28595915 Car Bibles the Car Suspension Bible

7/21/2019 28595915 Car Bibles the Car Suspension Bible

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ar Bibles : The Car Suspension Bible

hnically, they are velocity-sensitive hydraulic damping devices - in other words, the faster they move, the more resistance there it movement. They work in conjunction with the springs. The spring allows movement of the wheel to allow the energy in the roadck to be transformed into kinetic energy of the unsprung mass, whereupon it is dissipated by the damper. (phew!....and you thouy just leaked oil didn't you?)

modern coil-over-oil unit

image above shows a typical modern coil-over-oil unit. This is an all-in-one system that carries both the spring and the shockorber. The type illustrated here is more likely to be an aftermarket item - it's unlikely you'd get this level of adjustment on yourular passenger car. The adjustable spring platecan be used to make the springs stiffer and looser, whilst the adjustable dampingvecan be used to adjust the compression damping of the shock absorber. More sophisticated units have adjustable rebound dampwell as a remote reservoir. Whilst you don't typically get this level of engineering on car suspension, most motorbikes do haveoad, rebound and spring tension adjustment. See the section later on in this page about the ins and outs of complex suspension

ts.

uspension Types

heir infinite wisdom, car manufacturers have set out to baffle use with the sheer number of different types of suspension availablboth front and rear axles. The main groupings are dependant and independent suspension types. If you know of any not listed he

mail me and let me know - I would like this page to be as complete as possible.

ront suspension - dependent systems

called because the front wheel's suspension systems are physically linked. For everyday use, they are, in a word, shite. I hate to ensive, but they are. There is only one type of dependant system you need to know about. It is basically a solid bar under the fronhe car, kept in place by leaf springs and shock absorbers. It's still common to find these on trucks, but if you find a car with one ose you should sell it to a museum. They haven't been used on mainstream cars for years for three main reasons:

Shimmy - because the wheels are physically linked, the beam can be set into oscillation if one wheel hits a bump and the othedoesn't. It sets up a gyroscopic torque about the steering axis which starts to turn the axle left-to-right. Because of the axle'sinertia, this in turn feeds back to amplify the original motion.

Weight - or more specifically unsprung weight. Solid front axles weigh a ton and need huge springs to keep their wheels on throad.

Alignment - simply put, you can't adjust the alignment of wheels on a rigid axis. From the factory, they're perfectly set, but ifthe beam gets even slightly distorted, you can't adjust the wheels to compensate.

I frequently get pulled-up on the above statements from people jumping to defend solid-axle

ttp://www.chris-longhurst.com/carbibles/suspension_bible.html (2 of 20)8/10/2005 10:46:32 AM


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suspension. They usually send me pictures like this and claim it's the best suspension system fooff-road use. I have to admit, for off-roadstuff, it probably is pretty good. But let's face it; howmany people with these vehicles evergo off-road? The closest they come to having maximumwheel deflection is when the mother double-parks the thing with one wheel on the kerb during tschool-run.......

ront suspension - independent systems

named because the front wheel's suspension systems are independent of each other (except where joined by an antiroll bar) The

me into existence around 1930 and have been in use in one form or another pretty much ever since then.

MacPherson strut

This is currently, without doubt, the most widely used front suspension system in

cars of European origin. It is simplicity itself. The system basically comprises of astrut-type spring and shock absorber combo, which pivots on a ball joint on thesingle, lower arm. At the top end there is a needle roller bearing on some moresophisticated 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 the spring.The steering gear is either connected directly to the lower shock absorber housing,or to an arm from the front or back of the spindle (in this case). When you steer, itphysically twists the shock absorber housing (and consequently the spring) to turnthe wheel. Simple. The spring is seated in a special plate at the top of theassembly which allows this twisting to take place. If the spring or this plate areworn, you'll get a loud 'clonk' on full lock as the spring frees up and jumps intoplace. This is sometimes confused for CV joint knock.

Potted history of MacPherson:Earle S. MacPherson of General Motorsdeveloped the MacPherson strut in 1947. GM cars were originally design-bound byaccountants. If it cost too much or wasn't tried and tested, then it didn't get built/used. Major GM innovations including the MacPherson Strut suspension system satstifled on the shelf for years because innovation cannot be proven on aspreadsheet until after the product has been produced or manufactured.Consequently, Earle MacPherson went to work for Ford UK in 1950, where Fordstarted using his design on the 1950 'English' Ford models straight away.

Further note:Earle MacPherson should never be confused with Elle McPherson -the Australian ber-babe. In her case, the McPherson Strut is something she doeson 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 the same theme.



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Coil Spring type 1

This is a type of double-A armsuspension. The wheel spindles(purple) are supported by an upper and lower 'A' shaped arms(green). If you look head-on at this type of system, what you'll findis that it's a very basic lever system that allows the spindles totravel vertically up and down. When they do this, they also have aslight side-to-side motion caused by the arc which the levers scribe

around their pivot point. This side-to-side motion is known asscrub. Unless the links are infinitely long the scrub motion is alwayspresent. There are two other types of motion of the wheel relativeto the body when the suspension articulates. The first and mostimportant is a toe angle (steer angle). The second and leastimportant, but the one which produces most pub talk is the camberangle, or lean angle. Steer and camber are the ones which weartyres. Alsonote that the springs/shocks in this example are in a socalled 'coil over oil' arrangement whereby the shock absorbers(yellow) sit inside the springs (red).

Coil Spring type 2

This is also a type of double-A armsuspension although the lower arm in thesesystems can sometimes be replaced with single solid arms. The only realdifference between this and the type 1 system mentioned above is that thespring/shock combo is moved from between the arms to above the upper arm.This transfers the load-bearing capability of the suspension almost entirely to theupper arm and the spring mounts. The lower arm in this instance becomes a

control arm. This particular type of system isn't so popular in cars as it takes up alot room.

Double Wishbone

So-called because the lower and upper arms are theshape of wishbones. Yes I know they don't looklikewishbones here, but believe me, they are. Thespindle is a highly complex construction in this



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system, as are the wishbones themselves. Thisrapidly becoming one of the most favouredsuspension types for new cars as it gives excellentroad-holding capabilities whilst taking up very littleroom under the car. This allows for smoother lineson the bodywork, and less intrusion in to the enginebay. A 3D rendering such as that on the right doesnot do this system any justice. To really appreciateit, you need to get your head in a wheel well andhave a look. And I know a few mechanics who'vestill not been able to figure it out even then.

Multi-link suspension

This is the latest incarnation of the double wishbone system described above. It'scurrently being used in the Audi A8 and A4 amongst other cars. The basicprinciple of it is the same, but instead of solid upper and lower wishbones, each'arm' of the wishbone is a separate item. These are joined at the top and bottomof the spindle thus forming the wishbone shape. The super-weird thing about thisis that as the spindle turns for steering, it alters the geometry of the suspensionby torquing all four suspension arms. They have complex pivot systems designedto allow this to happen.Car manufacturers claim that this system gives even better road-holdingproperties, because all the various joints make the suspension almost infinitely

adjustable. There are a few variations on this theme appearing at the moment,with differences in the numbers 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 shaped suspension arm is joinedat the front to the chassis, allowing the rear to swing up and down. Pairs of



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these become twin-trailing-arm systems and work on exactly the sameprinciple as the arms in the coil spring type systems described above. Thedifference is that instead of the arms sticking out from the side of thechassis, they travel back along it. If you want to know what I mean, find aVW beetle and stick your head in the front wheel arch - that's a double-trailing-arm suspension setup. Simple. It's used mostly in older cars andbeach buggies now.

Moulton rubber suspension

This suspension system is based on the compression of a solid mass of rubber - red in boththese images. The two types are essentially derivatives of the same design. It is namedafter Dr. Alex Moulton - one of the original design team on the Mini, and the engineer whodesigned its suspension system in 1959. This system is known by a few different namesincluding 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 used Moulton's rubbersuspension system, but laid out horizontally rather than vertically, to save space again.The Mini was originally intended to have Moulton's fluid-filled Hydrolastic suspension, butthat remained on the drawing board for a few more years. Eventually, Hydrolastic wasdeveloped into Hydragas (see later on this page), and revised versions were adopted onthe Mini Metro and the current MGF-sportscar.Ultimately, Moulton rubber suspension is now used in a lot of bicycles - racing andmountain bikes. Due to the compact design and the simplicity of its operation andmaintenance, it's an ideal solution.

ear suspension - dependant systems

ntrary to the front version of this system, many many cars are still designed and built with dependant (linked) rear suspensiontems.



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Solid-axle, leaf-spring

This system wasfavoured by theAmericans for yearsbecause it was deadsimple and cheap tobuild. The ride qualityis decidedly

questionable though.The drive axle (purplein this image) isclamped (green) tothe leaf springs (red).The shock absorbers(yellow) are alsoattached to theclamps. The ends ofthe leaf springs areattached directly tothe chassis, as are theshock absorbers.Simple, notparticularly elegant,

but cheap. The maindrawback with thisarrangement is thelack of lateral locationfor the axle.

Solid-axle, coil-spring

This is a variation and update on the systemdescribed above. The basic idea is the same,but the leaf springs have been removed infavour of 'coil-over-oil' spring and shockcombos. Because the leaf springs have beenremoved, the axle now needs to have lateralsupport from a pair control arms. The frontends of these are attached to the chassis, therear ends to the axle. A variation on this hasthe shock absorbers separate from thesprings, allowing much smaller springs. This inturn allows the system to fit in a smaller areaunder the car.



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Beam Axle

This system is used in front wheel drive cars,where the rear axle isn't driven. (hence it's fulldescription as a "dead beam"). Again, it is arelatively simple system. The beam runs acrossunder the car with the wheels attached toeither end of it. Also at the ends, the springsand shock absorbers are attached. The beamhas two integral trailing arms built in instead of

the separate control arms required by the solid-axle-coil-spring system. Variations on thissystem can have either separate springs andshocks, or the combined 'coil-over-oil' varietyas shown here. One notable feature of thissystem is the track bar (or panhard rod). Thisis a diagonal bar which runs from the rearcorner of the beam to a point either just infront of the opposite corner, or in this case,above the opposite spring mount. This is toprevent side-to-side movement in the beamwhich would cause all manner of nasty handlingproblems. A variation on this them is the twistaxlewhich is identical with the exception of thepanhard rod. In this system, the axle is

designed to twist slightly. This gives, in effect,a semi-independent system whereby a bumpon one wheel is partially soaked up by thetwisting action of the beam. Yet anothervariation on this system does away with thesprings and replaces them with torsion barsrunning across the chassis, and attached to theleading edge of the beam supports. Thesebeam types are currently very popular becauseof their simplicity and low cost.

4-Bar

4-bar suspension can be used on the front and rear of vehicles - I've chosen to show it in the "rear" section of this page becausethat's where it's normally found. 4-bar suspension comes in two varieties. Triangulated, shown on the left here, and parallel,shown on the right.The parallel design operates on the principal of a "constant motion parallelogram". The design of the 4-bar is such that the rearend housing is always perpendicular to the ground, and the pinion angle never changes. This, combined with the lateral stabilityof the Panhard Bar, does an excellent job of locating the rear end and keeping it in proper alignment. If you were to comparethis 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-bar setupis far less severe. This, combined with the relatively compact installation design means that it's ideal for cars and trucks wherespace 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 endhousing much closer to the centre. This eliminates the need for the separate panhard bar, which in turn means the whole setupis even more compact.



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ear suspension - independent systems

ollows, that what can be fitted to the front of a car, can be fitted to the rear to without the complexities of the steering gear.mplified versions of all the independent systems described above can be found on the rear axles of cars. The multi-link system isrently becoming more and more popular. In advertising, it's put across as '4-wheel independent suspension'. This means all theeels are independently mounted and sprung. There are two schools of thought as to whether this system is better or worse fordling than, for example, Macpherson struts and a twist axle. The drive towards 4-wheel independent suspension is primarily to

rove ride quality without degrading handling.

ydrolastic Suspension

ou've got this far, you'll remember that Dr. Alex Moulton originally wanted the Mini to have Hydrolastic suspension - a system whfront and rear suspension systems were connected together in order to better level the car when driving. principle is simple. The front and rear suspension units have Hydrolastic displacers, one per side. These are interconnected by aall bore pipe. Each displacer incorporates a rubber spring (as in the Moulton rubber suspension system), and damping of the systechieved by rubber valves. So when a front wheel is deflected, fluid is displaced to the corresponding suspension unit. Thatssurises the interconnecting pipe which in turn stiffens the rear wheel damping and lowers it. The rubber springs are only slightlyught into play and the car is effectively kept level and freed from any tendency to pitch. That's clever enough, but the fact that it

this without hindering the full range of motion of either suspension unit is even more clever, because it has the effect of producingt ride. Pictures and images of anything to do with hydrolastic suspension are few and far between now, so you'll have to excuse thgiarism of the following image. The animation below shows the self-leveling effect - notice the body stays level and doesn't pitch.

what happens when the front and rear wheels encounter bumps or dips together? One cannot take precedent over the other, so d suspension stiffens in response to the combined upward motion and, while acting as a damper, transfers the load to the rubberngs instead, giving a controlled, vertical, but level motion to the car.

member I said the units were connected with a small borepipe? The restriction of the fluid flow, imposed by this pipe, rises with thed of the car. This means a steadier ride at high speed, and a softer more comfortable ride at low speed.

drolastic suspension is hermetically sealed and thus shouldn't require much, if any, attention or maintenance during its normalrking life. Bear in mind that hydrolastic suspension was introduced in 1965 and you'd be lucky to find a unit today that has had anrk done to it.

image below shows a typical lateral installation for hydrolastic rear suspension. The purple structure is the subframe, the greents are the suspension swingarms, and the red cylinders are the displacer units containing the fluid and the rubber spring. The pipe

ding from the units can be seen and they would connect to the corresponding units at the front of the vehicle.



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drolastic suspension shouldn't be confused with Citron's hydropneumatic suspension (see below). That system uses a hydraulicmp that raises and lowers the car to different heights. Sure it's a superior system but it's also a lot more costly to manufacture anntain. That's due in part to the fact that they don't use o-rings as seals; the pistons and bores are machined to incredible toleran

crons), that it makes seals unnecessary. Downside : if something leaks, you need a whole new cylinder assembly.

drolastic was eventually refined into Hydragas suspension.......

ydragas Suspension

dragas is an evolution of Hydrolastic, and essentially, the design and installation of the system is the same. The difference is in theplacer unit itself. In the older systems, fluid was used in the displacer units with a rubber spring cushion built-in. With Hydragas, tber spring is removed completely. The fluid still exists but above the fluid there is now a separating membrane or diaphragm, andve that is a cylinder or sphere which is charged with nitrogen gas. The nitrogen section is what has become the spring and dampit whilst the fluid is still free to run from the front to the rear units and back.



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dragas suspension was famously used in the 1986 Porsche 959 Rally car that entered the Paris-Dakar Rally, and today you can finthe MGF Roadster.

ydropneumatic Suspension

anks to Jonathan Bruce and Pieter Melissen for some updates to this information.}ce the late forties, Citron have been running a fundamentally different system to the rest of the auto industry. They call itropneumatic and it encompasses features as diverse as brakes, suspension & steering. As its name may suggest, its core technol mainstay of its functionality is hydraulics. Superblysmooth suspension is provided by the fluid's interaction with a pressurised gay pioneered in the rear suspension of the 15 (Traction Avant) model, and it has been fitted to many of their cars since. I've had tarate it into it's own category because it is quite different from any other type of suspension system.

system is powered by a large hydraulic pump operated directly by the engine in much the same way as an alternator or an airditioner is, and provides fluid to an "accumulator" at pressure, where it is stored ready to be delivered to servo a system. (This

mp is also used for the power steering and the brakes, and in the DS for the semi-auto box.)ause this page is all about suspension, for clarity we'll look at the simplifiedsion of this as installed in the "BX" model. The Citron BX was a major turningnt in the company's history as it was the first car to be produced under the

mpany's new Peugeot management, following the 1970s take-over of Citron bygeot. As a direct consequence of the Peugeot influence, the car is somewhatre conventional than its larger sibling designed earlier - the CX. This Peugeot-orced "normalisation" of the design makes it easy enough to examine as anstration of how hydropneumatic suspension works.re are two main components you need to familiarise yourself with and to

erstand. The spheres are like the springs on the car, and the struts are theraulic components that make the fluid act like a spring.s start with the sphere. The spring in this suspension system is provided by araulic component called an accumulator, which is gas under pressure in a bottletained within a diaphragm, effectively a balloon which allows pressurised fluid to

mpress the gas, and then as pressure drops the gas pushes the fluid back to keepsystem's pressure up. As you can see in the drawing above the pink gasrogen) is compressed when the pressure in the green fluid (LHM) overcomes thepressure, and pushes back the diaphragm which compresses the gas. Then aspressure in the fluid reduces, the gas pushes back the diaphragm and as theovercomes the fluid, it expels the fluid from the sphere, returning gas and fluid to equilibrium. This is the hydropneumaticivalent to the spring getting compressed (bound) and getting depressed, ie springing back (rebound). with me? We can keep going...

w can a gas, a diaphragm and a hydraulic fluid compressing, form a spring? Simple(ish): The pressure of the gas is the equivalentspring weight. The inlet hole at the bottom of the sphere restricts the flow of the fluid and provides an element of damping. By

acing the sphere for ones of different specs, it is possible to adjust the ride characteristics with these cars. Rumour even has it thacing team in Anglesey is customising their car by pressurising their own spheres to custom pressures to make an exact match forcircuit the are on.ore we go any further it is pretty important that you understand where the fluid acting on the diaphragm in the sphere gets its fom, and to do that we are going to have to look at the 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 strut in itself acts like a syringto inject fluid into the sphere. When the wheel hits a bump it rises, pushes the piston of the strut back athis squeezes fluid through the tiny hole in the sphere to let the gas spring absorb the energy of the bumThen when the car is over the bump and its time to let the wheel back down, the gas pushes the diaphraback out, pushing the fluid down to the strut, pushing the wheel down to the ground.Some interesting possibilities were opened up by the company deciding to use this system to spring theicars. One or two of the more obvious ones are that since the system is hydraulic, the ride height can easbe altered, a trend low riders are now following on with in California, nearly fifty years later. Also, theycould link the four corners together to make a system that prepared the car for the bump to keep it evenand offer the passengers a smoother ride. Basically they put fancy valves called height correctors on the



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anti-roll bar. These were mounted in such a way that as the suspension twisted, this operated the valvesthat controlled the transfer of fluid to the struts. It was possible to isolate the front and rear systems andhave the front suspension set at a height which required 'x' litres. So when the front nearside wheel takeknock compressing its sphere, x/2 L is lost in the sphere, then the height correctors allow another x/2 L to inflate the offside strut by that 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 that fluid, the strut returns to itsown height pulling the anti roll bar back true with it which in turn tells the height corrector to lose that exx/2 litres of fluid from the other 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 above the road. Neat huh?A further mechanical advantage of hydraulic suspension is that the car is able to link its braking effort tothe weight on the wheels. In the Citron BX, the rear braking effort comes from the pressure exerted onthe LHM fluid by the weight on 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 to exert less pressure on its fluand as weight and grip diminish on the wheels, so does the braking effort, thus the hydropneumatic syst

vents rear wheel lock ups.addition to these benefits, Citron pioneered computer controlled suspension in the early nineties by inserting a computer to takedings from the cars' chassis and control systems and let the computer make informed decisions about how to handle the carspension. The computer could then effect these decisions by things like servo valves, and offered benefits like soft suspension forsing, but stiffer, sportier suspension for faster harder driving, allowing the driver to cruise in comfort and still enjoy a responsive It also moves substantially towards eliminating body roll and if used for a sportier driver will save tyre wear as well (they claim).

re was a further refinement / development in this suspension design in the 1990s called the Activa system, designed to compens

body roll. It was quite effective although only the Xantia has been fitted with it. The main setback was that ride comfort was evenrse than a BMW (although cornering speeds were fantastic) which did not go too well with the traditional Citron clientele. Therent adjustable systems (computer controlled) lack this anti roll characteristic, and there are owners who always prefer the "comfting rather than the "sporty" one, because again, that is not what Citron is about.worth noting that when Mercedes launched their latest 600 SLC version with a computer controlled anti roll system, Auto Motor uort then proudly claimed that to be the first such anti roll system in world, only having to correct that one issue later by having tontion a French invention.s Royce was the only company ever to buy the patent and they used in in the rear suspension of the Silver Shadow. When Citroe

s the owner of Maserati some of their cars were also hydropneumatised.

re in-depth information can be found here - http://www.citroen.mb.ca/citroenet/html/h/hydro.html- or - http://www4.tpgi.com.a

way/page5.html. Meanwhile, the rest of us can hopefully feel satisfied with our newly enriched understandings of hydropneumatic

pension. If you're still awake.

ydraulic Suspension

draulic suspension is an innovation making its way into motor sports, no doubt to trickle down to consumer vehicles eventually. Itbeen designed and pioneered by the Racing For HollandDome S101 sports car team. In the image below you can see both the

ditional coilover system (the yellow/blue/red units) at the front of the car. This photo was taken before scrutineering for the 2005 urs of Le Mans race. The team had both systems online and when scrutineering passed the car, the coilover units were removed, te for the first time completely with hydraulic suspension.tral to their system is a control unit mounted next to the cockpit. They tell me the system can't be compared to the hydropneumpension Citron uses because this system doesn't use a pump and has less than a litre of hydraulic fluid in the entire system.re news on this development as I get it.nks to Sander van Dijk for sending me this photo, plus a ton of others of their racing car.

http://www.citroen.mb.ca/citroenet/html/h/hydro.htmlhttp://www4.tpgi.com.au/ozway/page5.htmlhttp://www4.tpgi.com.au/ozway/page5.htmlhttp://planetlemans.com./http://planetlemans.com./http://www4.tpgi.com.au/ozway/page5.htmlhttp://www4.tpgi.com.au/ozway/page5.htmlhttp://www.citroen.mb.ca/citroenet/html/h/hydro.html


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near Electromagnetic Suspension

s is the latest innovation in suspension systems, invented by Bose. The idea is that



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ead of springs and shock absorbers on each corner of the car, a single linerctromagnetic motor and power amplifier can be used instead.de the linear electromagnetic motor are magnets and coils of wire. When electrical powerpplied to the coils, the motor retracts and extends, creating motion between the wheel andbody. It's like the electromagnetic effect used to propel some newer rollercoaster cars on

nch, or if you're into videogames and sci-fi, it's like a railgun.e of the big advantages of an electromagnetic approach is speed. The linearctromagnetic motor responds quickly enough to counter the effects of bumps and potholes,s allowing it to perform the actions previously reserved for shock absorbers.t's second mode of operation, the system can be used to counter body roll by stiffening thepension in corners. As well as these functions, it can also be used to raise and lower rideght dynamically. So you could drop the car down low for motorway cruising, but raise it up

the pot-hole ridden city streets. It's all very clever. power amplifier delivers electrical power to the motor in response to signals from thetrol algorithms. These mathematical algorithms have been developed over 24 years ofearch. They operate by observing sensor measurements taken from around the car andding commands to the power amps installed with each linear motor. The goal of the controlorithms is to allow the car to glide smoothly over roads and to eliminate roll and pitching driving. amplifiers themselves are based on switching amplification technologies pioneered by Dr.e at MIT in the early 1960s. The really smart thing about the power amps is that they areenerative. So for example, when the suspension encounters a pothole, power is used toend the motor and isolate the vehicle's occupants from the disturbance. On the far side ofpothole, the motor operates as a generator and returns power backthrough the amplifier.doing this, the Bose system requires less than a third of the power of a typical vehicle'sconditioner system. Clever, eh?

e have also managed to package this little wonder of technology into a two-point harness - basically needs two bolts to attach it to your vehicle and that's it. It's a pretty compactign, not much bigger than a normal shock absorber.

official Bose suspension page can be found hereif you want more info.

It's worth noting that a company called Aura Systemsdevised (or at least tried to market) a similar linearelectromagnetic suspension system around 1991. Theypublished an article in the Automotive Engineering Journal

ming that electromagnetic actuators could be used for vehicle suspensions and it saidt small devices could be designed with a typical thrust capability of about 2500wtons and for a reasonable power demand. This happened at the same time that linearctromagnetic rams were being developed for entertainment simulators and full flightulators to replace hydraulic systems. In fact, it could be argued that the Aura Systems

m was a direct descendant of the rams found on Super-X entertainment simulators.

http://www.bose.com/learning/project_sound/bose_suspension.jsphttp://www.bose.com/learning/project_sound/bose_suspension.jsp


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units looked very similar to the Bose devices and had the same limitation - theyldn't carry the dead weight of the vehicle. Aura Systems ran into financial troubles in

00, and filed for Chapter 11 in 2005. The time scales fit quite nicely into the declarede time frame (start of development versus going public). Of course they could haven parallel developments, but the bigger question is why was Aura not able to sell theirtem to an OEM at some time during the previous 15 years? Could it be to do withchanical limitations - that the sway bars carrying vertical loads are very good atnsmitting road inputs into the vehicle structure even if the bar rate is low? Time willif Bose manage to succeed where Aura Systems failed.

nti-roll Bars & Strut Braces

rut Braces

ou're serious about your car's handling performance, you will first be looking at lowering the suspension. In most cases, unless're a complete petrolhead, this will be more than adequate. However, if you are a keen driver, you will be able to get far betterdling out of your car by fitting a couple of other accessories to it. The first thing you should look at is a strut brace. When youner, the whole car's chassis is twisting slightly. In the front (and perhaps at the back, but not so often) the suspension pillars will ving relative to each other because there's no direct physical link between them. They are connected via the car body, which can ending on its stiffness. A strut brace bolts across the top of the engine to the tops of the two suspension posts and makes that disical contact. The result is that the whole front suspension setup becomes a lot more rigid and there will be virtually no movemen

tive to each side. In effect, you're adding the fourth side to the open box created by the subframe and the two suspension pillars

mple straight brace(highlighted). Complex brace (highlighted).

ti-roll Bars (Sway Bars/Stabilizers)

these aren't the things that are bolted inside the car in case you turn it over - those are rollover cages. Anti-roll bars do preciselyat their name implies - they combat the roll of a car on it's suspension as it corners. They're also known as sway-bars or anti-swas. Almost all cars have them fitted as standard, and if you're a boy-racer, all have scope for improvement. From the factory they sed towards ride comfort. Stiffer aftermarket items will increase the road-holding but you'll get reduced comfort because of it. It'sch-22 situation. Fiddling with your roll stiffness distribution can make a car uncomfortable to ride in and extremely hard to handleget it wrong. The anti-roll bar is usually connected to the front, lower edge of the bottom suspension joint. It passes through two

ot points under the chassis, usually on the subframe and is attached to the same point on the opposite suspension setup. Effectiveoins the bottom of the suspension parts together. When you head into a corner, the car begins to roll outof the corner. For exampou're cornering to the left, the car body rolls to the right. In doing this, it's compressing the suspension on the right hand side. Wood anti-roll bar, as the lower part of the suspension moves upward relative to the car chassis, it transfers some of that movemenhe same component on the other side. In effect, it tries to lift the left suspension component by the same amount. Because this i

sically possible, the left suspension effectively becomes a fixed point and the anti-roll bar twists along its length because the othe is effectively anchored in place. It's this twisting that provides the resistance to the suspension movement.



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ou're loaded, you can buy cars with active anti-roll technology now. These sense the roll of the car into a corner and deflate thevant suspension leg accordingly by pumping fluid in and out of the shock absorber. It's a high-tech, super expensive version of thd old mechanical anti-roll bar. You can buy anti-roll bars as an aftermarket add-on. They're relatively easy to fit because most ca

e anti-roll bars already. Take the old one off and fit the new one. In the case of rear suspension, the fittings will probably alreadyre even if the anti-roll bar isn't.

ical anti-roll bar (swaybar) kits include the uprated bar, a set of new mounting clamps with polyurethane bushes, rose joints for ts which connect to the suspension components, and all the bolts etc that will be needed.

uspension bushes

se are the rubber grommets which separate most of the parts of your suspension from each other. They're used at the link of an m with the subframe. They're used on anti-roll bar links and mountings. They're used all over the place, and from the factory, I ca

ost guarantee they're made of rubber. Rubber doesn't last. It perishes in the cold and splits in the heat. Perished, split rubber waat brought the Challenger space shuttle down. This is one of those little parts which hardly anyone pays any attention to, but it'slly important for your car's handling, as well as your own safety, that these little things are in good condition. My advice? Replacem with polyurethane or polygraphite bushes - they are hard-wearing and last a heck of a lot longer. And, if you're into presentingr car at shows, they look better than the naff little black rubber jobs. Like all suspension-related items though, bushes are a tradeween performance and comfort. The harder the bush compound, the less comfort in the cabin. You pays your money and makesr choice.

he Ins and Outs of complex suspension units.



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nerally speaking, this section will be more relevant to you if you ride a motorbike, but you can get high-end spring / shock combocars that have all these features on them. The thing to realise is that if you're going to start messing with all these adjustments, d's sake take a digital photo of the unit first, or somehow mark where it all started out. It's a slippery slope and you can very quicger up the ride quality of your vehicle. If you don't know what the "stock" setting was, you'll never get it back.

mpression damping.

s is the damping that a shock absorber provides as it's being compressed, ie. as you hit a bump in the road. It's the resistance of t to alter from its steady state to its compressed state. Imagine your riding along and you hit a bump. If there is too little

mpression damping, the wheel will not meet enough resistance as the suspension compresses. Not enough energy is dissipated bytime you reach the crest of the bump and because the wheel and other unsprung components have their own mass, the wheel wtinue to move upwards. This unweights or unloads the tyre and in extreme cases, it can lose contact with the road. Either way, yo

efly lose traction and control. opposite is true if compression damping is too heavy. As the wheel encounters the bump in the road, the resistance to moving ish and so at the crest of the bump, the remaining energy from the upward motion through the shock absorber is transferred into tme of the bike or the chassis of the car, lifting it up.

bound damping.

on - have a guess at what this is. Well in case you're not following along, this is the damping that a shock absorber provides as iturns from its compressed state to its steady state, ie. after you've crested the bump in the road. Too light, and the feeling of contour vehicle is minimised because the wheel will move very quickly. The feeling is the soft, plush ride you find in a lot of Americans. Or mushy as we like to call it. Too heavy, and the shock absorber can't return quickly enough. As the contour of the road dropsay after the bump, the wheel has a hard time "catching up". This can result in reduced traction, and a downward shift in the heighvehicle. If that happens, you can overload the tyre when the weight of the vehicle bottoms-out the suspension.

mping controllers.

h-end kit has controls on the shock absorber for both compression and rebound damping. Typically the rebound damping will be aewdriver slot at the top of the shock absorber, and compression damping will be a knob either on the side or on the remoteervoir. Ultra-high-end kit has separate controls for high- and low-speed damping. ie. you can make the shock absorber behaveerently over small bumps (low speed compression and rebound) than it does over large bumps (high speed compression andound). Of course you could buy yourself a nice big TV, a DVD player, dark curtains, a new couch and a year's supply of popcorn fosame cost as four of these units.

ring preload.

me motorbike suspension units, as well as some found on cars, give you the ability to alter the spring preload or pre-tension. Thisans that you're artificially compressing the spring a little which will alter the vehicle's static sag - the amount of suspension travelvehicle consumes all by itself. For example, if you ride a motorbike on your own, the preload might work on the factory setup. Buput a passenger on the back, the tendency is for the bike to sag because there's now more sprung weight. Increasing the preloa

the spring plate will help compensate for this.



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prung vs. unsprung weight.

mply put, sprung weight is everything from the springs up, and unsprung weight is everything from the springs down. Wheels, shoorbers, springs, knuckle joints and tyres contribute to the unsprung weight. The car, engine, fluids, you, your passenger, the kidsbags of candy and the portable Playstation all contribute to the sprung weight. Reducing unsprung weight is the key to increasingformance of the car. If you can make the wheels, tyres and swingarms lighter, then the suspension will spend more time

mpensating for bumps in the road, and less time compensating for the mass of the wheels etc. greater the unsprung weight, the greater the inertia of the suspension, which will be unable to respond as quickly to rapid changhe road surface.an added benefit, putting lighter wheels on the car can increase your engine's apparent power. Why? Well the engine has to turn

rbox and driveshafts, and at the end of that, the wheels and tyres. Heavier wheels and tyres require more torque to get turning,ch saps engine power. Lighter wheels and tyres allow more of the engine's torque to go into getting you going than spinning theeels. That's why sports cars have carbon fibre driveshafts and ultra light alloy wheels.

rogressively wound springs

se are the things to go for when you upgrade your springs. In actual fact, it's difficult notto get progressive springs when yourade - most of the aftermarket manufacturers make them like this. Most factory-fit car springs are normally wound. That is to sayt their coil pitch stays the same all the way up the spring. If you get progressively wound springs, the coil pitch gets tighter theser to the top of the spring you get. This has the effect of giving the spring increasing resistance, the more it is compressed. spring constant (stiffness) of a coil spring equals:compression / force = D^4 * G / (64*N*R^3)

ere D is the wire diameter, G an elastic material property, N the number of coils in the spring, and R the radius of the spring.ncreasing the number of coils decreases the stiffness of the spring. Thus, a progressive spring is progressive because the two parcompressed equally until the tightly wound part locks up, effectively shortening the spring and reducing its compliance.for normal driving, you'll be using mostly the upper 3 or 4 'tight' winds to soak up the average bumps and potholes. When you geo harder driving, like cornering at speed for example, because the springs are being compressed more, they resist more. The effeceduce the suspension travel at the top end resulting in less body roll, and better road-holding. Invariably, the fact that the springprogressively wound is what accounts for the lowering factor. The springs aren't made shorter - they're just wound differently. Orse the material that aftermarket springs are made of is usually a higher grade than factory spec simply because it's going to beected to handle more loads.te:Make sure you get powder-coated springs! This means they've been treated with a good anti-corrosion system and then covereowdered paint. The whole lot is then baked to make the paint seal and stick and bring out it's polyurethane elastic properties. It'sbest type. If you just get normally painted springs, the paint will start to flake on the first bump, and surface rust will appear wit

s of the first sign of dampness. Not good. Besides - powder coated springs look cool too!

orsion bars

Torsion bars deserve their own section because they are a type of spring which can be used inplace of coil- or leaf-springs. It's one of the topics I get the most e-mail on, so instead ofcontinually sending the same answer, I thought I'd cover it on this page.



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A torsion bar is a solid bar of steel which is connected to the car chassis at one end, and free tomove at the other end. They are almost always mounted across the car, one for each side of thsuspension. The springing motion is provided by the metal bar's resistance to twisting. To over-simplify, stick your arm out straight and get someone to twist your wrist. Presuming that yourmate doesn't snap your wrist, at a certain point, resistance in your arm (and pain) will cause yoto twist your wrist back the other way. That is the principle of a torsion bar.Torsion bars typically have splines on one end so that they can be removed, twisted round onespline and re-inserted. This can be used to raise or lower a car, or to compensate for the natura'sag' of a suspension system over time.

ut What if.......?

Wh a t i f I g e t s h o r t e r s p r i n g s t o lo w e r t h e c a r ? W i l l I n e e d t o a d j u s t m y c a st e r a n d c am b e r a n g l e s a n d / o r m y s h o c k

o r b e r s ?

Generally the answer would be no. Most cars have a good 10-13cm (4-5 inches) movement in their suspension from the factoAs most of the lowering springs you can buy only lower by 2-7cm (1-3 inches), your suspension should still be well within it'sdesigned operating limits. Therefore, caster and camber angles shouldn'tneed looking at.

Wh a t i f I g e t s h o r t e r s p r in g s t o l o w e r t h e c a r ? W i l l m y t y r e s r u b o n m y a r c h e s?

They shouldn't unless you start messing about with wheel and tyre sizes. Again, given that most suspension kits lower within car's normal operating limits, there shouldn't be a problem. If there was, then every time you went over a big hump withstandard suspension, the tyres would rub. Rubbing against the arches will almost certainly only occur if you lower the car andwiden the wheels. See the Wheel & Tyre Biblefor more info on this.

uncy Links

e's some links for you to follow.Kinetic Suspension systems

Tim Stiles Racing - VW and Audi suspension mods etc

Monroe shock absorbers Suspension

Eibach Suspension

TMS Suspension catalogue for BMWs

http://www.chris-longhurst.com/carbibles/tyre_bible.htmlhttp://www.kinetic.au.com/http://www.tsr-performance.com/http://www.monroe.com/http://www.eibach.com/http://www.turnermotorsport.com/catalog/suspension.htmhttp://www.turnermotorsport.com/catalog/suspension.htmhttp://www.eibach.com/http://www.monroe.com/http://www.tsr-performance.com/http://www.kinetic.au.com/http://www.chris-longhurst.com/carbibles/tyre_bible.html


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These pages were last updated on 5thAugust 2005.

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28595915 Car Bibles the Car Suspension Bible