Car steering characteristics?

To clarify the tendencies that may result from a turn, one should look at the tread pattern of the tires in contact with the ground, the steering forces that occur therein, and the change in the angle of side slip. Assuming that a car turns to the right, the rolling wheels are subjected to a lateral force (centrifugal force), which creates another steering force of equal strength but in the opposite direction.

Because the tire itself has a certain deformability, and the tread pattern in constant contact with the road will be slightly pressed to the left due to the change in the center of gravity when the tire is turned to the right, the angular difference between the right turn and the left pressure is the tire's sideslip angle, which corresponds to the steering force of the tire.

The steering force and the slip angle are related to each other, and this relationship is largely structural. While steering force becomes greater as the angle of slip increases, this can only go up to a certain point. When the sideslip angle is in a moderate range, the steering force of the tire can reach a smooth stage, once beyond this smooth stage, the steering force will gradually decline as the sideslip angle increases.

Side slip angle is a rolling friction, not sliding friction. A sliding tire will produce less steering force than a rolling tire, and if the tire loses traction completely, the angle of slip will no longer be an effective characteristic. To put it bluntly, the concepts of slip angle and steering force are only important factors in characterizing a vehicle's understeer, oversteer, and steering balance. For example, when a car is steering at a fixed speed along a corner of constant radius, if the angle of slip of the front wheels is greater than that of the rear wheels as the steering force is stabilized, the car will inevitably follow a greater arc of the turn. In the case of a fairly fast speed, you must change the angle of steering until the dead center, the car at such a limit, the body will be in the tangential direction of the curve out.

Driving around a curve, the angle of slip is small when the car is slow, and the frictional resistance required when the car is fast is increasing rapidly as the square of the car's speed. The centrifugal force at this time pushes the car out of the arc, and the driver feels compelled to turn the steering wheel some more to maintain the required steering arc. The driver is then forced to twist the steering wheel a little more toward the inside of the arc (the direction of the turn) to reduce the radius of gyration. At this point, the side slip angle of the front wheels is much greater than that of the rear wheels, a condition called understeer.

On the other hand, if the rear wheels have a larger slip angle than the front wheels, the car turns along a smaller arc. As the speed of the car increases, the steering angle must be reduced, or adjusted somewhat in the opposite direction. In extreme conditions, the car will begin to flop. If the steering wheel is accidentally twisted too far into the corner, the rear wheels may immediately lose their tendency to grip and make a larger arc outward from the curve, due to the inertia of the body.

When this imagery occurs, it is necessary to rely on greater lateral force, that is, to increase the rear wheel's sideslip angle, in order to push the car back into the arc of the steering wheel's steering angle, and the driver is naturally inclined to correct for the reduced front wheel's sideslip angle, which is oversteer.

What we often call neutral steering is, of course, a balance between understeer and oversteer. The steering angle is exactly equal to the arc drawn by the curve radius of the corner, and the tires fall correctly on the tangent of the arc. The front and rear axles move outside the arc at the same speed. This situation can occur on any car with any steering characteristics.