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How to Read a Tire Sidewall

June 21, 2019

*** CO Alt Tag Update Statements **

Whether you're new to the truck world or not, knowing how to read the sidewall of a tire is important.

There are actually 2 different versions of tire measurements, standard and metric. This is pretty self-explanatory, but we'll get into it a little deeper. Standard tires are measured in inches by height, width, and diameter, versus metric tires are measured in millimeters by width, aspect ratio, and diameter. Let's get more specific.

how to read a tire sidewall

Sizing Numbers in Standard

In the truck world, standard measurements is well, standard.

  • The 1st numbers is your height, which is how tall the tire is from the ground to the top of the tire in inches.
  • The 2nd number is your width, which is the measurement in inches from bulge to bulge or sidewall to sidewall in inches.
  • The R is the Radial Construction
  • The 3rd number is your diameter, which is the size of the wheel this tire fits in inches.
  • Sometimes, there are letters after. For example, LT means Light Truck, and P means Passenger rated tire. This determines what type of vehicle this tire can be ran on, for example, a Passenger tire is for mini vans and small SUVs and not your full sized truck.

Sizing Numbers in Metric

  • The 1st number, which is your width, ishow wide your tire is from sidewall to sidewall in mm.
  • The 2nd number is your aspect ratio, which is the sidewall height in ratio to the width. For example, if your aspect ratio is 55, your sidewall height will be 55% of your tire width.
  • The R is the Radial Construction
  • The 3rd number is your diameter, which is the size of the wheel this tire fits in inches.

For your aspect ratio, if you wanted to go with a wider tire you'd go with a larger first number with a lower aspect ratio. If you stick with a similar aspect ratio of a skinnier tire, the sidewall will be much taller.

Don't want to try and figure out the differences? We made some calculators to help out. Check them out here.

DOT Numbers

This is how the tire manufacturers determine what batch the tire was made in, like what week in what year. If there are any problems, this can help them determine what batch they were made in and narrow it down.

Load Index

The Load Index is normally found listed after the sizing on the sidewall. The load index is all about the performance of the tire. There will be numbers followed by a letter, for example, 125Q. The numbers are your load index rating, which is how much weight capacity the tire has when at full PSI. The higher the number, the more the tire can handle. The letter is your speed rating. This information can usually be found on a sticker on the driver's side door jam. The letter following the numbers is your speed rating, Q is 100mph for example.

Ply Numbers

After your sizing and load index numbers, you'll have your ply numbers. The ply is an expression of the tire's strength and capacity.

Load Range

Your load range will be clearly stated as what it needs to be for the size of vehicle you're using. This number references how much load the tire can handle.