How to Read the Numbers on Your Tyre Sidewall
The numbers on your tyre sidewall, such as 205/55 R16 91V, tell you its size and ratings. 205 is the width in millimetres, 55 is the sidewall profile, R16 is the wheel diameter in inches, 91 is the load index and V is the speed rating. Matching these correctly is essential when buying new tyres.
Width, profile and rim size
The first three figures describe the physical size. Take 205/55 R16 as an example.
- 205 is the tyre width in millimetres across the tread.
- 55 is the profile, meaning the sidewall height is 55% of the width.
- R means radial construction, used on virtually all modern car tyres.
- 16 is the wheel diameter in inches that the tyre fits.
Load index and speed rating
After the size comes a number and a letter, such as 91V. The number is the load index, which corresponds to the maximum weight the tyre can carry. The letter is the speed rating, the maximum speed the tyre is designed for.
Your car maker sets a minimum load index and speed rating. Fitting a lower rating than specified is unsafe and can be illegal, so always match or exceed the figures your car requires. Going higher is fine; going lower is not.
The DOT date code
Beyond size, the sidewall carries a DOT code ending in four digits that give the week and year of manufacture. For example, 3621 means the tyre was made in the 36th week of 2021.
This matters because rubber ages whether or not the tyre is used. A tyre with plenty of tread can still be unsafe if it is old and the rubber has perished, which is especially relevant on low-mileage cars, spares and caravans. It is always worth a glance when buying a used car or a part-worn tyre.
Other markings to know
Sidewalls carry several other useful markings beyond the size code.
- M+S or a three-peak snowflake symbol indicates winter or all-season capability.
- XL means extra load, a reinforced construction.
- Symbols like a star, AO or MO show approval for specific car makers.
- An arrow or "outside" marking shows directional or asymmetric fitting.
The EU tyre label
Separate from the sidewall, every new tyre comes with an EU-style label rating three things: wet grip, fuel efficiency and external noise, each on a simple scale. Wet grip is the most safety-critical, as it reflects wet braking distance.
The label lets you compare tyres objectively beyond brand and price, which is handy when choosing between options in your size. If you want help weighing up the label ratings for your driving, just ask us when you book your fitting.
Buying the right tyre
The simplest way to buy correctly is to read the size and ratings off your current tyres, or check the handbook and door-sill label. If different tyres on the car show different sizes, check which is correct, as a previous fitting may have been wrong.
If you are unsure, tell us your registration or the sidewall code and we will confirm the right tyres for your car, including whether any maker-specific approval markings apply to your vehicle.
Frequently Asked Questions
What does the speed rating letter mean?
The speed rating letter shows the maximum speed the tyre is designed to sustain safely, such as V for 149mph or H for 130mph. Always fit at least the rating your car maker specifies. A lower rating than required can be unsafe and may invalidate insurance.
Can I fit a different size tyre to my car?
You should fit the size your car maker specifies. Changing size affects speedometer accuracy, handling and clearance, and the wrong load or speed rating can be illegal. If you want to change size, check it is an approved option for your car first and ask us.
Where do I find my tyre size?
Read it from the sidewall of your current tyres, where it appears as a code like 205/55 R16 91V. You can also find the recommended size in your handbook and on the label inside the driver's door sill or fuel filler flap.
How do I check how old my tyres are?
Look for the four-digit DOT code on the sidewall: the first two digits are the week and the last two the year of manufacture, so 3621 is the 36th week of 2021. Rubber ages over time, so an old tyre with good tread may still need replacing.
What does XL mean on a tyre?
XL stands for extra load, meaning the tyre has a reinforced construction able to carry more weight at a given pressure. Some cars require XL tyres, so if yours specifies them, fit XL rather than a standard-load equivalent. Check your handbook or ask us if unsure.
Book With Norwich Tyres & Auto Service
Need a hand from a real, independent Norwich garage? Call 07933 900901 or pop into Ber Street, NR1 3ES. Same-day tyre fitting is available on most common sizes, with free parking on site.
Hero image: “It's a crime! 1973-76 Ford Cortina Mark 3 automatic in a state!” by charles cars (source), licensed under CC BY.