We’ve covered the journey of forces from the tyre contact patch through the wheels and suspension into the springs and dampers, and now we arrive at their final destination, the chassis.
In this penultimate article of the racecar vehicle dynamics series, tyre dynamics, suspension, kinematics and spring-damper systems all come together and interact with the chassis to complete the puzzle of vehicle performance.
Chassis control is a large part of effective vehicle dynamics. That means keeping all 4 contact patches on track! [Macau Photo Agency]
Chassis Modes
In the vehicle dynamics world, we refer to chassis modes. Modes are combinations of wheel deflections that produce a particular form of chassis displacement. Traditionally these modes are discussed concerning road inputs, but the concept is also used to illustrate chassis displacements caused by longitudinal and lateral forces generated whilst driving. There are four displacement modes: Heave, Pitch, Roll, and Warp. For brevity, I’ll summarise the modes in the table below.

Chassis Modes; Illustration 1 [Zapletal. (2000) Balanced Suspension]
Heave is an interesting mode in motorsport due to its relationship with ride height and underbody aerodynamics. With huge aerodynamic loads forcing the chassis towards the track surface, spring stiffnesses must be specified very high to maintain the chassis in the optimal window of its aero map; this introduces some significant compromises when those loads aren&#...