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How to Read Tyre Markings
Posted on July 15, 2018 – Car Maintenance
Have you ever wondered what the markings on the sidewall of your tyres mean? Although it may look like the encrypted code of a secret, occult society, that text actually gives you invaluable information about your tyre and how to look after it. And the health of your tyres is crucial as it will impact on your fuel consumption and, most important of all, your safety. So let’s take a look at what means what.
Brand and model
This one is easy and doesn’t require too much guessing. The tyre wall shows the brand and model of the tyre. If you need to have it changed, you will be asked for that information. It will also enable a tyre workshop to look for equivalents if you are looking into buying a similar but cheaper tyre. However, you should note that if you are considering mixing tyres, the same model must be fitted on the wheels of the same axle. Not doing so is dangerous and would lead your car to fail its Warrant of Fitness whether it be during its annual routine check of during import.
Tyre profile
Right, let’s go into the meaty stuff: ‘245/40 ZR19 (96Y)’.
This esoteric string of numbers and letters tells you a lot about the specifications of your tyres. In this case, it means that your tyre is 245mm wide. Now, get your calculator out for the next part: the number 40 indicates the ratio of the height of the sidewall to the tyre’s width, i.e. in this example 245 x 40% = 98mm so the tyre is 98mm high.
The ‘R’ refers to the type of construction of your tyre. ‘R’ stands for ‘Radial’ which is the most common type of tyre nowadays. It means that the plies are perpendicular to the direction of travel. It is a modern standard though so, on older classic cars you may find a ‘D’ instead, for ‘Diagonal’ which means that the plies overlap one another.
The figure ‘19’ simply indicates the rim diameter of the wheel the tyre is designed for.
Choosing tyres with a lower profile (height) will give you a greater control over the car in corners but it will make for a harder ride. If you decide to do that, don’t mix your tyres and change them all as a combination could lead to a loss of control of the back tyres sending you into a spin.
In addition, a low-profile tyre fitted on the same size wheel will give you false speedometer readings so you will need this adjusted.
It is also important to remember that using tyres that are not of the type recommended by the manufacturer can void your insurance so you may want to give them a ring before you commit to this type of customisation.
You may occasionally come across other markings such as ‘F’, for ‘Flat’, which means that you can drive your car slowly for a short distance if you have a puncture, which can be very useful, typically, this would mean around 50km at speeds under 50km/h.
Handling bad weather
You may encounter the marking ‘M+S’ on your tyres, which means that they are able to cope with some mud and snow. However, it is important to understand that they are not snow tyres and aren’t sufficient for mountain weather. They just offer better grip in mildly challenging conditions.
Snow tyres can be identified by their graphic of a mountain with a snowflake on their sidewall. They are made with a softer rubber compound and deeper treads to improve grip on the ice and in snow. They must have a tread at least 50% greater than that of normal summer tyres to be road-worthy in NZ, and at least a 4mm depth. They can also be recognised by their square-patterned tread blocks with fine blades.
Due to several fatal accidents in the past, the New Zealand Transport Agency (NZTA) prohibits mixing snow tyres and normal tyres, and a car with mixed tyres will fail its Warrant of Fitness inspection.
The NZTA advised that our climate didn’t generally warrant the need for snow tyres in the winter so you are unlikely to find them if you purchase a car from your local dealer, but they are found quite often on cars imported from the colder parts of Japan. If your Japanese import appears to have snow tyres fitted, arrange for them to be changed to the summer type when you import it into NZ.
Load index
96Y is what is called the service description of your tyre. The number 96 is the load index and indicates the weight the tyre can carry. It isn’t a direct equivalence, so 96 doesn’t mean that each tyre can carry only 96kg.
The load index is calculated by dividing the weight of the vehicle by 4, the number of tyres, to get the load per tyre. To that, at least 20% is added for passengers and luggage. In practice, cars are always fitted with tyres with a much higher load index that they will ever need.
The letter after the number indicates at which maximum speed the tyre is safe to be driven. There is an array of speed ratings, and the letter ‘Y’ is the best and can be driven at 300km/h.
Maximum load & tyre pressure
If you are importing a car from the US, you may see a ‘Max Load ‘ and ‘Max Press’ (pressure) as it is a legal requirement in the country. ‘Maximum pressure’ is not the same as ‘Recommended pressure’, which will be in the owner’s manual. It is not recommended to inflate your tyres to the maximum pressure allowed as it will damage them.
So there you go, tyres hold no more mystery to you now and you will be able to take better care of them.
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