How to Read Tyre Details: Size, Age, Load and Speed Codes

 

How to Read Tyre Details: Size, Age, Load and Speed Codes

Learn how to read tyre sidewall markings, including size, aspect ratio, load index, speed rating, DOT date, tread, pressure and safety codes.

How to Read Every Number on Your Tyre

Look closely at the sidewall of a tyre and you will find a mixture of numbers, letters and symbols. To many drivers, they look like technical codes. In reality, they provide useful information about the tyre's dimensions, construction, load capacity, speed category and manufacturing date.

Understanding these markings can help you select the correct replacement, identify an ageing tyre and avoid using the wrong inflation pressure.

This guide explains the most important tyre details in simple English, with practical calculations and checks that you can use before buying or maintaining a tyre.

What Are Tyre Details?

Tyre details are the markings moulded or printed on the sidewall. Depending on the tyre and market, they can include:

• Tyre size
• Aspect ratio
• Construction type
• Rim diameter
• Load index
• Speed rating
• Manufacturing date or tyre identification number
• Tubeless or tube-type information
• Tread-wear indicators
• Maximum inflation pressure
• Regulatory or certification markings

Think of these markings as the tyre's technical identity. They tell you what the tyre is designed to fit and the operating limits specified for it.

 

How to Read a Tyre Size

Consider this common example:

205/55 R16 91V

Each part has a specific meaning.

205 — Section Width

The number 205 represents the nominal section width of the tyre in millimetres.

So, 205/55 R16 has a nominal width of approximately 205 mm.

Width alone does not tell you whether a tyre will fit a vehicle. Wheel width, clearance, load capacity, speed rating and the vehicle manufacturer's specifications also matter.

55 — Aspect Ratio

The 55 means that the sidewall height is approximately 55% of the tyre's nominal width.

For this tyre:

205 × 0.55 = 112.75 mm

So the nominal sidewall height is about 113 mm.

A lower aspect ratio generally means a shorter sidewall. This can contribute to more immediate steering response, while a taller sidewall generally provides more sidewall compliance and cushioning.

R — Radial Construction

The R means radial construction.

Radial tyres are the standard construction used on most modern passenger vehicles. Older or specialised tyres may use other construction markings.

16 — Rim Diameter

The 16 indicates that the tyre is designed for a 16-inch rim.

This is not the overall diameter of the tyre. It is the diameter of the wheel on which the tyre is mounted.

91 — Load Index

The 91 is the tyre's load index. It is not a weight measurement by itself; it corresponds to a specified maximum load per tyre.

For example, load index 91 corresponds to 615 kg per tyre under the applicable rating conditions.

V — Speed Rating

The V is the tyre's speed symbol. V corresponds to 240 km/h under the applicable test conditions.

Importantly, a speed rating is not a recommendation to drive at that speed. It is part of the tyre's performance classification and must be considered together with the vehicle manufacturer's specification.

 

A Useful Calculation: Overall Tyre Diameter

Knowing the approximate overall diameter is useful when comparing alternative sizes.

The basic calculation is:

Overall diameter = rim diameter in mm + (2 × sidewall height)

For 205/55 R16:

• Rim diameter = 16 × 25.4 = 406.4 mm
• Sidewall height = 205 × 0.55 = 112.75 mm
• Overall diameter = 406.4 + (2 × 112.75)
• Overall diameter = 631.9 mm

Now consider 215/50 R17:

• Rim diameter = 17 × 25.4 = 431.8 mm
• Sidewall height = 215 × 0.50 = 107.5 mm
• Overall diameter = 431.8 + (2 × 107.5)
• Overall diameter = 646.8 mm

The second tyre is approximately 2.4% larger in calculated diameter.

However, there is no universal rule saying that every tyre change within 3% is automatically safe. A replacement size must also have suitable load capacity, speed rating, wheel compatibility, clearance and vehicle-system compatibility.

Never choose an alternative size simply because the calculated diameter is close. Check the vehicle manufacturer's approved tyre sizes first.

 

Load Index: How Much Weight Can the Tyre Carry?

The load index tells you the maximum load assigned to one tyre under the relevant rating conditions.

Load Index	Maximum Load per Tyre
82	475 kg
86	530 kg
88	560 kg
91	615 kg
94	670 kg
99	775 kg
102	850 kg

For example, four tyres with a load index of 91 have a nominal combined load capacity of 2,460 kg.

But this does not mean you can simply load a 2,460 kg vehicle.

The vehicle's permitted gross weight, axle limits, tyre pressure, wheel rating and the manufacturer's specifications must all be considered. The load index is one part of the vehicle's load-carrying system.

Practical rule: never select a tyre with a load index below the vehicle manufacturer's requirement.

Some vehicles also specify XL (Extra Load) or reinforced tyres. These designations should not be treated as a universal substitute for checking the manufacturer's specification.

 

Speed Rating: More Than a Maximum-Speed Number

The speed symbol indicates the tyre's rated speed category under specified test conditions.

Speed Symbol	Rated Speed
Q	160 km/h
S	180 km/h
T	190 km/h
H	210 km/h
V	240 km/h
W	270 km/h
Y	300 km/h

A higher speed rating does not automatically mean a tyre is better for every vehicle.

The correct choice depends on the vehicle manufacturer's specification and the intended operating conditions.

Use the specified speed rating or an approved higher rating. Do not downgrade it simply to save money.

 

DOT Code: How to Check Tyre Age

On tyres carrying a U.S. DOT Tyre Identification Number, the final four digits identify the week and year of manufacture.

For example:

DOT XXXX XXXX 3124

• 32 = 32st week
• 26 = 2026

So the tyre was manufactured during the 31st week of 2024.

The complete tyre identification marking may not appear on both sidewalls, so you may need to inspect the inner side of the tyre.

Why Tyre Age Matters

Tyre rubber and other materials change with time. Heat, sunlight, ozone, storage conditions, inflation and service conditions can accelerate ageing.

This is why tread depth alone cannot determine whether a tyre is safe.

There is also an important distinction between manufacturing age and service age. A tyre that has spent years in storage may have relatively little mileage but is still an ageing product.

There is no technically sound universal rule that says every tyre must be replaced after exactly five or ten years. NHTSA notes that some vehicle and tyre manufacturers recommend replacement when tyres are six to ten years old, regardless of tread remaining. Always follow the specific tyre and vehicle manufacturer's recommendation.

Before buying, check the manufacturing date and inspect the tyre for cracks, deformation or other damage.

Read this related guide: What Is Natural Rubber? Production, Properties and Uses.

 

Tread Depth: When Is a Tyre Worn Out?

Tread depth affects wet-road performance because grooves help channel water away from the contact area.

The legal minimum varies by jurisdiction, but 1.6 mm is a commonly used threshold for passenger-car tyres in many markets. NHTSA uses 2/32 inch, approximately 1.6 mm, as its replacement threshold.

However, legal minimum and optimum wet-weather performance are not the same thing.

Continental testing shows that tyres with around 3 mm of remaining tread retain considerably more water-displacement capability than tyres worn to 1.6 mm.

Therefore, drivers who regularly encounter heavy rain may choose to replace tyres before they reach the legal limit.

Tread-Wear Indicators

Modern tyres have small raised bars inside the main grooves. These are called tread-wear indicators.

When the tread surface becomes level with these indicators, the tyre has reached its wear limit and should be replaced.

A tread-depth gauge is much more reliable than judging tread visually.

 

Tyre Tread Patterns Explained

Symmetrical Tread

The tread pattern is broadly the same across the tyre.

These designs are common on everyday passenger tyres and can provide predictable road behaviour and simple rotation options.

Directional Tread

Directional tyres normally have a pattern designed to rotate in one direction.

An arrow on the sidewall indicates the intended direction of rotation.

Mounting a directional tyre incorrectly can compromise the design's intended water evacuation and handling characteristics.

Asymmetrical Tread

An asymmetrical tyre has different tread zones on the inner and outer portions.

Look for markings such as OUTSIDE and INSIDE. The tyre must be mounted in the correct orientation.

 

Other Important Tyre Sidewall Markings

TL and TT

• TL generally means tubeless.
• TT generally indicates a tube-type tyre.

M+S

M+S indicates mud-and-snow capability under the relevant marking criteria. It should not automatically be treated as equivalent to a severe-snow certification.

3PMSF

The Three-Peak Mountain Snowflake (3PMSF) symbol indicates that the tyre meets the relevant standardized snow-performance requirement.

This is more meaningful for severe-snow performance than simply seeing M+S on the sidewall.

RFT or ZP

These are manufacturer-specific markings associated with run-flat or extended-mobility technology.

Run-flat tyres are designed to provide limited mobility after certain types of pressure loss, but the permitted speed and distance depend on the tyre and vehicle.

For a deeper explanation, read:Run Flat Tyres: How They Work and How Far You Can Drive .

Maximum Inflation Pressure

The pressure moulded on a tyre sidewall is generally the tyre's maximum permissible inflation pressure under the applicable specification.

It is not necessarily the pressure you should use every day.

 

Tyre Pressure: The Number Drivers Get Wrong

The correct operating pressure normally comes from the vehicle manufacturer's tyre placard or owner's manual, not from the maximum-pressure number moulded into the tyre.

NHTSA specifically advises checking cold tyre pressure using the vehicle manufacturer's recommended value.

Check Pressure When Cold

Ideally, check pressure before driving or after the vehicle has been stationary long enough for the tyres to cool.

A warm tyre normally shows a higher pressure because the air inside has heated up.

Temperature Changes Pressure

Tyre pressure changes with temperature. A commonly used approximation is around 1 psi for every 10°F temperature change, although the actual change depends on the tyre, temperature range and conditions.

Therefore, do not release air from a hot tyre simply because its pressure is higher than the cold specification.

Check Pressure Under Different Loads

Many vehicles have separate recommended pressures for normal and heavily loaded conditions.

Follow the pressure information supplied by the vehicle manufacturer.

For a detailed explanation of pressure and its effect on safety, read: PSI in Tires: The Pressure That

Drives Your Safety and Performance. 

What Your Wear Pattern Can Tell You

Uneven tread wear can provide clues about inflation, alignment, suspension or tyre maintenance.

Both Edges Worn

Can indicate under-inflation, although other mechanical or usage factors should also be checked.

Centre Tread Worn

Can be associated with over-inflation.

One Edge Worn

May indicate an alignment or suspension issue.

Cupping or Scalloping

May be associated with wheel imbalance, worn suspension components or other mechanical problems.

Feathered Tread

A feathered pattern can indicate an alignment issue, particularly incorrect toe settings.

These patterns are diagnostic clues, not definitive diagnoses. A technician should inspect the vehicle before replacing parts.

 

Rotation, Balancing and Wheel Alignment

Tyre maintenance is not limited to inflation.

Front tyres may wear faster on many front-wheel-drive vehicles because the front axle handles steering, braking and driving forces.

However, there is no single rotation interval suitable for every vehicle. Follow the vehicle and tyre manufacturer's recommended schedule.

Wheel balancing should be checked when tyres are fitted and whenever vibration develops.

Alignment should be inspected when there is abnormal wear, steering pull, an impact with a pothole or kerb, or other symptoms suggesting a geometry problem.

 

UTQG: A Rating Many Buyers Misread

If you buy tyres in the United States, you may see UTQG information covering treadwear, traction and temperature.

One important correction to many online explanations is that a treadwear rating of 400 does not mean the tyre will last exactly four times as long as a tyre rated 100 in normal road use.

UTQG treadwear is a comparative rating from a controlled test. Real-world wear varies with vehicle, driving style, inflation, road surface, climate and maintenance.

That makes UTQG useful for comparison, but not a guaranteed mileage forecast.

 

BIS and ISI Marking in India

For tyres sold in India, certification requirements depend on the applicable Indian Standard and Quality Control Order.

BIS identifies automotive tyre standards such as IS 15633 for passenger-car tyres, and passenger-car tyre standards are subject to applicable compulsory certification requirements.

Therefore, it is better to say that the BIS Standard Mark indicates conformity with the applicable Indian Standard under the relevant certification scheme—not simply that the mark guarantees that a tyre is “high quality.”

This distinction matters because certification is about compliance with specified requirements; it does not replace checking the tyre's size, age, condition, load rating and suitability for your vehicle.

 

Tyre Buying Checklist

Before paying for a new set, check:

1. Correct size according to the vehicle manufacturer.
2. Correct load index.
3. Correct or approved speed rating.
4. Manufacturing date.
5. No cracks, bulges or visible damage.
6. Correct tread pattern and application.
7. Required certification markings for your market.
8. Correct inflation pressure after installation.
9. New valves where appropriate.
10. Wheel balancing after fitting.

If only two tyres are being replaced, fitting the newer pair on the rear axle is widely recommended because greater rear-axle grip can reduce the risk of oversteer and loss of stability on wet roads. However, always check the vehicle manufacturer's instructions because some vehicles have specific tyre arrangements.

 

Common Tyre Mistakes to Avoid

Using the pressure printed on the tyre

The sidewall maximum is not the same as the vehicle's recommended cold inflation pressure.

Choosing a replacement based only on size

A tyre that fits the wheel physically may still be unsuitable because of its load index, speed rating, clearance or vehicle-system requirements.

Ignoring age because the tread looks good

A tyre can have plenty of tread and still show age-related deterioration.

Treating 3% as an automatic safe-size rule

Diameter calculations are useful, but vehicle approval is more important than an arbitrary percentage.

Assuming UTQG predicts exact mileage

It does not. It is a comparative test rating.

Ignoring sidewall damage

Cuts, bulges, exposed cords and serious cracking require professional assessment. A bulge can indicate internal structural damage and should not be treated as cosmetic.

 

Conclusion

The markings on a tyre are more than a collection of numbers. They describe the tyre's dimensions, construction, load capability, speed category, age and operating limits.

The most useful habit is to read the complete specification, rather than focusing on size alone.

Before buying or fitting a tyre, compare the size, load index and speed rating with the vehicle manufacturer's requirements. Check the manufacturing date, inspect the sidewall and tread, use the correct cold inflation pressure and pay attention to abnormal wear.

A few minutes spent reading the sidewall can prevent an expensive mistake—and can help you choose a tyre that is genuinely suitable for your vehicle and driving conditions.

 

Frequently Asked Questions

What do the numbers on a tyre mean?

In a marking such as 205/55 R16 91V, 205 is the nominal section width in millimetres, 55 is the aspect ratio, R indicates radial construction, 16 is the rim diameter in inches, 91 is the load index and V is the speed symbol.

How do I check the age of a tyre?

Look for the tyre identification/date code. On tyres using the DOT system, the last four digits identify the week and year of manufacture. For example, 3124 means the 31st week of 2024.

How long do tyres last?

There is no single mileage figure that applies to every tyre. Service life depends on tyre design, vehicle, road conditions, inflation, alignment, load and driving style. Age also matters, and manufacturers may specify an age limit.

Can I use a different tyre size?

Only if the alternative size is approved or otherwise confirmed as suitable for the vehicle. Check overall diameter, load index, speed rating, wheel width, clearance and vehicle-system compatibility. Do not rely on a simple 3% rule.

Which pressure should I use?

Use the vehicle manufacturer's recommended cold inflation pressure shown on the vehicle placard or in the owner's manual. Do not use the tyre's maximum sidewall pressure as the normal operating pressure.

What is the minimum tread depth?

The legal limit depends on the country and vehicle category. 1.6 mm is a commonly used passenger-car threshold in many markets, but wet-weather performance can deteriorate before the legal limit.

Should new tyres go on the front or rear?

When replacing only two tyres on a vehicle with the same-size tyres front and rear, tyre-industry guidance commonly recommends putting the newer tyres on the rear axle to improve rear-axle stability on wet roads. Always follow the vehicle manufacturer's instructions where they differ.

Does a higher speed rating mean a better tyre?

Not necessarily. A higher rating indicates a different performance classification, but the best tyre is one that matches the vehicle's requirements and intended use.

Does a higher UTQG treadwear number guarantee longer life?

No. UTQG treadwear is a comparative test rating, not a guaranteed mileage figure. Real-world wear can differ substantially between vehicles, drivers and road conditions.