In a ground vehicle with a suspension, the unsprung weight, or more properly, unsprung mass, is the mass of the suspension, wheels or tracks (as applicable), and other components directly connected to them, rather than supported by the suspension. (The mass of the body and other components supported by the suspension is the sprung mass.) Unsprung weight includes the mass of components such as the wheel spindles, wheel bearings, tires, and a portion of the weight of driveshafts, springs, shock absorbers, and suspension links. If the vehicle's brakes are mounted outboard (i.e., within the wheel), their weight is also part of the unsprung weight. Image File history File links original diagram GNU Free Documentation License File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The Trikke is a Human Powered Vehicle (HPV) This article is about the means of transport. ... The front suspension components of a Ford Model T. Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. ... A driving wheel on a steam locomotive. ... U.S. M60 Patton tank. ... In a vehicle with a suspension, such as an automobile or a tank, sprung mass (or sprung weight) is the portion of the vehicles total mass that is supported by the suspension. ... The word spindle might (or might not) have several meanings: A spindle (shrub), a poisonous shrub or small tree of the genus Euonymus. ... Bearing is the following: Often, bearing is the state of having something as a quality, characteristic, or permanent attribute. ... A tire or tyre (see spelling differences and etymological origins) is a device covering the circumference of a wheel. ... Cardan driveshaft with universal joints A driveshaft or driving shaft or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. ... Helical or coil springs designed for tension A spring is a flexible elastic object used to store mechanical energy. ... Gasfilled Shock absorber. ... A brake is a device for slowing or stopping the motion of a machine or vehicle, and to keep it from starting to move again. ...

Effects of Unsprung Weight

The unsprung weight of a wheel controls a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tire compression--which induces a force on the unsprung weight. In time, the unsprung weight then responds to this force with movement of its own. The amount of movement is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip when tracking over an imperfect road. For this reason, lighter wheels are often sought for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration; the irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence ride quality is deteriorated.

Pneumatic or elastic tires (tyres) help by providing some springing for most of the (otherwise) unsprung mass, but the damping that can be included in the tires is limited by considerations of fuel economy and overheating. The shock absorbers, if any, damp the spring motion also and must be less stiff than would optimally damp the wheel bounce. So the wheels execute some vibrations after each bump before coming to rest. On dirt roads and perhaps on some softly paved roads, these motions form small bumps, known as "corduroy" because they resemble smaller versions of the bumps in roads made of logs. These cause sustained wheel bounce in subsequent vehicles, enlarging the bumps.

High unsprung weight also exacerbates wheel control under hard acceleration or braking. If the vehicle does not have adequate wheel location in the vertical plane (such as a rear-wheel drive car with Hotchkiss drive, a live axle supported by simple leaf springs), vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe wheel hop, compromising traction and steering control. This article or section does not cite its references or sources. ... The dominant form of power transmission for front-engine, rear-drive cars in the twentieth century is called the Hotchkiss drive. ... A live axle is a type of beam axle suspension system that uses the driveshafts that transmit power to the wheels to connect the wheels laterally so that they move together as a unit. ... semi-elliptical spring in a 1937 Bugatti Type 57SC A leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles. ...

Though this is usually not considered important, at least in the popular literature, there is a positive effect. High frequency road irregularities, such as the gravel in an asphalt or concrete road surface, are isolated from the body more completely because the tires and springs act as separate filter stages, with the unsprung weight tending to uncouple them. This can improve overall safety.

Unsprung Weight and Vehicle Design

Unsprung weight is largely a function of the design of a vehicle's suspension and the materials used in the construction of suspension components. Beam axle suspensions, in which wheels on opposite sides are connected as a rigid unit, generally have greater unsprung weight than independent suspension systems, in which the wheels are suspended and allowed to move separately. Heavy components such as the differential can be made part of the sprung weight by connecting them directly to the body (as in a de Dion tube rear suspension). Lightweight materials, such as aluminum, plastic, carbon fiber, and/or hollow components can provide further weight reductions at the expense of greater cost and/or fragility. Solid axle and Panhard rod on a 2002 Mazda MPV A beam axle is a suspension system, also called a solid axle, in which one set of wheels is connected laterally by a single beam or shaft. ... An independent suspension is an automobile suspension system that allows the wheels on an axle to move independently of each other. ... A differential can mean one of several things: Differential (mathematics) Differential (mechanics) Differential signaling is used to carry high speed digital signals. ... A de Dion tube is an automobile suspension technology. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... Household items made out of plastic. ... Carbon fiber composite is a strong, light and very expensive material. ...

Inboard brakes make a big difference, but put more load on half axles and (constant velocity) universal joints and require space that may not be easily accommodated. An inboard braking system is an automobile technology where the brakes are not located in the wheels, as is common today, but instead near the differential. ...

See also

• Car handling
• Center of mass
• Drifting
• Electronic Stability Control
• Fishtailing
• Inboard brake
• Oversteer
• Steering
• Suspension (vehicle)
• Tire
• Understeer
• Unsprung weight
• Vehicle dynamics
• Weight transfer

Car handling and vehicle handling is a description of the way wheeled vehicles perform transverse to their direction of motion, particularly during cornering and swerving. ... In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it were concentrated. ... A Toyota Supra in drifting exhibition in Atlanta in 2005. ... Electronic Stability Control (ESC) is the generic term for systems designed to improve a vehicles handling, particularly at the limits where the driver might lose control of the vehicle. ... Fishtailing is a problem with rear wheel drive vehicles. ... An inboard braking system is an automobile technology where the brakes are not located in the wheels, as is common today, but instead near the differential. ... Oversteer is a phenomenon that can occur in an automobile which is attempting to turn. ... Steering is the term applied to the collection of components, linkages, etc. ... The front suspension components of a Ford Model T. Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. ... A tire or tyre (see spelling differences and etymological origins) is a device covering the circumference of a wheel. ... Understeer is a term for a car handling condition during cornering in which the circular path of the vehicles motion is of a markedly greater diameter than the circle indicated by the direction its wheels are pointed. ... Vehicle dynamics is the Dynamics of Vehicles, here assumed to be ground vehicles. ... In automobiles, weight transfer (often confused with load transfer) refers to the redistribution of weight supported by each tire during acceleration (both longitudinal and lateral). ...

External links

• Sprung Vs. Unsprung Weight: effects on handling, definitions