Sidewall markings

Tyre size is the most important information given on the tyre. The size designation is specified as a series of numbers and letters, for example, 205/55 R 16 94 V XL, where:

205 is the width of the tyre in mm
55 is the aspect ratio (height to width ratio)
R denotes radial construction
16 is the rim diameter in inches
94 is the load index
V is the speed rating
XL Extra load capacity.

The speed rating shows the maximum continuous driving speed capability of the tyre. The speed rating to be selected depends on the make and model of car. The use of tyres with speed ratings that are too low can affect the driving qualities and tyres with speed ratings that are too high may reduce driving comfort.

The most important speed ratings are:

Q = 160 km/h
R = 170 km/h
S = 180 km/h
T = 190 km/h
H = 210 km/h
V = 240 km/h
W = 270 km/h
Y = 300 km/h

Are you confused by the tyre information in your car's registration document? Here's how to read it properly

Does the sequence 205/55 R 16 94 V XL say anything to you? You can find this alphabet soup in your registration document, and it will tell you the type of summer tyre that fits your car. However, registration documents often contain several tyre choices, allowing the driver to choose one based on whether they value driving comfort or a sensitive steering feel, for example. Read below for information that you should take into account to find tyres that are right for you.

What do the first two figures in the marking 205/55 R 16 94 V XL tell us?

They tell us the width of the tyre and its profile. In this case, the car accepts a tyre that is 205 millimetres wide. The tyre profile refers to the ratio between the height and width of the tyre. In this case, the height of the tyre is 55 per cent of its sectional width.

The registration document also offers a tyre with a width and profile of 225/45. Which one should you choose?

In this option, the tyre is 20 millimetres wider than in the first example, and it has a substantially lower profile.

A wider, lower-profile tyre has a better steering feel than a narrower, higher-profile tyre. This means that the tyre will be more sensitive to the driver's steering movements. A tyre like this is suited for a driver who values quick steering response and a sporty feel.

On the other hand, a wide tyre will be more sensitive to the grooves in the road, and so a driver looking for more comfort may be tempted to select a narrower, higher-profile tyre.A narrower tyre is also safer on wet roads, as it will displace water better than a wider tyre.

What does the letter R that follows the width and tyre profile tell us?

It indicates the tyre structure. R refers to a radial tyre, which is much more stable and precise than its predecessor, the bias-ply tyre.

All passenger car tyres sold in Finland today are radial tyres, so the driver does not really need to pay much attention to this marking.

The number 16 that follows tells us the rim diameter in inches. What should we take into account when choosing rims?

It is important to follow the car manufacturer's instructions. For example, sportier cars will often require rim sizes of 17–19 inches, as smaller sizes will not be able to accommodate the brake systems.

Especially when fitting aftermarket rims and tyres, you should pay attention to choosing the correct tyre width for your rims. Large rims require low-profile tyres, whereas smaller rims are suited for higher-profile tyres. In other words, if a car requires rims of a size above 16 inches, the driver can no longer choose a higher-profile tyre, even if they value driving comfort over a precise driving feel.

What does the last figure in the tyre marking tell us?

The last figure is the load index. In our example, the load index is 94, which means that one tyre can carry a load of 670 kg. For load index 91, the load per tyre is 615 kg. You should choose the correct load index for your car since, otherwise, the tyres will wear out quicker than usual and they may become damaged while driving.

The penultimate letter V gives us the speed rating, or the highest allowed speed for the tyre. What difference does it make in Finland, since the highest speed limit here is 120 km/h?

V means that the tyre cannot be driven above 240 kilometres per hour. While it is true that these speeds are illegal in Finland, an EU directive states that the tyre's speed rating must match the vehicle's top speed. This makes the tyres safe for when you go on holiday in Germany, for example.

You should also follow the car manufacturer's recommendation when choosing the speed rating because a lower rating may have an adverse effect on the car's handling characteristics, such as steering. A higher speed rating, on the other hand, will reduce driving comfort.

The last letter combination “XL” is not found in all tyre markings, why is that?

XL means that the car is suitable for an Extra Load index tyre. In our example, the load index is 94. If the index were 91, the XL marking would not be required.

Most tyre models offer an Extra Load model and a normal load model. An Extra Load model can carry a heavier load, which means that even if you pack more for your summer holiday, you do not need to worry about breaking your tyre due to excess load or wearing it out quicker than normal. The sturdier structure of an Extra Load tyre means lower heat generation, which makes it more tolerant of wear.

What does the DOT marking on the tyre's sidewall indicate?

This marking makes it easy to check the tyre's place of manufacture and age. The two first markings indicate the factory where the tyre was made. The four last digits indicate the week and year of manufacture. If the code is 1314, for example, then the tyre was manufactured in week 13 of 2014.

The recommendation is to use the same tyres for a maximum of six years. Even if you do not use your car frequently in the summer, and your tyres appear to be in good shape, you should nevertheless replace them at the latest when ten years have passed since their date of manufacture. Over the years, the rubber compound will harden and the tyres will lose grip, even if the tyres do not wear out otherwise.