Question: How does suspension work and why is it important?

BACKGROUND

Answer: During the horse and buggy days someone figured out that if the wheels weren't mounted solidly to the frame of a carriage and they could articulate enough to follow the contours of the roads the ride quality was greatly enhanced. The jarring of the wheels as they impacted the irregularities of the surface that they were rolling over wasn't transmitted directly to the chassis and hence the wagon occupants kidneys. The other benefit of the suspended carriage was that when the wheel impacted a bump the fact that it could give a bit meant less broken wagon wheels. With less danger in breaking wheels and a better ride quality that meant that the wagon could be pulled at a higher rate of speed over a bumpy surface.

In Canada the McLaughlin family in Tyrone Ontario had the western worlds best suspension they moved there tiny carriage works to Oshawa and built there patented suspension for carriages and sold these components all over North America to other carriage builders. Eventually they got into building motorized carriages , then automobiles based on the design and components of a manufacturer in Michigan called Buick. The sons of the founder of the carriage works primarily the younger son Sam McLaughlin were instrumental in the creation of General Motors. In Toronto we have a planetarium donated by Sam that carries the family name and a street named after Sam's wife Adelaide.

With the arrival of motorized carriages on the scene and eventually rubber coated wagon wheels then Pneumatic tires it became evident during all this other development that it wasn't enough to just suspend the frame or chassis on springs but necessary to dampen the movement or control the energy of the springs. The spring damper is still called a damper in Europe, this side of the pond we have labeled them shock absorbers. The fact is that they really do both these things , they keep the suspension and springs from bottoming or hitting the end of the movement range when a large bump is encountered and they stop the vehicle from continuing to bounce up and down after the bump has been encountered.

THE MODERN CAR

In a lot of ways what we desire from suspension for the modern car and the
modern passenger are still very similar in terms of suspension) to the old horse drawn carriage, the difference is in the required capabilities. We are not
just satisfied with a slightly smoother ride into town from the farm over the rutted gravel road. In some of our specialty race vehicles we want to maintain
control at speeds of 440 Km /hr up the Mulsanne straight plus we want to have
ultimate quiet in the back of the limo on the way to the airport while we negotiate that million dollar deal on the cell phone. 

Modern suspensions are like many other mechanical components a collection of compromises. We want a wheel to move ultimately in a certain way when it negotiates the roads irregularities to give a smooth ride usually this means a softer ratio spring so that the wheel can react very easily --but the spring cannot be too weak because it must hold the weight of the vehicle suspended.
We want the vehicle to be stable and not move around too much so we want
perhaps a stiffer spring but this will compromise ride. Depending on the spring rate the spring damping rate or shock rate must be adjusted to match the spring characteristics - - too much damping on either compression or on extension will not allow the spring to do its job and too little damping and the spring will not be controlled and the car will bounce around - - - we've all seen these guys driving down the highway with bad shocks the car porposing away after every bump.

Of course it gets more complicated - - - the wheel hub or the unit that the wheel is bolted to that contains bearings that allows the wheel to spin and the vehicle consequently to roll along the road is housed in what is called the upright. This upright has attachment points where connecting arms fasten. These arms have pivoting ends and are the bits that connect the whole assembly to the chassis or frame of the vehicle. The arms can take many forms - - usually what each manufacturer considers to be the best system for the application of his vehicle but anyway this whole system allows the wheel assembly to move up and down and follow the bumps on the road. Now if the wheels are on the front of the vehicle they are usually the ones that also have to turn as well. When someone refers to "suspension geometry" what they are referring to is the arch that the wheel scribes as it moves up and down which is a function of the geometric relation ship of all of the articulating arms and there attachment points. Which geometry arch is used buy any one manufacturer is determined by all the ride and handling qualities that they think that they want plus a pile of packaging issues that all surface when you try and pick your ultimate geometry an fit it all under the body of the car add in the fancy alloy wheels and stick a shock and spring combination in among the collection of pivoting arms. Remembering of course that where you put the spring and shock landing points has a huge impact on the leverage that the weight of the vehicle puts on the shock and spring combination so every time you move it slightly you have to change the rates of both.

There is a couple of other huge factors that we haven't even mentioned yet one of those is tires the other is alignment. Every time that a different tire is put on the car the inputs that the suspension sees change. Every tire manufacturer has a slightly different construction which of course is the best as far as they are concerned but each has a different ability to conform or resist conforming to the road surface and in fact has is own sort of internal suspension this coupled with the different types of rubber that is used to give different wear or traction characteristics all changes the way that the inputs are fed into the suspension system. You may even have a situation where a certain type of tire will reverberate at a frequency that will excite certain elements of the suspension and you may get a hum or roar from the tires on certain road surfaces and it may only haven on one vehicle design with a certain tire and not on another.

Alignment is another story it is as simple in one sense as making sure that all the wheels are pointed in the same direction or are "aligned" however there is always more to it rolling wheels are and operating dynamic system so suspension settings are created that will create an aligned condition when the vehicle is moving. the static settings are all based on what the tire will see in action. In the old days of the carriage and speeds up to that attained by a running team of horses as long as the wheels were bolted to the opposite ends of the same straight axle and the two axles were parallel the system was happy.

Not these days - - - Front wheel drive cars require a totally different set of
settings than a rear or four wheel drive vehicle because of the way the torque from the engine is fed to the wheels. Taller high center of gravity 4x4 vehicles with longer suspension travel require totally different settings to the low slung sporty types factors here include the speed that the vehicle spends most of its time traveling at coupled with the areo dynamic loads that the vehicle sees at these speeds due to its shape plus the type of lateral loads that the vehicle is likely to see negotiating corners. The settings that the manufacturers give in the manuals and set the cars at when they go over the curb are for general all round vehicle use and reasonable tire wear. They sometimes can guess wrong at the type of driving that their vehicles will see in service and certain vehicles can have a reputation for wearing tires prematurely even though the alignment shop or dealer swears that the settings are exactly what the factory recommends. Here is where a good alignment shop can shine by assessing the type of use the vehicle gets by listening to the customer and looking at how the tire wear patterns are developing they can solve a lot of these wear and handling problems. An example of this was the Acura NSX that seemed to have a habit of eating up tires on the rear of the car when set at factory settings but by modifying the settings slightly using the wear pattern as a guide normal wear could be easily attained. When it comes to the more sporty cars the settings become even more critical as the suspension pivot bushings tend to be firmer to give better handling response and control at higher speeds not that on todays highways they will always see higher speed but they are capable of it and could be driven at higher operating speeds so the tire type and suspension settings are accordingly adjusted. Now if the owner has a habit of playing Schumacher at the local track on weekends the suspension will have to set up totally different than for the Yorkville poser.

The higher loads that the track use puts on everything may require much more
aggressive static settings in order that the dynamic positioning of the tire allows the tire to do its job best. If these settings were put on the posers car he would experience premature or abnormal tire wear and consequently the highway driving settings of the poser or the touring driver would not allow the tire on the track to develop the traction levels necessary for ultimate cornering
ability in fact you would get premature or abnormal wear on the track with
the touring settings. The tough alignment is for the car that sees the track a
few times and only goes touring a few times this is where listening to the customer to find out where they are willing to accept the biggest compromise is so important - - if you are the customer make sure they understand what you think is your priority.

Now just a bit on the setting jargon - - - 
in the world of suspension when they talk about toe what they are referring to is the parallel of the wheels in relation to each other and to the chassis "Toe In" or "positive toe" is when the wheels are closer together at the front than at the back (in direction of travel ) or I guess you could say their pigeon toed if you've ever watched a pigeon walk you Know what we mean "Toe Out " or "positive toe is when the wheels are set so they want to roll away from each other (standing like the average sailor ). 

The next important setting is the camber that's were the top of the wheel leans slightly in or out at the top in relation to the car "positive camber" is where the bottom of the tire is in further and the top out further so the tires leaning away from each other "negative camber " is where the tires are leaning in towards each other at the top. There was a car called a Corvair that got a rough time from a chap named Nader due to the Corvair's suspensions ability to go from negative camber to a high degree of positive camber in certain handling situations at high speed the car could be launched by the operator quite effectively into a rollover. Other vehicles at this time in history were guilty of this characteristic as well but Chevrolet took the hit and the design didn't survive. The final setting that we will mention is Castor - this is the amount of tilt in the vertical theoretic pivoting point of a wheel when it moves to steer - - we say theoretical because even wheels that don't steer (like rear wheels generally ) can have caster settings the caster is the angle that the vertical pressure of the weight is forward or aft of the vertical "positive caster tends to want to make the wheel return to the forward rolling position (like shopping cart wheels or bicycle wheels ) More caster can give a car a great feeling of stability - - - but it can make the thing a bear to manipulate around a parking lot Thank you for power steering when you are parking that big Benz in the corner plaza lot - - - vehicles with a lot of caster look a bit like a road grater when the wheels are turned because lots of caster gives lots of induced camber when the wheels are turned- - - - oh oh here we go again - - you guessed it - - - the settings are all interdependent when you adjust one - - the others change so it is even necessary for the alignment guys to adjust the settings in a certain order due to the geometric interdependency

Sounds complicated - - - it is and not everyone gets it right - - manufacturers do the best that they can to give everyone they think might be a customer what they think they might like and hope that the styling and marketing guys can convince every that they just have to have one and then the customer may not use the vehicle for any thing like the designer thought the vehicle might be good for

When it comes to racing the whole thing is really the same but different - - - the settings are the same things being adjusted but the only rubber in a Formula One or Indy car suspension is the tire - - -every thing is suspended
on very precise spherical or articulating bearings that are aerospace strong and when you add a pile of extra downforce from various on board aerodynamic devices the spring rates can be in the thousands of pounds as opposed to a couple of hundred for the average grocery getter the shocks to control these spring rates cost more than some cars each and are fully track side adjustable to get that little extra from the car and its tires and speaking of tires the operating temperature of these huge donuts is a least 100 deg C on the surface hot enough to cook a greasy egg breakfast although with the sticky tar like surface that they have while operating you might have trouble getting you plate off the tire. all this means that the settings are ultra critical and teams will take hours to set the car just right to get the most out of the driver and his chariot for the day - - - but sometimes the team doesn't get it right either as a slight temperature change of the track surface or the driver getting too much or not enough heat in the tires either too fast or not fast enough changes the whole picture and these slight little changes because of the precision of the suspension and its components amplify the effects and make a huge difference to how the car sticks to the track and makes the difference of a second or so in lap times and the difference between 1st and last when the flag drops.