Calculate Tyre Dimensions for Plus Sizing/Up-Stepping
On the inside of your wheel, you will find markings similar to this:
6 ½ J x 15 H2 5/112 ET39
Let’s see what each of these symbols mean.
- 6 ½
- Inner width of wheel in inches (6 ½ x 25.4mm= 152.4mm).
- Indicates the shape of the wheel on the place where the tyre bead sits on the wheel.
- Indicates that the construction of the wheel is one-piece.
- Nominal wheel diameter in inches (15 x 25.4mm= 381mm).
- Type of wheels flange. Wheels flange is a bulge on the wheel in the place where the tyre bead lies on the wheel. It prevents the tyre from falling inside of the wheel.
- First number is the number of bolts (in our case 5). The number 112 indicates the so-called PCD (Pitch Circle Diameter) which is the diameter of an imaginary circle drawn through the center hole of the screws on which the wheel is mounted.
- ET is the offset, that is the distance between the centerline of the wheel and the plane of the hub-mounting surface of the wheel. The offset is measured in millimetres and can be positive or negative. In our case it is positive: 39 mm.