What do the Numbers on Tires Mean?

Have you ever observed the numbers on the sidewalls of your tires? For the average driver, there is nothing more confusing than these numbers. What do the numbers on the tires mean?

The numbers on the tires can be divided into seven sections, each representing a different meaning.

Numbers on Tires

A: Tire type

The first letter on the tire will tell you what class of tire it is.

  • PPassenger vehicle tires. Cars, SUVs, crossovers, minivans, and small pickup trucks will use them.
  • LTLight truck tires. Towing trailers or vehicles looking for an extra heavy-duty option will use these tires. They are usually equipped on 0.75-ton or 1-ton trucks and SUVs.
  • STSpecial Trailer. Trailers will use this tire, including fifth wheels, boat trailers, utility trailers, etc.

But there are also some tires that do not have a letter before the first number. Please don’t worry, this is normal. This means that your tire is a metric tire, often referred to as a European size. It is also measured in millimeters but has a different load capacity than the P or LT tires.

B: Tire width

The three digits after the letter represent the tire width, which is also known as the section width. It is measured in millimeters.

C: Aspect Ratio

There is a slash split between the aspect ratio and the tire width. The bigger the aspect ratio, the higher the tire’s sidewall. It is not measured in millimeters, but in percentages.

For example, an aspect ratio of 65 means that the sidewall height is 65% of the tire width. Using the width of the tire before the slash, multiplied by 65%, will give you the sidewall height in millimeters.

D: Type of structure

This letter means the internal structure of the tire.

  • RRadial tires. This is the industry standard for most tires. These tires have better road grip and lower rolling resistance. It is able to reduce the fuel consumption of the car and enhance the comfort of people’s rides.
  • D – Tires made with diagonal plies, also known as bias-constructed tires. This is a traditional tire, and some motorcycle and trailer tires still use this construction.

E: Wheel Diameter

Tire diameter is measured in inches. It refers to the distance between two bead seat areas.

wheel_diameter

F: Load index

The number of digits of the load index is variable, it may be two digits or three digits, from 65 to 150. This means the weight that the tire can withstand. In the example, a load index of 89 means that the maximum weight it can withstand is 1,279 pounds. The values corresponding to each number can be viewed in the table below.

G: Speed Rating

This letter stands for the top speed at which it is safe to drive for an amount of time. Tires with a higher speed rating can handle heat better and provide more control at faster speeds. You should always keep your car below the speed rating which your tires can handle, and obey the rules of the road to ensure safe driving. You can also check the speed rating by looking at the table below.

tire load index

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