Tyre markings explained: what every number and letter on your sidewall means
A sidewall like 205/55 R16 91V looks like a serial number and is actually a specification. Once you can read it, you can check in seconds whether a tyre is right for your car — and whether the one being quoted to you is the same as the one you have.
Reading 205/55 R16 91V
This is the code that matters most. Every part of it does a job:
- 205 — the section width in millimetres, measured across the tread from sidewall to sidewall.
- 55 — the aspect ratio, given as a percentage of the width. Here the sidewall height is 55 per cent of 205 mm, so roughly 113 mm. A lower number means a shorter, stiffer sidewall.
- R — radial construction. Virtually every modern car tyre is radial. You may occasionally see D for diagonal or bias-ply on trailers and classics.
- 16 — the wheel rim diameter in inches. Yes, the code mixes millimetres and inches, which is a historical quirk rather than a mistake.
- 91 — the load index, a coded maximum weight per tyre.
- V — the speed rating, a coded maximum speed.
The correct size for your vehicle is in the handbook, and usually on a placard inside the driver’s door frame or the fuel filler flap. That placard is the authority, not whatever happens to be fitted now — previous owners fit the wrong thing more often than you would expect.
What the load number means in kilograms
The load index is the maximum weight one tyre can carry at its correct pressure. Multiply by four for the whole vehicle, though axle limits matter too. These are the values in the range covering most cars and vans:
- 82 = 475 kg · 84 = 500 kg · 86 = 530 kg · 88 = 560 kg
- 90 = 600 kg · 91 = 615 kg · 92 = 630 kg · 94 = 670 kg
- 95 = 690 kg · 96 = 710 kg · 98 = 750 kg · 100 = 800 kg
- 102 = 850 kg · 104 = 900 kg · 106 = 950 kg · 108 = 1,000 kg
Fitting a lower load index than your vehicle requires is genuinely unsafe, not merely a technicality. The tyre is being asked to carry more than it was built for, which builds heat — and heat is what destroys tyres at speed. It can also affect an insurance claim. Going higher is generally acceptable, though a much stiffer tyre can make the ride noticeably harder.
What the speed letter means
The letter is the maximum sustained speed the tyre is approved for under test conditions. The figures are set in km/h, which is why the mph equivalents look uneven:
- N = 87 mph · P = 93 mph · Q = 100 mph · R = 106 mph
- S = 112 mph · T = 118 mph · U = 124 mph · H = 130 mph
- V = 149 mph · W = 168 mph · Y = 186 mph
H sitting between U and V is not a typo. It is a historical leftover from when H meant “high performance”, and it has stayed out of sequence ever since.
You can fit a higher speed rating than your car needs. You should not fit a lower one: it is not automatically illegal, but it is dangerous and may allow an insurer to decline a claim. The one common exception is a winter tyre, where a lower rating is permitted on some vehicles provided a sticker showing the maximum speed is displayed in the cab.
The DOT code: how old is the tyre?
Somewhere on the sidewall is a four-digit number, often inside an oval. It is the manufacturing date, and it is the single most overlooked marking on a tyre.
- The first two digits are the week of the year, 01 to 53.
- The last two digits are the year.
- So 3419 means week 34 of 2019 — late August 2019.
- 0225 means week 2 of 2025, early January.
The code is only moulded in full on one side of the tyre, so if you cannot find it, look at the other sidewall. Tyres made before 2000 used a three-digit code; if you find one of those, the tyre is at least twenty-six years old and should not be on the road.
Age matters because rubber hardens and cracks whether or not the tyre is used. Tread depth tells you about wear; the date code tells you about ageing. A trailer, caravan or low-mileage second car will often reach the end of its tyres’ safe life with most of the tread still there. If that applies to you, our caravan and motorhome tyre checklist covers it in detail.
The other markings you will see
- XL or Reinforced — a stronger casing carrying a higher load at higher pressure. If your car specifies XL, fit XL.
- C after the size, as in 195/70 R15C — a commercial tyre for vans and trailers, built for heavier loads.
- CP — specifically for motorhomes and campervans, with a stiffer construction for standing at heavy loads for long periods.
- M+S — mud and snow. It is a self-declared marking with no test behind it, so on its own it means very little.
- 3PMSF, the three-peak mountain and snowflake symbol — this one is tested for snow grip. If you want a genuine winter tyre, this is the marking to look for, not M+S.
- Run-flat — every manufacturer uses its own code: RFT, ROF, ZP, SSR, DSST, EMT, RSC. They all mean the tyre can be driven on for a limited distance at reduced speed after losing pressure.
- TWI — tread wear indicator. Follow the marking inward to find the raised bars set at 1.6 mm.
- Rotation arrow — a directional tyre that must turn a particular way. Fitted backwards, it loses much of its wet performance.
- Outside / Inside — an asymmetric tyre with different tread patterns across its width. It must be fitted the correct way round.
- E in a circle — European type approval, with a number identifying the approving country.
- Max Press — the tyre’s maximum pressure, not the pressure your car should run. Use the vehicle’s placard for that.
The Max Press figure catches people out regularly. It is a limit for the tyre, not a recommendation for your vehicle, and inflating to it will leave you riding on the centre of the tread — which wears the middle out and reduces grip.
The EU tyre label
New tyres come with a standardised label carrying three ratings, which is the only straightforward way to compare across brands:
- Fuel efficiency, A to E — rolling resistance. The gap between best and worst is worth a few per cent on fuel over a tyre’s life.
- Wet grip, A to E — wet braking performance. This is the rating worth paying for. The difference between A and E can be several car lengths in an emergency stop.
- Noise, in decibels with a three-bar symbol — exterior noise, which correlates loosely with cabin noise.
If you are choosing between two tyres at similar money, wet grip is the rating we would prioritise in North Wales. It rains here, and the label difference is real.
What you can and cannot mix
- Never mix radial and cross-ply on the same axle. This one is a legal requirement, not a recommendation.
- Keep the same size, construction and tread pattern across an axle. Different grip left to right makes braking and cornering unpredictable.
- Do not mix winter and summer tyres across an axle. Fit four winters or none.
- Fit the better pair to the rear when replacing only two. Losing rear grip in the wet is far harder to recover than losing front grip, which is why fitters do this even when the fronts are more worn.
- Check your handbook before mixing brands on four-wheel-drive vehicles. Some are sensitive to small differences in rolling radius and can damage the transmission.
While you are looking at the sidewall, it is worth checking the tread at the same time — our guide to tread depth and the UK legal limit covers the 20p test and why the legal minimum is not the safe minimum.
Tell us the code and we will sort it
Read the numbers off your sidewall and give them to us over the phone, and we will confirm what fits. Our mobile tyre fitting service supplies, fits and balances at your home, work or the roadside anywhere in North Wales.
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Questions, answered
What does 205/55 R16 91V mean?
205 is the tyre width in millimetres. 55 is the aspect ratio, meaning the sidewall height is 55 per cent of the width. R means radial construction. 16 is the rim diameter in inches. 91 is the load index, equal to 615 kg per tyre. V is the speed rating, equal to 149 mph.
Where do I find my correct tyre size?
In the vehicle handbook, and usually on a placard inside the driver's door frame or behind the fuel filler flap. Use that rather than whatever is currently fitted, because previous owners do not always fit the correct size.
How do I tell how old a tyre is?
Find the four-digit code on the sidewall. The first two digits are the week and the last two the year, so 3419 means week 34 of 2019. It is moulded in full on only one sidewall, so check the other side if you cannot find it.
Can I fit a tyre with a different load index or speed rating?
You can go higher on both. You should not go lower. A lower load index means the tyre is carrying more than it was designed for, which builds heat, and a lower speed rating is unsafe at your vehicle's capability. Either may affect an insurance claim.
What is the difference between M+S and the snowflake symbol?
M+S is self-declared by the manufacturer with no test behind it, so it guarantees very little. The three-peak mountain and snowflake symbol (3PMSF) is awarded only after tested snow performance. Look for 3PMSF if you want a genuine winter tyre.
What does XL mean on a tyre?
XL, sometimes shown as Reinforced, means a stronger casing that can carry a higher load at a higher inflation pressure. If your vehicle specifies XL tyres, fit XL tyres, because the standard equivalent will not carry the required load.
Should I inflate to the Max Press figure on the sidewall?
No. Max Press is the maximum the tyre itself can take, not the pressure your vehicle should run. Use the figure on your vehicle's placard or in the handbook. Inflating to the sidewall maximum causes the centre of the tread to wear out and reduces grip.
What do run-flat markings like RFT, ZP and SSR mean?
They all indicate a run-flat tyre, with each manufacturer using its own code: RFT, ROF, ZP, SSR, DSST, EMT and RSC among others. All mean the tyre can be driven for a limited distance at reduced speed after losing pressure. Check your handbook for the distance and speed limits.