Tire marking: how to decipher tire sizes and avoid mistakes when purchasing

Choosing the right tires for your car is a task that requires attention to detail. Even experienced drivers sometimes get confused by the designations on the sidewall of the tire, where key parameters are encrypted: width, profile, diameter, speed and load indices. An error in decoding can lead to the purchase of unsuitable tires, which will affect the safety, controllability and even legality of operating the car.

In this article we will look at every number and letter in tire marking using the example of a popular size 195/65 R15 91T, we will explain how these parameters affect the behavior of the car, and warn against common mistakes. You will also find correspondence tables and practical advice on selecting tires for specific operating conditions.

If you've ever wondered, "What does the R in tire size mean?" or “is it possible to install tires with a different load index?”, this material will help you understand everything without fuss and unnecessary technical terms.

1. Main markings: what do the numbers 195/65 R15 mean?

The most noticeable block on the sidewall of a tire is its size, e.g. 195/65 R15. These numbers and letters describe the geometric parameters of the tire, which determine whether it will fit your car. Let's look at them in order:

• 📏 195 — tread width in millimeters. This is the distance between the side walls of an inflated tire (excluding bulges from letters or designs). The higher this value, the wider the “sole” of the tire and the better the grip, but the higher the risk of aquaplaning on wet asphalt.
• 📉 65 — tire profile (sidewall height) as a percentage of its width. In our example, the sidewall height is 65% of 195 mm, that is, ~126.75 mm. Low profile tires (such as 40 or 35) improve handling but make the ride harsher.
• 🅱️ R - designation of radial cord construction (the most common type of tire today). Sometimes mistaken for "radius", but this is incorrect. Letter B (obsolete diagonal design) or D (diagonal) are extremely rare.
• 🔄 15 — tire mounting diameter in inches, corresponding to the diameter of the rim. This is the only parameter that must match exactly with the vehicle manufacturer's recommendations. Installing a tire with a different diameter (for example, R16 instead of R15) will require replacing the rims.

Important: some manufacturers indicate the size in inches (for example, 31×10.5 R15 for SUVs). Here the first number is the outer diameter of the tire in inches, the second is the width, and R15 is the seat diameter. This marking is typical for light truck rubber (LT).

⚠️ Attention: If the tire size is indicated 195/65 R15, and on the disk - 6Jx15 ET45, digit 15 must match! A discrepancy in diameter will lead to impossibility of installation or damage to the tire.

2. Load and speed indices: what do the 91T numbers hide?

After the size on the tire there are always two key parameters - load index and speed index, for example, 91T. They are often underestimated, but they directly affect safety:

• 🏋️ 91 — load index. This is a conditional number that indicates maximum permissible weight, per one wheel. For passenger cars, typical values ​​are from 80 (450 kg) to 100 (800 kg). In our example 91 corresponds 615 kg per wheel.
• 🚗 T — speed index. The letter stands for maximum speed, at which the tire retains its properties. T allows driving up to 190 km/h. Exceeding this limit leads to overheating of the rubber and the risk of rupture.

Below is a table of the most common indices for passenger cars:

Load Index	Max. load (kg)	Speed index	Max. speed (km/h)
80	450	Q	160
85	515	S	180
91	615	T	190
95	690	H	210
100	800	V	240

Critical error: install tires with a speed rating lower than that recommended by the vehicle manufacturer. For example, if the instructions indicate H (210 km/h), and you set T (190 km/h), this will lead to denial of insurance in case of an accident at high speed.

3. Additional symbols: what else is written on the tire

In addition to the size and indexes, you can find a lot of other useful information on the sidewall of the tire. Here's what else you should consider when choosing:

• 🌍 DOT - manufacturer code and production date (for example, DOT XXXX 2523 means the tire was released in the 25th week of 2023). The freshness of the rubber is critical: even an unused tire older than 5 years loses its elasticity.
• ❄️ M+S (Mud + Snow) - designation of winter or all-season tires. However, since 2026, a rule has been in effect in Russia: labeling is required for winter 3PMSF (snowflake against the background of a mountain). M+S without a snowflake it is considered all-season, but not winter!
• 🔊 DB or numbers (for example, 72 dB) — tire noise level. The lower the value, the quieter the tire. The European Union requires this information to be included on the label.
• 💧 Aquatred / Aquacontact — technologies for improved water drainage (useful for rainy regions). Such tires are less likely to “float” on wet roads.

The tire may also have the following symbols:

• 🔄 Rotation or arrow - directional tire (installed strictly in the direction of rotation).
• 🔀 Outside/Inside — asymmetrical tire (outer and inner sides are indicated on the sidewall).
• 🚛 Reinforced or XL — reinforced tire with a higher load index (for example, for minibuses).

What should I do if my tire does not have a DOT date?

If the production date is not visible, check the other side of the tire - sometimes the code is duplicated. If it is not there at all, it may be a fake or a tire older than 2000 (before the introduction of mandatory labeling). It is better to avoid purchasing such tires, since tires older than 10 years are considered potentially dangerous, even if they look new.

4. How to choose the right tire size for your car

Main rule: Tire size must comply with vehicle manufacturer's recommendations. They can be found:

• 📄 In the instruction manual (section “Wheels and Tires”).
• 🚗 On a sticker on the driver's door pillar or gas tank flap.
• 🔧 In the electronic tire catalog (for example, on websites Nokian, Michelin or Kama).

Minor deviations from factory parameters are allowed, but with reservations:

• 🔄 Can be enlarged width by 10–20 mm (for example, instead of 195 put 205), but only if the disk allows it (check the parameter J on disk).
• 📉 Can be reduced profile, but no more than 10% (for example, from 65 to 60), and only if you increase the width. Otherwise, there is a risk of damage to the disc in the pits.
• ⚠️ Diameter (R15, R16, etc.) You can't change it without replacing the disks! The exception is a temporary “dokatka” with a different size.

Example of a valid replacement for 195/65 R15:

• ✅ 205/60 R15 — wider and slightly lower, but the overall diameter of the wheel remains close to the original.
• ❌ 185/70 R15 - narrower and higher, which will worsen handling and may touch the arches.

Make sure that the bore diameter (R15, R16...) matches the disc

Check the load index - it should not be lower than recommended

Compare the speed index - it should not be lower than the factory one

Measure the gap to the arches - the new tire should not rub when turning ->

5. Common mistakes when choosing tires and their consequences

Even experienced car owners sometimes make mistakes when buying tires. Here are the most dangerous mistakes and their consequences:

⚠️ Attention: Installation of tires with speed index below factory (for example, T instead of H) may cause denial of insurance compensation in the event of an accident at a speed above the tire limit. Insurance companies check this parameter!

• 🔄 Diameter mismatch (for example, R16 instead of R15) - the tire simply will not fit on the rim or will break during installation. Exception: Some SUVs support two diameters (eg. Toyota RAV4 - R17 and R18).
• 📉 Profile too high on a sports car - it worsens handling and can lead to the tires “breaking” when cornering.
• ❄️ Summer tires in winter (or vice versa) - in addition to a fine (in Russia from 2026 - 2,000 rubles), this sharply increases the braking distance. For example, on ice at 60 km/h, summer tires slow down by 30–40 meters longerthan winter.
• 🔊 Ignoring production date — a tire older than 5–6 years loses its elasticity, even if the tread is new. The risk of explosion at high speed increases 3 times.

Another common mistake is buying tires with different tread pattern on one axis. This is prohibited by traffic rules (clause 5.5 of Appendix 8 to the Technical Regulations of the Customs Union) and leads to:

• 🔄 Unpredictable behavior of the car in turns.
• 🚗 Accelerated wear of the transmission (especially for all-wheel drive cars).
• 💰 Denial of warranty for the suspension.

6. How to decipher American tire markings (LT, P, Euro-metric)

On tires for the American market (especially for SUVs and pickup trucks) you often see the designation LT, P or Euro-metric. They point to vehicle class and affect the load capacity:

• 🚗 P (Passenger) - tires for passenger cars (for example, P215/65 R16). They have a lower safety margin than LT.
• 🚛 LT (Light Truck) - tires for light trucks, pickups and SUVs (for example, LT235/75 R15). They can withstand greater loads, but are tougher and noisier.
• 🌍 Euro-metric - European marking standard (without letter P or LT, for example, 205/55 R16). Often used for universal tires.

Important: tires LT can be installed on passenger cars (if the size is suitable), but they will:

• ✅ More wear-resistant (thicker cord).
• ❌ Harder and noisier on asphalt.
• ⚠️ May have a different load index (check the labeling!).

Example: tire LT215/75 R15 withstands 20–30% greater load than P215/75 R15, but it may be 2–3 kg heavier.

7. The influence of tire size on the odometer, speedometer and fuel consumption

Changing tire size affects not only handling, but also instrument readings. Here's how it works:

• 📏 Increasing the outer diameter of the wheel (for example, due to a high profile or larger disc diameter) leads to:
• ⬇️ Lowering the speedometer readings (10% larger than the size = the speedometer shows 90 km/h when the actual speed is 100 km/h).
• ⬇️ Reducing odometer readings (mileage “winds up” more slowly).
• ⬆️ Increased fuel consumption (by 1–3% for every 10 mm increase in diameter).
• 📉 Diameter reduction has the opposite effect: the speedometer overestimates the speed, and the odometer overestimates the mileage.

Example: if you replaced 195/65 R15 (diameter ~635 mm) on 205/55 R16 (diameter ~632 mm), the difference is minimal. But if they put 225/45 R17 (diameter ~615 mm), the speedometer will show 3–5 km/h more than the actual speed.

How to calculate the actual speed? Use the formula:

Real speed = (Speedometer reading × Old diameter) / New diameter

Where the wheel diameter in millimeters can be found in tire size calculators.

⚠️ Attention: If the outer diameter of a new wheel differs from the factory one by more than 3%, this can lead to malfunctions of the ABS, ESP and gearbox (especially on modern cars with electronic assistants).

FAQ: Frequently asked questions about tire sizes

❓ Is it possible to put tires of different sizes on the front and rear axles?

Yes, but with reservations:

• 🔄 On front-wheel drive cars, you can install wider tires on the rear axle (for example, on the front 195/65 R15, behind 205/60 R15). This improves directional stability.
• 🚗 On rear wheel drive and all-wheel drive on vehicles, tires must be identical on all wheels (or a difference in width of no more than 10 mm is allowed). Otherwise, problems with the differential are possible.
• ⚠️ Profile and diameter must match on all wheels!

Important: even with permissible differences in width, tread pattern on the same axis should be the same.

❓ What does the letter C mean in a tire size (for example, 195/70 R15C)?

Letter C (Commercial) denotes tires for light commercial vehicles (for example, Gazelle, Ford Transit). They have:

• ⬆️ Reinforced cord (withstands heavy load).
• ⬆️ Higher load index (e.g. 104/102S instead of 91T).
• ⬇️ Less comfort (harder sidewalls).

Such tires can be installed on passenger cars, but they will be less comfortable. Reverse replacement (with C on regular tires) on commercial vehicles prohibited - this is a violation of load capacity.

❓ Which tire size is better for winter: narrow or wide?

For winter use Narrower tires are preferredbecause:

• ❄️ A narrow tire “crashes” into the snow more, improving grip.
• 💨 Less rolling resistance on loose snow.
• 🚗 Sidewalls are less susceptible to damage from ice and curbs.

Recommendations:

• If you have summer 205/55 R16, in winter you can put 195/65 R16 (the diameter remains almost the same, but the tire is narrower).
• The profile is optimal for deep snow 60–70 (a high tread “rows” better).

Exception: sports cars with wide rims (e.g. BMW M5). Narrow winter tires are not suitable for them due to the risk of “changing shoes” to wheels of a smaller width.

❓ Is it possible to drive on tires with different profiles, but the same diameter?

No, it's prohibited by traffic rules (clause 5.5 of the Technical Regulations). A different profile on the same axis leads to:

• 🔄 Uneven wear of the transmission (especially on all-wheel drive cars).
• 🚗 I pull the car to the side when braking.
• 💰 Refusal for warranty repair of suspension.

Differences in profile are allowed only between axles (for example, in front 205/55 R16, behind 205/60 R16), but not more than 10 mm and provided that:

• The car is not all-wheel drive.
• The wheel diameter remains the same (checked with a calculator).

❓ What happens if you install larger diameter tires (for example, R17 instead of R16)?

Increasing the wheel diameter requires:

• 🔧 Replacement of disks (the seat diameter of the tire and disk must match).
• 📏 Checking the gaps in the arches (the tire should not rub when turning or loading).
• 🔄 Speedometer adjustments (if the outer diameter of the wheel has changed by more than 3%).

Consequences:

• ⬆️ Handling will improve (less roll in corners).
• ⬇️ The load on the suspension will increase (the life of the shock absorbers will be reduced).
• ⬆️ Fuel consumption will increase (by 2–5%).

Example: replacement 205/55 R16 (diameter 632 mm) on 225/45 R17 (diameter 635 mm) is acceptable if:

• 17" wheels fit the parameters PCD and ET.
• The width of the rim corresponds to the width of the tire (for example, 7J for 225).