Deciphering Car Tire Codes

Deciphering Car Tire Codes

Deciphering Car Tire Codes
Reading Time: 3 minutes

Have you noticed the letters and numbers on the sidewall of your car’s tires? Most people don’t, but there’s a tonne of information you can learn about your vehicle from these codes. If read correctly, car tire codes give you details about the size, type, and performance of the tire. Here’s an example of a tire code you might find on your tire’s sidewall.

P 220/50 R 15 89 H

Look confusing? It probably does. In this guide, we’ll break down exactly what this code means and how you can use it to learn more about your car and the tires it requires. 

Tire Type

The first letter at the beginning of the tire code tells you what kind of car the tire belongs to. In our example above, ‘P’ refers to a passenger vehicle. You may find other letters here as well. “LT” stands for Light Truck, “ST” stands for Special Trailer, and “T” is for Temporary, which is used for spare tires. Tires without a letter at the beginning of the code follow European tire specifications. 

Tire Width

Just after the tire type letter, you’ll be presented with a three-digit number. This refers to the tire’s width or distance from one edge of the sidewall to another. It’s measured in millimeters. The code in our example above has a tire width of 220 millimeters. The larger this number is, the wider your tire will be. 

Aspect Ratio

The number after the slash mark on your tire code indicates the tire’s aspect ratio. To keep it simple, the aspect ratio tells you how tall your tire is. Aspect ratios are expressed in percentages. In a tire with a ‘75’ aspect ratio, this means that the height is equal to 75% of the tire’s width. The bigger this ratio, the bigger your tire’s sidewall. Lower ratios indicate shorter sidewalls, which are used for improved steering and overall handling.

Construction Type

In tire codes, the second letter represents your tire’s construction. Most passenger vehicles have an “R” as the second letter. This refers to radial construction, an industry standard for the past several decades. Alternatively, you may see tires with diagonal or bias ply construction, symbolized by the letters D, B, or a hyphen.

Wheel Diameter

After the second letter, you’ll notice another number − the wheel diameter. This is self-explanatory for most drivers. The wheel or rim is the metal part inside the tire. In our example above, the tire can handle 15-inch wheels, as denoted by the 15 after the second letter. While you might fit a wheel that is slightly smaller or larger, the wheel diameter number will tell you the best rim size for the optimal speed, handling, and performance of your vehicle. 

Load Index

One of the last numbers on the tire is the load index number, which measures how much weight the tire is designed to support. Keep in mind that this rating is for each tire, not the total all four tires can hold. For example, our tire has a load rating of 85. According to the index, this means that each tire can hold up to 515 kg worth of weight. To get the full carrying load of all tires, you’ll need to multiply by four, giving you 2,060 kg for the entire vehicle. Some vehicles come standard with XL, or ‘extra load’, tires. This equipment carries extra weight than the regular load, so it’s important to check the tire’s load index before replacement.

Speed Rating

Finally, the tire’s speed rating is represented by the last letter. This is an important measurement, as travelling at speeds over this rating may severely damage the tire. Each letter signifies a different speed. The lowest is S, allowing vehicles to travel safely up to 180 km/hr. The highest load rating is Y for tires, with a speed rating over 300 km/hr. While your tire may not explode if you’re exposed to higher speeds, it absolutely could. Regardless, you can be sure it will deteriorate your tire faster and force you to replace it earlier than usual. 

Whether you realize it or not, understanding tire codes is a vital part of car ownership. Choosing the wrong tire for your car can be detrimental to the health of your vehicle and could even cause a catastrophic failure while driving. Whenever you’re in the market for brand-new tires, reference this guide to make sure you’re buying the right one for your car!

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