Indices on summer tires: full decoding of markings

Every driver when buying a new tire is faced with mysterious alphanumeric codes on the sidewall of the tire. To the inexperienced motorist, these symbols may seem like a marketing package, but they determine how safe your car will feel on the road. Incorrect choice of parameters can lead to cord rupture, aquaplanning or even accidents at high speed.

In this article, we will discuss in detail what the indexes on summer tires mean, how to read the marking correctly and why you can not ignore the recommendations of the car manufacturer. Understanding these nuances will help you save money and, more importantly, save your life.

Basic marking and place of indices on the sidewall

Searching for the right information on the sidewall of the tire is the first step to a competent choice. Usually all key data are grouped in one line after the size is specified. For example, in the marking 205/55 R16 91V The numbers and letters at the end are the indexes that we are interested in. Number. 91 It indicates the permissible load, and the letter V - at maximum speed.

Many drivers mistakenly believe that these parameters are only important for racing tracks. In fact, summer tires operate in extreme temperature conditions, where the rubber mixture overheats much faster than in winter. That is why the speed index corresponds to real operating conditions is a critical safety factor.

It is worth noting that manufacturers apply markings on different sides of the wheel. If you do not find the right numbers from the outside, look at the inside of the tire. Sometimes, especially on high-end brands like Michelin or Bridgestoneduplicative information can be printed in small print next to the landing rim.

Load index: calculation of permissible weight

The first number in the codechain, following the size, denotes the load index. This is not a direct weight in kilograms, but a conditional coefficient, which corresponds to a certain mass. For example, the index 91 This means that one wheel has a permissible load of 615 kg. For a passenger car, the total load capacity of four tires should exceed the total weight of the equipped car with passengers and cargo.

Ignoring this parameter when buying summer tires for a crossover or a loaded van is fraught with serious consequences. When exceeding the limit weight, excessive deformation of the sidewall, heating and eventual rupture of the frame at high speed occurs. This is especially true for the summer period, when the asphalt is hot, and the resistance to rolling increases.

It is important to note that the load index is designed for movement at a certain speed. If you are planning a long trip at high speed with a full load of the trunk, it makes sense to choose tires with a margin of safety. For example, instead of the minimum inx of 91, it is better to take 94 or 95.

⚠️ Note: Installation of tires with a load index below the recommended car manufacturer is prohibited by law and may lead to denial of insurance indemnity in case of an accident.

For accurate selection, you need to know the curb weight of your vehicle. This information can be found in the technical passport or on the plate located on the driver's door counter. Always round the result in a big way.

Speed Index: letter designations and limitations

The letter symbol immediately after the load numbers indicates the maximum speed that the tire is able to withstand at full load. Summer tires usually have higher indices than winter tires, since the composition of the rubber mixture is designed to work at high temperatures. However, this does not allow you to constantly exceed the speed limit.

Common indexes for passenger cars vary from H (up to 210 km/h) Y (up to 300 km/h). If you own a sports sedan with an index Wtyre installation marked T (up to 190 km / h) is absolutely unacceptable, even if you do not plan to accelerate above 150 km / h. The design of the cord and the tread pattern simply will not withstand dynamic loads.

There is a rule according to which on the car you can install tires with a speed index above the recommended, but not lower. This is because a stronger tire design won’t harm the suspension, while a “weak” rubber can burst.

Table of conformity of load and speed indices

For ease of decoding the markings on summer tires, a summary table is given below. This will help you quickly determine the physical limitations of your tires. It is recommended to save this data or take a picture of the table before going to the store.

Note that the load values are nonlinear. The difference between neighboring indices can be from 10 to 30 kg or more. Therefore, when switching to larger-radius disks (for example, from R15 to R17), the bus profile becomes lower, and the load on the sidewall increases, requiring a recalculation of the index in a larger direction.

It is also important to remember seasonality. Winter tires often have double speed markings, for example, Q/HThis means that it can be used under different conditions, but for the summer period only one value is valid – the main symbol.

Additional markings and special indices

In addition to the main figures, on summer tires you can find additional designations that affect performance characteristics. For example, letters XL or Reinforced It indicates a reinforced sidewall design. These tires have a higher load index and are designed for heavy vehicles or bad roads.

Another important parameter is the adhesion and temperature resistance index, which is often denoted by the letters AA, A, B or C. Temperature index is critical for summer tires A or AAIt ensures that the rubber does not “float” during long-term movement on hot asphalt.

• 🔵 RunFlat (RSC, ZP, SSR) The technology allows you to travel up to 80 km on a flat wheel. These tires have rigid sidewalls and require a pressure control system.
• 🟢 Green X, EPIQ - Marking of environmentally friendly tires with low rolling resistance, which reduces fuel consumption, but may slightly worsen traction.
• 🔴 M+S Although it is a marking for dirt and snow, it is common on summer all-season tires, but does not guarantee safety in the cold.

The presence of these symbols can affect comfort and noise. Reinforced tires or models with ranflat technology are often tougher than usual, which should be considered by owners of cars with low-profile rubber.

Installation rules and seasonal nuances

When installing summer rubber, it is necessary to strictly observe the direction of rotation, if the tread is directed. This is indicated by an arrow with an inscription. Rotation. Violation of this rule will lead to rapid wear and aquaplanning effect, since the grooves will not be able to drain water efficiently.

There is also a rule for installing tires with different speed indices. If you have to use a set with different parameters, then tires with a higher speed index should always be installed on the rear axle. This ensures the stability of the car and prevents the skidding of the rear during sharp maneuvering.

⚠️ Warning: It is forbidden to install tyres with different speed indices on one axle. The difference is only allowed between the front and rear axles, and then temporarily.

Don't forget the pressure in the tires. Tires with a high load index (XL) often require slightly more pressure than standard models. The exact values are indicated on the plate in the doorway of the car, not on the tire itself.

Frequent questions about tire labeling (FAQ)