I wrote a series of articles back in 1991, called Back To Basics, and re-edited them in 1995 under the pseudonym of Ed McCannick, for the T.O.R.C Club Newsletter, TORC TALK. I've condensed some of the articles for this page.
Please bear in mind that the vehicles covered here are specifically mini buggies and that not all the set-ups and procedures discussed will work on larger cars without revaluation.

"…..we will be looking at what constitutes good off-road suspension and steering. I put the emphasis on off-road, because, as we will see, what works on the bitumen is not always applicable to the dirt.

The first thing that must be understood is that designing most areas of a buggy's running gear presents a paradox. Often compromises have to be made; robbing Peter along the way to pay Paul.

Imagine you are standing in a room in which you have just placed your favourite CD into your surround sound system. With all settings to default, the ideal place to stand to achieve optimum sound quality and effect would be the middle of the room.

Unfortunately, when 'Fido' chewed the remote last week he upset the balance, so, to try and compensate, you take a step toward the sub woofer to improve the bass effect. Sods Law; as you do that, you are simultaneously taking a step away from a  corner with a tweeter, and so you loose some treble...etc., etc. Such is the case with suspension and steering.

Every time you make an improvement in one area, it is usually at the expense of another.

Hopefully though, by the end of this series of articles the relationship of the variables involved with suspension and steering will be more easily understood, and the effect an adjustment in one area can have on another will be better appreciated.

Off-road technology shares little in common with that used in road-going cars. One example is brakes. The average family car runs on relatively sticky rubber, with large diameter disc brakes on the front and less efficient drum brakes or disc brakes on the rear.

When you stamp your foot hard on the brake pedal, the tyres bite into the bitumen and everything in the car flies forward. Actually the entire weight of the car and its contents transfers to the front. Coincidently, that is where the most effective brakes on the car are, and combined with the grippy tyres on firm bitumen, manage to pull the vehicle up.

When racing off-road, the surface is usually grass, dust, gravel, mud, or a combination of these. Now, if you have huge disc brakes on the front and press your foot on the pedal, the loose surface offers little resistance to a tyre whose rotation has been retarded, and so locks up. Locked-up front wheels don't steer! That's not to say we use huge brakes on the rear, remember - compromising is the key!

Do we really need suspension?
Well, yes. If we didn't have any suspension, two things would happen. Firstly, we would be shaken about so much, that apart from the risk of personal injury, we would have little control over the vehicle as it bounced around (have you ever watched a Honda FL250 Odyssey?).

Secondly, without suspension, the driving wheels would spend more time in the air. This would obviously result in reduced forward propulsion, and unnecessary duress on the engine and driveline every time the wheels came back to earth.

The elements of suspension design.
Let's start with a buggy with four wheels which all work independently of each other. Each wheel is attached to a hub, which is integral with either an upright - which in turn is attached to the chassis with a pair of A-arms (wishbones), or to a trailing arm, which pivots directly off the back of the cabin.

To keep the chassis up off the ground (and to provide the suspension) a spring must be used for each wheel and in turn, some form of damping must also be used in conjunction with the springs to harness the effects of them compressing and decompressing as the buggy travels over obstacles.

The spring and the damper are normally combined in one unit called a coil-over shock absorber, or just "coilover".

The coilover is attached at its top end to the chassis, and at its lower end to either the upright or outer end of an A-arm or trailing arm.

Rear suspension.
Once the rear suspension has been designed and built, it is not normally necessary to make any major adjustments to it. There are only four variables anyway; toe in/out, used to enhance understeer/oversteer, camber (negative); useful for improving grip during cornering and in roll, track; seldom altered, but varying it can make minor changes to roll centre heights, ride height adjustments are made by either changing the location of the top or lower coilover mounts, moving the spring pack on the shock body, or by altering the spring pre-load.

Contrary to common belief, compressing a spring by turning the threaded spring platform, does not increase the spring's rate. It merely adjusts the amount of preload, thus raising or lowering the buggy's ride height.

Front suspension.
The front end is somewhat more complex than the rear end, but does share some principles in common. The wheel is similarly located via a hub in an upright to a trailing arm ('J') arm, A-arms, or swing axle. As with the rear, camber and toe-in also play a part in front end geometry.

Unlike the rear though, the front upright must swivel for the purpose of steering. The axis about which the upright swivels is often called the kingpin axis. Kingpins were an early form of stub axle location formerly used in horse-drawn vehicles, and cars up until the 1960's.

The more common method of upright rotation nowadays is the use of two ball joints - one at the top of the upright and one at the bottom. A line drawn through the centres of the ball joints (as viewed from the front), describes the kingpin angle or just KPI.

As will be explored later, the KPI and its proximity to the tyre's centre line (scrub radius), has its effect on steering ease, steering feel, changes to camber during body roll and tyre wear (which for the purposes of racing we will totally ignore!).

Not only is the top of the upright inclined towards the centre of the car (as viewed from the front), but it is also inclined towards the rear of the car (as viewed from the side). This fore/aft tilt is called castor and positive castor when leaning back. Positive castor provides self-centring and is also essential for stability at speed. Too much castor though, can lead to excessively heavy steering – about 6° at ride height is sufficient.

That essentially covers the absolute fundamentals of suspension, however, suspension is a very complex subject involving many other parameters and possibilities. 

Steering.
Front suspension and steering function are so closely allied that they must be considered simultaneously when designing the front end. KPI, scrub radius, castor and camber are all interconnected and through suspension movement can directly affect the stability of the front wheels.

There are a number of different steering mechanisms to choose from, but only the rack and pinion (or just "rack") is of any interest to us. The rack achieves its lateral movement by means of the pinion which is rotated indirectly by the steering wheel and the rack transfers movement to the tie rods, from either the ends of the rack (end load rack), or from closely spaced rod ends in the middle of the rack (centre load rack).

The location and positioning of the rack in the chassis and its relationship to the steering arms on the front uprights is critical if bump steer is to be minimised (more about bumpsteer below).

Rack position tuning. 
With the amount of suspension travel employed in modern long travel buggies, it is nigh on impossible to totally eliminate bump steer. If bumpsteer can't be completely eradicated, then the solution is to tuck it away where it least affects performance... at full droop.  

There are only two scenarios when a wheel, or wheels, will be at full droop: The first is during roll (as when cornering) when the inside wheel may extend to full droop. However, the outside wheel is the one that's loaded, so a slight deviation in the inside wheel won't matter.

The second scenario when the wheels will be at full droop is when the buggy becomes airborne. A small amount of bumpsteer will not be felt as the suspension quickly returns to ride height (or beyond).

If bumpsteer were present above full droop, it would be very noticeable during normal driving or when landing hard or nose-first off a jump - the buggy would dart off in the direction of which ever front tyre had the most grip.

When installing a front-steer rack (forward facing steering arms): Moving the rack up in the chassis increases toe-out in bump, and toe-in in droop. Moving the rack down, toe-out increases in droop, and toe-in increases in bump. 

Moving the rack rearwards in the chassis, increases toe-in in bump and droop. Last but not least, if you move the rack foreword, toe-out increases in both bump and droop.  

When you have satisfied yourself with the amount and location of the bump steer, you can finalise the dimensions of the rack mounts and tack them into the chassis.

Some Suspension & Steering Fundamentals.

This list is by no means exhaustive and some aspects, while supremely critical in a road car (such as the roll axis), feature quite far down the list of importance in an off-road buggy.

Ackerman
Anti-dive/Dive
Bump
Bump Steer
Camber
Camber Gain
Castor
Castor Gain
Droop
Oversteer
Ride Height
Roll
Roll Axis
Roll Centre
Scrub
Scrub Radius
Toe
Understeer

Ackermann Principle.
This is everybody's favourite, and quite a controversial topic. Rudolph Ackermann was a German-born publisher who joined his father's coach building business for a short time before moving to London. Ackermann didn't invent, but is credited with perfecting and patenting the method of geometrically correct steering.

By angling rearward pointing steering arms to intersect the centre of the rear axle, in a turn, the inner front wheel turns about a smaller radius than the outer front wheel.

So simple it was perfect. Well, at least it was for 19th century horse-drawn carriages with narrow iron tyres. The problem is that nowadays we have wide rubber tires with much larger slip angles; so modern car manufacturers use 'modified Ackermann'.

This can range from the steering arms intersecting a point about a car's length aft of the rear axle, to the arms actually being parallel to each other.

Many race cars, and fast road cars use "reverse Ackermann", whereby the outside wheel turns more acutely than the inside wheel. This works better for sports cars with stiff suspension because of the more heavily loaded outside wheel when cornering at speed.

And then there are the steering set-ups where the steering arms are located on the front of the uprights. What is a man to do!

So where does all this leave us off-road types? Well, we have neither sticky tires nor a grippy surface to drive on, plus, we spend a large percentage of the time applying large proportions of oversteer. So, just forget about Ackermann! There, I said it!

Having said that, the last time I built a grass car chassis with a true differential, I used true Ackermann just to make it easier to manoeuvre the car in the pits. Seeing as we run a locked "diff" in our cars, they are almost impossible to push around anyway. So, just run your steering arms parallel and put a "big-tyre" trolley jack under the diff to manoeuvre it!
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Anti-dive/dive & anti-squat/squat.
First of all let's eliminate rear anti-dive from the discussion as it really only applies to the rear end of high-powered road cars. Both of these instruments can be found on road cars, but the only one of debatable interest on an off-road buggy is front anti-dive.

There is a school of thought that accepts anti-dive has a place on an off-road buggy, however, I don't subscribe to the notion. Those who do argue its benefits are also those who argue for raked front suspension which I simply can't see any reason for in buggies of our size and weight.

The calculation and theory are beyond the scope of this article, but anti-dive is achieved by slightly tilting the upper A-arm pivot axis up at the rear. When the buggy begins to pitch forward under braking, the front suspension stiffens up, thus preventing the front from diving. You can immediately appreciate why this would be of benefit in a road car, but the result of stiffened suspension in an off-road buggy on a loose surface, is lost grip. Lost grip at the front end means loss of steering. 

Road car designers have an abundance of grip available to them and they can afford to push suspension geometry to the limits for a more compliant ride and ultimately superior occupant comfort. We however, in the dirt, don't have the luxury of much grip and have to coerce it at every opportunity.

Contrary to anti-dive, the level of dive present in a buggy whose A-arm pivots are all parallel and horizontal, will actually assist in setting-up the car under braking and will therefore promote better grip when cornering.

Anti-squat is again, employed in road cars for passenger comfort and safety and works because of adequate tyre grip, but in an off road buggy, the suspension-binding forces (in a rear A-arm buggy) would promote copious wheelspin. Parallel and horizontal rear A-arms will naturally permit weight transfer under acceleration which will increase traction. Off-road racing can be a rough experience and a pitching car is just one of the effects a driver should anticipate in the search of grip and traction.    

In an attempt to simulate the path of a wheel on a VW beam front axle, the whole nose and front suspension in some buggies is raked back by the desired amount of the castor. The idea is that with the arms' pivot axes parallel to the angle of rake and the upright perpendicular to the angle of rake, castor will by necessity, be included and the wheels will rise backwards as well as upwards over bumps and large rocks etc. 

It's an understandable course to take, but in the process of trying to better absorb obstacles, dive is actually increased with the result that under braking, the buggy is more likely to get squirrelly and then one has to consider some anti-dive to balance out the ill effects. In the mean time, all this playing about with angles, axes and load paths will certainly increase bumpsteer and make it all the more difficult to eradicate it.
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Bump.
Bump is the upward travel of the suspension from ride height position, controlled by the coil spring, and its own area of damping. Note I use the term "damping", not "dampening". "Dampening" is making something wet!
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Bumpsteer.
Bump steer is simply the change in direction of one or both front wheels while cycling up or down, but without any input from the steering wheel.

Bump steer is unsettling, but can be avoided in most vehicles by careful location of the steering rack and ensuring the rack is the correct length.

A good friend, Dave Wynne (former chief design engineer for both Honda, and Lola Formula 1 teams), once offered me some software he had written which would accurately position any rack to be free from bumpsteer. I pointed out to Dave, that any car with less than 30mm (1.2") of wheel travel would be relatively easily cured of bump steer!

Our mini buggies commonly have 350mm to 480mm (13.75" to 19") total wheel travel. With these sorts of figures, it's extremely difficult to achieve zero bump steer.

A while ago I watched a video of one of the Stadium Races in Sydney. One buggy in particular was jumping hard and high. It suffered so badly from bump steer, that every time it landed, it shot to one side - depending on which front tyre got the best traction on landing.

The solution is to design any bump steer into an area where its effect will be least felt. The area where you definitely don't want bump steer is from a little above full droop up to full bump. That only leaves the area of full droop. On the occasions when the front wheels are clear of the ground, the bump steer is almost instantly eliminated upon contact with the ground again, thus restoring full steering control.
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Camber.
If you stand about 3 meters (10') in front of your buggy, and look at the front wheels, they appear to be standing vertically. In actual fact they are probably leaning in (hopefully not out) a little at the top.

This is camber... negative camber when the top of the wheel leans in towards the centre of the machine...and positive when the top leans out.

Camber is measured in degrees and usually in very small amounts. Typically a road car will run half a degree of positive camber providing safe straight-line driving, good tyre wear, and a little bit of under steer in the corners. The powers that be deem it preferable that Mrs Bogg's car understeers a bit in the corners rather than going around arse first!

This is one of those occasions when we take the "bitumen brain" out of our heads, place it carefully on the shelf, and replace it with the "off-road brain".

Understeer is the bane of all off-road racers ... pushing the front end wide through a turn, while someone passes you up the inside, can be very frustrating!

Not that every case of understeer is caused by bad suspension or steering set-up, but still, let's give ourselves every advantage we can!

Anywhere from one degree to three degrees of negative camber will give us much improved grip and feel because the steering effort will be transmitted through the tyres' tread, rather than through the sidewall. The added bonus of a little induced oversteer will be beneficial too.

A warning though before moving on. When designing the suspension links, (A-arms etc.) check that body roll doesn't exaggerate any negative camber too much, or for that matter, induce positive camber. We do not want positive camber!
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Camber gain.
Camber needs to be dynamic to cope with the vagaries of long wheel travel buggies: There needs to be sufficient gain towards full bump to counteract body roll in turns. (In reality, a little more is required than the anticipated angle of body roll so the tyre still retains a negative stance.)
Adequate camber gain is also required to counter the effects of scrub (see under Scrub elsewhere in this article).
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Castor.
Now, pull the front wheel off and take a few steps out to the side of the buggy. Draw an imaginary line through the centres of the upright's upper and lower ball joints and compare that line with a line drawn vertically through the centre of the hub.

It will be seen that the two lines converge at an angle rather than lie parallel with each other. This angle is the castor angle, and its purpose is to bestow the front end with some measure of stability at speed, combined with the ability to self-centre the steering.

Positive castor is when the top of the kingpin leans towards the rear, and negative castor is when it leans towards the front... but, like positive camber, we never want to go there!

Around two to four degrees of positive castor is the norm for road cars, but on the dirt, we are better off going as high as six or even eight degrees with low ratio steering, or, reduce it to around two or three degrees for high ratio steering. We need to be careful not to over do the castor, as it will make the steering very heavy, especially if combined with a large scrub radius.
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Castor gain.
For a similar reason to raking the front end of a buggy, it is possible to achieve greater degrees of castor at different stages of the suspension's travel. An obvious choice would be for the castor to gain increased negative angle in droop.

The argument for this is quite apparent; if the buggy lands nose-first after a jump, then increased castor would, in some circumstances result in the uprights being at a more favourable approach angle to the ground, thus providing straight-line stability for the initial moments of the landing.

However, to achieve castor gain, it's necessary to angle the upper arms' pivot axes in either plan or side view (or both if you really want!) which by necessity also introduces anti-dive. Anti-dive (as you can read above) can create instability under braking and in my opinion should be avoided at all cost. 
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Droop.
Droop is the downward movement of the suspension from ride height with its own individual damping control.
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Oversteer.
Oversteer is the result of cornering forces being too great for the available grip. The rear of the vehicle swings towards the outside of the corner, and to prevent a spin, the front wheels are turned into the slide.

Too much oversteer can be caused by suboptimal steering/suspension design and can also be the result of either late braking or early acceleration.
On the dirt, we typically use acceleration to oversteer our buggies around corners.
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Ride Height.
Ride height is the stance of a vehicle when "wet", i.e. with a half-full tank of fuel, and fully kitted up driver (and passenger where appropriate) onboard. With long-travel A-arm suspension, it may be necessary to roll the machine back and forth a few times to achieve true ride height, due to scrub characteristics of the A-arms cycling through their arcs.
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Roll.
Caused by centripetal force, roll is the action of the buggy tilting, or "rolling" when the direction of travel is altered. An obvious example is when cornering and the buggy's body rolls towards the outside of the corner.
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Roll Axis.
The roll axis is an imaginary line drawn through both the front and rear roll centres about which the buggy rolls. It is a static measurement taken only at ride height. Any suspension movement immediately alters the location of the axis.

Road racers pour over the roll axis for hours in attempts to perfect their car's handling, but because it moves around so wildly in a buggy with long travel suspension, its importance is far down the list of design criteria when compared to other aspects of the suspension. Remember – compromise!
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Roll Centre.
Both front and rear axles have their roll centres and seldom do they match. It's usually desirable that they don't actually match.

A roll centre height is calculated by extending imaginary lines through a pair of upper and lower A-arms and then drawing a line diagonally from the point where they converge to the point where the tyre's centre line meets the ground.
The point where this diagonal line intersects the buggy's centre line (as viewed from the front) is the roll centre and marks the height about which that particular axle will roll.
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Scrub.
Scrub (not to be confused with scrub radius) is the pushing, or "scrubbing" of the tyres when they move laterally as the suspension cycles.

All A-arm suspensions exhibit scrub in varying degrees, however, scrub is less noticeable on rear suspensions that employ trailing arms (zero scrub if the arms are actually true trailing arms and not semi-trailing arms). (On most occasions, people mean semi-trailing arms when referring to 'trailing arms'.)

Sometimes rear scrub has to be ignored in favour of optimal axle angles, but front-end scrub should be eliminated if at all possible.

When a buggy's front A-arms droop, the arcs they follow dictates the track width will narrow. The lateral change between a tyre's footprint at full droop and when the arms are parallel with the ground is the amount of scrub present.

When the suspension is compressed from full droop (such as when landing after a jump), any scrub present can create large amounts of suspension resistance, causing partial binding of the suspension. Even if the car lands reasonably level, the suspension binding can obviously cause some very harsh landings. If the buggy lands on just one front wheel, things can get a lot worse; the tyre can dig in, throwing the buggy in the opposite direction, or if the momentum is sufficient, the buggy can at worst, roll right over the dug-in wheel, or peel the tyre off the rim.

It is therefore desirable to design the suspension so that sufficient negative camber is induced in droop to preserve (as far as is possible), the car's static track dimension.
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Scrub Radius.
While the front wheel is still off, have a look from the front again, and note the inclination of the kingpin. Imagine this line extending down to meet the ground. Now remount the wheel, and trace an imaginary line down the centre of the tyre to the point where it touches the ground. The distance between these two points (at ground level - when the vehicle is at ride height) is the radius that the tyre contact patch rotates (scrubs) about the kingpin axis ... hence scrub radius.

Positive scrub radius is when the kingpin axis meets the ground inside the tyre centre line, zero scrub radius is when the two lines meet, and negative scrub radius is when the kingpin axis falls outside the tyre centre line.

Zero scrub radius leaves the steering with directional instability, and no 'feel'. The larger the scrub radius, the more effort is required to turn the steering. Mrs. Bogg's family shopper, runs about a 10-25mm (.38"-1.0") of scrub radius, which provides excellent feel yet still permits easy parking at the supermarket.

We, on the other hand, when messing around on slippery surfaces (and also because our buggies are so light), require somewhat more scrub radius to restore some of that "feel". If you have really strong arms, you should be capable of handling up to 32mm (1.25"), and lesser mortals would do better closer to 16mm (.63").

Even with True Ackermann Steering, a large scrub radius will impose heavy steering around the pits, but don't worry, once speed exceeds walking pace, the steering will lighten up.

If you have an existing car a large scrub radius and you don't particularly feel the urge to build new uprights, it may be possible to improve it quite simply: Fitting wheels with deeper insets will move the tyre centres inwards, thus reducing the scrub radius. Unfortunately this also has the effect of narrowing the track, resulting in other unfavourable changes to the suspension geometry and handling, though reversing the rear wheels (where possible) may bring the rear track back into line with the front. Changing to a smaller tyre will increase the scrub radius, while taller tyres will reduce the scrub radius or even move into the area of negative scrub radius!
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Toe.
Nothing to do with assistance after a smash or break down, but the angular adjustment of the wheels as viewed from above.

The collective effects of braking, surface friction, and suspension action, cause the front of the tyres to point outwards… or toe-out. This action needs to be controlled.

The trick is to dial-in a preset amount of toe-out. Simply put, with the vehicle sitting at ride height, steering straight ahead, and camber and castor already set, adjust the tie-rods to make the front of the tyres toe-out.

The technique I prefer is to first jack the front of the buggy up, spin each wheel, and then with a tyre marker, scribe a line centrally around the periphery of the tyres. This method discounts the possibility of bent wheel rims when using devices that take the reading from the rims.
The buggy is then lowered again, and pushed back and forth a few times to settle it to ride height, and ensure the steering is dead ahead.

At tyre centre height, measure the distance from the scribed line on the front of one tyre directly across to the line on the opposite tyre. Make the same measurement at the back of the tyres.

The correct toe-out is when the front measurement is between 3mm and 10mm (.125" and .38") more than the rear (depending on tyre diameter of course).

Toe doesn't only affect the front, it can also have implications on the rear. Obviously, a rigid rear axle such as in an FL 250 can't be adjusted for toe, but suspensions employing A-arms, and some trailing arms may be. Be aware though, that adjusting trailing arms at their pivots will result in track changes too!

"But surely", I hear you say, "the rear wheels should lie parallel with each other". Not necessarily so. Rear toe can be a useful aid to enhance handling characteristics too.

As part of routine maintenance rear toe should be checked periodically as per the front-end method. Threaded bushes or rod ends in your suspension will make toe adjustment a breeze, otherwise major metallurgical surgery may be required to make alterations!

Rear toe-in induces understeer, so we'll move right away from there, but rear toe-out can really enhance the buggy's oversteering attitude when cornering. Too much rear toe-out though, will leave the rear end wanting to overtake the front at high straight-line speeds, so don't over do it!
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Understeer.
In our sport, everybody likes oversteer in varying amounts, but no one likes understeer. Essentially, understeering equals loss of control - no matter how much the steering is turned, the buggy just wants to keep ploughing straight ahead.

The causes of understeer are usually late or too much front braking, or late or too much acceleration, or just plain bad chassis design!
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