.....Moving the upper link further from the rear wheel definitely isn't going to reduce flexing at that point (and really isn't designed to affect that anyway). The upper link's real purpose is to keep the drivetrain (engine, trans, and rear wheel) aligned vertically with the frame and front wheel. Side to side alignment is controlled by the lower link and the rear trans/swingarm mount.....
Jerry
I agree with Jerry and Chief, the major problem related to the motor/trans is the rubber mount on the motor, trans and swing arm. The flex allowed by this design allows the rear wheel to change camber while cornering......
I believe we all agree that keeping the rear wheel aligned vertically with the front is necessary in order to achieve stable handling at high speeds. Actually I don’t think that it matters as much that the wheels are perfectly aligned, but that the relative alignment doesn’t change substantially when riding.
My sense of the benefit for moving the top stabilizer link from the center of the frame to the steering head is to reduce the affect of torsional chassis flex on wheel alignment. This is most evident during times when the machine is being ridden hard at high speed. The benefit from moving the link is realized by allowing the midpoint of the chassis to move independent of the top stabilizer link. The steering head is the logical choice for the anchor because it also maintains the vertical alignment of the front wheel.
The rear tire is going to follow the lateral movement of the top stabilizer link at nearly a 1:1 ratio; an 1/8” of lateral stabilizer movement will result in nearly an 1/8” of movement at the tire tread’s centerline. This isn’t a question of whether the frame is going to flex under high load; it’s a question of how much.
The folks marketing the aftermarket stabilizers boldly assert that the rear powertrain mounts are the weakest link in the Twin Cam’s chassis. There is no mention of the inherent flexibility of the double cradle frame relative to contemporary perimeter frame designs. This makes good sense if the goal is to sell stabilizer links, but if the intent is to explore the possible reasons for high speed instability, the frames ability to resist torsional loading should considered. It is my strong sense that the issues resulting from the torsional flexibility of the Twin Cam’s double cradle chassis far exceed the overhead of properly functioning rear powertrain mounts.
These ramblings are not intended to be presented as fact, but simply as my humble opinion.
djkak