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How to read tyre sidewall markings.
If you take a look at any tyre, on any vehicle on our roads, you will see a whole lot of letters and numbers. The brand of tyre and the model are easy to read, but what about the rest of the markings? A tyre sidewall can tell you a lot of important information about the tyre, including its size, width and height, as well as load carrying capacity, date of manufacture and more!
What the markings mean on your sidewalls.
Most often, tyre manufacturers will write this information in a standardised format that is seen across all common brands. For tyre size, let’s use a 235/40/19 tyre as an example, as fitted to several luxury performance sedans.
- 235/40 R19 - The surface of the tyre tread is 235mm wide (also known as section width).
- 235/40 R19 - The sidewall height (also known as the aspect ratio) is 40% of the width of the tyre, in this case roughly 94mm.
- 235/40 R19 - This tyre was manufactured to fit onto a 19 inch wheel.
When it comes to offroading, drivers prefer to measure the total diameter of the tyre as that is more important than tyre width or wheel size. For example, a 285/75 R16 Mud Terrain tyre would be described as a 32 inch tyre. It’s easy enough to do the maths, rim size + 2x sidewall height, rounded off to the nearest inch.
Tyre sizes only cover a small part of the markings on a tyre sidewall, there are a lot of other important bits of information to let you know about.
Tyre Load Index
As much as there is a huge variety of sizes and tread patterns available, there are a huge range of vehicle weights that tyres are expected to perform under. A tyre to suit a large SUV or flat tray ute has wildly different requirements to a small hatchback tyre. Fortunately, there is a standardised chart to take the guesswork out of what your tyre can cope with.
Load index is shown as a two digit number that corresponds to the maximum static load a tyre is expected to reliably perform under.
Speed ratings
Just as there are different load ratings, there are different tyre speed ratings. The forces put on a semi slick tyre at a track day can be much higher than even what a light truck tyre can expect under normal use. As such, have a look at your sidewall and you will see a speed rating represented by a letter. There’s easy to find charts online to decode which maximum speed that equates to.
Date of manufacture
Somewhere on the sidewall of your tyre, you’ll find 4 numbers in a small box. This tells you the week the tyre was manufactured. The first two digits are the week number, while the second two digits tell you the year of manufacture. For example a stamp of ‘2618’ means the tyre was made in the 26th week of 2018.
The reason why tyre age is important is because natural rubber degrades over time. It is recommended to have your tyres inspected regularly once they reach 5 years of age. Old tyres have increased chances of cracking, becoming delaminated or blowing out.
Treadwear, Traction and Temperature markings?
The UTQG rating system is a requirement for tyres sold in the United States as part of their DOT roadworthy scheme, similar to Australian Design Regulations (ADRs). While UTQG markings are not required in Australia, most manufacturers sell the same tyres across multiple countries. The UTQG scheme covers 3 labels:
- Treadwear - a 3 digit number that arbitrarily compares one tyre to the next. There is no chart signifying exactly how many kms each number refers to as each tyre is tested against a control tyre. However, it is taken that a treadwear 600 tyre will last twice as long as a tyre with a 300 treadwear rating when used in the same conditions.
- Temperature -the tyre temperature is measured after sustained high speeds and is given a rating based on how well the design self cools on an A, B, C scale.
- Traction- rates how well a tyre can perform an emergency stop on a wet road. Ratings are: AA, A, B, from best performing to worst.
Come chat to the professionals.
Whether you’re after tyre advice, vehicle servicing, suspension and brake checkups or just an alignment, come chat with our friendly, expert staff at Donnellans, the Tyremen.
With 5 locations across the Melbourne area we have a store near you.
