The official definition of a roll centre, as given by the Society of Automotive Engineers, is ‘The point in the transverse vertical plane through any pair of wheel centres at which lateral forces apply to the sprung mass without producing suspension roll.’
The focus is on force application, and the roll centre represents the pivot point of the suspension system in its entirety. Any force that is parallel to the swing arm of the suspension will act in line with the roll centre and result in zero suspension deflection ? hence, no body roll.
The roll centre is a hot topic for enthusiasts and professionals alike. In this article, we?ll dive into the roots of the definition, what it means for vehicle performance, and how it is used as a setup tool. Instant Centres
To understand the roll centre, one must first understand what is known as the instant centre. Figure 1 represents a simple linkage made up of a single beam. At one end is a pivot about which the beam rotates, and the other end sees an applied force.
Figure 1

The force can be separated into two different components: a perpendicular force and a parallel force. The sum of these forces will equal the magnitude of the overall force. However, the contribution of each is applied differently. The beam resists the parallel force as it is supported by the pivot point, while the perpendicular force causes a rotation of the beam about the pivot point as seen in figure 2.
Figure 2

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