Tyre sidewall markings, explained
There is a lot written on the side of a tyre, and most of it matters more than people think — particularly the little manufacturer codes that decide whether a tyre is right for your car or merely the right size.
Start with the big number
The one everyone knows, in the form 225/45R17 94Y:
- 225 — the section width in millimetres, wall to wall.
- 45 — the aspect ratio. The sidewall height is 45% of the width, so about 101 mm here. A lower number means a shorter, stiffer sidewall.
- R — radial construction. Effectively every car tyre you’ll meet.
- 17 — the wheel diameter in inches, because tyre sizing has never fully committed to one system.
- 94 — the load index. 94 means 670 kg per tyre. Never go below what your car specifies.
- Y — the speed rating. Y is 186 mph. Also never go below the original.
Those last two are the ones that fail MOTs and void insurance, and they’re the ones people skip past when they’re shopping on price. If you’re thinking about a different size entirely, our rolling radius calculator will tell you what else is close enough to fit.
Common speed ratings
| Letter | Maximum speed | Typically |
|---|---|---|
| T | 118 mph | Vans, older family cars |
| H | 130 mph | Most family hatchbacks and saloons |
| V | 149 mph | Larger or sportier cars |
| W | 168 mph | Performance cars |
| Y | 186 mph | Fast performance cars |
The date code — how old is this tyre?
Look for DOT followed by a string of characters. The last four digits are the ones that matter: the first two are the week, the last two the year. 2325 means the 23rd week of 2025.
Tyres age whether they’re used or not. On a car, the tread usually wears out long before age becomes the issue. On a caravan, trailer or a low-mileage classic, age is almost always what finishes the tyre — see our guide on how old is too old for caravan tyres.
It’s also worth a look when you buy: a “new” tyre that has been sat in a warehouse for four years is legal to sell, but you’re buying less life than you think.
The other markings you’ll see
| Marking | What it means |
|---|---|
| XL or Reinforced | Extra load. A stronger casing that carries more weight at a given pressure — and needs higher pressures. If your car specifies XL, fit XL. |
| M+S | Mud and snow. Self-declared by the manufacturer and not a reliable winter indication on its own. |
| 3PMSF (a snowflake in a mountain) | The real winter certification — tested and earned. This is the one that counts for winter and all-season tyres. |
| Run-flat: RSC, ROF, RFT, ZP, SSR, EMT, DSST, MOE | Every maker has their own name for it. All mean a self-supporting sidewall. See our run-flat guide. |
| Outside / Inside, or an arrow | Asymmetric or directional tread. Fitted the wrong way round, the tyre doesn’t clear water properly. Easy to get wrong, and it happens. |
| TWI | Tread wear indicator — small raised bars in the grooves at 1.6 mm, the legal minimum. When the tread is level with them, the tyre is done. |
| Treadwear / Traction / Temperature | American UTQG ratings. Of limited use in the UK, though treadwear gives a rough sense of how hard the compound is. |
| Seal, Silent, Acoustic, ContiSeal, SoundComfort | Built-in sealant, or acoustic foam bonded inside to cut cabin noise. Common on EVs. |
The part most people miss: manufacturer approval marks
This is the one worth reading properly.
A small code on the sidewall — MO, a ★, N0, AO, VOL — means that tyre was developed with that car maker, for those cars, and signed off by them. It is not marketing. A tyre in the same size, from the same brand, with the same tread pattern but without the mark can be a genuinely different tyre: different compound, different casing stiffness, sometimes a different internal construction entirely.
Car makers spend years on this. The suspension, the stability control thresholds, the ABS calibration and the steering weight were all developed against a specific tyre. On an EV, the approved tyre is usually also carrying low rolling resistance targets that feed directly into the official range figure, and often acoustic foam because an electric car has no engine noise to hide road roar behind.
The marks you’ll actually meet
| Mark | Car maker | Worth knowing |
|---|---|---|
| MO, MO1, MOE | Mercedes-Benz | MOE is the run-flat (“Extended”) version. MO1 is AMG-specific. |
| ★ (a star) | BMW and MINI | Often alongside RSC, which denotes a BMW run-flat. |
| AO, RO1 | Audi | AO is standard Audi approval; RO1 is Audi Sport / quattro GmbH and also appears on Lamborghini. |
| N0 to N6, NA0, NF0 | Porsche | The number is the generation of approval, not a quality grade. Mixing generations across an axle is not recommended. |
| VOL, V | Volvo | VOL is the common one; some Polestar tyres carry their own mark. |
| J, LR, JLR | Jaguar Land Rover | Worth looking for on Range Rovers in particular, where air suspension and off-road modes were calibrated around them. |
| K1, K2, F | Ferrari | Model-specific — a K1 tyre is approved for particular cars, not the whole range. |
| MGT | Maserati | |
| AM, AML | Aston Martin | |
| AR | Alfa Romeo | |
| T0, T1, T2 | Tesla | Usually paired with acoustic foam inside the tyre and a low rolling-resistance compound, both of which affect range and cabin noise. |
| TPC followed by digits | General Motors | GM’s Tire Performance Criteria — seen on Chevrolet, Cadillac and Corvette. |
There are more, and some makers use marks that never appear in the UK. If you find a code on your sidewall that isn’t here, it’s almost certainly an approval mark for whoever built your car — ring us with it and we’ll tell you.
So do you have to replace like-for-like?
Legally, no. An MOT tester checks size, condition, load index, speed rating and that the tyres match across an axle in construction. There is no law requiring an approval mark.
In practice, it depends on the car and on what you value.
When it genuinely matters
- Performance cars. Porsche, AMG, M-cars, Audi RS. These were developed on a specific tyre and they feel different on anything else. The approval mark exists for a reason on these.
- Electric cars. A non-approved tyre can cost you real range and bring noticeably more road noise into a quiet cabin.
- Air suspension and adaptive dampers. Range Rovers in particular — the systems were tuned around the approved tyre.
- Anything still in warranty, on PCP or leased. Check the agreement. Some require approved tyres at hand-back, and an end-of-lease inspection is an expensive place to discover that.
- Replacing only one or two. If the tyres already on the car are approved, match them. A mismatch across an axle is worse than fitting a set of four non-approved tyres to everything.
When it honestly doesn’t
- An ordinary family car out of warranty. A good non-approved premium tyre is a fine choice — often a better one than a budget tyre that happens to carry a mark.
- When all four are being replaced together. The car will be consistent with itself, which is most of what matters.
- When the approved tyre isn’t available. Sometimes it just isn’t, and waiting three days on a car you need today is the worse outcome.
The rule we work to: consistency across an axle beats the approval mark, and the approval mark beats brand loyalty. Four matched non-approved tyres are better than two approved and two not.
Where to find what your car should have
Three places, in order of reliability: the plate in the driver’s door shut or inside the fuel flap, which lists the approved sizes and pressures; your handbook; and the sidewalls of the tyres already on the car — bearing in mind those may have been changed by a previous owner.
Or just ring us with your registration. We look this up dozens of times a week, we’ll tell you what your car came on and what we can get, and we fit at your home, work or the roadside — see mobile tyre fitting.