How to Read Your Tyre Size: A Complete Guide

When you need new tyres, the first thing you will be asked is your tyre size. It might look like a random string of numbers and letters — something like 205/55 R16 91V — but every character has a specific meaning. Understanding your tyre size ensures you get the right fit for your vehicle and stay safe on the road.

Where to Find Your Tyre Size

There are several places to check:

• On the tyre sidewall — the most reliable source. Look for a sequence like 205/55 R16 91V moulded into the rubber.
• Inside the driver's door frame — most vehicles have a sticker or plate here showing the recommended tyre sizes and pressures.
• In the vehicle handbook — the manufacturer's recommended size will be listed in the specifications section.
• Inside the fuel filler cap — some vehicles display tyre information here too.

Breaking Down the Numbers: 205/55 R16 91V

Let us take the common size 205/55 R16 91V and explain each part:

205 — Tyre Width

This is the width of the tyre in millimetres, measured from sidewall to sidewall. In this case, the tyre is 205mm wide. Wider tyres generally offer more grip but may increase rolling resistance.

55 — Aspect Ratio (Profile)

This number is a percentage representing the height of the sidewall relative to the width. So 55 means the sidewall height is 55% of 205mm, which works out to approximately 113mm. A lower number means a shorter sidewall (a lower-profile tyre), which gives sportier handling but a firmer ride.

R — Construction Type

The letter R stands for Radial, which is the construction method used in virtually all modern car tyres. Radial tyres have layers of cord running at right angles to the direction of travel, giving them better grip, longer life, and a more comfortable ride than the older cross-ply design.

16 — Rim Diameter

This is the diameter of the wheel rim in inches. This tyre is designed to fit a 16-inch wheel. Getting this wrong means the tyre simply will not fit.

91 — Load Index

The load index indicates the maximum weight each tyre can support when properly inflated. An index of 91 means the tyre can carry up to 615kg. You should never fit a tyre with a lower load index than specified by your vehicle manufacturer.

V — Speed Rating

The speed rating tells you the maximum speed the tyre is designed to handle safely. Common ratings include:

• T — up to 190 km/h (118 mph)
• H — up to 210 km/h (130 mph)
• V — up to 240 km/h (149 mph)
• W — up to 270 km/h (168 mph)
• Y — up to 300 km/h (186 mph)

You can fit a tyre with a higher speed rating than recommended, but never a lower one.

Other Markings You Might See

• XL or RF — Extra Load or Reinforced, indicating the tyre can carry more weight than standard
• M+S — Mud and Snow, indicating some winter capability
• The snowflake symbol (3PMSF) — indicates the tyre meets the required performance standard for severe snow conditions
• DOT code — the last four digits indicate the week and year of manufacture (e.g., 2524 means week 25 of 2024)

Why Getting the Right Size Matters

Fitting the wrong tyre size can affect your speedometer accuracy, handling, braking performance, and even damage your vehicle's suspension. It will also result in an MOT failure. If you are unsure about your size, a quick call to NN Mobile Tyres can sort it out — we deal with tyre sizes every day across Oxford and Oxfordshire.

Frequently Asked Questions

Can I fit a different tyre size to my car?

In some cases, yes — there may be alternative sizes approved by your vehicle manufacturer. However, you should only ever fit sizes that are listed as acceptable for your specific vehicle. Fitting an unapproved size can compromise safety and invalidate your insurance.

What does the DOT code on my tyre mean?

The DOT (Department of Transportation) code is a series of characters on the sidewall. The most useful part is the last four digits, which tell you the week and year the tyre was manufactured. For example, 0326 means the tyre was made in week 3 of 2026.

Do all four tyres need to be the same size?

Most vehicles require the same size on all four corners. However, some performance and luxury cars use a staggered setup with wider tyres on the rear axle. Always check your vehicle handbook for the correct specification.

Need help? Call NN Mobile Tyres on 07362 638978 or WhatsApp us — we are available 24/7 across Oxfordshire.