How to Read Tyre Codes

Educational

Sep 23rd, 2020

How to Read Tyre Codes

The next time you take your car over to the petrol station take a few moments to look at your tyres up close. Aside from the brand name, you’ll notice a series of alphabets and numbers printed on the side of the tyres. But what do they mean? Well, those are your tyre codes! Together, those alphanumeric tyre markings will tell you a whole story about your tyres. 

That ‘story’ includes the tyre’s width, aspect ratio, speed rating, and so much more! By learning what they mean, you’ll be able to understand everything about the tyre’s purpose (other than letting your car move around). Plus, the next time you need a tyre, you’ll be able to pick the right one by yourself!

In this article, we’re going to take a quick look at every part of a tyre marking so you can read it like a book! Bear in mind that different tyres will have slightly different markings on them. Some have more markings, while others have less. That’s why some countries require the use of UTQG or ‘Uniform Tyre Quality Grading’.

About the Uniform Tyre Quality Grading System (UTQGS)

Some countries like the United States require UTQG markings on tyres by law. That’s great since it ensures that consumers can always refer to the same consistent set of information when choosing their tyres. 

Australia and New Zealand do NOT require UTQG by law. As a matter of fact, Australia doesn't have a formally-recognised system to test for tyre quality. Still, some manufacturers choose to adhere to UTQG anyway, so their tyres offer an easy way for buyers to compare with other brands before choosing one.

What Each of the Tyre Markings Mean

Now, let’s take a look at the critical information that you can pick up by reading the tyre markings on the sidewalls. Remember: most tyres present the following information in the same sequence, so this article will start with the tyre codes beginning from left to right.

Section Width

First and foremost, we have the section width. This number (for example, ‘225’) will show you the nominal width of the tyre measured in millimetres. The manufacturer takes that measurement from one sidewall of the tyre to the other. Typically, this number ends with a slash and following that is the next marking which represents the aspect ratio of the tyre.

Aspect Ratio

The aspect ratio refers to the percentage of the tyre’s section height over its section width. Suppose the tyre has an aspect ratio of 45. That means that the tyre’s height is 45% of its width. That's why this tyre marking is displayed in conjunction with the section width. These dimensions are measured when the tyre is under no load and inflated to max air pressure. 

Tyre Construction

The next tyre marking refers to the construction of the tyre. An alphabet represents the exact type of tyre construction. For example, a radial tyre will have an ‘R’ marking, while bias-ply tyres will have a ‘B’ tyre code and tyres with a diagonal construction will carry a ‘D’ instead. The odds are that you’ll see an R tyre marking on yours since radial tyres are the most common type used in vehicles today. 

Rim Diameter

Next, we have the rim diameter which the tyre marking expresses in inches. As you can see, the measurement units used by the tyre markings aren’t always the same (like how the section width number appears in millimetres instead). The rim diameter is a measurement of the tyre’s inner diameter. In simpler terms, this tyre marking will tell you what sized rims you can fit the tyre on. 

Load Index

Here’s an essential tyre marking to pay attention to - the load index. This figure is expressed in codes that represent different load indeces. Each index will tell you how much weight a tyre can handle when it’s fully inflated. At the same time, it’ll also tell you what tyre pressure you need to use when filling it up with air. On a personal vehicle like a car, the index numbers can be anywhere from 75 to 105. To know how much weight each index number can sustain, check your car’s manual or any documentation that comes with the tyre.

Speed Rating

Not all tyres are built for speed, you better believe it. So, if you plan on driving your car at high speeds and racing other vehicles (legally, of course!), you’ll need to pay close attention to the speed rating. These ratings will tell you what speeds are safe to drive with those tyres. You may read our other article about car tyre speed ratings to get more info about it. It’ll tell you everything you need to know about speed ratings in much greater detail!

Other Tyre Markings

Depending on the brand of the tyre, you may see other markings on it as well. Their exact meaning will depend on the manufacturer, but quite often you’re able to interpret them by yourself. For example, some tyres will have markings showing what week or year they were made. They may also indicate the tyre’s suitability for snowy or muddy driving conditions, or whether or not they comply with local transportation standards.

Additional Tyre Information

While the tyre codes will tell you plenty about your tyres, there are other places that provide information as well. For instance, the inside of the driver’s side door will usually show the recommended tyre pressure for your car. Depending on the make and model of your vehicle, you may also find this information etched on the glove compartment box or somewhere in the trunk. 

Of course, there’s no better source of information than your car owner’s manual. Other than the recommended tyre pressure, the manual is an excellent place to learn how to remove or attach a tyre, should the need ever arise.

Did you find this article useful? Visit us regularly for more topics like this to keep you up-to-date on everything you need to know about your daily drive. If you'd like to find tyres or other auto parts for your vehicle, you can head on over to Carpart.com.au and request for a part.  


By Ray Hasbollah