Car Suspension Bible

7/27/2019 Car Suspension Bible

http://slidepdf.com/reader/full/car-suspension-bible 1/24

Car Suspension Bible

What does it do?

Apart from your car's tires and seats, the suspension is the prime mechanismthat separates your bum (arse for the American) from the road. It also preventsyour car from shaking itself to pieces. No matter how smooth you think the roadis, it's a bad, bad place to propel over a ton of metal at high speed. So we relyupon suspension. People who travel on underground trains wish that thosevehicles relied on suspension too, but they don't and that's why the ride is soharsh. Actually it's harsh because underground trains have no lateralsuspension to speak of. So as the rails deviate side-to-side slightly, so does theentire train, and it's passengers. In a car, the rubber in your tyre helps with thislittle problem. In its most basic form, suspension consists of two basiccomponents:

Springs These come in three types. They are coil springs, torsion bars and leaf springs.Coil springs are what most people are familiar with, and are actually coiledtorsion bars. Leaf springs are what you would find on most American cars up toabout 1985 and almost all heavy duty vehicles. They look like layers of metalconnected to the axle. The layers are called leaves, hence leaf-spring. Thetorsion bar on its own is a bizarre little contraption which gives coiled-spring-likeperformance based on the twisting properties of a steel bar. It's used in thesuspension of VW Beetles and Karmann Ghias, air-cooled Porsches (356 and911 until 1989 when they went to springs), and the rear suspension of Peugeot

205s amongst other cars. Instead of having a coiled spring, the axle is attachedto one end of a steel shaft. The other end is slotted into a tube and held there bysplines. As the suspension moves, it twists the shaft along it's length, which inturn resist. Now image that same shaft but instead of being straight, it's coiledup. As you press on the top of the coil, you're actually inducing a twisting in theshaft, all the way down the coil. I know it's hard to visualize, but believe me,that's what is happening. There's a whole section further down the pagespecifically on torsion bars and progressive springs.

Shock absorbers Strangely enough, absorb shocks. Actually, shock absorbers are one of those

great misnomers in life. They're really called dampers, because they actuallydampen the vertical motion induced by driving your car along a rough surface. Ifyour car only had springs, it would boat and wallow along the road until you gotphysically sick and had to get out. Or at least until it fell apart. Shock absorbersperform two functions. Firstly, they absorb any larger-than-average bumps in theroad so that the shock isn't transmitted to the car chassis. Secondly, they keepthe suspension at as full a travel as possible for the given road conditions.Shock absorbers keep your wheels planted on the road. Without them, your car



would be a traveling deathtrap. Technically, they are actually dampers. Evenmore technically, they are velocity-sensitive hydraulic damping devices - in otherwords, the faster they move, the more resistance there is to that movement.They work in conjunction with the springs. The spring allows movement of thewheel to allow the energy in the road shock to be transformed into kinetic energy

of the unsprung mass, whereupon it is dissipated by the damper. (Phew!....andyou thought they just leaked oil didn't you?)

A modern coil-over-oil unit

The image above shows a typical modern coil-over-oil unit. This is an all-in-onesystem that carries both the spring and the shock absorber. The type illustratedhere is more likely to be an aftermarket item - it's unlikely you'd get this level ofadjustment on your regular passenger car. The adjustable spring plate can beused to make the springs stiffer and looser, whilst the adjustable damping valve can be used to adjust the compression damping of the shock absorber. Moresophisticated units have adjustable rebound damping as well as a remotereservoir. Whilst you don't typically get this level of engineering on car

suspension, most motorbikes do have preload, rebound and spring tensionadjustment. See the section later on in this page about the ins and outs ofcomplex suspension units.

Suspension Types

In their infinite wisdom, car manufacturers have set out to baffle use with thesheer number of different types of suspension available for both front and rear



axles. The main groupings are dependant and independent suspension types. Ifyou know of any not listed here, e-mail me and let me know - I would like thispage to be as complete as possible.

Front suspension - dependent systems

So-called because the front wheel's suspension systems are physically linked.For everyday use, they are, in a word, shite. I hate to be offensive, but they are.There is only one type of dependant system you need to know about. It isbasically a solid bar under the front of the car, kept in place by leaf springs andshock absorbers. It's still common to find these on trucks, but if you find a carwith one of these you should sell it to a museum. They haven't been used onmainstream cars for years for three main reasons:• Shimmy - because the wheels are physically linked, the beam can be set intooscillation if one wheel hits a bump and the other doesn't. It sets up a gyroscopictorque about the steering axis which starts to turn the axle left-to-right. Becauseof the axle's inertia, this in turn feeds back to amplify the original motion.

• Weight - or more specifically unsprung weight. Solid front axles weigh a tonand need huge springs to keep their wheels on the road.

• Alignment - simply put, you can't adjust the alignment of wheels on a rigidaxis. From the factory, they're perfectly set, but if the beam gets even slightlydistorted, you can't adjust the wheels to compensate. I frequently get pulled-upon the above statements from people jumping to defend solid-axle suspension.

They usually send me pictures like this and claim it's thebest suspension system for off-road use. I have to admit,for off-road stuff, it probably is pretty good. But let's face it;how many people with these vehicles ever go off-road?The closest they come to having maximum wheeldeflection is when the mother double- parks the thing withone wheel on the kerb during the school-run.......

Front suspension - independent systems

So-named because the front wheel's suspension systems are independent of

each other (except where joined by an antiroll bar) These came into existencearound 1930 and have been in use in one form or another pretty much eversince then.



MacPherson strut

This is currently, without doubt, the most widely used front suspension system incars of European origin. It is simplicity itself. The system basically comprises ofa strut-type spring and shock absorber combo, which pivots on a ball joint on

the single, lower arm. At the top end there is a needle roller bearing on somemore sophisticated systems. The strut itself is the load-bearing member in thisassembly, with the spring and shock absorber merely performing their duty asoppose to actually holding the car up. In the rendered image here, you can't seethe shock absorber because it is encased in the blue strut tower, inside thespring. The steering gear is either connected directly to the lower shockabsorber housing, or to an arm from the front or back of the spindle (in thiscase). When you steer, it physically twists the shock absorber housing (andconsequently the spring) to turn the wheel. Simple. The spring is seated in aspecial plate at the top of the assembly which allows this twisting to take place.If the spring or this plate are worn, you'll get a loud 'clonk' on full lock as the

spring frees up and jumps into place. This is sometimes confused for CV jointknock.

Potted history of MacPherson: Earle S. MacPherson of General Motorsdeveloped the MacPherson strut in 1947. GM cars were originally design-bound by accountants. If it cost too much or wasn't tried and tested, then it didn'tget built/used. Major GM innovations including the MacPherson Strut

suspension system sat stifled on the shelf for years because innovation cannotbe proven on a spreadsheet until after the product has been produced ormanufactured. Consequently, Earle MacPherson went to work for Ford UK in1950, where Ford started using his design on the 1950 'English' Ford modelsstraight away.

Further note: Earle MacPherson should never be confused with ElleMcPherson – the Australian über-babe. In her case, the McPherson Strut is



something she does on a catwalk, or in your dreams if you like that sort of thing.And if you're a bloke, then you ought to....

The following four types of system are all essentially a variation on thesame theme.

Coil Spring type 1

This is a type of double-A arm suspension. The wheel spindles (purple) aresupported by an upper and lower 'A' shaped arms (green). If you look head-onat this type of system, what you'll find is that it's a very basic lever system thatallows the spindles to travel vertically up and down. When they do this, they alsohave a slight side-to-side motion caused by the arc which the levers scribearound their pivot point. This side-to-side motion is known as scrub. Unlessthe links are infinitely long the scrubmotion is always present. There aretwo other types of motion of the wheelrelative to the body when thesuspension articulates. The first andmost important is a toe angle (steerangle). The second and leastimportant, but the one which producesmost pub talk is the camber angle, orlean angle. Steer and camber are theones which wear tires. Also note thatthe springs/shocks in this example arein a so-called 'coil over oil'arrangement whereby the shockabsorbers (yellow) sit inside the springs (red).

Coil Spring type 2

This is also a type of double-A arm suspensionalthough the lower arm in these systems cansometimes be replaced with single solid arms. Theonly real difference between this and the type 1

system mentioned above is that the spring/shockcombo is moved from between the arms to abovethe upper arm. This transfers the load-bearingcapability of the suspension almost entirely to theupper arm and the spring mounts. The lower armin this instance becomes a control arm. Thisparticular type of system isn't so popular in cars asit takes up a lot room.



Double Wishbone

So-called because the lower andupper arms are the shape ofwishbones. Yes I know they don'tlook like wishbones here, but believe me, they are. The spindleis a highly complex construction inthis system, as are the wishbonesthemselves. This rapidly becomingone of the most favouredsuspension types for new cars asit gives excellent road-holdingcapabilities whilst taking up verylittle room under the car. Thisallows for smoother lines on thebodywork, and less intrusion in tothe engine bay. A 3D renderingsuch as that on the right does notdo this system any justice. To really appreciate it, you need to get your head in awheel well and have a look. And I know a few mechanics who've still not beenable to figure it out even then.

Multi-link suspension

This is the latest incarnation of the double wishbonesystem described above. It's currently being used inthe Audi A8 and A4 amongst other cars. The basicprinciple of it is the same, but instead of solid upperand lower wishbones, each 'arm' of the wishbone is aseparate item. These are joined at the top and bottomof the spindle thus forming the wishbone shape. Thesuper-weird thing about this is that as the spindleturns for steering, it alters the geometry of thesuspension by torquing all four suspension arms.They have complex pivot systems designed to allow

this to happen.Car manufacturers claim that this system gives evenbetter road-holding properties, because all thevarious joints make the suspension almost infinitelyadjustable. There are a few variations on this themeappearing at the moment, with differences in thenumbers of joints, numbers of arms, positioning of theparts etc. But they are all fundamentally the same.



Trailing-arm suspension

The trailing arm system is literally that - a shapedsuspension arm is joined at the front to thechassis, allowing the rear to swing up and down.Pairs of these become twin-trailing-arm systemsand work on exactly the same principle as thearms in the coil spring type systems describedabove. The difference is that instead of the armssticking out from the side of the chassis, theytravel back along it. If you want to know what Imean, find a VW beetle and stick your head in thefront wheel arch - that's a double-trailing-armsuspension setup. Simple. It's used mostly in oldercars and beach buggies now.

Moulton rubber suspension

This suspension system is based on the compression of asolid mass of rubber - red in both these images. The twotypes are essentially derivatives of the same design. It isnamed after Dr. Alex Moulton - one of the original designteam on the Mini, and the engineer who designed itssuspension system in 1959. This system is known by a fewdifferent names including cone and trumpet suspension (due

to the shape of the rubber bung shown in the lower image).The rear suspension system on the original Mini also usedMoulton's rubber suspension system, but laid outhorizontally rather than vertically, to save space again. TheMini was originally intended to have Moulton's fluid-filledHydrolastic suspension, but that remained on the drawingboard for a few more years. Eventually, Hydrolastic wasdeveloped into Hydragas (see later on this page), andrevised versions were adopted on the Mini Metro and thecurrent MGF-sports car. Ultimately, Moulton rubbersuspension is now used in a lot of bicycles - racing and

mountain bikes. Due to the compact design and thesimplicity of its operation and maintenance, it's an idealsolution.



Rear suspension - dependant systems

Contrary to the front version of this system, many many cars are still designedand built with dependant (linked) rear suspension systems.

Solid-axle, leaf-spring

This system was favoured by the Americans for years because it was deadsimple and cheap to build. The ride quality is decidedly questionable though.The drive axle (purple in this image) is clamped (green) to the leaf springs (red).The shock absorbers (yellow) are also attached to the clamps. The ends of theleaf springs are attached directly to the chassis, as are the shock absorbers.

Simple, not particularly elegant, but cheap. The main drawback with thisarrangement is the lack of lateral location for the axle.



Solid-axle, coil-spring

This is a variation and updateon the system described above.The basic idea is the same, but

the leaf springs have beenremoved in favour of 'coil-over-oil' spring and shock combos.Because the leaf springs havebeen removed, the axle nowneeds to have lateral supportfrom a pair control arms. Thefront ends of these are attachedto the chassis, the rear ends tothe axle. A variation on this hasthe shock absorbers separate

from the springs, allowing muchsmaller springs. This in turnallows the system to fit in asmaller area under the car.

Beam Axle

This system is used in

front wheel drive cars,where the rear axle isn'tdriven. (hence it's fulldescription as a "deadbeam"). Again, it is arelatively simple system.The beam runs acrossunder the car with thewheels attached to eitherend of it. Also at theends, the springs and

shock absorbers areattached. The beam hastwo integral trailing armsbuilt in instead of theseparate control arms required by the solid-axle-coil-spring system. Variationson this system can have either separate springs and shocks, or the combined'coil-over-oil' variety as shown here. One notable feature of this system is thetrack bar (or panhard rod). This is a diagonal bar which runs from the rear corner



of the beam to a point either just in front of the opposite corner, or in this case,above the opposite spring mount. This is to prevent side-to-side movement inthe beam which would cause all manner of nasty handling problems. A variationon this them is the twist axle which is identical with the exception of the panhardrod. In this system, the axle is designed to twist slightly. This gives, in effect, a

semi-independent system whereby a bump on one wheel is partially soaked upby the twisting action of the beam. Yet another variation on this system doesaway with the springs and replaces them with torsion bars running across thechassis, and attached to the leading edge of the beam supports. These beamtypes are currently very popular because of their simplicity and low cost.

4-Bar

4-bar suspension can be used on the front and rear of vehicles - I've chosen toshow it in the "rear" section of this page because that's where it's normallyfound. 4-bar suspension comes in two varieties. Triangulated, shown on the lefthere, and parallel, shown on the right. The parallel design operates on theprincipal of a "constant motion parallelogram". The design of the 4-bar is suchthat the rear end housing is always perpendicular to the ground, and the pinionangle never changes. This, combined with the lateral stability of the PanhardBar, does an excellent job of locating the rear end and keeping it in properalignment. If you were to compare this suspension system on a truck with a 4-link or ladder-bar setup, you'd notice that the rear frame "kick up" of the 4-barsetup is far less severe. This, combined with the relatively compact installationdesign means that it's ideal for cars and trucks where space is at a premium.You'll find this setup on a lot of street rods and American style classic hot rods.The triangulated design operates on the same principle, but the top two bars are

skewed inwards and joined to the rear end housing much closer to the centre.This eliminates the need for the separate panhard bar, which in turn means thewhole setup is even more compact.



Rear suspension - independent systems

It follows, that what can be fitted to the front of a car, can be fitted to the rear towithout the complexities of the steering gear. Simplified versions of all theindependent systems described above can be found on the rear axles of cars.

The multi-link system is currently becoming more and more popular. Inadvertising, it's put across as '4-wheel independent suspension'. This means allthe wheels are independently mounted and sprung. There are two schools ofthought as to whether this system is better or worse for handling than, forexample, Macpherson struts and a twist axle. The drive towards 4-wheelindependent suspension is primarily to improve ride quality without degradinghandling.

Hydrolastic Suspension

If you've got this far, you'll remember that Dr. Alex Moulton originally wanted theMini to have Hydrolastic suspension - a system where the front and rearsuspension systems were connected together in order to better level the carwhen driving.The principle is simple. The front and rear suspension units have Hydrolasticdisplacers, one per side. These are interconnected by a small bore pipe. Eachdisplacer incorporates a rubber spring (as in the Moulton rubber suspensionsystem), and damping of the system is achieved by rubber valves. So when afront wheel is deflected, fluid is displaced to the corresponding suspension unit.That pressurizes the interconnecting pipe which in turn stiffens the rear wheeldamping and lowers it. The rubber springs are only slightly brought into play andthe car is effectively kept level and freed from any tendency to pitch. That's

clever enough, but the fact that it can do this without hindering the full range ofmotion of either suspension unit is even more clever, because it has the effect ofproducing a soft ride. Pictures and images of anything to do with hydrolasticsuspension are few and far between now, so you'll have to excuse theplagiarism of the following image. The animation below shows the self-levelingeffect - notice the body stays level and doesn't pitch.



But what happens when the front and rear wheels encounter bumps or dipstogether? One cannot take precedent over the other, so the fluid suspensionstiffens in response to the combined upward motion and, while acting as adamper, transfers the load to the rubber springs instead, giving a controlled,vertical, but level motion to the car. Remember I said the units were connected

with a small bore pipe? The restriction of the fluid flow, imposed by this pipe,rises with the speed of the car. This means a steadier ride at high speed, and asofter more comfortable ride at low speed.

Hydrolastic suspension is hermetically sealed and thus shouldn't require much, ifany, attention or maintenance during its normal working life. Bear in mind thathydrolastic suspension was introduced in 1965 and you'd be lucky to find a unittoday that has had any work done to it.

The image below shows a typical lateral installation for hydrolastic rearsuspension. The purple structure is the subframe, the green parts are the

suspension swingarms, and the red cylinders are the displacer units containingthe fluid and the rubber spring. The pipes leading from the units can be seenand they would connect to the corresponding units at the front of the vehicle.

Hydrolastic suspension shouldn't be confused with Citron's hydropneumaticsuspension (see below). That system uses a hydraulic pump that raises and

lowers the car to different heights. Sure it's a superior system but it's also a lotmore costly to manufacture and maintain. That's due in part to the fact that theydon't use o-rings as seals; the pistons and bores are machined to incredibletolerances (microns), that it makes seals unnecessary. Downside : if somethingleaks, you need a whole new cylinder assembly.

Hydrolastic was eventually refined into Hydragas suspension.......



Hydragas Suspension

Hydragas is an evolution of Hydrolastic, and essentially, the design andinstallation of the system is the same. The difference is in the displacer unititself. In the older systems, fluid was used in the displacer units with a rubber

spring cushion built-in. With Hydragas, the rubber spring is removed completely.The fluid still exists but above the fluid there is now a separating membrane ordiaphragm, and above that is a cylinder or sphere which is charged with nitrogengas. The nitrogen section is what has become the spring and damping unitwhilst the fluid is still free to run from the front to the rear units and back.

Hydragas suspension was famously used in the 1986 Porsche 959 Rally car thatentered the Paris-Dakar Rally, and today you can find it on the MGF Roadster.

Hydropneumatic Suspension

Since the late forties, Citron have been running a fundamentally differentsystem to the rest of the auto industry. They call it hydropneumatic and itencompasses features as diverse as brakes, suspension & steering. As itsname may suggest, its core technology and mainstay of its functionality ishydraulics. Superbly smooth suspension is provided by the fluid's interaction with a



pressurized gas. They pioneered in the rear suspension of the 15 (TractioAvant) model, and it has been fitted to many of their cars since. I've had toseparate it into it's own category because it is quite different from any other typeof suspension system.

The system is powered by a large hydraulic pump operated directly by theengine in much the same way as an alternator or an air conditioner is, andprovides fluid to an "accumulator" at pressure, where it is stored ready to bedelivered to servo a system. (This pump is also used for the power steering andthe brakes, and in the DS for the semi-auto box.)

Because this page is all about suspension, for clarity we'll look at the simplifiedversion of this as installed in the "BX" model. The Citron BX was a majorturning point in the company's history as it was the first car to be producedunder the company's new Peugeot management, following the 1970s take-overof Citron by Peugeot. As a direct consequence of the Peugeot influence, the

car is somewhat more conventional than its larger sibling designed earlier - theCX. This Peugeot-enforced "normalisation" of the design makes it easy enoughto examine as an illustration of how hydropneumatic suspension works.

There are two main components you need to familiarize yourself with and tounderstand. The spheres are like the springs on the car, and the struts are thehydraulic components that make the fluid act like a spring.

Lets start with the sphere. The spring in this suspension system is provided by ahydraulic component called an accumulator, which is gas under pressure in abottle contained within a diaphragm, effectively a balloon which allowspressurized fluid to compress the gas, and then as pressure drops the gaspushes the fluid back to keep the system's pressure up. As you can see in thedrawing above the pink gas (nitrogen) is compressed when the pressure in thegreen fluid (LHM) overcomes the gas pressure, and pushes back the diaphragmwhich compresses the gas. Then as the pressure in the fluid reduces, the gaspushes back the diaphragm and as the gas overcomes the fluid, it expels thefluid from the sphere, returning gas and fluid to equilibrium. This is thehydropneumatic equivalent to the spring getting compressed (bound) andgetting depressed, i.e. springing back (rebound). Still with me? We can keepgoing...

How can a gas, a diaphragm and a hydraulic fluid compressing, form a spring?Simple(ish): The pressure of the gas is the equivalent to the spring weight. Theinlet hole at the bottom of the sphere restricts the flow of the fluid and providesan element of damping. By replacing the sphere for ones of different specs, it ispossible to adjust the ride characteristics with these cars. Rumour even has itthat a racing team in Anglesey is customizing their car by pressurizing their ownspheres to custom pressures to make an exact match for the circuit the are on.Before we go any further it is pretty important that you understand where the



fluid acting onthe diaphragm in the sphere gets its force from, and to do that we are going tohave to look atthe operation of the other key component in the Citron system - the strut.

As you can see in this diagram, the strut has a sphere on top of it and the strutin itself acts like a syringe to inject fluid into the sphere. When the wheel hits abump it rises, pushes the piston of the strut back and this squeezes fluid throughthe tiny hole in the sphere to let the gas spring absorb the energy of the bump.Then when the car is over the bump and its time to let the wheel back down, thegas pushes the diaphragm back out, pushing the fluid down to the strut, pushingthe wheel down to the ground. Some interesting possibilities were opened up bythe company deciding to use this system to spring their cars. One or two of themore obvious ones are that since the system is hydraulic, the ride height caneasily be altered, a trend low riders are now following on with in California,nearly fifty years later. Also, they could link the four corners together to make a

system that prepared the car for the bump to keep it even and offer thepassengers a smoother ride. Basically they put fancy valves called heightcorrectors on the anti-roll bar. These were mounted in such a way that as thesuspension twisted, this operated the valves that controlled the transfer of fluidto the struts. It was possible to isolate the front and rear systems and have thefront suspension set at a height which required 'x' litres. So when the frontnearside wheel takes a knock compressing its sphere, x/2 L is lost in the sphere,then the height correctors allow another x/2 L in, to inflate the offside strut bythat much. This keeps the front of the car level in a horizontal plane.

As the car clears the bump, the reverse happens; the sphere displaces thatfluid, the strut returns to its own height pulling the anti roll bar back true with itwhich in turn tells the height corrector to lose that extra x/2 litres of fluid from theother side. As one side extends its strut in reaction to clearing the bump, theother is retracting by the same amount to return the car to its set height abovethe road. Neat huh?

A further mechanical advantage of hydraulic suspension is that the car is able tolink its braking effort to the weight on the wheels. In the Citron BX, the rearbraking effort comes from the pressure exerted on the LHM fluid by the weighton those struts. This means that as the weight travels forward under braking,there is less pressure on the back suspension. The suspension is the able toexert less pressure on its fluid, and as weight and grip diminish on the wheels,so does the braking effort, thus the hydropneumatic system preventsrear wheellock ups.

In addition to these benefits, Citron pioneered computer controlled suspensionin the early nineties by inserting a computer to take readings from the cars'chassis and control systems and let the computer make informed decisionsabout how to handle the cars suspension. The computer could then effect thesedecisions by things like servo valves, and offered benefits like soft suspension



for cruising, but stiffer, sportier suspension for faster harder driving, allowing thedriver to cruise in comfort and still enjoy a responsive car. It also movessubstantially towards eliminating body roll and if used for a sportier driver willsave tyre wear as well (they claim).

There was a further refinement / development in this suspension design in the1990s called the Activa system, designed to compensate for body roll. It wasquite effective although only the Xantia has been fitted with it. The main setbackwas that ride comfort was even worse than a BMW (although cornering speedswere fantastic) which did not go too well with the traditional Citron clientele.The current adjustable systems (computer controlled) lack this anti rollcharacteristic, and there are owners who always prefer the "comfort" settingrather than the "sporty" one, because again, that is not what Citron is about. Itsworth noting that when Mercedes launched their latest 600 SLC version with acomputer controlled anti roll system, Auto Motor und Sport then proudly claimedthat to be the first such anti roll system in world, only having to correct that oneissue later by having to mention a French invention.Rolls Royce was the only company ever to buy the patent and they used in therear suspension of the Silver Shadow. When Citroen was the owner of Maseratisome of their cars were also hydropneumatised.

More in-depth information can be found here -http://www.citroen.mb.ca/citroenet/html/h/hydro.html - or -http://www4.tpgi.com.au/ozway/page5.html. Meanwhile, the rest of us canhopefully feel satisfied with our newly enriched understandings ofhydropneumatic suspension. If you're still awake.



Hydraulic SuspensionHydraulic suspension is an innovation making its way into motor sports, nodoubt to trickle down to consumer vehicles eventually. It has been designed andpioneered by the Racing For Holland Dome S101 sports car team. In the image below you can see both the traditional coil over system (the yellow/blue/red

units) at the front of the car. This photo was taken before scrutineering for the2005 24 Hours of Le Mans race. The team had both systems online and whenscrutineering passed the car, the coilover units were removed, to race for thefirst time completely with hydraulic suspension. Central to their system is acontrol unit mounted next to the cockpit. They tell me the system can't becompared to the hydropneumatic suspension Citron uses because this systemdoesn't use a pump and has less than a litre of hydraulic fluid in the entiresystem. More news on this development as I get it.



Linear Electromagnetic Suspension

This is the latest innovation in suspension systems,invented by Bose. The idea is that instead of springsand shock absorbers on each corner of the car, asingle liner electromagnetic motor and power amplifiercan be used instead.Inside the linear electromagnetic motor are magnetsand coils of wire. When electrical power is applied to

the coils, the motor retracts and extends, creatingmotion between the wheel and car body. It's like theelectromagnetic effect used to propel some newerrollercoaster cars on launch, or if you're intovideogames and sci-fi, it's like a railgun.







suspension moves upward relative to the car chassis, it transfers some of that movement tothe same component on the other side. In effect, it tries to lift the left suspension componentby the same amount. Because this isn't physically possible, the left suspension effectivelybecomes a fixed point and the anti-roll bar twists along its length because the other end iseffectively anchored in place. It's this twisting that provides the resistance to the suspensionmovement.

If you're loaded, you can buy cars with active anti-roll technology now. These sense the rollof the car into a corner and deflate the relevant suspension leg accordingly by pumping fluidin and out of the shock absorber. It's a high-tech, super expensive version of the good oldmechanical anti-roll bar. You can buy anti-roll bars as an aftermarket add-on. They're

relatively easy to fit because most cars have anti-roll bars already. Take the old one off andfit the new one. In the case of rear suspension, the fittings will probably already be thereeven if the anti-roll bar isn't.

Typical anti-roll bar (sway bar) kits include the upgraded bar, a set of new mounting clampswith polyurethane bushes, rose joints for the ends which connect to the suspensioncomponents, and all the bolts etc that will be needed.

Suspension bushes

These are the rubber grommets which separate most of the parts of your

suspension from each other. They're used at the link of an A-Arm with the subframe. They're used on anti-roll bar links and mountings. They're used all overthe place, and from the factory, I can almost guarantee they're made of rubber.Rubber doesn't last. It perishes in the cold and splits in the heat. Perished, splitrubber was what brought the Challenger space shuttle down. This is one ofthose little parts which hardly anyone pays any attention to, but it's vitallyimportant for your car's handling, as well as your own safety, that these littlethings are in good condition.



My advice? Replace them with polyurethane or polygraphite bushes - they arehard-wearing and last a heck of a lot longer. And, if you're into presenting yourcar at shows, they look better than the naff little black rubber jobs. Like allsuspension-related items though, bushes are a tradeoff between performanceand comfort. The harder the bush compound, the less comfort in the cabin. You

pays your money and makes your choice.

The Ins and Outs of complex suspension units.

Generally speaking, this section will be more relevant to you if you ride amotorbike, but you can get high-end spring / shock combos for cars that have allthese features on them. The thing to realise is that if you're going to startmessing with all these adjustments, for God's sake take a digital photo of theunit first, or somehow mark where it all started out. It's a slippery slope and youcan very quickly bugger up the ride quality of your vehicle. If you don't knowwhat the "stock" setting was, you'll never get it back.

Compression damping.

This is the damping that a shock absorber provides as it's being compressed,i.e. as you hit a bump in the road. It's the resistance of the unit to alter from itssteady state to its compressed state. Imagine your riding along and you hit abump. If there is too little compression damping, the wheel will not meet enoughresistance as the suspension compresses. Not enough energy is dissipated bythe time you reach the crest of the bump and because the wheel and otherunsprung components have their own mass, the wheel will continue to moveupwards. This unweights or unloads the tyre and in extreme cases, it can losecontact with the road.

Either way, you briefly lose traction and control. The opposite is true ifcompression damping is too heavy. As the wheel encounters the bump in theroad, the resistance to moving is high and so at the crest of the bump, theremaining energy from the upward motion through the shock absorber istransferred into the frame of the bike or the chassis of the car, lifting it up.



Rebound damping.

Go on - have a guess at what this is. Well in case you're not following along, thisis the damping that a shock absorber provides as it returns from its compressedstate to its steady state, i.e. after you've crested the bump in the road. Too light,and the feeling of control in your vehicle is minimized because the wheel willmove very quickly. The feeling is the soft, plush ride you find in a lot of Americancars. Or mushy as we like to call it. Too heavy, and the shock absorber can'treturn quickly enough. As the contour of the road drops away after the bump,the wheel has a hard time "catching up". This can result in reduced traction, anda downward shift in the height of the vehicle. If that happens, you can overloadthe tyre when the weight of the vehicle bottoms-out the suspension.

Damping controllers.

High-end kit has controls on the shock absorber for both compression andrebound damping. Typically the rebound damping will be a screwdriver slot atthe top of the shock absorber, and compression damping will be a knob eitheron the side or on the remote reservoir. Ultra-high-end kit has separate controlsfor high- and low-speed damping. i.e. you can make the shock absorber behavedifferently over small bumps (low speed compression and rebound) than it doesover large bumps (high speed compression and rebound). Of course you could

buy yourself a nice big TV, a DVD player, dark curtains, a new couch and ayear's supply of popcorn for the same cost as four of these units.



Spring preload.

Some motorbike suspension units, as well as some found on cars, give you theability to alter the spring preload or pre-tension. This means that you'reartificially compressing the spring a little which will alter the vehicle's static sag -

the amount of suspension travel the vehicle consumes all by itself. For example,if you ride a motorbike on your own, the preload might work on the factory setup.But if you put a passenger on the back, the tendency is for the bike to sagbecause there's now more sprung weight. Increasing the preload on the springplate will help compensate for this.

Sprung vs. unsprung weight.

Simply put, sprung weight is everything from the springs up, and unsprungweight is everything from the springs down. Wheels, shock absorbers, springs,knuckle joints and tyres contribute to the unsprung weight. The car, engine,fluids, you, your passenger, the kids, the bags of candy and the portablePlaystation all contribute to the sprung weight. Reducing unsprung weight is thekey to increasing performance of the car. If you can make the wheels, tyres andswingarms lighter, then the suspension will spend more time compensating forbumps in the road, and less time compensating for the mass of the wheels etc.The greater the unsprung weight, the greater the inertia of the suspension,which will be unable to respond as quickly to rapid changes in the road surface.As an added benefit, putting lighter wheels on the car can increase yourengine's apparent power. Why? Well the engine has to turn the gearbox anddriveshafts, and at the end of that, the wheels and tyres. Heavier wheels andtyres require more torque to get turning, which saps engine power. Lighter

wheels and tyres allow more of the engine's torque to go into getting you goingthan spinning the wheels. That's why sports cars have carbon fibre driveshaftsand ultra light alloy wheels.

The Ins and Outs of complex suspension units.

Generally speaking, this section will be more relevant to you if you ride amotorbike, but you can get high-end spring / shock combos for cars that have allthese features on them. The thing to realise is that if you're going to startmessing with all these adjustments, for God's sake take a digital photo of the

unit first, or somehow mark where it all started out. It's a slippery slope and youcan very quickly bugger up the ride quality of your vehicle. If you don't knowwhat the "stock" setting was, you'll never get it back.

Documents

Car Suspension Bible