How does caster affect which way a vehicle pulls?

Caster, which refers to the angle of the steering pivot point in relation to the vertical axis of the vehicle when viewed from the side, plays a significant role in the vehicle's stability and directional control. When a vehicle has negative caster, it means that the top of the steering axis tilts towards the rear of the vehicle. This configuration can lead to reduced straight-line stability, often causing the vehicle to pull to one side or the other.

Specifically, with negative caster, the side with the lower caster angle can cause the vehicle to be less stable, particularly at higher speeds, as it tends to follow the road's contours more readily. This manifests as a pull towards the side with the more negative caster angle. Conversely, positive caster generally promotes straight-line stability, allowing the vehicle to track more reliably down the road without pulling to either side.

In summary, when a vehicle is equipped with more negative caster, it tends to pull towards the side that exhibits this configuration due to the stability issues associated with that angle.