Tyre Plus Sizing
- Wheel or Rim Diameter: This is the diameter of the wheel or rim, not including the tyre. Usually measured in inches, modern vehicles usually have rims ranging from 16” to 20”. Although some high performance or modified vehicles can have rim diameters in excess of 20”. For a detailed description of how to identify your rim size please click here.
- Overall Rolling Diameter: This is the outside diameter of the tyre, while it is fitted to the chosen rim. This measurement is usually given in millimetres and can be calculated by adding the diameter of the rim to the sidewall height of the tyre. Sidewall height is also known as sidewall aspect ratio, profile or series. For a detailed description of how to calculate this value please click here.
- A larger rim with a lower sidewall profile tyre will provide better handling, with increased steering and braking response. The reason being that the smaller sidewall is stiffer, which gives the driver a more direct feeling of control over the vehicle rather than the more spongy feel of a large sidewall profile tyre.
- The larger rim will enhance the look of the vehicle, giving it a more aggressive stance. You will notice that most modern performance vehicles have large rims with low sidewall profile tyres.
- Speedometer accuracy: Your speedometer is calibrated to suit the manufacturers overall rolling diameter. If this is changed your speedo will no longer be accurate.
- Traction Control, Stability Control and ABS: These sophisticated electronic systems are also calibrated to suit the vehicle’s original overall rolling diameter. These systems can be very precise and even a small change in overall diameter may alter their functionality.
- Interference: Clearances can already be quite tight on some vehicles and a change in overall rolling diameter or tyre width may lead to the tyre touching the wheel arches, the body of the car or suspension and brake components. This interference can be dangerous and will definitely damage your tyres.