The photo above shows an early style Gruppe A semi-trailing arm pickup point. Careful observation
reveals that the attachment point of the trailing arm to the subframe is adjustable for both camber
and toe. Also, the actual pickup point is slightly relocated relative to the stock location
(it is farther up and to the rear).
These Gr A trailing arms had an extra member connecting the two "legs" of the "V", turning
it into an "A". At first blush this would appear to be similar to what is currently done on the
BMW M Roadster/M Coupe. However, there is a subtle difference. In the case of the M Coupe the
reinforcement is engineered to handle compression, tension and bending forces. The reinforcement
on the Gr A car (which is really no more than a "rod") is primarily designed to handle tension
loads. The reason for this is apparent from the photo below. The attachment method used for
the outer trailing arm pickup point does not locate the rod end in the lateral direction.
The rod end is free to "float" laterally, which it has to be as the distance between the inner
and outer pickup points changes as the rod end is screwed in or out to adjust toe. But to keep
the trailing arm from "spreading" under load, the Motorsport boys welded in the tension rod.
The newer style
M Coupe trailing arm reinforcement
achieves the same effect certainly, but it
does a lot more, acting in compression and to some degree in bending as well.