What is a Multi-Link Suspension? | How Does a Multi-Link Suspension Differ From a Fixed Rear Axle? | Advantages and Disadvantages of Both Systems
| Stanley Subaru's Technical Schmecnical Lesson 4: Multi-Link Suspensions

As described by Steven Rupp of Popular Hot Rodding Magazine:

Suspension 101

In a perfect world, all the roads would be perfectly flat, without bumps, and suspensions wouldn't even be needed. But as we all know, that is far from reality. (And far from fun, especially if you have an All Wheel Drive Subaru!) Once you start talking about curves and performance then a properly functioning suspension becomes essential. One area of confusion lies in the numerous choices for your rear suspension. Terms like four-link, three-link, triangulated-four-link, Panhard, Watt's and such get tossed about and if you don't know what they mean, picking the right rear suspension can be difficult at best.

The suspension on your car has two main functions. Its first job is to smooth the ride of your car. According to Mr. Newton and his famed laws of physics, all forces of motion have both a magnitude and a direction. A bump in the road causes the wheel to move up and down perpendicular to the road surface. The bigger the bump encountered, the bigger the movement. The movement experienced by the wheel is called vertical acceleration.

Without an intervening structure, all of the wheel's vertical energy is transferred to the frame, which tries to move in the same direction. In such a situation the wheels can lose contact with the road completely. Then, under the downward force of gravity, the wheels can slam back into the road surface. What you need is a system that will absorb the energy of the vertically accelerated wheel allowing the frame and body to ride undisturbed while the wheels follow bumps in the road and stay in contact with the asphalt.

Unless a dampening structure is present, a spring will extend and release the energy it absorbs from a bump at an uncontrolled rate. The spring will continue to bounce at its natural frequency until all of the energy originally put into it is used up. A suspension built on springs alone would make for an extremely bouncy ride and, depending on the terrain, an uncontrollable car. Enter the shock absorber--a device that controls unwanted spring motion through a process known as dampening. Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated. The shock can be air-filled, gas-filled, or oil-filled. In any case, its job is to control the rate of spring and suspension movement.

All rear suspension systems use some sort of shock and spring combination, but there are huge differences in how they are mounted and in the overall design of the systems. Knowing the differences in the choices out there can go a long way to helping you pick the one right for your ride.

Advantages of Multi-Link Suspensions:

Hyperlogos describes the advantages of multi-link suspensions below:

"The multilink suspension design is the most advanced and functional independent rear suspension|independent rear suspension available for an automobile. It has all of the features of the double wishbone, but takes less space, generally weighs less, and is potentially more adjustable, especially if adjustable links are used. The idea of the multilink suspension is to use several short links to ensure that camber, caster and toe either do not change or change predictably when the suspension is compressed or extended.

Multilink suspensions typically come in three, four, and five-link models. Strictly speaking, any suspension design which utilizes three or more links is a multi-link. Consider the alternatives: The MacPherson strut suspension has two links, a lower control arm and a radius rod or tension control rod depending on who you talk to. Torsion beam suspension has one link (per wheel.) Trailing-arm suspensions have a single A-arm, and the related Weissach axle design has two links.

Four and five-link multilink suspension designs offer the greatest customizability. Adjustable links are readily available for most sports cars and can easily be made in any case, for example using threaded tubing. In the case of a five-link there are five separate rods, where a four link usually has an A-arm on the bottom, and upper, upper front, and upper rear links. If adjustable upper front and rear links are used, the toe angle can be changed by adjusting them. If an adjustable upper link is utilized, then the camber can easily be changed. Using either dual adjustable lower arms (in a five link) or an A-arm whose two inboard attachment points can be moved in and out will allow you to adjust the caster angle. This allows a degree of customization not available on any other type of suspension. In addition, multilink suspension nearly always utilizes a coil-over design for springs and damping, which also allows the greatest control over the ride of the vehicle.

The only drawback to the multilink design is increased complexity and hence more potential points of failure, and increased cost. However, through the use of polyurethane bushings, the lifetime of suspension components can be extended dramatically. The smaller size of the links generally saves considerable weight as compared to a double wishbone design.

Multilink suspensions are usually mounted to a subframe which bolts to the bottom of the car, though on a full-frame car they might be connected directly to the chassis. As they are usually used on unibody vehicles a subframe is nearly mandatory. The upper mounts for the shock absorbers may be integrated into the unibody or implemented as part of the subframe. The subframe is usually attached to the unibody through bushings which are a potential source of wheel hop and spacers (or washers) are sometimes used to compress the bushings to reduce flex, or the bushings may be replaced with metal bushings which result in transmission of greater vibration into the body, but completely eliminate flex between the body and subframe. They are primarily used in rear suspensions but may sometimes be found in the front as well.

UPDATED 6/20/2013:

One of our readers asked "What type does WRX and STi have?"and Neil Harriman, our service manager explained it as follows: 

Subaru uses multi link suspensions on both the front and rear of the vehicle. All Subarus, being all-wheel-drive vehicles, have multi-link suspensions. This is the safest suspension to have, so that control can be maintained especially when cornering or driving on rough roads. If one wheel hits a bump, it only affects that one wheel, as all the others have their own unique drive shaft. A fixed rear axle means the two rear wheels are connected to the same axle, so if one wheel hits a bump, the other one reacts like it has hit the bump too, and can cause the vehicle to skid, bounce or otherwise react to the bump. This can cause the driver to lose control of the car. The multi-link suspension on both the front and rear of the vehicle is just one way Subaru prioritizes safety and vehicle control. 

Do you find our Technical Schmecnical Series helpful? Do you have questions or suggestions for future lessons? Let us know!

Have a great day and Happy Reading!

About Technical Schmecnical Lesson Series:
"Technical Schmecnical" is an ongoing series and serves as a helpful guide and resource for vehicle owners to better understand their vehicles. All of our information comes from Subaru Owners Manuals, Quick Reference Guides, technical manuals, and even our Subaru Certified Master Technicians themselves!

Source 1: "Rear Suspension Guide" in Popular Hot Rodding, June 2004 issue < http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html#ixzz1tWwbnBfe> 30, April 2012.

Source 2: Hyperlogos, a car enthusiast's blog,created by
Martin Espinoza, post titled "Multi-Link" written 02/16/2006 <http://hyperlogos.org/Automotive-Technology/Parts/Suspension/Multilink> 30, April 2012. Multi-Link Suspension image courtesy Hyperlogos.

Tags: what is that