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A dropped axle is the axle of a vehicle that is bent upwards towards the ends, i.e. the centre is 'dropped'. This gives two advantages: the centre of gravity of the bodywork is lowered relative to the wheels, which improves stability; secondly the wheels may be of larger diameter, giving a smoother ride over a rough surface.
Dropped axles were first used for carts: light two-wheeled horse-drawn vehicles.
Note that the weight of the springs has turned the axle upside down.
Their introduction represents one of the safety improvements from the high and unstable dog cart or jaunting car to the lower and more stable governess cart. Their ultimate development was in the float or milk float, where a dropped axle was used to give a low load bed for easy loading of churns or similar unstable liquid cargo.
Dropped axles were made of forged wrought iron. Although wood was widely used for axles, owing to its lightness, it could not easily be shaped with the sharp curves required to drop an axle. Shaping such an axle by sawing or cutting would place an area of cross-grain across the upright part and would rapidly break.