Finding the correct truck tyre size can be quite a challenging task. On this page, we explain how to determine the correct tyre size and how to interpret this size. This way, you will know exactly which tyre to buy for your truck.
We also explain the most common tyre sizes, what the tyre’s load index is and how to determine the tyre’s speed rating.
The tyre size of a truck tyre is shown on the sidewall of the tyre. This side is also referred to as the ‘sidewall’. On this side, you will find a sequence of information consisting of a combination of letters and numbers.
A truck tyre consists of several elements: the tyre width, height, and the inch size of the tyre.
We found the following alphanumeric combination on the sidewall of a random truck tyre in our warehouse.
On the sidewall of the tyre, you will find the following combination: 315/70R22.5 156/150L
Using this combination, we will explain how to interpret this number.
A truck tyre has several characteristics. To explain them clearly, we use the combination mentioned above: 315/70R22.5 156/150L
The width of the tyre is indicated by the first three digits. In our example: 315/70R22.5 156/150L, the width is 315 mm.
The tyre height is shown after the slash (/). In this case, it is 70.
The height is always expressed as a percentage of the width. This means the height is 70% of 315 mm. This does not need to be calculated.
In the example 315/70R22.5 156/150L, the letter R indicates a radial tyre. This is the most common type. Previously, diagonal tyres (D) were standard, but these have been replaced by radial tyres.
Truck tyres are available in sizes such as 22.5 inch, 20 inch, 19.5 inch, and 17.5 inch. The inch size is always shown after the letter R.
After the rim size, there is always a number and a letter. In our example, 315/70R22.5 156/150L, this refers to the numbers: 156/150L. The number 156/150 indicates the load index of the tyre. This number corresponds to a value that shows how much weight the tyre can carry. For example, tyres with a load index of 156 can carry up to 4000 kg.
The load index indicates the maximum load capacity of a tyre at the correct tyre pressure. It is important that tyres are not overloaded.
During periodic inspections (such as APK or TÜV), this is checked and enforced. If your vehicle does not have the correct load index, it will be rejected. The load index is indicated by codes on the tyre.
You can always find the load index code on the sidewall of the tyre.
The speed index indicates the maximum speed at which a tyre may be used. It is shown as a letter after the load index. For example, in 315/70R22.5 156/150L, the load and speed index is 156/150L. The numbers 156/150 indicate the load index, and the letter L indicates a maximum speed of 120 km/h.
