Originally Posted by RoverDover
The bow you are seeing is "camber" (corrected) and is there by design to reduce/eliminate trailer sway.
It really has no effect on sway, it is a pre stress on the axles for loading. The sway is controlled by caster, which is the inclination of the king pins or ball joints on a steering axle. If the spindle is on the centerline of the axle, there is no caster available. Torsion axles also do not have caster adjustment.
A drop axle which has the spindle above the centerline of the axle can be tilted for caster adjustment which would make the trailer track better.