How to Read Tire Size

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Where is My Tire Size?

Before you start shopping around for new tires, you’ll want to find out what the recommended size for your vehicle is. There are typically three main places you can find this information: in your owner’s manual, on a placard located on the driver’s side door jamb, or on the sidewall of the tires themselves.

When you find the tire size, it will appear as a code made up of letters and numbers. For example, you may find something like this: P 215/65 R 15 89 H.

While it may seem like a random assortment of characters, each letter or number in this code corresponds to a different part of your tire’s size.

Reading Tire Size

To help you understand how to decipher your tire’s size, we’ll go through each part using our above example: P 215/65 R 15 89 H.

Tire Type

The first letter in our code, in this case P, lets you know what class of tire you’re looking at. There are typically three main tire classes you’ll find:

• P – Stands for Passenger vehicle tire. P-class tires include your everyday cars, SUVs, crossovers, minivans, and smaller pickup trucks
• LT – Stands for Light Truck tire. These are designed for vehicles carrying heavy loads and can include three-quarter or 1-ton trucks and SUVs.
• ST – Stands for Special Trailer. These tires are mostly meant for trailers, including fifth-wheels and boat and utility trailers

The first step is making sure your vehicle and the tire class match up for your needs.

Tire Width

Also known as Section Width, this is the 3-digit number following the letter or 215. This is simply your tire’s width measured from side to side in millimeters.

Aspect Ratio

After the forward slash is the tire’s Aspect Ratio. This number, in our case 65, measures how tall the tire’s sidewall is, measuring from the wheel rim to the top of the tread. This is presented as a percentage of the tire width, meaning this tire’s Aspect Ratio is 65 percent as tall as the tire is wide.

Construction Type

The next letter in our code tells us about the tire’s internal construction. R, which is found in our example, indicates this is a Radial tire, which is the industry standard for most tires today. You may also find D, or diagonal tires, which can be found on motorcycle and trailer tires.

Wheel Diameter

The number following the construction type indicates the wheel diameter measured in inches. In this case, our wheel diameter is 15 inches across.

Load Index

Our next number indicates how much weight a tire can support. This is represented by an Index number, in our case 89. This number is then used to refer to a load index chart, which tells us our vehicle’s total load capacity, which is 1279 pounds!

Speed Rating

The final part of our code refers to the tire’s speed rating, which indicates the top speed that it is safe to travel at on this tire. Usually represented by a single letter, in our case H, this is also then checked against a chart to find maximum operating speed, which would be 130 MPH.