4 link question for the Engineer types

[DynoDon]

I notice that there are basically two types of Triangulated 4 Links; Upper links mounted near the center of the diff and angling out towards the frame rails, and upper links mounted out near the brakes and angled towards the driveshaft.
What are the pros and cons of each and are there different handling characteristics between the two types?
Thanks, Don

[exwestracer]

Don,
The main difference (lengths and angles being equal, etc.) has to do with roll center location. The roll center is defined as the point around which the axle assembly revolves. In a tri-4 link setup, this is intersection point of the angled links. If this point is at or near the rear axle centerline (links angled OUT to the front), then only the lower link motion will contribute to roll steer. If the intersection point is ahead of the axle (links angled IN to the front), then both the upper and lower links contribute to axle steer in roll. This isn't necessarily BAD, but it does complicate the setup somewhat...

As a practical matter, angling the links in usually requires more chassis weight and fabrication, as a pretty beefy crossmember is required ahead of the axle to handle the upper link push /pull loads from acceleration and braking. If the links are angled out from the axle, they can usually be attached directly to the frame rails.

Hope this helps.

[MonzaRacer]

also one simple point not mentioned,well 2.
Angling the uppers make it self centering and and as for pointing in or out has to do with packaging.
Another point is you will get better ability to adjust with them pointed out as the ones pointed inside converge at one point.
Think of it this way, if you lift a bar bell do you put your hands close together or farther apart?
With them pointed out and varying the angles and such you can allow for torque steer, axle lift etc and get a balance of all factors and still maintain a proper ride.
Parallel 4 link and a Watts link work better in performance areas as the triangulated system has some bind built in.
Now some do swap in Johnny Joints to remove even more of the bind.

[AMC Racer]

Parallel 4 link and a Watts link work better in performance areas as the triangulated system has some bind built in. Now some do swap in Johnny Joints to remove even more of the bind.

Understanding is a triangulated 4-link is kinematically free (no bind) if the links are free to rotate at their pivots ... using rigid or semi-rigid bushings causes the bind. A 5-link (4-bar with panhard or Watts) is over-constrained so requires compliance in the bushings or links to prevent bind in roll. A 4-link (parallel 3-link with panhard or Watts) is kinematically free like the tri-4-link, with advantage of RCH adjustment and lateral location with just the panhard or Watts.

[silver69camaro]

Parallel 4 link and a Watts link work better in performance areas as the triangulated system has some bind built in.

Typically the bind shouldn't show until 5 degrees or more of roll (assuming the design is decent), which is about 2 degrees higher than what will actually happen. See our triangulated 4-bar to 3-link comparison...the only advantage was the adjustable RC with the 3-link.

[DynoDon]

Matt, what are your thoughts on the original question I posed concerning how the upper links are positioned? You were one of the ones I was hoping would weigh in on this.