Wheel Sizes

The wheel size is the size designation of a wheel given by its diameter, width, and offset. The diameter of the wheel is given by measuring the distance from one side of the wheel to the other, through the center point of the wheel. The width is the distance measured from the bead seat to the other bead seat.

The offset is the distance from the wheel's true centerline (half the width) to the wheel's mounting surface. Offset is covered in more detail further below. A typical wheel size will be listed beginning with the diameter (in inches), then the width (in inches), and lastly the offset (+ or - for positive or negative, respectively).

For example, 17x8.5 +35, the wheel's diameter is 17 inches, its width is 8.5 inches, and it has a +35 positive offset.

The size of the disc, however, is denoted like 8.5" X 20.0". This means that the width (of thickness) of the wheel is 8.5 inches and the diameter is 20 inches.

Metric-diameter rims cannot be fitted with inch-diameter tyres, or vice-versa.

Wheel Rim Dia [2]

Next article: "Wheel Balance"

References:

[1] https://en.wikipedia.org/wiki/Wheel_sizing#Wheel_size

[2] Figure: "Wheel Rim Dia": https://www.lesschwab.com/on/demandware.static/-/Library-Sites-LesSchwabLibrary/default/dwa0f6ffdb/images/learningCenter/article/content/wheel-diameter.jpg