WARNING: This page is about a different car, the 2016 BMW Z4, 2015 BMW Z4, and 2014 BMW Z4. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Side Wall (000222)
Courtesy of BMW OF NORTH AMERICA, INC.
NOTE:
(side wall) Left side wall. Only required once to set up the base frame, discontinued, available as part of set of special tools only