Testing and Improving a Tyre Shear Force Computation Algorithm

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Testing and Improving a Tyre Shear Force Computation Algorithm

Sharp, R.S.

Summary Existing computational procedures are applied to the parametric description of tyre shear force and moment data under pure slip conditions and to the subsequent generation of combined slip results. The methods rely on the Magic Formula, normalization of forces and slips and nonlinear slip transformations. These contribute to equivalence between longitudinal and lateral slips when, as is usual, tyre forces are substantially anisotropic. Recently published experimental results are used to test the methods. It is shown that good descriptions of pure slip behaviour result and that the combined slip results are smooth and reasonable. Systematic differences are shown to occur between computed and measured results however and the physics behind the differences are explained. Modifications to the computational algorithmare made, based on the physics, and the combined slip results retain their smoothness and improve their accuracy significantly. It is concluded that the method is effective in allowing information to be gleaned from pure slip testing and to be applied to the calculation of completely general steady state forces and moments. The information can be contained in a relatively small number of parameters. It is apparent that little accuracy is lost, as compared with a full spectrum of tests and much more extensive parameter identification. Considerable potential for economy of testing is implied and some computational economy is also likely to result from use of the methods. The updated algorithm is given in an appendix to the paper.