Have you ever wondered what the information found on the side of your vehicle tyres means? This is something that many motorists do not know about which can actually be dangerous as this is important information that can help an individual to operate their vehicle safely and find the right replacement, especially if it is driven within a commercial environment carrying heavy loads.

With this in mind, here is everything that you need to know about tyre sidewall information.

Tyre Width & Aspect Ratio

The first three digits on the tyre sidewall are the nominal width of the tyre from one sidewall to the other. The fourth and fifth digits that immediacy follow the slash after tyre width refers to the tyres aspect ratio - the height of the tyre's profile outward from the rim as a percentage of the width. As an example, 55 would mean that the profile height of the tyre is 55% of its width.


Next in the sequence will be a letter which will refer to the type of construction used within the casing. R is for Radial constriction, B is for Bias-ply and D is for Diagonal construction. The vast majority of modern tyres are Radial tyres which are made with the cord plies at a 90-degree angle to the direction of travel for additional strength.

Rim Diameter

The rim diameter follows the construction letter and simply represents the diameter of the wheel rim in inches.

Load Index

The next number in the sequence is the load index which lets you know the maximum load that can be supported when the tyre is fully inflated. This is not particularly straightforward as the number is a code which corresponds to a load capacity which can be found in your vehicle documentation or online. It is important to know what your load index is as it is a legal requirement to stay within this, plus if you were to exceed the load limit you could damage the tyre and make the car unsafe to drive. Additionally, load capacity will decrease as a tyre air pressure reduces so you need to keep your tyres topped up, especially before driving with a heavy load.

Speed Rating

Speed rating follows this and will be a letter between A and Z. Each letter signifies a maximum speed that the tyre is legally approved for - the difference between each letter is roughly 6mph and increases as you go through the alphabet. Tyre speed ratings should be matched to the official top speed of your car, so it is important to choose the right speed rating if buying replacements.

Different Types of Tyre

On the market today you will find a wide range of tyres available which are manufactured specifically for different types of vehicle or scenario. Variants range from those designed for 4x4's, extra load or ‘reinforced', high performance and even seasonal tyres that offer optimal performance in summer or winter. As well as these, you will also find run flat tyres available for certain vehicles. These allow the driver to remain safely on the road for a short period of time in the event of a puncture using a reinforced sidewall. Knowing what type of tyre your vehicle is designed to use is crucial

As you can see, there is a lot of important information when it comes to tyre safety and understanding, particularly when it comes to load capacity and speed rating. It is vital that you know what these are, especially if you work in a commercial setting and if you plan on replacing your tyres so that you can find suitable ones which will be safe to drive on and maximise the performance of your automobile.

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