confidence.

Examples

Here are a few examples for reference. To be clear, the format we used in these examples is the following: [Category]: [Markup] / [Meaning].

Example #1: 235/45R18 94V M+S

• Tire Number: 235/45R18 94V M+S
• Tire Type: (No letter) / P - Passenger
• Tire Width: 235 / 235mm
• Aspect Ratio: 45 / 45%
• Construction Type: R / Radial
• Wheel Diameter: 18 / 18 inches
• Load Index: 94 / 1477 lbs
• Speed Rating: V / 149 Mph
• Additional Markup: M+S / Mud and snow

Example #2: LT285/50R22 121/118S

• Tire Number: LT285/50R22 121/118S
• Tire Type: LT / Light truck
• Tire Width: 285 / 285mm
• Aspect Ratio: 50 / 50%
• Construction Type: R / Radial
• Wheel Diameter: 22 / 22 inches
• Load Index: 121 / 3197 lbs - 118 / 2910 lbs
• Speed Rating: S / 112 Mph
• Additional Markup: M+S / Mud and snow

1. Tire Type

In this specific example, there's no letter at the beginning, indicating that it is a Euro-Metric tire. The first letter (or lack of one) on your tire's sidewall tells you what kind of tire you're looking at. Here's what each code means:

• P - Passenger Vehicle Tire: Found on cars, SUVs, crossovers, minivans, smaller pickup trucks, and electric vehicles. These tires offer a smooth ride, solid traction, and plenty of load-carrying capacity for lighter vehicles. For certain electric vehicles, you might also see tires marked with the letters "EV". These tires are designed specifically for the unique demands of battery-powered cars.
• LT - Light Truck Tire: Built for vehicles that tow or carry heavy loads. You'll often see them on ¾-ton or 1-ton trucks and SUVs. LT tires use stronger materials and more durable rubber, giving them the extra strength needed for heavy-duty jobs and off-road adventures.
• ST - Special Trailer Tire: Made for trailers, including boat trailers, travel trailers, fifth wheels, and utility trailers.
• T - Temporary Tire: Marked with a "T," these are your spare tires. They're only meant to get you to a repair shop, not for long-term driving.

Quick note: If there's no letter before the numbers, you're looking at a Euro-Metric tire. Both P-Metric and Euro-Metric sizes are designed for passenger vehicles.

2. Tire Width

The three-digit number that comes right after the first letter tells you the width of the tire in millimeters, measured from sidewall to sidewall. This is also called the "section width".

3. Tire Aspect Ratio

Right after the tire width, you'll see a forward slash, followed by a two-digit number; this is the aspect ratio. The aspect ratio refers to the height of the tire's sidewall and is shown as a percentage of the tire's width. The larger the number, the taller the sidewall (also called the tire's "profile").

4. Tire Construction Type

Next, you'll find a single letter that reveals how the tire is built on the inside. This letter tells you about the internal construction, which affects everything from stability to durability. The most common letters you'll see are:

• R - Radial Tires: This is the industry standard for most modern vehicles. The internal layers of durable cords (called plies) run from one sidewall bead to the other and are arranged perpendicularly in the direction of travel. These tires feature steel or polyester cords that make them even more durable.
• D - Diagonal Plies Tires: These were the standard before radial tires took over. They're built with layers of nylon cord laid diagonally across each other at about a 55° angle. They are also called bias-constructed tires and are still used in motorcycle and trailer applications.
• B - Belted Bias Tires: These include a belted bias. A belted bias is a diagonal bias tire that is further reinforced with a diagonal belt of a durable material, such as steel. These tires provide enhanced performance and the load-bearing characteristics that made bias-constructed tires so popular for decades.

5. Wheel Diameter

The two-digit number that follows the construction type indicates the wheel diameter in inches. This is the distance between the two points where the tire seals onto the rim. In other words, it's the distance measured in inches across the face of the rim. It's an important number to know because when someone asks for your tire size, this is usually the part they are referring to. Keep in mind that wheels and tires must have the same diameter to fit safely. For example, a 16" tire can only be mounted on a 16" rim.

6. Load Index

Next, you'll see a two or three-digit number that refers to the tire's load index, which indicates how much weight the tire can safely support when inflated to its maximum inflation pressure. Load index values range from 0 to 150, but most cars and light trucks have load index values ranging from 70 to 124.

7. Speed Rating

The last letter tells you the speed rating, which represents the top speed your tire can safely handle over a period of time. A tire with a higher speed rating is built to handle heat better and can stay more stable at higher speeds, giving you extra control on the road. Most ratings are a single letter, like H or U, but sometimes you'll see a letter and number combo, such as A1 or A2. For tires designed to go faster than 149 mph, you might see "ZR" markup in the tire. However, this markup is not relevant anymore. The modern equivalents are V, W, or Y.

Additional Markup: M+S

In some tires, you will find the markup "M+S", which means Mud+Snow. These types of tires are usually used for off-road applications since they perform better on surfaces such as mud, rough snow, sand, and loose soil.

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Frequently Asked Questions

Where Do I Find My Tire Numbers?

You'll find the numbers and letters on the sidewall of your tire, usually along the outer edge facing away from the wheel. In some cases, you will also find them on the back of the tire. The font size can be either small or large, depending on the brand.

Does the Middle Number on Tires Matter?

Yes! The middle number is the aspect ratio, which affects your tire's appearance, handling, and overall performance. A higher number means a taller sidewall, while a lower number gives a sportier, lower-profile look.

What Do the Three Numbers on the Tire Size (in Inches) Mean?

The three-digit number after the first letter is the tire's width in millimeters.

Do All Four Tires Need to Have the Exact Same Numbers?

Ideally, yes. To maintain control, stability, and safe handling, it's recommended to avoid mixing constructions or sizes.

What Is the Second Number on the Tire Size?

The second set of numbers on a tire represents the tire width in millimeters. A wider tire has more contact with the road, improving handling and maneuverability.

What Does the First Number on a Tire Mean?

The first number, along with any preceding letter, indicates the tire type. These include (P) passenger tires, (LT) light truck tires, (ST) special trailer tires, and (T) temporary tires.