The tire data provided by the TTC includes Pacejka96 model coefficients. I am trying to model longitudional forces. There are 12 coefficients listed for the longitudional model. I'm having a problem reading the equations themselves. Several parts of the equation call for dfz (derivative with respect to z?). I don't understand this part - other sources seem to replace this with normal force. When I do this, thrust becomes constant for all ranges of wheel slip. I don't understand why calculus would be involved!