When choosing new tires for a car, the driver is often faced with a set of incomprehensible numbers and letters on the sidewall. To an inexperienced person, this looks like a complex code that cannot be deciphered without the help of a specialist. However, knowledge of these symbols is critical to the safe operation of the vehicle.
Correctly selected size affects acceleration dynamics, fuel consumption and road grip. The wrong choice can lead to damage to the suspension or even a high-speed accident. That is why it is necessary to learn to read the labels yourself.
In this article we will analyze each code element in detail. You will understand the difference between a radial design and a diagonal design and why the load index cannot be ignored. This knowledge will save you time and money when purchasing a new kit.
Basic markings and profile geometry
The most noticeable part of the inscription is a combination of numbers separated by a slash. For example, in the notation 205/55 R16 The first number indicates the tread width in millimeters. The wider the tire, the better the grip on dry asphalt, but the higher the risk of hydroplaning.
The second number after the slash indicates the profile height as a percentage of the width. This often causes confusion as many people think it is millimeters. If we take our example, the sidewall height will be 55% of 205 mm, which is approximately 112 mm.
⚠️ Attention: Installing tires with a profile below 50% on bad roads is not recommended. The risk of disc damage and hernias on the sidewall increases.
Low-profile tires improve handling, making the car more responsive when cornering. However, comfort when driving over uneven surfaces is significantly reduced. The driver will feel every hole and junction of the road surface.
How does changing the profile affect the speedometer?
When changing the profile height, the overall diameter of the wheel changes. If the new wheel is larger than the stock one, the speedometer will show less than the actual speed. This may result in speeding tickets.
When replacing a size, it is necessary to recalculate the total diameter to avoid errors in instrument readings.
Cord design and bore diameter
The letter following the profile numbers indicates the cord construction. The vast majority of modern passenger cars use a radial design, marked with the letter R. The cords in such tires are located perpendicular to the circumference of the wheel.
There are also bias tires, where the threads are woven at an angle. They are marked with the letter D, but are extremely rare and mainly on old equipment or special vehicles. For passenger cars, only radial technology is relevant.
The last number in the main group is the mounting diameter of the disk in inches. It is this parameter that determines whether the tire will fit on your rim. Standard values vary from 13 to 22 inches depending on the vehicle class.
The letter R does not mean radius, it is a marking of the radial construction of the cord. The bore diameter is always indicated in inches.
When selecting disks, it is necessary to strictly observe the mounting diameter. It is impossible to fit an R15 tire onto an R14 or R16 wheel, since the dimensions of the mounting hole do not physically match.
Load indices and speed limits
The size is often followed immediately by a combination of a number and a letter, e.g. 91V. The number here is the load index, showing the maximum weight that one wheel can support. For index 91 this value is 615 kg.
The letter index indicates the maximum speed at which the tire maintains its characteristics. Exceeding this limit may result in structural failure due to overheating. The correspondence table is an international standard.
| Speed index | Max. speed (km/h) | Load index (example) | Weight per wheel (kg) |
|---|---|---|---|
| T | 190 | 88 | 560 |
| H | 210 | 91 | 615 |
| V | 240 | 94 | 670 |
| W | 270 | 98 | 750 |
Installing tires with a load index lower than that recommended by the vehicle manufacturer is prohibited. This can lead to a tire explosion when the car is fully loaded or driving on a bad road.
The speed index also affects the rigidity of the frame. Tires with a high index (W, Y) have a stiffer sidewall to hold their shape at high speeds, which can feel like an increased ride harshness.
Seasonality and additional designations
Manufacturers use special markings to indicate the season of use. Winter tires are marked with a snowflake symbol against a mountain background (3PMSF) or letters M+S. Summer models do not have a special pictogram, but may be marked "Summer".
All-season tires are often referred to by the abbreviation AS (All Season) or AW (All Weather). However, it is worth understanding that versatility always sacrifices efficiency in extreme conditions.
⚠️ Attention: The M+S (Mud + Snow) marking is often found on summer off-road tires. It does not guarantee the properties of winter tires at temperatures below +7 degrees.
Also on the sidewall you can find a designation of the direction of rotation. Arrow Rotation indicates which way the wheel should turn when moving forward. Violation of this rule dramatically worsens water drainage.
There are tires with an asymmetric tread pattern. There are inscriptions on them Inside (inner side) and Outside (external side). When mounting on a rim, it is important not to mix up the sides, otherwise the tire will not function correctly.
Production date and wear resistance
Rubber ages over time even without use, losing elasticity. The production date is stamped in an oval stamp and consists of four digits. The first two are the week, the second two are the year of release.
For example, code 3523 means the tire was manufactured in the 35th week of 2023. It is not recommended to buy tires older than 5-6 years, even if the tread looks new.
When purchasing new tires from a store, always check the production date on all four wheels. Often the display cases contain products from previous years.
In addition to the date, the wear resistance class may be indicated on the tire. Treadwear. The base value is 100 units. If 200 is indicated, it means that theoretically such a tire runs twice as long as the base model.
However, the actual resource depends on driving style, tire pressure and suspension condition. Soft sports tires have a low wear index but provide better grip.
Compatibility check and size chart
Before you buy new tires, you need to make sure that they fit your car. Information about acceptable dimensions is usually located on the driver's door pillar or in the gas tank flap.
Using tires that are too wide can cause them to rub against the arches when turning the steering wheel or loading. Tires that are too narrow will not be able to support the weight of the vehicle and will wear out quickly.
☑️ Check before purchase
When changing tire sizes, it is important to keep the overall wheel diameter close to factory. The permissible deviation is usually no more than 2-3%. This will maintain the correct operation of the ABS and ESP systems.
To accurately select analogues, you can use tire calculators. They automatically calculate changes in ground clearance and speedometer readings when installing a non-standard size.
Is it possible to install tires with a load index higher than the original?
Yes, you can. Installing tires with a higher load index is acceptable and often even beneficial for improving stability. The main thing is that the index is not lower than the factory one.
What happens if you mix up the inner and outer sides of an asymmetrical tire?
The tire will not work efficiently. The inner part of the tread is responsible for draining water, and the outer part is responsible for grip when turning. By mixing up the sides, you will compromise security.
How often should you change your tires, even if the tread is still deep?
The recommended service life of rubber is 5-6 years from the date of production. After this, the material hardens, cracks and loses its grip properties, regardless of the tread height.