Can we really predict rubber friction? I suppose not yet!

"Prediction" of friction is an old dream. Even in the field of rubber friction, where we think we understand the various mechanisms of hysteresis and adhesion, we are very far from this achievement. Here, you find an interesting independent study on the Persson model for friction.  After you have made huge effort to characterize the surface, with various instrument across scales from cm to nm (!), and another huge effort to characterize material using DMA to extract viscoelastic modulus in decades of frequencies, all you seem to be able to do with Persson's model is to get a cloud of points with correlation as low as R^2=0.2 ...  This seems very poor to any engineer, nothing close to a prediction! We really require a better model. Any better idea to use these data perhaps any other old and simpler fitting equation for friction??
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