Independent suspension

A multi-link type rear independent suspension on an AWD car. The anti-roll bar has some yellow paint on it.

Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically (i.e. reacting to a bump in the road) independently of each other. This is contrasted with a beam axle, live axle or deDion axle system in which the wheels are linked – movement on one side affects the wheel on the other side. Note that “independent” refers to the motion or path of movement of the wheels/suspension. It is common for the left and right sides of the suspension to be connected with anti-roll bars or other such mechanisms. The anti-roll bar ties the left and right suspension spring rates together but does not tie their motion together.

Most modern vehicles have independent front suspension (IFS). Many vehicles also have an independent rear suspension (IRS). IRS, as the name implies, has the rear wheels independently sprung. A fully independent suspension has an independent suspension on all wheels. Some early independent systems used swing axles, but modern systems use Chapman or MacPherson struts, trailing arms, multilink, or wishbones.

Independent suspension typically offers better ride quality and handling characteristics, due to lower unsprung weight and the ability of each wheel to address the road undisturbed by activities of the other wheel on the vehicle. Independent suspension requires additional engineering effort and expense in development versus a beam or live axle arrangement. A very complex IRS solution can also result in higher manufacturing costs.

The key reason for lower unsprung weight relative to a live axle design is that, for driven wheels, the differential unit does not form part of the unsprung elements of the suspension system. Instead it is either bolted directly to the vehicle's chassis or more commonly to a subframe.

The relative movement between the wheels and the differential is achieved through the use of swinging driveshafts connected via universal (U) joints, analogous to the constant-velocity (CV) joints used in front wheel drive vehicles.

Description

Suspension is the only component that separates the driver and/or passenger from the ground. The suspension in a vehicle helps absorb harshness in the road. There are many systems and designs that do this, such as independent suspension.

Definition

Independent suspension : “An automotive suspension system in which each wheel is attached to the frame independently, so that a road bump affecting one wheel has no effect on the others” .

Advantages

This system provides many advantages over other suspension systems. For example, in solid Axel suspension systems, when one wheel hits a bump, the wheel across from it is affected as well as the one that hit the bump. This will compromise traction, smoothness of the ride, and could also cause a dangerous wheel shimmy when moving at high speeds. According to “Car Suspension Bible” with independent suspension systems, only the wheel that hits the bump would be affected. This offers many advantages such as: greater ride comfort, better traction, safer more and stable vehicles on the road and off the roads.<refname="Longhurst">Longhurst, Chris. "Car Bibles : The Car Suspension Bible Page 1 of 5." The Car Maintenance Bibles. Car Bibles, 14 Oct. 2011. Web. 14 Nov. 2011.</ref>

Types

Suspensions in the simplest form contain two major components, springs and shock absorbers. The spring’s main function is to help rebound the shock back and control the stiffness of the suspension. A shock absorbers main function is to dampen vertical motion created when a wheel hits a rough surface or any other imperfection on the road.<refname="Longhurst">

Coil Over independent suspensions system

This is most often an aftermarket part, it doesn’t come with a vehicle from the factory, and it offers a high level of adjust-ability. It is a system that can be fitted to any vehicle. There is an adjustable spring plate on the shock that lets the stiffness and the looseness to be adjusted. Also there is often an adjustable damping valve that can change the rebounding effect of the shock absorbers (Longhurst1-2). Also the ride height can be lowered or raised with ease, this is a desirable aspect of the system. This system is used by many people to modify their street, race, and off road cars.

MacPherson Strut

Main article: MacPherson strut

According to “Car suspension bibles” this is the most common, widely used front suspension system in cars of European origin. It is a very simple and effective design that uses a strut-type spring and shock absorber that work as a team that will pivot on a ball joint on the single lower arm. This system has been used the BMW E21 series, which are the first generation 3 series from 1976-1983 and this system is still used on cars today. One problem with this system is once the spring or the top plate becomes worn, the driver of a car with this system may here a loud “clonk” like noise at full lock when the spring jumps back into place. People can often confuse this with a CV joint knock.

Transverse leaf-spring

The Chevrolet Corvette is known for using a rear transverse leaf-spring suspension design. This system uses two systems to work as one. It uses a double wishbone which is supported by a leaf spring rather than the more common coil spring. The leaf spring is not used as they were commonly used before. It is very rare on modern cars. In the past it was more widely used in many Triumphs. The Triumph Herald, Vitesse, Spitfire and the GT6 all used a rear transverse leaf spring, as well as a rare Swedish sports car that was made in the 1990s called the JC Indigo.

See also

• damper
• wishbone suspension
• hydro-elastic suspension
• Coil spring
• leaf-spring
• Live axle