The quick answer
Read the size together with the load index, speed rating and any required tyre-type markings. Check the vehicle’s approved specification as well: the tyre already fitted is useful evidence, but it is not proof that the current fitment is correct.
Read an example without turning it into a recommendation
Take 205/55 R16 91V as an illustrative car marking. It is an example, not a suggested tyre for your vehicle. Michelin’s sidewall guide explains the size format.
| Marking | Meaning |
|---|---|
| 205 | Nominal section width, in millimetres. |
| 55 | Aspect ratio: sidewall height as a percentage of nominal width. |
| R | Radial construction. |
| 16 | Nominal wheel diameter, in inches. |
| 91 | Load index: a code to be looked up, not 91kg. |
| V | Speed category, subject to the tyre’s specified conditions. |
Why the size is not enough
Two tyres can have the same width, profile and wheel diameter but different load capacities or speed categories. In the illustrative example, load index 91 corresponds to 615kg per tyre under the specified conditions. That does not tell you the permitted payload of the whole vehicle. Michelin publishes the load-index table.
Do not choose a lower required rating because your usual journey is slow or the vehicle looks lightly loaded. The approved vehicle specification and use must be established. A higher tyre capacity does not raise the vehicle’s legal axle or gross-weight limits.
Look for additional fitment information
XL or Extra Load, commercial-tyre markings, run-flat designations and manufacturer-specific codes can matter. Write them down or include them in a safe photograph. A symbol or name should not be guessed from a blurry image.
Some vehicles use different front and rear sizes, so specify the affected wheel. Tell the fitter about aftermarket wheels or other modifications. A registration lookup may help, but it must be checked against the vehicle actually presented.
Commercial tyres need the full service description
HGV markings may include service descriptions relevant to single and twin fitments. Do not delete the second number because it looks unnecessary. Supply the entire marking, tractor or trailer identity, axle position and operator records where available.
Tyre selection for a commercial vehicle involves the approved specification, axle use and operating conditions. This guide does not provide a load calculation or approval for a substitution. Let the operator and competent tyre professional confirm the requirement.
Do not confuse pressure markings with the vehicle setting
A maximum-pressure marking on the sidewall is not automatically the recommended running pressure for your car or van. Use the vehicle manufacturer’s information, normally in the handbook or on a vehicle label, for the relevant loading condition.
For commercial vehicles, use the operator’s approved pressure information and competent maintenance process. Do not infer a pressure by looking at a similar tyre on another vehicle.
Send a useful tyre photograph
Where it is safe, capture the whole size and nearby load/speed markings in focus. Tell us which wheel it is and whether there are different front/rear sizes. Add the registration and any available approved-fitment information.
If the numbers are hidden, damaged or on the inside of the wheel, call with what you know. You do not need to move the vehicle unsafely or reach under it to complete the enquiry. Fix My Tyre checks the replacement requirement before confirming attendance.
Common questions
Does “R16” mean a 16cm tyre?
No. The number identifies the nominal wheel diameter in inches; R describes radial construction.
Is load index the same as tyre pressure?
No. Load index is a capacity code. The required inflation setting comes from the appropriate manufacturer and vehicle information.
Can I copy the size from another wheel?
It may help, but make clear that it is a different wheel. Some vehicles have different axle fitments, and the damaged wheel’s requirement must be confirmed.
Sources and further reading
Guidance checked on 10 October 2026. Use the current official instructions for your vehicle and circumstances.