Reading a tyre
What to know about tyres
Reading a tyre
Tyres are often neglected and the last thing you check on your car. If you’re diligent you might check their air pressure when you put fuel in, and every now and again you might have a look to see if they still have some tread left. And when you do need to buy new tyres, it’s often a grudge purchase – there are so many other things you’d rather spend your hard-earned money on!
But tyres are crucial to road safety and so deserve your attention (and, unfortunately, your money!). But do you even know what size your tyres are, and what all that writing on the sidewall means? Here are some tips:
The most basic and important writing on a tyre relates to its size, such as 225/50R17.
The ‘225’ is the tyre width, if you’re looking at the tyre from the front, and is in millimetres.
The ‘50’ refers to the profile of the tyre, which means the ratio of the tyre’s height to its width. In this case, the tyre is 50% as high as it is wide. A higher ratio means that the tyre has a higher profile, or taller sidewalls. Performance cars tend to have lower profile tyres (35 or 40) , passenger cars have something in the middle, like 50 or 55, and SUVs or bakkies have higher profile tyres, up to 75.
The ‘R’ stands for Radial, which is how the tyre is constructed. Radial is the most common, but there are also B (belted bias) and D (diagonal bias construction) tyres.
The final number, in this case ‘17’, is the size of the tyre rim that the tyre fits. So if your RAV4 has a 19-inch ally rim you will need a tyre with a 19 as the final letter in the tyre size indicator.
If you read a tyre fitted to a Toyota Supra you’d probably see something like 275/35ZR19, and on a Toyota Aygo it might be something like this: 165/65R14 79T
Load index and speed rating
Following the tyre size is the load index and speed rating, such as 98H. The load index is the number (98 in this case) and they range from 75 to 105 for passenger tyres, and the higher the number the higher load the tyre can bear.
The digit (H in this case) refers to the speed rating, and common ones are Q, S, T, U, H, V, W, Y and Z. H means that the tyre is rating to 210km/h, while Q refers to 160km/h and Y to 300km/h! ZR, as seen in the Supra’s tyre, means they are rated to over 300km/h.
Never replace a tyre with a tyre with a lower load index or speed rating than the original tyres fitted to the vehicle.