How to read the markings on your tyre sidewall
8 min readBy Wheel Fit
The short answer The string you need when ordering a tyre looks like 205/55 R16 91V. That is width in millimetres, profile as a percentage, construction, rim diameter in inches, load index and speed rating. It is moulded into the sidewall, usually more than once.
This is the single most useful thing you can read off a tyre. Give a fitter this string and your vehicle, and they can quote you accurately and turn up with the right rubber. Give them a guess and you risk a wasted journey.
Taking it apart
| Marking | Meaning |
|---|---|
| 205 | Section width in millimetres, sidewall to sidewall. |
| 55 | Aspect ratio: sidewall height as a percentage of the width. So 55% of 205mm. |
| R | Radial construction. Almost everything on the road is radial. |
| 16 | Rim diameter in inches. This one is not metric. |
| 91 | Load index — the maximum weight the tyre can carry. |
| V | Speed rating — the maximum speed it is certified for. |
A lower profile number means a shorter, stiffer sidewall. It looks sportier and responds faster, but it also means less rubber between your rim and the pothole — and low-profile tyres cost more to replace, for the life of the car.
How old is the tyre? The DOT code
Look for a four-digit number, often in an oval, after the letters DOT. It is a date, not a serial number:
- The first two digits are the week of manufacture.
- The last two are the year.
So 2523 means week 25 of 2023. This matters because rubber degrades with time as well as mileage. A tyre with plenty of tread that has sat on a caravan or a low-mileage car for a decade is not the same as a tyre made last year — see how long tyres last.
The full code may only be on one side Manufacturers are only required to mould the complete DOT code on one sidewall. If you cannot find the four digits on the face you can see, the tyre may be showing you its inner face — check the other side, or look at the wheel from underneath.
Other markings worth knowing
- C after the size — a commercial tyre, built for van loads. Not interchangeable with a car tyre of the same size — van tyres vs car tyres.
- XL or Reinforced — a stronger casing with a higher load capacity.
- M+S, or a snowflake-in-a-mountain symbol — mud and snow, or a genuine severe-snow certification. They are not the same thing — winter, summer or all-season.
- RSC, ROF, ZP, RunOnFlat — run-flat construction, which varies by manufacturer — run-flat tyres explained.
- A rotation arrow — the tyre is directional and must go on the correct side.
- OUTSIDE / INSIDE — an asymmetric tyre, which must be fitted with the marked face outward.
- Tread wear indicators — small raised bars in the grooves marking the 1.6mm legal minimum — tread depth and the law.
- An E-mark such as E11 — European type approval. A road tyre must carry one.
Manufacturer-specific fitment codes
Some tyres carry a short code showing they were developed for a particular manufacturer — for example MO (Mercedes), AO or RO1 (Audi), a star (BMW), N0–N5 (Porsche). These are not decoration: the compound and casing are tuned to that car's suspension.
You are not obliged to match them, and a good equivalent tyre without the code is perfectly legal. But if your car came with them and you want it to behave as designed, it is worth mentioning when you order.
Where to find your correct size
The tyre currently fitted is not automatically the right one — previous owners get it wrong. The manufacturer's specification is on a plate in the driver's door shut, sometimes inside the fuel flap, and always in the handbook.
If the fitted size and the door plate disagree, tell us when you call and we will work out which is correct for the vehicle.
Common questions
- Can I fit a different size to what is on the car?
- Only within what the manufacturer permits. Changing width or profile alters the rolling circumference, which affects the speedometer, ABS and — on four-wheel drive — the drivetrain. Check the handbook rather than eyeballing it.
- The four tyres on my car are different sizes. Is that wrong?
- Not necessarily — some cars run staggered fitments with wider rears by design. But different sizes on the same axle is always wrong. See mixing tyre brands and patterns.
- What does the number after the speed rating mean?
- If you see something like 91V and then more characters, it is usually a fitment code, a run-flat designation or an approval mark rather than part of the size.
- Is a newer DOT code always better?
- Fresher is better all else being equal, and it is worth checking on a "new" tyre — one that has sat in a warehouse for years has already used part of its life.
Reading it for a quote
When you call, read the whole string off the sidewall rather than from memory — it is the single biggest thing that prevents a wasted journey. Call 07989 606060.
