The physical forces applied to vehicle inertial dynamics derive primarily from the tires. These forces have a profound effect on handling. Tire force modeling therefore provides a critical foundation for overall vehicle dynamics simulation. This paper will describe the role tire characteristics play in handling, and will discuss modeling requirements for appropriately simulating these effects. Tire input and output variables will be considered in terms of their relationship to vehicle handling. General computational requirements will be discussed. An example tire model will be described that allows for efficient computational procedures and provides responses over the full range of vehicle maneuvering conditions.