Friction Circle Is BACKWARDS! -- As Far as the Driver is Concerned.
Custom-steering wheel inventor, Ed Dellis, explains how the Friction Circle is backwards from the driver's proprioception standpoint.
The original sign convention was based on the Free Body Diagram, and it describes the forces acting ON THE TIRE which is exactly opposite to what the driver feels inside the car.
This is counter intuitive -- and totally meaningless -- when you're seated behind the steering wheel and you're trying to find the limit of adhesion.
Instead, the Fuzzy Dice Paradigm corrects this, and is 100% consistent with the sensations you feel when you're out on a racetrack.
The Hairbursh and Balloon shows how a tire can go in a different dirction from where it's pointing BEFORE it loses traction due to the inherent flex in the system. Obviously, it can go in a different direction after it starts sliding.
A Rubber Rudder that's cut in 30% from the trailing edges is a good model to visualize how a tire transitions into the sliding coefficient of friction when traversing up the mu-slip curve (see yellow diagram above in the page header) and the cornering force INCREASE per degree of steering wheel angle starts to go away.
Since it's bouyant, it's also a good model for visualizing how the load curve affects traction since the friction coefficient diminishes with increasing load and the rubber will flex as it extends deeper.