Trying to decode a tyre’s sidewall without any prior knowledge is enough to leave your head in a spin. The reality, however, is that it’s pretty simple.
To help you get to grips with tyre markings, we’ve created this nifty guide. Want to quickly find out the physical measurements of your tyre? Check out our ‘Find Your Tyres’ tool.
When it comes to staying safe on the road, tyres are among the most important components of your vehicle. Whether you’re steering, braking or drifting along, they are at the epicentre of the action. After all, this is the only part of your vehicle which actually touches the ground. Thus, when it comes to tyre replacements, it’s crucial you get it right.
Enter, tyre markings. These are used to identify the specifications and physical features of a tyre, so you can find a replacement which works in tandem with your vehicle. While a few of these tyre markings are of little importance, most of them have a significant effect on performance and safety – so it’s important to get right.
“While tyres might look like they are just rings of rubber, each one is unique. Therefore, it’s crucial that you double-check your tyre markings before confirming any booking. Not doing so could result in you purchasing tyres that are incompatible with your vehicle and, thus, can’t be fitted. When in doubt, always get in touch with our friendly advisers for help and advice.”
It will probably come as no surprise that tyre labels are etched into a tyre’s sidewall (i.e. the external side facing you). But what you might not know is that you can find information relating to your manufacturer-recommended tyres in a few other places too, including:
It’s worth bearing in mind that your tyre’s sidewall only represents the specifications for that particular tyre. To be sure that a tyre is compatible with your vehicle, you should consult your owner’s manual or one of the above places.
When in doubt, you can also get in touch with the Tyres on the Drive team.
A tyre sidewall contains a lot of information. So, let’s start by focussing on the short sequence of letters and numbers which represent the size code.
We’ll use the example: 225/55 R 18 95 H
The next number in the sequence is “225.” This represents the tyre’s width in millimetres – measured from sidewall to sidewall.
The following two numbers (“55”) represent the aspect ratio – or measurement of the sidewall height (in mm). Essentially, this is the ratio of the tyre’s cross-section to its width. So, in the above example, a tyre that has an aspect ratio of 55 would have a height equal to 55 per cent of its width.
Next up is a letter. This tells you how a tyre is constructed. In this example, the “R” means that the tyre has radial construction. This is where the internal ply cords extend across the casing from bead to bead, in a radial direction.
Less common tyre constructions include diagonal or bias ply, represented by the letter “D”.
The next number represents the diameter code. Unlike the width, this is shown in inches. This is particularly important because it represents the diameter of the wheel rim. In the above example, the number “18” means that the tyre should be matched to a rim wheel of 18 inches.
After the rim diameter, we find the load rating. This tells you the maximum capacity of a passenger car tyre when it is inflated to its maximum safe pressure. The figure (in this example, “95”) refers to the index rather than the weight. As such, you will need to consult a load index table (below) which determines the load in kg for each rating. For a load index of “95”, the maximum load weight is 690kg/tyre.
|Load index||Load in kg||Load index||Load in kg||Load index||Load in kg|
The final tyre marking in this string represents the speed rating. As you might have guessed, this denotes the maximum speed a tyre can sustain when it is correctly inflated and under load. As with the load index, this letter references a look-up table which indicates the maximum permissible speed of a tyre. In this example, “H” means the vehicle has a maximum speed of 130mph under the maximum load.
|Speed rating||Mile /hour||Kilometers /hour||Speed rating||Mile /hour||Kilometers /hour|
“Although a speed rating table references the maximum speed a tyre can move under load, you should not use this as a threshold. Always drive at the speed limit and do not put your tyres under any undue stress.”
Aside from the above tyre size sequence, you may see a handful of other tyre markings. These could include:
Fitting tyres with different speed or load ratings can cause big problems if you don’t understand what these are and what your vehicle is equipped with. Let’s start with what each of these values represents:
The speed rating on a tyre converts to a maximum speed that the tyre is manufactured to travel at, in conjunction with a specified weight. This rating determines how well the tyre copes with cornering, acceleration and braking.
The load rating on a tyre converts to a maximum weight that each tyre is manufactured to support at a specified speed. The UK law requires the load rating to be equal to or higher than the tyre that is recommended by the vehicle manufacturer for the tyre size that is fitted.
“The only exception to fitting a lower speed rating to a vehicle is when you come to fit winter tyres to your vehicle – as long as you don’t exceed the tyres maximum speed limit.”
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