Identifying the wheel size:

Markings on the inner side of the wheels identify 18-inch Turbo wheels with the sizes 9J x 18 RO 52 and 10J x 18 RO 65.

The sizes together with the rim offset (RO) and spare part number are marked with A or B.

The correct version for the model is marked with an X which is struck into the "A" or "B" boxes provided.

Figure shows model "B".

Fig 1: Identifying Wheel Size - 18-inch Turbo Wheels (Technologie Wheels)

Courtesy of PORSCHE OF NORTH AMERICA, INC.