Is it time to change your car's tyres? At some point we all have to do it, as the wheels wear out and no longer offer the same grip or efficiency when driving.
But what tyres does your car have? It is extremely important to know, as you cannot buy just any tyre! Let us explain how to find out.
Why is it so important to know what wheels your car has?
Before buying new ones, whether you are going to buy second-hand tyres or new ones, it is extremely important to take a look at the old tyres to know exactly which ones you can buy.
Why? It is simple: if you buy tyres that are too wide or too tall, the car will not handle properly, especially if you are only changing a pair of wheels.
For this reason, it is important that you either buy the official tyres for your car's make or that they are compatible, but meeting certain conditions.
How can I find out what tyres my car has?
Well, the answer to this question is much simpler than it seems. What you need to do is look at the sidewall of the tyre, where you will find several printed codes that will tell you its characteristics and specifications.
Now let us look at what each one means and which ones you should pay attention to:
Tyre width
The first number you will see in the code refers to the tyre width, expressed in millimetres. This ranges between 125–335 millimetres. Your new tyres cannot exceed the original ones by more than 30 mm.
For example, imagine your old tyres were 200 mm — the new ones can be a maximum of 230 mm.
Wheel height
The next number indicates the height of the tyre, expressed as a percentage. For example, if it said 45, it would mean that the height is 45% of the total width.
This number is also very important, because if the height percentage is much higher than the manufacturer's, the wheel will not fit properly and you will find it hard to control the tyre, especially when cornering.
Tyre radial
After the previous numbers you will find a letter, the R, which indicates the radial. Nowadays, virtually all tyres are radial, although there are still older models known as diagonal tyres, which are made up of different overlapping and crossed layers.
The diameter
Right next to the R you will find a number referring to the diameter of the outer edge of the rim, expressed in inches. This can range between 10–23 inches.
If you are looking for slightly larger tyres, the margin will be 3% with respect to the originals.
Load index
The next number indicates the maximum load the tyres can support. To cross-reference the number with the weight, there are tables that allow us to find out the maximum supported load.
It is very important that the new tyres do not have a lower load index — it must always be equal to or higher than the previous ones.
Maximum tyre speed
Finally, there will be a letter indicating the maximum speed at which the vehicle can be driven safely. This ranges from A, which is the lowest, to Y, which is the highest. However, as an interesting fact, H refers to a high speed of 210 km/h.
What if I buy compatible tyres?
Sometimes we can opt for tyres that are compatible with your car's make, which are much cheaper than the brand's own tyres.
However, these must meet a series of requirements, as otherwise you will be penalised when you take the car for its MOT.
These are the most important points:
Approved dimensions
As we have already mentioned in the previous point, there is a maximum difference in tyre size. If the margin exceeds or is below 3%, you could be penalised when taking the car for its MOT.
On the other hand, and although it may seem obvious, it is extremely important that the size of all four tyres is identical, otherwise you could have problems while driving.
Same axle type
Another mandatory point is that the axle of the two wheels must be of the same type, meaning the same size, tread pattern and category.
To make it clear: you cannot have a winter tyre on one side and a summer tyre on the other. They must be the same. Of course, ideally all four tyres should be identical, but the law allows one axle to have a different brand or tread pattern, as this allows for balanced behaviour.
The load index and speed rating
To find out exactly this figure for your next tyres, we advise you to check the MOT card, which will specify those required by the manufacturer.
For example, if the car has a speed code W and a load index of 95, never look for tyres that are lower. You need to find ones that are equal or higher.
In fact, it is prohibited to drive with a speed rating lower than the approved one, whereas a higher one does not incur any penalty.
How to find out what rims my car has?
If you are going to take the opportunity to change the rims, it is important that you know which model they are. But where can you find out what type of rim your car has?
You can find it on the label on the driver's door, the vehicle manual or the vehicle's technical data sheet. If the rim is not too worn, you can also look at it to find the code that will tell you the size.
Label on the driver's door
This label, as a general rule, is stuck on the driver's door frame, and indicates the rim size recommended by the manufacturer along with the correct inflation pressure.
Vehicle manual
If you still have the vehicle manual, which is recommended, you will also find the recommended rim sizes there.
Vehicle technical data sheet
When you take your car for its MOT, you will be given a technical data sheet indicating the approved rim sizes for your vehicle.
Understanding the code on the sidewall of the rim
Have you decided to find out the type of rim your car has by looking at the sidewall? Great, so let us see what each part of the code means. Let us suppose it reads: 225/55 R17 97W.
· The 255 refers to the tyre width in millimetres.
· The 55 refers to the tyre height, expressed as a percentage of the width.
· R17 gives us two pieces of information: the R specifies that it is a radial tyre (if it is a different type, it will have a different letter), and the 17 is the diameter of the rim's inner ring in inches.
· Finally, 97W is the load index and speed rating.
As you can see, the code has a very similar interpretation to that of the tyre. And, just like the tyre, you must follow these specifications when buying a new rim.
Remember that they are not universal, so not all of them are suitable for all wheels.
What should I do if I change my tyres for ones with different characteristics?
You may decide to replace your old tyres with ones that have greater power, reach higher speeds, are a little taller…
Do you need to do anything in this case? Indeed, you are required to have the change approved at the MOT. Although going through the inspection can be a little inconvenient, it will allow you to drive without worry as the tyres will have been approved by the MOT technicians, and you will save yourself problems in the future.