Coefficients of friction

[JLB4344]

Hi there, could anyone tell me if there is a relationship between either Ra or Rz values and the coefficient of friction for the material. If so what is the equation that relates them. I am currently trying to work out the coefficient of friction between the piston rings and cylinder liner and also between the camshaft and shim on top of the cam follower.
Any ideas would be greatly appreciated.

Thanks
John