A steering dampener may be needed to reduce shimmy on vehicles that have a high positive _______.

When discussing the need for a steering dampener to reduce shimmy on vehicles, the focus is on the role of the caster angle. Caster refers to the angle of the steering axis when viewed from the side of the vehicle; a high positive caster angle indicates that the top of the steering axis tilts toward the rear of the vehicle. This design helps with stability and steering return but can also exacerbate the tendency of certain vehicles to develop shimmy, particularly at higher speeds or when there are imperfections in the road.

In instances where the caster angle is significantly positive, the increased steering axis angle can create a scenario where vibrations and oscillations become more pronounced, leading to shimmy. A steering dampener helps to absorb these vibrations and provides resistance to oscillations, effectively stabilizing the steering system and improving the overall driving experience.

In contrast, while other angles like included angle, toe, and camber each have their own specific impacts on vehicle dynamics and steering behavior, they do not directly address the shimmy issue in the same way that caster does. Thus, the relationship between a high positive caster angle and the need for a steering dampener is a critical aspect of steering and suspension systems in automotive service.