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This paper focuses on the effect of swingarm deformability on motorcycle stability and in particular on the weave mode. Multibody models for the analysis of stability and handling of single track vehicles require a lumped element representation of the deformability of the critical structural elements of the vehicle. The twist axis method is used to identify lumped stiffness and damping elements able to represent bending and torsion deformability of the swingarm. Experimental tests and identification results dealing with two different swingarms are presented. The identified lumped stiffness and damping elements are implemented in a multibody code and some numerical stability analyses are carried out. Calculated results show that swingarm deformability has a small effect on the stability of super sport motorcycles, whereas the stability of the weave mode of enduro motorcycles is affected by swingarm deformability in a specific range of speeds.

The effect on stability of mass, geometric and stiffness parameters of a bicycle with compliant frame, fork and wheel is studied. Critical stiffnesses of the structural elements are identified by means of specific experimental tests based on modal analysis and static stiffness measurement. Numerical stability analysis is carried out by means of a MATLAB code and simulations are planned with the design of experiment (DOE) approach. Numerical results show that the rigid body properties that have the main influence on self-stability are front wheel radius, longitudinal position of the center of mass and trail. Compliance of structural elements has a small effect on self-stability, but causes the appearance of a wobble mode that may be unstable at high speed.

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