question: What is the difference between sprung and unsprung weight on cars and why do they affect vehicle performance differently?
comment: You can divide your car into two parts: the part that rides above the suspension (everything that transfers its weight into the springs/shocks), and the part that rides below the suspension (everything the suspension pushes down on). The stuff above the suspension is "sprung" weight, the stuff below it is "unsprung" weight. So unsprung weight basically consists of the wheel assembly - the tire, the wheel, the rotor, the brake caliper. Unsprung weight has a disproportionate effect on how the car performs, because it has to be lifted over every bump the car encounters. Weight above the springs doesn't have to move as far - the motion is damped out by the suspension. That means you're using power to lift the wheel instead of move the car forward. Said a bit differently, unsprung weight travels further than sprung weight: it moves forward as much as everything else (obviously), but it moves up and down *more* than the rest of the car. Since it travels further, it uses more energy (per unit weight) than the rest of the car.
passages: Unsprung weight transfer is calculated based on the weight of the vehicle's components that are not supported by the springs. This includes tires, wheels, brakes, spindles, half the control arm's weight and other components. These components are then (for calculation purposes) assumed to be connected to a vehicle with zero sprung weight. They are then put through the same dynamic loads. The weight transfer for cornering in the front would be equal to the total unsprung front weight times the G-Force times the front unsprung center of gravity height divided by the front track width. The same is true for the rear.
   Fixing understeer or oversteer conditions is achieved by either an increase or decrease in grip on the front or rear axles. If the front axle has more grip than a similar vehicle with neutral steer characteristics, the vehicle will oversteer. The oversteering vehicle may be "tuned" by hopefully increasing rear axle grip, or alternatively by reducing front axle grip. The opposite is true for an understeering vehicle (rear axle has excess grip, fixed by increasing front grip or reducing rear grip).
   This unsprung weight includes the wheels and tires, usually the brakes, plus some percentage of the suspension, depending on how much of the suspension moves with the body and how much with the wheels; for instance a solid axle suspension is completely unsprung. The main factors that improve unsprung weight are a sprung differential (as opposed to live axle) and inboard brakes. (The De Dion tube suspension operates much as a live axle does, but represents an improvement because the differential is mounted to the body, thereby reducing the unsprung weight.) Wheel materials and sizes will also have an effect. Aluminium alloy wheels are common due to their weight characteristics which help to reduce unsprung mass. Magnesium alloy wheels are even lighter but corrode easily.
   Section::::Weight transfer.:Sprung weight transfer.
  
  Sprung weight transfer is the weight transferred by only the weight of the vehicle resting on the springs, not the total vehicle weight. Calculating this requires knowing the vehicle's sprung weight (total weight less the unsprung weight), the front and rear roll center heights and the sprung center of gravity height (used to calculate the roll moment arm length). Calculating the front and rear sprung weight transfer will also require knowing the roll couple percentage.
   With a MacPherson strut suspension system where the spring and shock absorber are combined in the one suspension unit which also replaces the upper control arm, the entire vertical suspension load is transmitted to the top of the vehicle's strut tower, unlike a double wishbone suspension where the spring and shock absorber may share the load separately. In general terms, a strut tower in a monocoque chassis is a reinforced portion of the inner wheel well and is not necessarily directly connected to the main chassis rails. For this reason there is inherent flex within the strut towers relative to the chassis rails.
   Inboard brakes can significantly reduce unsprung mass, but put more load on half axles and (constant velocity) universal joints, and require space that may not be easily accommodated. If located next to a differential or transaxle, waste heat from the brakes may overheat the differential or vice versa, particularly in hard use, such as racing. They also make anti-dive suspension characteristics harder to achieve because the moment created by braking does not act on the suspension arms.
   Section::::Spring, wheel, and roll rates.:Roll couple percentage.
  
  Roll couple percentage is a simplified method of describing lateral load transfer distribution front to rear, and subsequently handling balance. It is the effective wheel rate, in roll, of each axle of the vehicle as a ratio of the vehicle's total roll rate. It is commonly adjusted through the use of anti-roll bars, but can also be changed through the use of different springs.
  
  Section::::Weight transfer.
  
  Weight transfer during cornering, acceleration or braking is usually calculated per individual wheel and compared with the static weights for the same wheels.
   Lowering the CoM towards the ground is one method of reducing load transfer. As a result load transfer is reduced in both the longitudinal and lateral directions. Another method of reducing load transfer is by increasing the wheel spacings. Increasing the vehicle's wheelbase (length) reduces longitudinal load transfer while increasing the vehicle's track (width) reduces lateral load transfer. Most high performance automobiles are designed to sit as low as possible and usually have an extended wheelbase and track.
   The weight distribution of a vehicle at standstill will affect handling. If the center of gravity is moved closer to the front axle, the vehicle tends to understeer due to tire load sensitivity. When the center of gravity is toward the back of the vehicle, the rear axle tends to swing out, which is oversteer. Weight transfer is inversely proportional to the direction and magnitude of acceleration, and is proportional to the height of the center of gravity. When braking, weight is transferred to the front and the rear tires have less traction. When accelerating, weight will transfer to the rear and decrease front tire traction. In extreme cases, the front tires may completely lift off the ground meaning no steering input can be transferred to the ground at all. 
   Sprung mass (or sprung weight), in a vehicle with a suspension, such as an automobile, motorcycle, or a tank, is the portion of the vehicle's total mass that is supported by the suspension, including in most applications approximately half of the weight of the suspension itself. The sprung mass typically includes the body, frame, the internal components, passengers, and cargo, but does not include the mass of the components at the other end of the suspension components (including the wheels, wheel bearings, brake rotors, calipers, and/or continuous tracks (also called caterpillar tracks), if any), which are part of the vehicle's unsprung mass.
   While weight distribution and suspension geometry have the greatest effect on measured understeer gradient in a steady-state test, power distribution, brake bias, and front-rear weight transfer will also affect which wheels lose traction first in many real-world scenarios.
  
  Section::::Limit conditions.
  
  When an understeer vehicle is taken to the grip limit of the tires, where it is no longer possible to increase lateral acceleration, the vehicle will follow a path with a radius larger than intended. Although the vehicle cannot increase lateral acceleration, it is dynamically stable.
   Negative values are oversteering, positive values are understeering, for that axle. If the understeer contribution of the rear axle is greater than that of the front axle you get negative understeer, which is known as oversteer. The analysis is only applicable while the parameters remain constant, and thus only up to about 0.4 g.
  
  Section::::Explanation of terms.
  
  Load transfer effect and cornering stiffness of tire. As load transfers across the vehicle the tire's ability to provide cornering force for a given slip angle changes. The latter is known as the cornering stiffness of the tire. See also Tire load sensitivity
   High unsprung mass also exacerbates wheel control issues 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.
   Despite these drawbacks, the MacPherson strut setup is still used on some high performance cars, because they tend to have relatively small suspension travel, and so do not see the kinematic problems. 
  
  Porsche 911 up until the 1989 model year (964) used a similar strut design that does not have coil springs, using torsion bar suspension instead, after that point all Porsche 911s have had front MacPherson struts. 
   Raising a vehicle off of the ground by such a degree raises the center of mass to a point where rolling the vehicle becomes a distinct possibility. The suspension modifications required are often meant for trucks and larger vehicles (unless specialized). If the vehicle's brakes have not been upgraded to compensate for the significant increase in wheel diameter, its braking ability will be greatly diminished. In turning too fast, the weight of the vehicle may shift to extremes that were never considered for the vehicle in question, and may cause loss of traction or damage to the vehicle itself.
   Other vehicles of the 1960s era, including some Vauxhalls, had lower ball joints with considerable end float, because the joint was always in tension as the spring and damper loads were applied via the lower control arm and were always non-zero.
  
  Another example is the Ford Focus, which uses MacPherson struts, and the anti-roll bar is connected directly to the strut, so the lower ball joint is only carrying fore and aft traction/braking and lateral cornering loads.
  
  Section::::Front-wheel drive.
   The 8.8 IRS first saw use in the 1989 model year Ford Thunderbird and later Ford adapted independent suspension to its 3rd generation Explorer and 2nd generation Expedition SUVs.
  
  The Mustang first used the 8.8 IRS on 1999-2004 Cobra models. The IRS became standard across the Mustang line for the 2015 model year with the "super 8.8."
  
  Section::::8.8 Independent suspension.:8.8 IFS.
  
  The 8.8 IFS was first used in the 1997 model year Ford F-150 and Ford Expedition and has been in use ever since.
  
  Section::::Common Applications.
  
  BULLET::::- 1986-2014 Ford Mustang
  
  BULLET::::- 1982-2012 Ford F-150
  
  BULLET::::- 1982-1996 Ford Bronco
   Jacking forces are the sum of the vertical force components experienced by the suspension links. The resultant force acts to lift the sprung mass if the roll center is above ground, or compress it if underground. Generally, the higher the roll center, the more jacking force is experienced.
  
  Section::::Other properties.
  
  Section::::Other properties.:Travel.
   Section::::Vehicle modification.:Tires.:Sway Bar Removal.
  
  It is very common for newer 4x4's equipped with sway bars to have them removed. Sway bars limit the up and down travel of axle which limits the amount of flex a vehicle has. Some manufacturers have recognized that this is common and on newer Jeep Wranglers drivers have the option to electronically remove the sway bar with the Rubicon package.
  
  Section::::Vehicle modification.:Dangers of vehicle lifting.
   General Motors first used torsion bars on their light-duty pickup trucks in 1960 until it was phased out in 1963 where traditional coil springs are used up front for their 2WD trucks. Its first use in a passenger car was in 1966, starting with the E-platform vehicles (Oldsmobile Toronado, Cadillac Eldorado), 4WD S-10 pickups and Astro vans with optional AWD, and since 1988, full size trucks and SUVs with 4WD (GMT400, GMT800, and GMT900 series).
   In the automotive industry, handling and braking are the major components of a vehicle's "active" safety, as well as its ability to perform in Auto Racing. The maximum lateral acceleration is sometimes discussed separately as "road holding". (This discussion is directed at road vehicles with at least three wheels, but some of it may apply to other ground vehicles). Automobiles driven on public roads whose engineering requirements emphasize handling over comfort and passenger space are named sports cars.
  
  Section::::Factors that affect a car's handling.
  
  Section::::Factors that affect a car's handling.:Weight distribution.
   The total amount of weight transfer is only affected by four factors: the distance between wheel centers (wheelbase in the case of braking, or track width in the case of cornering) the height of the center of gravity, the mass of the vehicle, and the amount of acceleration experienced.
   Section::::Leaf spring lift.
  
  Many trucks are supported by leaf spring suspensions. Leaf springs offer exceptional articulation, a large payload and can take a substantial amount of abuse. With the correct methods they can be modified to help a vehicle carry more weight, have better articulation or to fit large oversized tires. Some vehicles may be equipped with front and rear leaf springs or just rear leaf springs with independent front suspension.
   Ignoring the flexing of other components, a car can be modeled as the sprung weight, carried by the springs, carried by the unsprung weight, carried by the tires, carried by the road. Unsprung weight is more properly regarded as a mass which has its own inherent inertia separate from the rest of the vehicle. When a wheel is pushed upwards by a bump in the road, the inertia of the wheel will cause it to be carried further upward above the height of the bump. If the force of the push is sufficiently large, the inertia of the wheel will cause the tire to completely lift off the road surface resulting in a loss of traction and control. Similarly when crossing into a sudden ground depression, the inertia of the wheel slows the rate at which it descends. If the wheel inertia is large enough, the wheel may be temporarily separated from the road surface before it has descended back into contact with the road surface.
   This is a method that is only usable on body-on-frame design found in some pickup trucks and some SUVs. A body lift is performed by placed spacers in between the normal mounting points of the vehicle's chassis and body. These typically are between . When a body lift is installed on a vehicle it is very common for linkages and other components on the vehicle to need drop brackets to function properly after the lift. Raising the body permits the fitting of over-sized tires.
  
  Section::::Vehicle modification.:Vehicle lifts.:Suspension lift.
  