Car tire sizes: what do the numbers and letters in the marking mean?

Choosing the right tires is key to driving safety and comfort. But the markings on the sidewall of the tire often look like a set of mysterious numbers and letters: 195/65 R15 91T. What do they mean? Why are some tires suitable for your car and others are not? In this article we will analyze each symbol, explain how to decipher tire sizes and why this is important for your car.

A mistake in choosing tires can lead to handling problems, increased suspension wear, or even failure to pass inspection. For example, if you install tires with the wrong profile or bore diameter, this will change the speedometer readings and affect the operation of the ABS. Let's figure out how to avoid such mistakes and learn to “read” tires like a pro.

Basic parameters: what do the numbers in tire sizes mean?

A typical tire marking looks like this: 205/55 R16 91V. All the key characteristics of the tire are encrypted here. Let's look at each element in order:

• 🔢 205 — profile width in millimeters. This is the distance between the side walls of an inflated tire (excluding protective belts, beech bars and markings).
• 📏 55 — profile height as a percentage of the width. In this example, the sidewall height is 55% of 205 mm, that is ~112.75 mm.
• ⭕ R16 - type of construction (Radial) and bore diameter in inches. Letter R means radial tire (99% of modern models), and the number 16 - the diameter of the rim on which this tire can be mounted.
• 🚗 91V — load indices (91 = 615 kg per wheel) and speed (V = up to 240 km/h).

It is important to understand that profile width and height - these are the overall dimensions, and bore diameter must exactly match the diameter of your disk. For example, a tire R17 won't fit on disk R16, even if the other parameters are the same.

Radial vs diagonal: why almost all tires are marked with the letter R

Letter R in labeling (for example, R15) denotes radial design cord - the threads that form the carcass of the tire. In radial tires, the cord threads are located perpendicular to the direction of movement, which ensures:

• ✅ Better traction due to uniform load distribution.
• ✅ Increased wear resistance (lasts 20–30% longer than diagonal ones).
• ✅ Less rolling resistance, which means reduced fuel consumption.

Diagonal tires (marked with the letter D or the absence of a letter in front of the diameter) are rare today—mostly on special equipment or vintage cars. They are cheaper, but inferior to radial ones in all key parameters. If you see the designation on the tire 185 R14 no letter before R, this is an outdated marking format where R does not mean radial construction, but just a word Radial (radius). Modern tires are always radial, so the letter R has become standard.

⚠️ Attention: If the tire indicates B or D instead of R, this is a diagonal design. Such tires are not recommended for installation on passenger cars due to worse handling and increased wear.

Load and speed indices: why they are safety critical

The last part of the marking (for example, 91T) contains two important parameters:

1. Load Index — a digital code indicating the maximum load on one wheel. For example, 91 corresponds to 615 kg. This does not mean that the tire will withstand 615 kg constantly - we are talking about the maximum load at maximum pressure.
2. Speed index - a letter code indicating the maximum speed at which the tire retains its properties. For example, T = up to 190 km/h, H = up to 210 km/h, V = up to 240 km/h.

Speed index	Max. speed (km/h)	Typical Application
L	120	Special equipment, trailers
T	190	City cars, crossovers
H	210	Sports cars, premium sedans
V	240	High speed cars
W	270	Supercars (Ferrari, Lamborghini)

Exceeding the speed index is fraught with tire destruction at high speed due to overheating. For example, if the index on the tire is H (210 km/h), and you are driving 230 km/h, the tires may burst. The same applies to overload: if the load index 88 (560 kg), and the wheel weighs 600 kg, the tire will quickly wear out or be damaged.

Additional designations: what the letters and pictograms on the side cover hide

In addition to the main dimensions, other important markings can be found on the tire:

• 🌧️ M+S (Mud + Snow) - dirt and snow. Indicates all-season or winter tires. But don't confuse it with 3PMSF (snowflake icon), which confirms compliance with winter standards.
• 🔄 Rotation and arrow - indicates the direction of rotation for asymmetrical or directional tires. Installation against the arrow impairs water drainage and adhesion.
• 📅 DOT XXXX — production date (week/year). For example, DOT 2523 means the 25th week of 2023. It is better not to buy tires older than 5 years, even if they are new.
• 🛡️ Reinforced or XL - reinforced tire with an increased load index (usually 3-4 units higher than standard).

There may also be pictograms on the sidewall:

• ❄️ — winter tires (required for use in Russia from December to February).
• 💧 Aquatred, Aqua - improved drainage properties.
• 🔊 Silent - reduced noise level.

What does the "Tubeless" marking mean?

This designation refers to a tubeless tire that fits tightly onto the rim and does not require a separate tube. Almost all modern passenger tires are tubeless. If there is no marking, it is a tube tire (an obsolete type, rarely used today).

How to choose tires by size: compatibility with wheels and car

There are three key rules to consider when choosing tires:

1. Bore diameter (R15, R17 etc.) must exactly match the diameter of the disk. For example, to disk 16 inches Only tires can be installed R16.
2. Profile width must match the width of the rim. A deviation of ±10–15 mm from that recommended by the manufacturer is allowed. For example, if the manual states 205/55 R16, you can choose 195/60 R16 or 215/50 R16, but not 185/65 R16 (too narrow).
3. Profile height affects ground clearance and suspension performance. Profile too low (40–45) impairs comfort on uneven roads, and too high (70+) may hit the arches when turning.

To check compatibility use tire calculator (for example, on sites Kama Tyres or Nokian). It will show how things will change:

• 📊 Wheel diameter (important for the speedometer).
• 🚘 Ground clearance (ground clearance).
• ⚙️ Suspension load.

⚠️ Attention: Installation of tires with a diameter other than the recommended one (for example, R17 instead of R16), requires disk resizing. Otherwise, the tire will either not sit on the rim or will wobble, which will lead to disassembly while driving.

Common mistakes when choosing tires and their consequences

Even experienced drivers sometimes make mistakes when buying tires. Here are the most common mistakes and their consequences:

Error	Consequences	How to avoid
Mismatch of landing diameter (R15 instead of R16)	The tire will not fit on the rim or will fall off while driving	Check disk markings (ET, PCD, diameter)
Profile too low (eg 40 instead of 55)	Shocks to the suspension, risk of damage to the discs	Do not reduce the profile by more than 10% of the recommended
Ignoring speed index (T instead of H)	Tire failure at high speed	Choose an index not lower than the original one
Installing tires of different sizes on one axle	Uncontrolled skidding, transmission wear	Change tires in pairs (at least on one axle)

It is especially dangerous to skimp on load and speed indices. For example, if for a car with the recommended index V (240 km/h) install tires with index T (190 km/h), when driving at a speed of 200+ km/h, the tires may burst due to overheating. The same applies to overload: if the load index 85 (515 kg), and the wheel weighs 600 kg, the tire quickly deforms.

How to read American tire labels (LT, P, T)

In the United States, an alternative designation system is used that may be found on SUV or commercial vehicle tires. Let's decipher the main prefixes:

• 🚛 LT (Light Truck) - tires for light trucks and SUVs with increased load capacity. For example, LT235/75R15.
• 🚗 P (Passenger) - tires for passenger cars. For example, P205/60R16.
• 🏗️ T (Temporary) - temporary tires (for example, T125/70D16). They have speed restrictions (usually up to 80 km/h) and mileage.
• 🚜 C (Commercial) - tires for commercial vehicles (minibuses, vans). For example, 195R14C.

American markings may include additional designations:

• XL or Extra Load — reinforced tire with increased load index.
• SL (Standard Load) — standard load.
• BSW (Black Side Wall) - black sidewalls (without white stripes).

If you see a type marking 31×10.50R15, this inch format, popular in the US for SUVs. Here:

• 31 — outside diameter of the tire in inches.
• 10.50 — profile width in inches.
• R15 — landing diameter.

FAQ: answers to frequently asked questions about tire sizes

Is it possible to install tires with a different speed index if it is higher than the original one?

Yes, you can. For example, if the manufacturer recommends an index H (210 km/h), you can install tires with index V (240 km/h) or W (270 km/h). It's safe and even useful if you drive at high speeds. The main thing is not to install tires with below speed index.

What happens if you put tires with a smaller diameter (for example, R15 instead of R16)?

Reducing the wheel diameter will lead to:

• Inflated speedometer readings (5–10 km/h more than actual speed).
• Deterioration of controllability at high speeds.
• Risk of damage to the suspension due to changes in ground clearance.

In addition, such tires may not fit over the brake mechanisms (if the diameter is too small).

How to find out the recommended tire size for your car?

There are several ways:

1. Look at the sticker on the driver's door pillar or in the glove compartment.
2. Check the vehicle's operating manual.
3. Enter the vehicle's VIN on the tire manufacturer's website (for example, Michelin or Continental).
4. Use online selection services based on car make and model.

Is it possible to install tires of different widths on the front and rear axles?

Yes, but with reservations:

• The difference in width should not exceed 20–30 mm (for example, 205 front and 225 rear).
• On four-wheel drive vehicles, this may adversely affect transmission performance.
• Tires on one axle necessarily should be the same.

It is better to consult with a car service before such installation.

What does the "E" in the circle on the sidewall of the tire mean?

Letter E in a circle (for example, E4 023456) is the European approval mark (E-mark). Number after E indicates the country that issued the certificate (for example, 4 - Netherlands), and the remaining numbers are the approval number. Without this sign, tires do not comply with European safety standards.