Are you trying to understand what a tyres sidewall markings mean without any prior knowledge? Well, it’s no rocket science and is quite simple. Makes and models of different vehicles have different tyre sizes. You will notice the tyre size on the vehicle tyre’s sidewall. Furthermore, you can search inside your car for the manufacturer’s notice to get the recommended tyre size and a minimum weight load rating. Typically, this information you will find in the glove box, on the driver’s door or under the bonnet. Location to find this information may vary from manufacturer to manufacturer and between vehicle models.
Decoding the Tyre Sidewall Code
You’ll notice a code stamped on the vehicle tyre sidewall rubber – it will tell you about the tyre size and other essential details about the tyre. The information includes the tyre’s dimensions, intended use, load and speed capability.
Tyre’s sidewall code includes the following:
- Tyre width
- The aspect ratio or profile
- Tyre construction
- Rim diameter in inches
- Load index
- Speed rating index
Here, we will take an example to decode the tyre code: 235/50 R 19 99V – This is how the code will appear on the tyre’s sidewall.
Tyre Width
The number “235” indicates the tyre’s width in millimetres (measured from sidewall to sidewall).
Profile or Aspect Ratio
The following number in the sequence is “50” – it indicates the profile or aspect ratio (or measurement of the sidewall height in mm). It is the ratio of the tyre’s cross-section to its width. As per the above example, a tyre with an aspect ratio of 50 will have a height that is equal to 50 per cent of its width.
Tyre Construction
The aspect ratio followed by the letter “R” in the example conveys that the tyre has radial construction. Here, the internal ply cords stretch across the casing from bead to bead in a radial direction. Diagonal or bias-ply is the less common tyre construction represented by the letter “D”.
Rim Diameter (in inches)
Then appears the number “19”, which indicates the diameter code and is in inches. It exhibits the diameter of the wheel rim. It conveys that the tyre should pair to a rim wheel of 19 inches.
Load Index
After the rim diameter, load rating follows. It tells you about the maximum capacity of a passenger car tyre when inflated to its maximum safe pressure. In this example, “99” refers to the index instead of the weight. The load index is determined by the load in kg for each rating. According to the standard load index table, 99 indicates the maximum load weight of 775kg/tyre.
Speed Rating Index
Speed rating marking concludes the tyre’s sidewall code. It indicates the maximum speed a tyre can withstand when inflated correctly and under load. This letter indicates the uppermost speed limit of the tyre. Here, in this example, “V” means the vehicle has a maximum speed of 240 kilometres per hour (per the standard speed rating chart) under the maximum speed limit.
Though a speed rating (per the standard speed rating chart) lays down the maximum speed a tyre can move under the load, don’t use this as a guide when driving; instead, follow safe speed limits without putting your vehicle tyres under any excessive stress.
Buy Tyres Online
Now you know how to read your tyre’s sidewall and choose the replacement tyre for your vehicle. That means you can buy tyres online from the comfort of your home or office, and all you need is a smartphone or laptop or desktop computer and Internet connectivity.
However, if you’re unsure about the right size of your vehicle tyres that you want to replace, it is better to contact an established wheels and tyres shop in Sydney to get the right replacement tyres and get them fitted to your vehicle.