A live-axle (also called solid-axle, beam, or dead-axle) suspension is an automobile suspension that uses a single-piece axle to connect the front or rear wheels, side-to-side. This contrasts with an independent suspension (IRS) design which uses constant velocity joints to link the wheels, allowing the wheel on one side to move vertically while the other does not.
Live-axle is considered inferior to independent suspension because the drive components (shafts, gears, etc) are part of the suspension and move with it, thus greatly increasing unsprung weight and decreasing traction. Until the 1980s it was the most common form of driving axle found in the average rear-wheel drive car.
A typical live axle consists of a solid tube with a central casing containing the differential, with the wheels mounted on each end of the tube. The drive shafts (for driven wheels) run inside the tubes. The whole assembly is connected to the vehicle body or chassis by links and springs. Because the axle follows the road, with the vehicle body moving above it, drive is supplied to the axle via a swinging propellor shaft and universal joints. While relatively cheap to manufacture due to its simplicity, its weight (which is part of a vehicle's unsprung weight) can lead to handling problems.
Live axles are still widely used on trucks and heavier vehicles, but in cars they have mostly been replaced with front-wheel drive or independent rear suspension (IRS) designs.
