Roll Center
Every suspension design has a point at which the truck "rolls" around when leaning from side to side. A higher roll center (relative to the center of gravity) will make the truck lean less in a corner, and a lower roll center will lean more. You might at first think you need a high roll center in order to eliminate excess body roll so the truck handles better, but that's not necessarily the case. When the chassis leans to the outside while cornering, the leaning adds extra weight to the "loaded" outside tires, increasing traction. To have more weight transferred onto the "loaded" tires offers better cornering traction but at the cost of excess body roll (this is where antisway bars come into play.) Calculating roll center is not so important for a daily driver, but knowing it exists and understanding how it can be changed is helpful when designing a quality system or if you intend on speeding around corners in your sport truck.

To find the "simple" roll center of a triangulated link system, you would first find the instant center of the overhead bars (Figure 10). Then, find the distance past the bars of the IC. From there, you would input that distance into the side view. That will give you a close enough roll center to figure from. From the side view (Figure 11), you can see that as the suspension runs through its travel, the roll center will move slightly up and down. That is not necessarily bad, just something to take note of.

From an overhead view, you can see that the roll center is or isn't centered to the chassis depending on the suspension design (Figure 11). And from a side view (which looks just like a nontriangulated link system), you can find the height (the single point of the wishbone.) An off-center roll center should be avoided if any performance is desired. Mounting the single point off center from the truck is not recommended because having an off-center roll center makes the chassis "think" that it's heavier on one side than the other. This can be interesting when driving aggressively on a windy road.

On a side note, a wishbone can take up a lot of extra space to properly set up on a truck designed to lay frame because of the need to mount the single point in the center of the chassis. As a rule, if the truck has a one-piece driveshaft, the system will take up more room than necessary.

Roll Steer
Geometry being what it is, all suspension systems have a steering effect that is induced when one wheel is higher in relation to the chassis than the other; generally this happens while cornering or "hitting sides." It also comes in two different flavors: roll oversteer and roll understeer. Oversteer will steer the truck farther into the corner, causing it to feel as though you have turned the steering wheel too far. Understeer does the exact opposite, needing more input from the wheel to keep on course. Understeer is generally more desirable for a stable-feeling truck, but it's not always that simple. Roll steer is somewhat important to be aware of, as a poorly set-up system can become nearly undriveable if there is too much roll steer of either type. You can see how the wheel moves forward and back in the chassis as the suspension runs through its travel (Figure 12). If one wheel were up and one wheel down, the rearend would have its own steering input, similar to a Radio Flyer wagon. A commonly overlooked characteristic of three- and four-links is the distance that the bars are mounted across from each other. In every case, it is desirable to mount the bars as far to the outside of the axle as possible. Mounting the bars this way helps to minimize roll-steer issues as well as offers more support for the rearend. Top-to-bottom mounting distances are much more complicated and less of a concern. Just try to keep them about 6 inches or so above or below each other at the rearend.