Both methods are intended to prevent relative sideways motion between the axle and body of the car. Watt's linkage approximates a vertical straight-line motion much more closely, and it does so while consistently locating the centre of the axle at the vehicle's longitudinal centreline, rather than toward one side of the vehicle as would be the case if a simple Panhard rod were used. It consists of two horizontal rods of equal length mounted at each side of the chassis. In between these two rods, a short vertical bar is connected. The center of this short vertical rod – the point which is constrained in a straight line motion - is mounted to the center of the axle. All pivoting points are free to rotate in a vertical plane. In a way, Watt's linkage can be seen as two Panhard rods mounted opposite each other. In Watt's arrangement, however, the opposing curved movements introduced by the pivoting Panhard rods largely balance each other in the short vertical rotating bar. The linkage can be inverted, in which case the centre P is attached to the body, and L1 and L3 mount to the axle. This reduces the unsprung mass and changes the kinematics slightly. This arrangement was used on Australian V8 Supercars until the end of the 2012 season. Watt's linkage can also be used to prevent axle movement in the longitudinal direction of the car. This application involves two Watt's linkages on each side of the axle, mounted parallel to the driving direction, but just a single 4-bar linkage is more common in racing suspension systems. See also Four-bar linkage Linkage (mechanical) Straight line mechanism Watt's Parallel motion linkage, a straight line linkage built off of Watt's linkage. References External links Watt Beam Engine How to draw a straight line, by A.B. Kempe, B.A. Lemniscoidal (figure 8 curved) linkage of the first kind by Watt Lemniscoidal linkage of the second and third kind by Watt A simulation using the Molecular Workbench software. Automotive suspension technologies Linkages (mechanical) Scottish inventions Linkage Linear motion Straight line mechanisms