You can find the car manufacturer’s recommended original size on a plate on the vehicle – this is usually on the driver’s door or door pillar, but could also be on the back of the fuel filler door, under the bonnet or in the glovebox compartment. If your car’s wheels are a different size to the ones that it came from the factory on, then the tyre size that was originally recommended by the manufacturer might no longer fit the vehicle. Instead you can check the size of the tyres that are on the car – the size is shown on the side of the tyre as shown in the diagrams above.
This number represents the width of the tyre and is measured in millimetres between the sidewalls of the tyre, at its widest point. The measurement is always done when the tyre is inflated and mounted on the rim size it is designed for.
This is the height of a tyre's sidewall as a percentage of it's width. In this example, the tyre's sidewall is 55% of 195, so it will measure approximately 107mm high all around the rim.
This is the diameter of the rim and with the exception of some rare European fitments, is always expressed in inches.