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Uncle AtiT
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 Posted: Fri Oct 23, 2009 4:20 pm Post subject: :: Official Automotive Suspension Thread - Q&A :: |
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How Car Suspensions Work
When people think of automobile performance, they normally think of horsepower, torque and zero-to-60 acceleration.
But all of the power generated by the engine is useless if the driver can't control the car.
If roads were perfectly flat, with no irregularities, suspensions wouldn't be necessary.
But roads are far from flat. Even freshly paved highways have subtle imperfections that can interact with the wheels of a car.
It's these imperfections that apply forces to the wheels.
According to Newton's laws of motion, all forces have both magnitude and direction.
A bump in the road causes the wheel to move up and down perpendicular to the road surface.
The magnitude, of course, depends on whether the wheel is striking a giant bump or a tiny speck.
Either way, the car wheel experiences a vertical acceleration as it passes over an imperfection.
Without an intervening structure, all of wheel's vertical energy is transferred to the frame, which moves in the same direction.
In such a situation, the wheels can lose contact with the road completely.
Then, under the downward force of gravity, the wheels can slam back into the road surface.
What you need is a system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road.
The study of the forces at work on a moving car is called vehicle dynamics, and you need to understand some of these concepts in order to appreciate why a suspension is necessary in the first place.
Most automobile engineers consider the dynamics of a moving car from two perspectives:
Ride - a car's ability to smooth out a bumpy road
Handling - a car's ability to safely accelerate, brake and corner
These two characteristics can be further described in three important principles
- road isolation, road holding and cornering.
The table below describes these principles and how engineers attempt to solve the challenges unique to each.
Car Suspension Parts
The suspension of a car is actually part of the chassis, which comprises all of the imp ortant systems located beneath the car's body.
Springs
Today's springing systems are based on one of four basic designs:
Coil springs - This is the most common type of spring and is, in essence,
a heavy-duty torsion bar coiled around an axis. Coil springs compress and expand to absorb the motion of the wheels.
Torsion bars -
Torsion bars use the twisting properties of a steel bar to provide coil-spring-like performance.
This is how they work: One end of a bar is anchored to the vehicle frame.
The other end is attached to a wishbone, which acts like a lever that moves perpendicular to the torsion bar.
When the wheel hits a bump, vertical motion is transferred to the wishbone and then, through the levering action, to the torsion bar.
The torsion bar then twists along its axis to provide the spring force.
Air springs/bags -
Air springs, which consist of a cylindrical chamber of air positioned between the wheel and the car's body,
use the compressive qualities of air to absorb wheel vibrations.
Springs: Sprung and Unsprung Mass
The sprung mass is the mass of the vehicle supported on the springs, while the unsprung mass is loosely defined as the mass between the road and the suspension springs.
The stiffness of the springs affects how the sprung mass responds while the car is being driven.
Loosely sprung cars, such as luxury cars (think Lincoln Town Car), can swallow bumps and provide a super-smooth ride;
however, such a car is prone to dive and squat during braking and acceleration and tends to experience body sway or roll during cornering.
Tightly sprung cars, such as sports cars (think Mazda Miata), are less forgiving on bumpy roads,
but they minimize body motion well, which means they can be driven aggressively, even around corners.
So, while springs by themselves seem like simple devices, designing and implementing them on a car to balance passenger comfort with handling is a complex task.
And to make matters more complex, springs alone can't provide a perfectly smooth ride. Why?
Because springs are great at absorbing energy, but not so good at dissipating it. Other structures, known as dampers, are required to do this.
Dampers: Shock Absorbers
Unless a dampening structure is present, a car spring will extend and release the energy it absorbs from a bump at an uncontrolled rate.
The spring will continue to bounce at its natural frequency until all of the energy originally put into it is used up.
A suspension built on springs alone would make for an extremely bouncy ride and, depending on the terrain, an uncontrollable car.
Enter the shock absorber, or snubber, a device that controls unwanted spring motion through a process known as dampening.
Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated through hydraulic fluid.
To understand how this works, it's best to look inside a shock absorber to see its structure and function.
A shock absorber is basically an oil pump placed between the frame of the car and the wheels.
The upper mount of the shock connects to the frame (i.e., the sprung weight),
while the lower mount connects to the axle, near the wheel (i.e., the unsprung weight).
In a twin-tube design, one of the most common types of shock absorbers, the upper mount is connected to a piston rod,
which in turn is connected to a piston, which in turn sits in a tube filled with hydraulic fluid.
The inner tube is known as the pressure tube, and the outer tube is known as the reserve tube.
The reserve tube stores excess hydraulic fluid.
When the car wheel encounters a bump in the road and causes the spring to coil and uncoil,
the energy of the spring is transferred to the shock absorber through the upper mount, down through the piston rod and into the piston.
Orifices perforate the piston and allow fluid to leak through as the piston moves up and down in the pressure tube.
Because the orifices are relatively tiny, only a small amount of fluid, under great pressure, passes through.
This slows down the piston, which in turn slows down the spring.
Shock absorbers work in two cycles -- the compression cycle and the extension cycle.
The compression cycle occurs as the piston moves downward, compressing the hydraulic fluid in the chamber below the piston.
The extension cycle occurs as the piston moves toward the top of the pressure tube, compressing the fluid in the chamber above the piston.
A typical car or light truck will have more resistance during its extension cycle than its compression cycle.
With that in mind, the compression cycle controls the motion of the vehicle's unsprung weight, while extension controls the heavier, sprung weight.
All modern shock absorbers are velocity-sensitive -- the faster the suspension moves, the more resistance the shock absorber provides.
This enables shocks to adjust to road conditions and to control all of the unwanted motions that can occur in a moving vehicle, including bounce, sway, brake dive and acceleration squat.
Dampers: Struts and Anti-sway Bars
A nother common dampening structure is the strut -- basically a shock absorber mounted inside a coil spring.
Struts perform two jobs: They provide a dampening function like shock absorbers, and they provide structural support for the vehicle suspension.
That means struts deliver a bit more than shock absorbers, which don't support vehicle weight --
they only control the speed at which weight is transferred in a car, not the weight itself.
Because shocks and struts have so much to do with the handling of a car, they can be considered critical safety features.
Worn shocks and struts can allow excessive vehicle-weight transfer from side to side and front to back.
This reduces the tire's ability to grip the road, as well as handling and braking performance.
Anti-sway Bars
Anti-sway bars (also known as anti-roll bars) are used along with shock absorbers or struts to give a moving automobile additional stability.
An anti-sway bar is a metal rod that spans the entire axle and effectively joins each side of the suspension together.
When the suspension at one wheel moves up and down, the anti-sway bar transfers movement to the other wheel.
This creates a more level ride and reduces vehicle sway. In particular, it combats the roll of a car on its suspension as it corners.
For this reason, almost all cars today are fitted with anti-sway bars as standard equipment, although if they're not, kits make it easy to install the bars at any time.
Suspension Types: Front
So far, ou r discussions have focused on how springs and dampers function on any given wheel.
But the four wheels of a car work together in two independent systems
-- the two wheels connected by the front axle and the two wheels connected by the rear axle.
That means that a car can and usually does have a different type of suspension on the front and back.
Much is determined by whether a rigid axle binds the wheels or if the wheels are permitted to move independently.
The former arrangement is known as a dependent system, while the latter arrangement is known as an independent system.
In the following sections, we'll look at some of the common types of front and back suspensions typically used on mainstream cars.
Dependent Front Suspensions
Dependent front suspensions have a rigid front axle that connects the front wheels.
Basically, this looks like a solid bar under the front of the car, kept in place by leaf springs and shock absorbers.
Common on trucks, dependent front suspensions haven't been used in mainstream cars for years.
Independent Front Suspensions
In this setup, the front wheels are allowed to move independently.
The MacPherson strut, developed by Earle S. MacPherson of General Motors in 1947, is the most widely used front suspension system,
especially in cars of European origin.
The MacPherson strut combines a shock absorber and a coil spring into a single unit.
This provides a more compact and lighter suspension system that can be used for front-wheel drive vehicles.
The double-wishbone suspension, also known as an A-arm suspension, is another common type of front independent suspension.
While there are several different possible configurations, this design typically uses two wishbone-shaped arms to locate the wheel.
Each wishbone, which has two mounting positions to the frame and one at the wheel,
bears a shock absorber and a coil spring to absorb vibrations.
Double-wishbone suspensions allow for more control over the camber angle of the wheel, which describes the degree to which the wheels tilt in and out.
They also help minimize roll or sway and provide for a more consistent steering feel.
Because of these characteristics, the double-wishbone suspension is common on the front wheels of larger cars.
Independent Rear Suspensions
If both the front and back suspensions are independent, then all of the wheels are mounted and sprung individually,
resulting in what car advertisements tout as "four-wheel independent suspension."
Any suspension that can be used on the front of the car can be used on the rear, and versions of the front independent systems described in the previous section can be found on the rear axles.
Of course, in the rear of the car, the steering rack -
- the assembly that includes the pinion gear wheel and enables the wheels to turn from side to side -- is absent.
This means that rear independent suspensions can be simplified versions of front ones, although the basic principles remain the same.
Coilover kit sample pic
Please feel free to use this thread for all Suspension questions
Springs, Shocks, sway bar kits, Coilover kits etc.......
PLEASE DO NOT POST PICS OF LOWERED VEHICLES
ANY PICS posted could possibly be deleted, this is not what this thread is for
If you wish to post pics of lowered cars, post them HERE
This thread is a Question and Answer Suspension Thread only
Hope that this will help you understand suspensions and how they work
If there is anything I missed, my apologies  Enjoy !
*Uncle
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Last edited by Uncle AtiT on Sun Oct 25, 2009 1:26 pm; edited 1 time in total |
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///\JM.
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| Posted: Fri Oct 23, 2009 5:36 pm Post subject: |
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Good thread and good read Uncle Atit 
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AKidNamedRaheem
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| Posted: Sun Oct 25, 2009 2:41 pm Post subject: |
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| ///\JM. wrote: | | Good thread and good read Uncle Atit |
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Loveforjordan
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| Posted: Sun Oct 25, 2009 9:14 pm Post subject: |
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| AKidNamedRaheem wrote: | | ///\JM. wrote: | | Good thread and good read Uncle Atit |
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NYsNumba1man
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| Posted: Sun Oct 25, 2009 10:09 pm Post subject: |
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Alright, so im thinking about upgrading my cars suspension. its original from 88 
What would you guys reccomend? i dont want to go any lower, i get enough scaping on speed bumps already. and i dont want to feel every single bump
i want a balance of ride and handling
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Uncle AtiT
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| Posted: Mon Oct 26, 2009 3:04 pm Post subject: |
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I would recommend going to a shop, lifting your car in the air, and see exactly how bad the original suspension is.
Then go from there, see what kinda shape all your suspension components are in, for safety and cost reasons.
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dunkXdrift831
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| Posted: Wed Oct 28, 2009 5:16 pm Post subject: |
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| NYsNumba1man wrote: | Alright, so im thinking about upgrading my cars suspension. its original from 88
What would you guys reccomend? i dont want to go any lower, i get enough scaping on speed bumps already. and i dont want to feel every single bump
i want a balance of ride and handling |
you got an S4 FC correct? FC actually have pretty who shocks from the factory. id say some performance springs and sway bars. you could also replace all those old bushings with new ones. what model S4 do you have?
you should also list the different types of struts
-single tube
-twin tube
-mono tube
-inverted mono tube
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NYsNumba1man
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| Posted: Wed Oct 28, 2009 5:44 pm Post subject: |
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| dunkXdrift831 wrote: | | NYsNumba1man wrote: | Alright, so im thinking about upgrading my cars suspension. its original from 88
What would you guys reccomend? i dont want to go any lower, i get enough scaping on speed bumps already. and i dont want to feel every single bump
i want a balance of ride and handling |
you got an S4 FC correct? FC actually have pretty who shocks from the factory. id say some performance springs and sway bars. you could also replace all those old bushings with new ones. what model S4 do you have?
you should also list the different types of struts
-single tube
-twin tube
-mono tube
-inverted mono tube |
you are correct. yeah the shocks are pretty good right now, and the middle console for normal/sport still works great too. So preformance springs and sway bars? i have a GXL
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The Anti-Hype is the new HYPE.
99 Metallics, 01 Royals, Retro Metallic 5s, Fire red 3s Sz 9.5-10:
http://www.solecollector.com/forums/nyc-sz-9-5-11-vnds-jordans-air-maxs-and-blazer-nyc-t880137.html
I'm a size 9.5-10.5. I'm interested in jordans, sb's, airmaxes, air trainers, bapes etc etc, located in NYC lets work something out |
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dunkXdrift831
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| Posted: Wed Oct 28, 2009 8:25 pm Post subject: |
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from what i remember you have a factory lsd and damper control. yea, i think upgraded springs,sway bars,and bushing will do. if you want you could also swap out the struts/shocks for something like tokico illuminas.
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Uncle AtiT
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| Posted: Wed Oct 28, 2009 8:30 pm Post subject: |
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Either way you look at it, be prepared to spend some dollars on labor and parts.
Its not gonna be cheap fixing/replacing all the stock parts from your car.
and without any doubt you are gonna need shocks.......get that wallet ready $$$$
If you are planning on doing some of the work yourself, obviously you will save some coin.
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NYsNumba1man
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| Posted: Wed Oct 28, 2009 8:43 pm Post subject: |
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Yeah it does come with a factory lsd im not sure about damper control though. Do you think its really worth it to upgrade to tokico illuminas though? its not a track car or anything.
Atit about how much would you say? i'm just making a list of what i need to do and prices.
I dont have a garage or anywhere else to do the work so i cant be doing it by myself 
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The Anti-Hype is the new HYPE.
99 Metallics, 01 Royals, Retro Metallic 5s, Fire red 3s Sz 9.5-10:
http://www.solecollector.com/forums/nyc-sz-9-5-11-vnds-jordans-air-maxs-and-blazer-nyc-t880137.html
I'm a size 9.5-10.5. I'm interested in jordans, sb's, airmaxes, air trainers, bapes etc etc, located in NYC lets work something out |
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Uncle AtiT
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| Posted: Wed Oct 28, 2009 8:49 pm Post subject: |
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Shocks are not gonna be a killer on the wallet but I would recommend them for sure
you gotta remember, your car is not 4/5 years old...once you start taking apart one thing, other things tend to brake/seize.
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dunkXdrift831
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| Posted: Wed Oct 28, 2009 10:47 pm Post subject: |
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| Uncle AtiT wrote: | Shocks are not gonna be a killer on the wallet but I would recommend them for sure
you gotta remember, your car is not 4/5 years old...once you start taking apart one thing, other things tend to brake/seize. |
true. id say springs N just sway bars.
please also remember that certain shocks/coilovers have adjustable damping which controls how much oil is being ran through the valve. some go from 4 to 32 weight adjustable.
certain coilovers have pillow ball uppers or also known as camber plates. this is used to adjust your camber.
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tlas
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| Posted: Thu Nov 05, 2009 2:20 pm Post subject: |
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| dunkXdrift831 wrote: | | Uncle AtiT wrote: | Shocks are not gonna be a killer on the wallet but I would recommend them for sure
you gotta remember, your car is not 4/5 years old...once you start taking apart one thing, other things tend to brake/seize. |
true. id say springs N just sway bars.
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i'd buy after market struts with springs. Stiffer springs don't do well with stock struts.
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Criminology™
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| Posted: Thu Nov 05, 2009 4:12 pm Post subject: |
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How much should I be paying to have a set of coilovers and lower control arms installed?
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