Figure 7
Moving on, take your center of gravity height measurement and multiply it by 0.5 (50 percent) and write down your answer. Now multiply the height by 0.8 (80 percent) and write that down. Next, draw a vertical line through the front axle perpendicular to the ground, and plot two points using your answers above as the number of inches from the ground. The space between these two points represents the percent of antisquat you will be aiming for. This will be discussed further in Figure 9.
Figure 8
Next draw a vertical line down from the LCPs to the sideview drawing. Extend lines from the upper links back and lower links forward until they cross the lines you brought down from the LCPs. This will show you the heights of the LCPs. Now when you connect the two LCPs on the lower drawing with a straight line, you will get the roll axis. This is the imaginary line perpendicular to which the axle will articulate. As such, you want the front of the roll axis slightly lower than the rear. This will give better handling and less rear oversteer as the axle articulates. If your roll axis leans toward the back of the truck, you may need to lower the upper link's frame mount or increase the height of the axle bridge. Just don't let the upper link's frame-mounting point get lower than the lower-link's frame-mounting point--better yet, keep them apart. As you can see, there will be many opportunities to adjust and diverge from the original design to get the geometry correct.
Figure 9
To make sure your suspension transmits power to the ground, you want a certain amount of antisquat. This will let the tires move the vehicle forward without the energy compressing or expanding the suspension. The perfect amount of antisquat is debatable, depending on the driver's desires. Some want the vehicle to crouch when accelerating, but this is sending the power into the springs. Some want the vehicle to lift under acceleration to gain more traction, but this can let the axle walk under the vehicle instead of propelling it forward. We will try to design the suspension not to squat or lift excessively, while erring on the squat side. The way to determine antisquat is to run a line from the contact patch (CP), or center of where the rear tire touches the ground, to a point where the upper and lower links would converge in the front of the vehicle while viewed from the side.
The point towards the front of the vehicle where the links would converge is known as the instant center (IC). The line from the instant center to the contact patch of the rear tire should run across the vertical line through the front tire. If it is within the 50 percent to 80 percent of the center of gravity height at the front tire that we determined in Figure 7, then it should be a good amount of antisquat to start from. If you want it to lift more, you need the line to be closer to the center of gravity or above 80 percent. If you want it to squat more, you want the line closer to the ground or below 50 percent. Now if the antisquat is not where you want it, you must start adjusting the link-mounting points. If you move the lower axle point up on the axle, remember to raise the upper link's axle mount as well. If you move the lower link's frame mount, then you may need to move the upper link's frame mount as well. Then after you think you have gotten the links where you want them, move your new dimensions back to those of Figure 8 and make sure your roll axis is angled towards the front of the truck. Expect to spend many long hours moving your measurements back and forth between Figures 8 and 9 until you have everything dialed in.