6. A Panhard/J-bar mounted on the left side of the chassis produces a more stable dynamic condition and more consistent handling due to the limited movement of the left rear corner of the car and so too the rear moment center.
Fact: While it is true that the rear moment center stays relatively at the same height through chassis dive and roll with a left-side chassis mount, that is not what you want.
As the car dives and rolls, the center of gravity of the car moves downward because, in most cases, the entire car is lower in the turns than at ride height. At the same time, with a right side chassis mounted bar, as the right rear (RR) corner of the car is moving lower, so is the bar and with it the rear moment center. With both the CG and the rear MC moving down, the rear moment arm stays relatively the same length and the dynamics remain consistent. With the bar mounted on the left side of the chassis, the opposite would be true. The moment arm becomes shorter as the CG moves down and the rear MC stays at the same height. This loosens the car in the middle of the turns-the exact reason why this design came about and was a useful crutch for a chassis that would not turn well.
A Simple Experiment
It is difficult to understand the importance of an imaginary point and how it could possibly be integral to the dynamics of the front suspension. We generally think in terms of hard points that you can put a bolt through and that are attached to the chassis. The MC is not directly connected to the chassis and has no bolt through it. Some years ago, while I was trying to understand how the moment center really worked, I decided to build a model to find out exactly what influence the MC had on a AA arm suspension.
A two-dimensional model of a double A-arm suspension was built on a board, with spindles and upper and lower control arms. The "chassis" portion was weighted and supported by springs. A series of holes was drilled along the centerline of the chassis between the control arm mounts to simulate the CG of the "car." Arm angles could be changed to create different locations for the moment center.
For each configuration and location of MC, I began at the top CG hole and attached a string and pulled laterally to the right on the string. The "chassis" would roll to the right each time as I moved down from hole to hole. When I reached the hole that represented the MC, the suspension locked up and would not roll. As I proceeded below the MC, the chassis rolled to the left because the moment arm was now inverted.
I changed the MC location several times. Each time I put the CG nail in the hole that represented the MC, the suspension locked up. That told me that the MC was indeed the bottom of the moment arm. When the MC is in the same location as the center of gravity, there is no moment arm and therefore no lever arm to roll the chassis. I finally had my proof-but the research did not end there.
The Industry Begins to Understand MC Racers, as well as race car builders around the country, have experimented with MC location and design and found the correlation between the MC location and front end dynamics to be significant. Front suspension efficiency, as well as camber change characteristics, all depend on the MC height and width. To understand how the lateral MC location affects the dynamics of the car, you need to understand how the forces are applied to the center of gravity and the MC.
Forces and Moment Arms
The true moment arm that tries to roll the suspension is represented as a line between the moment center and the resultant force line. This is called the "Effective Moment Arm." You can see how, with the effective moment arm pointed down and to the right from the center of gravity that as the moment center is located farther to the right, the effective moment center becomes shorter.