Tyre size by reg
Enter a registration to decode the plate and see exactly what a tyre fitment lookup returns: front and rear sizes, load and speed ratings, and the pressures the manufacturer recommends.
That does not look like a UK registration.
Try a current-style plate such as .
Plate decoded
- Registration
- Format
- First registered
What a fitment lookup returns
Representative sample data, so you can see the exact shape before you integrate anything.
{
"data": {
"vrm": "AB12CDE",
"registration_number": "AB12CDE",
"make": "FORD",
"model": "FIESTA",
"colour": "BLUE",
"fuel_type": "PETROL",
"engine_capacity": 1499,
"year_of_manufacture": 2019,
"month_of_first_registration": "2019-03",
"co2_emissions": 119,
"tax_status": "Taxed",
"tax_due_date": "2026-09-01",
"mot_status": "Valid",
"mot_expiry_date": "2026-03-14",
"wheelplan": "2 AXLE RIGID BODY",
"export_marker": false,
"tyres": {
"front": {
"size": "215/50R17",
"pressure_psi": 33,
"load_index": "95",
"speed_rating": "V"
},
"rear": {
"size": "215/50R17",
"pressure_psi": 33,
"load_index": "95",
"speed_rating": "V"
}
}
},
"credit_balance": 499
}This tool decodes the registration and shows the response shape. It does not look up the live fitment for your vehicle, because that data is licensed. For a real lookup, see the Tyre Data API, from 5p a lookup.
Every field you get back
| Field | Type | Description |
|---|---|---|
| registration_number | string | The vehicle registration mark (VRM). |
| make | string | Manufacturer, as recorded by the DVLA. |
| model | string | Model, resolved from the MOT record where available. |
| colour | string | Current registered colour, normalised. |
| fuel_type | string | Fuel type, normalised (PETROL, DIESEL, ELECTRIC…). |
| engine_capacity | integer | Engine capacity in cc. |
| year_of_manufacture | integer | Year the vehicle was manufactured. |
| month_of_first_registration | string | Year and month the vehicle was first registered (YYYY-MM). |
| co2_emissions | integer | CO₂ emissions in g/km. |
| tax_status | string | Current tax status (Taxed, Untaxed, SORN). |
| tax_due_date | date | Date the current tax expires. |
| mot_status | string | Current MOT status. |
| mot_expiry_date | date | Expiry date of the current MOT certificate. |
| wheelplan | string | DVLA wheelplan description. |
| export_marker | boolean | Whether the vehicle is marked for export. |
| tyres.front.size | string | Front tyre size. |
| tyres.front.pressure_psi | integer | Recommended front pressure (psi). |
| tyres.rear.size | string | Rear tyre size. |
| tyres.rear.pressure_psi | integer | Recommended rear pressure (psi). |
| tyres.*.load_index | string | Tyre load index. |
| tyres.*.speed_rating | string | Tyre speed rating. |
How to read a tyre size
A fitment such as 225/45R17 91W is five separate facts written as one string. 225 is the tread width in millimetres. 45 is the aspect ratio, meaning the sidewall height is 45 per cent of that width, so a lower number is a shorter sidewall. R means radial construction, which is what almost every modern car uses. 17 is the rim diameter in inches. 91 is the load index and W is the speed rating.
The load index and speed rating are the two people skip, and they are the two that matter most. They are not a recommendation. Fitting a tyre below the manufacturer's rating can invalidate insurance and is an MOT failure, and on a heavily loaded van the load index is the difference between a legal tyre and a dangerous one.
Why front and rear can differ
A staggered fitment puts a wider tyre on the driven axle, usually the rear. It is common on performance and rear-wheel-drive cars, and it means the vehicle has no single tyre size. Any system that stores one size per vehicle will quote the wrong tyre for half the axles it touches. Pressures diverge for the same reason: a car loaded at the back is specified differently front to rear.
Where a model-level lookup goes wrong
- Optional wheels. The same model can leave the factory on 16, 17 or 19 inch wheels. Quoting against the model rather than the vehicle picks one and hopes.
- Run-flats. A run-flat is not interchangeable with a standard tyre on a car with no spare, and the distinction does not appear in the size string.
- Winter and all-season sizes. Some manufacturers specify a narrower winter fitment on a smaller wheel, which is a legitimate alternative rather than an error.
- Vans and light commercials. Reinforced and commercial-rated tyres carry a higher load index for the same nominal size, and fitting a passenger tyre is not equivalent.
Pressures, and why the placard still wins
Recommended pressures come back with the fitment, and they are a good default. They are not a substitute for the placard in the driver's door shut or the filler flap, which is specific to that vehicle and often lists a laden figure as well as a normal one. Where a lookup and a placard disagree, the placard wins. Treat the returned pressure as the value to pre-fill and the placard as the value to confirm.
Fitting this into a booking flow
For a tyre retailer, the registration is the shortest path from a visitor to a priced basket. Asking for a size loses anyone who has not gone out to look at their car; asking for a plate loses nobody. Resolve the fitment, show the sizes you have in stock for that vehicle, and keep the manual size entry as a fallback rather than the front door.
Tyre Data does that in one call per registration, priced per successful lookup with no contract. Try the response shape in the sandbox, and size your spend with the API cost calculator.
Car spec check
See the factory specification and fitted options a lookup returns for a registration.
Open the tool → Free toolNumber plate checker
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