The method for finding the...
The method for finding the MC location is to use extensions of the control arms through the centers of rotation of the ball joints and inner mounts to form instant centers. The two lines extending from the instant centers to the center of the contact patch of the tire on the same side cross to create the moment center location.
In another scenario, what if when we visualize this car, the ends are not inline, but rolling different angles? What does that mean? It means the overall race car setup is not balanced and the result is obvious, because the two ends don't line up and the overall look is much different than before the car was cut in half.
It's this equality or difference in the front and rear roll angles that constitutes modern chassis setup analysis. We now design our setups based on trying to achieve a balance in roll angles, and in doing so, a dynamic balance in the setup of the car.
Why Is Balance Important?
When the two ends of the car are in sync, meaning desiring to roll to the same angle our load transfer is predictable, all four tires are working to their maximum meaning that they have the most load possible on each tire. The two tires at each end are more equally loaded and therefore produce more grip resulting in faster speeds through the turns.
When the two ends aren't in sync and not rolling to the same angle, an imbalance exists that will cause less than optimum load transfer. The sets of tires become more unequally loaded resulting in less overall traction and less resistance to lateral force. The car must go slower through the turns than if it were balanced because the tires have less grip.
It's Not So Complicated
To create the measurements...
To create the measurements for finding the MC, in a two dimensional diagram, we measure the distance from the centerline, half way between the centers of the two contact patches, out to the points and the height from the ground to the points as shown.
OK, you might have to re-read the preceding parts of this discussion a few times, but getting a grasp on the above is necessary in understanding how our race car works and what our goals are in setting it up.
To help know what influences the chassis roll angle in our cars, I have created the following list in order of importance, the most significant at the top. The understanding of this principle will influence your decisions when making changes to your car.
1. Moment center location, front and rear. Moving the front MC left or right will have a significant effect on the stiffness of that suspension and moving the rear MC up or down will have the same effect.
2. Spring split on a straight axle system. More than spring rate stiffness changes, a difference in rates left to right has a significant effect on the amount of roll angle, especially on higher banked tracks.
3. Spring stiffness and sway bar stiffness.
4. Center of gravity height. The height of the CG helps determine the amount of roll angle, the higher the CG the more roll angle.
5. Lateral g-force. The more grip and faster we go through the turns, the more lateral force, or g-force we develop. And, therefore, the greater roll angle we see.
6. The track banking angle has an effect on the amount of roll angle. The higher the banking, the greater the g-force, but the less roll angle.