Simulation results should have the required degree of accuracy and reliability, that is, a model should be investigated adequately in the real process. Model of a "wheel" class was used as a standalone model for testing of the control algorithms for ABS, as elements of the other, broader models, reproduced adequately the braking forces on the wheels of the car. Analysis of the works of the domestic and foreign researchers shows that currently many different versions of models for calculation of jX - s diagrams are used. However, there are no recommendations concerning selection and use of particular models in the study of the braking process of the car wheels in various conditions. In this regard, the purpose of this study is analysis of the degree of conformity of the values of the coefficient of adhesion to the road wheels, calculated by various dependencies, the values obtained in experiments, and development of recommendations for determination of the optimal formula for calculation of the diagrams depending on the type and condition of a road. The article describes various versions of the dependency of the coefficient of tire to the road coefficient of the longitudinal slip. It also presents the results of the road experiments for different types and conditions of the road surface. The article presents an analysis of conformity of the values of the coefficient of friction of a tire for calculation of various dependencies, and development of recommendations concerning search for the optimal formula for calculation of jX - s diagrams for various types and conditions of the road surface.