The size of the mechanical trail due to caster may not be too large compared to the Pneumatic trail from the tire. The pneumatic trail will approach zero as the tires reaches the slip limit. This will result in lowering the self-centring torque
that is present due to the lever arm between the tires rotation point at the ground and the point of attack for the lateral force. This will be a signal to the driver that the tire is near breakaway. This “breakaway signal” may be lost if the mechanical trail is large compared to the pneumatic trail.