Early forms of suspension on ox-drawn carts had the platform swing on iron chains attached to the wheeled frame. This system remained the basis for most suspension systems until the 19th century, although the iron chains were replaced with the use of leather straps called thoroughbraces by the 17th century. No modern automobiles have used the thoroughbrace suspension system. By approximately 1750, leaf springs began appearing on certain types of carriage, such as the Landau. By the middle of the 19th century, elliptical springs might additionally start to be used on carriages.
Automobiles were initially developed as self-propelled versions of horse-drawn vehicles. The first workable spring-suspension required advanced metallurgical knowledge and skill, and only became possible with the advent of industrialisation. Obadiah Elliott registered the first patent for a spring-suspension vehicle; each wheel had two durable steel leaf springs on each side and the body of the carriage was fixed directly to the springs which were attached to the axles. In 1901, Mors of Paris first fitted an automobile with shock absorbers. Henri Fournier won the Paris-to-Berlin race on 20 June 1901, with a time of 11 hours 46 minutes and 10 seconds, beating Léonce Girardot’s 12 hours, 15 minutes, and 40 seconds [https://en.wikipedia.org/wiki/Car_suspension]. The use of shock absorbers is noted as contributing to Fournier’s success [https://en.wikipedia.org/wiki/Car_suspension]. Coil springs first appeared on a production vehicle in 1906 in the Brush Runabout.
Leaf springs have been around since the early Egyptians. Ancient military engineers used leaf springs in the form of bows to power their siege engines. Leaf springs were the first modern suspension system, and, along with advances in the construction of roads, heralded the single greatest improvement in road transport until the advent of the automobile. In 1920, Leyland Motors used torsion bars in a suspension system. In 1922, Lancia Lambda pioneered independent front suspension, and became more common in mass market cars from 1932. Today, most cars have independent suspension on all four wheels.
The spring rate (or suspension rate) is a component in setting the vehicle's ride height [https://en.wikipedia.org/wiki/Car_suspension]. When a spring is compressed or stretched, the force it exerts is proportional to its change in length. The spring rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. Vehicles that carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke).
Wheel rate is the effective spring rate when measured at the wheel, as opposed to simply measuring the spring rate alone [https://en.wikipedia.org/wiki/Car_suspension]. Roll rate is analogous to a vehicle's ride rate, but for actions that include lateral accelerations, causing a vehicle's sprung mass to roll [https://en.wikipedia.org/wiki/Car_suspension]. It is expressed as torque per degree of roll of the vehicle sprung mass. Weight transfer during cornering, acceleration, or braking is calculated per wheel and compared with the static weights for the same wheels.
Suspension systems can be broadly classified into two subgroups: dependent and independent. Dependent systems normally have a beam or a live axle that holds wheels parallel to each other and perpendicular to the axle. Independent suspension allows wheels to rise and fall on their own without affecting the opposite wheel. Semi-independent suspensions allow the wheels of an axle to move relative to one another, but they are not rigidly attached.
Damping controls the motion or oscillation, as seen with the use of hydraulic gates and valves in a vehicle's shock absorber. Travel is the measure of distance from the bottom of the suspension stroke to the top of the suspension stroke. Roll center height is a product of suspension instant center heights and is a useful metric in analyzing weight transfer effects. Anti-dive and anti-squat are percentages that indicate the degree to which the front dives under braking, and the rear squats under acceleration.
Suspension systems are also used in armoured fighting vehicles, including tanks, which require specialized designs to handle heavy weight and rough terrain. Early tanks had fixed suspension, which was improved with leaf springs and coil springs. Later designs incorporated torsion bar suspension. Tracked vehicles also utilize specialized suspension systems to distribute weight and provide traction.