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 In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...

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

cart A cart or dray (Australia and New Zealand) is a vehicle designed for transport, using two wheels and normally pulled by one or a pair of draught animals. A handcart is pulled or pushed by one or more people. It is different from the flatbed ...

s: light two-wheeled horse-drawn vehicles. Cart wheels with dropped axle

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 Float may refer to: Arts and entertainment Music Albums * ''Float'' (Aesop Rock album), 2000 * ''Float'' (Flogging Molly album), 2008 * ''Float'' (Styles P album), 2013 Songs * "Float" (Tim and the Glory Boys song), 2022 * "Float", by Bush ...

milk float A milk float is a vehicle specifically designed for the delivery of fresh milk. Today, milk floats are usually battery electric vehicles (BEV), but they were formerly horse-drawn floats. They were once common in many European countries, ...

, where a dropped axle was used to give a low load bed for easy loading of churns or similar unstable liquid cargo. Milk float, c 1904

Dropped axles were made of forged

wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...

. 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. {{-

Cars

As cars increased in speed after

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...

, the use of a dropped front

beam axle A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have als ...

became almost universal, so as to lower the mass of their heavy front-mounted engines, improving stability when cornering. Rear axles were also beam axles, but needed to remain straight as they contained the halfshafts. Axles were made of drop-forged

H girder An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an or -shaped ...

sections, so forging their upswept ends was a simple addition. To avoid creating

stress riser In solid mechanics, a stress concentration (also called a stress raiser or a stress riser) is a location in an object where the stress is significantly greater than the surrounding region. Stress concentrations occur when there are irregulariti ...

s, the drop was formed as smooth curves, not as sharp corners.

Bugatti Automobiles Ettore Bugatti was a German then French manufacturer of high-performance automobiles. The company was founded in 1909 in the then-German city of Molsheim, Alsace, by the Italian-born industrial designer Ettore Bugatti. The cars ...

famously used a round bar for their axles, with the spring passing through holes within it and avoiding the

U bolt A U-bolt is a bolt in the shape of the letter U with screw thread A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a ...

s that ''il patron'' found so ungainly. For further lowering, at the cost of reduced

suspension travel Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/ handling and ride q ...

, some axles were also prepared for racing by being mounted above the leafsprings, rather than below, although this was more common for straight rear axles than dropped front axles.

Cars

See also