So it’s time to buy a new set of tyres. You’ve read our blog on checking tread depth and realised your current set have served their time. But you notice something else. Someone has scrawled strange hieroglyphics on the sidewall of your tyres. Peering closer, you realise that, no, they’re not hieroglyphics – they’re familiar letters and numbers arranged in a nonsensical order. Is this the work of a deranged person? Is it a secret message you’ve written to yourself while sleepwalking again?
Sadly, no. It’s nothing quite as exciting. It’s simply the strange language of tyre people who use these markings to help determine which tyres are appropriate for your vehicle. Here’s your crash course in how to read tyre size and specifications.
Understanding Tyre Specifications
Tyres come in a range of sizes and specifications, and your vehicle is probably compatible with more than one option. While variety is the spice of life, too much choice can lead to paralysis. Learning to decipher the specifications printed on the sidewall of your tyres will narrow the field and simplify the process, while ensuring your car is fitted with the right tyres.
Where is the tyre size located?
The first place to look is the vehicle’s owner manual, which is that bulky book taking up space in the glove box. Failing that, you can check the sidewall of your current tyres. Once deciphered, the numbers and letters will not only tell you which tyres are appropriate for your car, but they will also tell you those tyres’ technical capabilities.
Reading tyre size
The sidewall code provides information on four things: tyre size, construction, load-carrying capacity and speed rating. Nothing teaches like examples, so let’s look at one now.
Here’s a common tyre code: 205/55R17 95H
205 is the width of the tyre in millimetres (205mm).
55 refers to its aspect ratio, which is a fancy way of describing the tyre’s height compared to its width (so 55 tells us that the tyre’s height is 55% of its width).
R indicates the internal construction of the tyre. R indicates radial, which means the internal ply cords are oriented in a radial direction, perpendicular to the axis of rotation.
17 indicates the diameter of the wheel rim, measured in inches, onto which the tyre can be mounted. So, this tyre can be mounted onto a 17 inch rim.
95 tells us how much weight a tyre can support when inflated correctly (tyre pressure matters). Us tyre boffins call it the load index, because we match the number to an index, which then correlates to specific weights. On this index, 96 indicates a maximum load of 710kg per tyre.
H represents the maximum speed at which the tyre can be operated safely. It’s another index, on which H represents a maximum speed of 210km/h.
There it is. Now you can speak tyre.
The takeaway is that the codes on your tyre’s sidewall matter. When you contact Eastern Tyres to book in your car for a new set of treads, have this information at hand. Make sure you note the code on one front wheel and one back wheel as they can have differing widths. Once you realise your tyres are in need of replacement, don’t dilly dally; driving on unsafe tyres is dangerous for you and those around you.