The Function-based Behavioral Modeling (FBBM) design tool was introduced in prior work as a means of using formal functional modeling as the foundation for creating detailed mathematical models of system behavior. The overall objective of this work is to create a framework for partitioning modeling efforts into functional elements and promoting model storage and re-use through the use of functional models. In prior work, the FBBM method was introduced to model the complete vehicle dynamics of a Formula SAE racecar, highlighting the representation of functionality and the development of behavioral models. The objective of the work presented in the current paper is to demonstrate the ability to incorporate models of varying fidelity within a function-based behavioral model of a complex system. Additionally, the impact of model fidelity on the models predictions is addressed. A previously developed model is used as a foundation for developing the necessary new models and illustrating the impact of model fidelity on performance predictions when selecting a tire during early design. The results illustrate that the FBBM framework allows models of varying fidelity to be quickly made and their effect on predicted performance to be measured in order to assist critical early design choices.