Well, I guess I had this coming didn't I
Let's distinguish between two things:
(1) the length of the upper link
(2) the angle of the upper link
Let's assume upper link and lower suspension arm are parallel to each other and have equal length. Let's also assume the camber angle is zero degrees when the car is at rest. In this case when the suspension compresses both arms will follow a similar arc. As a result the camber angle on the
will stay the same, i.e. remain at zero degrees irrespective how far the suspension compresses. So, no camber change!
Now shorten the upper link to say half the previous length. Now the upper link will follow a tighter arc and therefore the
will increase (i.e. top of wheel will lean in towards the car's centerline). Obviously making the top link longer than the lower suspension arm will have the opposite effect...
Now for the angle. Let's assume the link is parallel with the arm and the of the same length again. In this case the roll center is as low as it can pragmatically go given the position of the lower suspension arm. Now angle the link down towards the centerline of the car. This will have two effects:
(1) The roll center at that end of the car is raised higher!
(2) When the suspension is compressed the top of the
will start lean in again (positive camber change)!
Given the above it should now be clear what the shorter and slightly angled rear upper link gives us: higher roll center and positive camber change. The higher roll center makes the car more reactive while the increased camber change minimizes the resulting loss of rear traction when cornering
. This helps us destroy the competition