Begin with the correct certificate
CoC means Certificate of Conformity. It records technical information about the vehicle’s approved specification. When the registration certificate lists only one tyre size, the CoC may show further combinations. It is not a general catalogue covering every variant within a model range.
First establish that the certificate belongs to your vehicle rather than searching immediately for a preferred wheel diameter. A document found online for a similar-looking car may concern a different version. If your own certificate is missing, ask the manufacturer or its authorised representative how to obtain a replacement or a definitive vehicle-specific answer.
A combination is more than a tyre size
Read the tyre-and-wheel entries and their associated notes. Depending on the document format, additional alternatives may appear elsewhere. A page or field number quoted from another certificate will not necessarily apply to every version. Follow the headings and cross-references in your own paperwork.
Record each possible combination as one connected set of information: front axle, rear axle, tyre specification and corresponding wheel dimensions. Do not combine the front entry from one option with the rear entry from another simply because both appear somewhere in the document. A listed tyre dimension also cannot be transferred to any aftermarket wheel without checking suitability.
Separate original specification from later alterations
A CoC describes the approved vehicle specification. Subsequent changes to suspension, brakes or wheels may require additional documentation and inspection. On a used car, check the records of modifications as well. An approved original-equipment combination does not automatically answer every question about a modified vehicle.
Have unclear combinations confirmed before ordering. State whether you intend to use original wheels or aftermarket products. A tyre business needs that distinction to check more than availability of a tyre size. Keep the response with the relevant documents so that the reasoning can be followed later.
When the goods arrive, compare them with that exact confirmed combination. A different load rating, axle allocation or similar but non-identical size should not first become apparent during fitting. The CoC is most useful when its information remains traceable all the way through to the order.
