Lightweight wheels can be bent fairly easily by placing your knee or foot right on the peak of the bend, and pulling with your hands on either side of the bend.

Each of these elements has a center; the top of the mound, the deepest part of the fold or depression.

The top of the bump (50) contacts the incident side of the light guide plate (30) so as to limit the displacement of the light guide plate (30) at the incident direction.

Accordingly, when the drive wheel comes atop the bump, the motor-driven actuator (30) has been extended so that the above-spring member has reached an estimated below-spring ascent speed (Vdp).