What is defined as the closest inside usable portion of the roadway in racing or driving?

The term that defines the closest inside usable portion of the roadway in racing or driving is "Course apex." The apex of a racing course refers to the point where you can take the tightest line through a turn. This is the ideal spot to start accelerating out of the corner, as it allows a driver to maintain speed while navigating bends in the track. Finding the apex is crucial for optimizing lap times, as it enables the driver to maximize the vehicle's performance through a turn.

Different terms may relate to aspects of vehicle control and racing techniques, but they do not specifically capture the concept of the closest usable portion of the roadway in the way that "Course apex" does. For example, "Track limit" pertains to the boundaries of the racing surface itself, while "Corner entry" focuses on how a driver approaches the beginning of a turn, not specifically the innermost part of the driving line. Thus, "Course apex" accurately conveys the strategic point within the turn where maximum speed can be maintained.