How to check your tyre size

A Guide to Checking your vehicle tyre size.

Understanding Aspect Ratio

Immediately following the tyre width, the fourth and fifth digits denote the tyre's aspect ratio, or the sidewall's height as a percentage of its width. An aspect ratio of 55 means the tyre's profile height is 55% of its width.

 

Recognizing Radial Tyres

Radial tyres are marked with an "R" and have cord plies positioned at a 90-degree angle to the travel direction for added strength. Most modern tyres are radial.

 

Determining Wheel Diameter

The subsequent two digits indicate the wheel rim size the tyre fits, which is also the tyre's diameter from bead to bead. A tyre marked 16 fits a 16-inch wheel rim.

 

Decoding Speed Rating

A letter at the end of the tyre size code signifies the tyre's maximum speed capability. Speed ratings are based on tests measuring a tyre's ability to handle a specific speed for an extended time.

 

Assessing Load Index

The load index offers information on the tyre's maximum weight capacity. Located after the tyre size marking and before the speed rating, the load index is a numerical code. Avoid using tyres with a lower speed rating or load index than the manufacturer's recommended specifications for your vehicle or mixing tyre construction types. Refer to your vehicle's handbook for this information.

 

Identifying Date of Manufacture

Tyres display manufacturing details, including when and where they were made. Starting with the letters DOT, a series of letters and numbers follow, with the last four digits indicating the tyre's age. The first two digits represent the week of the year, while the last two indicate the year. Tyres older than six years should be inspected for roadworthiness.

 

Run-flat Tyres

Run-flat tyres feature reinforced sidewalls that allow for continued use after a puncture or pressure loss for a short distance until a proper stop and tyre replacement can occur. Run-flat tyre markings vary by manufacturer.

Sidewall on tyres

Understanding the information on your tyre's sidewall is crucial for selecting the right replacement tyre and maintaining your vehicle's performance and safety. Familiarize yourself with these markings to make informed decisions about your tyres.