Tyre speed index - what is it and how do I adjust it?

The speed index of a tyre is a parameter that causes some consternation among many people. However, it is extremely important and should be taken into account when deciding on a new set of tyres. In this article, you will find out what it does, what it means, and the danger of using tyres with an incorrect speed rating.

Before buying new tyres, make sure they have the correct speed index.

When deciding to buy a new set of tyres, many motorists look first and foremost at the size. This is, of course, a key aspect of deciding whether a model will fit on the rims and the car. However, the speed index is also an extremely important factor, which is of great importance in terms of driving safety. The tyre should be chosen in such a way that it will not only be easy to fit but will also be able to meet the demands we are placing on it.

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What is the speed index of tyres?

When looking at the tyre labels, the speed index will undoubtedly be one of the first to catch the eye. This index indicates the maximum speed at which the tyre can be driven. It is important to know that this value refers to the driving of a vehicle with a maximum load, specified in a separate load index. As you can see, load index and speed index are closely linked and it is essential to pay attention to both factors when replacing tyres.

Find out more about the second marking in the article: The load index of a tyre - what is it and how to choose the correct one?

All car tyre markings can be found on the sidewall of the tyre. The speed index, together with the load index, is located next to the size. Special codes consisting of letters or letters and numbers are used to indicate its value. Each determines a different permitted speed. For example, the speed index H in code 225/50 R16 96H represents the maximum permitted speed of 210 km/h.

For all information on the symbols on the tyres, please refer to the text: Vehicle tyre labels - A complete guide

If you are wondering which speed index to choose, it is worth remembering that before changing your tyres it is essential to consult the information provided by the car manufacturer, e.g. in the vehicle handbook or on the so-called "rating plate" located at the fuel filler lid or on the door pillar. The tyres must meet the requirements contained therein. This also applies to the approved speed index. This is extremely important, as these findings take into account many important factors, such as the car's power, weight, and other important aspects that determine safety, but also driving comfort.

Is the speed index of motorbike tyres different from that of cars?

The speed index markings of car tyres, including truck tyres, do not differ from those used on motorbike tyres. The letters used indicate the same speeds. For example, on all tyres, the speed index V indicates a maximum speed of 240 km/h. It is worth knowing, however, that in the case of strictly racing tyres, intended for the track and not having road homologation, there may be no speed index marking at all.

Seasonal tyres vs speed index

It is worth knowing that the speed index on winter tyres may differ from that on summer versions. The major design differences between the two tyre versions are responsible for this. The former is made from softer compounds, while much harder rubbers are used for the latter. The tread patterns are also completely different and adapt to the road conditions at certain times of the year. How does this translate into a speed index?

According to the regulations, the speed index of summer tyres must not be lower than that specified by the car manufacturer. Failure to comply with this requirement means that there is a risk of the harder compound rubber breaking. This will be extremely dangerous at high speeds and often results in a serious accident. If, on the other hand, you choose a higher index, which is permissible, the car may drive more stably, but this will result in reduced wear and tear on the suspension components.

The speed index is indicated right next to the load index.

It is different for the speed index of winter tyres, which is governed by EU regulations. According to these established standards, these tyres may have a lower speed index than that recommended by the manufacturer, but this may not be lower than the Q index, which indicates a maximum speed of 160 km/h. If tyres with a lower speed index are fitted, this must be indicated so that it is visible to the driver. It is important to know that winter tyres generally use lower speed indices, as the rubber needs to be softer to provide better grip on snow.

Whilst it is legally permissible for winter tyres to use models with a speed index other than that recommended by the car manufacturer, it is worth remembering that such a solution should be a last resort.

Tyre speed index - the consequence of selecting the wrong parameter

Regardless of whether the speed index H or V or any other is recommended for your car, failure to follow the instructions will result in several consequences. The most dangerous is the risk of tyre blow-out. This is a dangerous situation that poses an immediate danger on the road. The car may also react differently to steering movements, which translates not only into less driving comfort but also into poorer control of the vehicle.

Failure to adjust the speed index may result in tyre blow-out.

It is worth bearing in mind that failure to comply with speed index guidelines often also has formal consequences. In the event of a road traffic incident or accident, the insurer may refuse to pay out compensation on the grounds of the wrong tyre choice. Furthermore, a person who uses the wrong tyre will lose the manufacturer's warranty. An unpleasant situation can also arise in the event of a routine check: the police officer can fine the driver for not having the right tyres on the car.

Tyre speed index – table

Before buying summer, winter, or all-season tyres, it is a good idea to become familiar with the speed index symbols. They are not complicated, and knowing them will make it much easier to choose the right tyre. It is important to know the maximum speed rating for your tyres and this has a direct impact on your safety. Below you will find a table containing the designations and the speeds assigned to them. A glance at the table may lead you to believe that the speed ratings are alphabetical, but a closer look will reveal slight differences, so it is worth bearing this in mind.

Speed Index ­­– table