Contact and friction play a key role in many industrial applications and their modeling is becoming accessible in vibration applications. Two strategies are commonly considered: idealized or perfect contact which assumes no interpenetration of structures at contact points and functional representations that use pressure penetration relationships. The two strategies imply widely different solvers so that the choice between the two is almost always based on a priori decisions. For an application to the prediction of unstable modes in railway brake squeal, the objective of this paper is to objectively compare results obtained with the two models and to show how this comparison can be used to determine parameters of functional laws giving the same results as idealized contact.