How to set own contact forces by plugin?

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Hi

I am trying to create a plugin to implement more complicated tire model like Pacejka model. I have found a plugin which implements a calculation of friction coefficient in depend on a slip ratio. In this plugin contact messages are used to obtain input data namely the slip ration between contact points. Also in this plugin the algorithm applies a calculated friction coefficient to surface by the following lines:

  surface->FrictionPyramid()->SetMuPrimary(friction);
  surface->FrictionPyramid()->SetMuSecondary(friction);

However, I would like to calculate longitudinal and lateral forces separately in my plugin. Then I would like to apply these forces directly to tire(wheel) body. How can I do it? In this case should I disable regular contact forces and how can I do it?

Maybe I am on a wrong way completely and there is another way to implement tire model in Gazebo?

with regards, Alex