(hip-hop music)
- "All I wanna do is see ya bounce with me, bounce with me."
Those are the words of young Lil Bow Wow
from the song "Bounce With Me"
("Bounce With Me" by Lil' Bow Wow)
The concept of bouncing is great in this classic song.
You know where bounce is bad?
Suspensions!
(electronic music)
There's billions of types of suspension, not literally,
but I'm not gonna go look up the exact number
like some kind of a nerd so maybe not billions,
but there's a lot of different types of suspension.
There's suspensions like when you're suspended from work
for biting the camera man,
there's suspensions like the suspension of disbelief
which allows you to believe in make believe stuff
like Superman can fly or life's gonna work out,
and there's the suspension system on your vehicle,
and those vehicle suspensions
have a huge variety of types as well.
There's more types of vehicle suspensions
than the types of DNA strands that were found in my bedroom
nine years ago on that fateful night in September.
(crowd gasps) That number was three.
We got a knife.
With such a wide variety of types,
we're barely gonna scratch the surface here
and touch on the basics in a few of the most common types.
So all of you in the comments
saying I forgot about this thing or that thing,
nah, I didn't, I know all about it,
In fact, I just left it out to tick you off.
(crowd booing) So get off my back, David.
Alright, when they invented the car it was awesome,
they're all smoking cigars
and patting each other on the back, eating some cold cuts
and congratulating each others like,
"This will revolutionize travel.
"The piston engine will get us places so fast."
"I love cold cuts."
But then, record scratch, (record scratches)
they realized all the power generated by an engine's useless
if the driver can't control the car.
(engine revving)
And almost as soon as the four stroke
internal combustion engine was mastered,
engineers went to work on perfecting the suspension.
Horse drawn carriages had suspensions,
but they only went so fast.
You hit those same bumps in the road at a greater speed,
it's gonna get a lot bouncier.
- Ow!
- The job of a car suspension is to one,
maximize the friction between the tires and road surface
during acceleration, cruising, and braking,
and two, provide steering stability with good handling,
and three, ensure the comfort of the passengers.
If all roads were perfectly flat
with no irregularities or bumps or waves or anything,
suspension wouldn't be as necessary,
but unlike me, even fresh laid pavement
has some imperfections.
Now, let's get science-y up in this garage.
Newton's Law of Motion says forces have both
magnitude and direction.
A bump in the road causes the wheel to move up and down,
perpendicular to the road surface, direction.
The magnitude depends on whether the wheel
is striking a giant bump or a tiny speck.
The wheel experiences a vertical acceleration
as it passes over an imperfection,
and that means the wheel goes up.
Without an intervening structure,
the vehicle's vertical energy
is transferred to the car's frame,
which moves the same direction, up.
The wheels can lose contact with the road completely
and then, 'cause of gravity,
the wheels would slam back down into the road surface,
and that is bounce, brother.
And if there was no gravity,
that bump could send you hurdling into space
until you go out into hyper space and see the event horizon.
Spooky.
You need a system that absorbs the energy
of the vertically accelerated wheel,
allowing the frame and body to ride undisturbed
while the wheels follow bumps in the road,
and that's all part of vehicle dynamics,
the study of forces at work on a moving car.
Auto engineers come at this from two perspectives, ride,
(engine revving) a car's ability to smooth out
a bumpy road and handling, oop,
and handling, a car's ability to safely accelerate,
brake, and corner
and those break down into these principles,
road isolation, the vehicle's ability to absorb
or isolate road shock from the passenger compartment,
cornering, the ability of a vehicle to travel a curved path,
and road holding, the degree to which a car maintains
contact with the road surface
in various types of directional changes
and in a straight line.
For example, the weight of a car will shift
from the rear tires to the front tires during braking
because the nose of the car dips toward the road.
This type of motion is known as dive.
The opposite effect, squat, occurs during acceleration,
which shifts the weight of the car
from the front tires to the back.
These are the challenges
that the suspension system has to handle.
Like I said earlier,
there's a buttload of suspension varieties
and a car can, and usually does,
have a different type of suspension on the front and back,
and in those you can either have a dependent system,
where a rigid axle binds the wheels,
or an independent system where the wheels
are permitted to move independently,
but the three fundamental components of any suspension
are springs, dampers, and anti sway bars.
Those are the bars that hate former MTV News reporter, Sway.
Wait, oh no, I'm being told that
they're actually just used along with shock absorbers
or struts to give a moving automobile additional stability.
Sway bars a metal rod that spans the entire axle
and effectively joins each side of the suspension together.
You suck, Sway.
Let's get back to talking about
one of three fundamental components of suspensions,
and my third favorite season, spring.
Now there's a couple of types of springs that can be used,
there's leaf springs, several layers of metal
bound together to act as a single unit,
and these are usually used on a lot of trucks.
They haven't been on a ton of US cars since '85.
There's torsion bars, here
one end of a bar is anchored to the vehicle frame
and the other end is attached to wishbone.
The wishbone acts like a lever that moves
perpendicular to the torsion bar.
When the wheel hits a bump,
vertical motion's transferred to the wishbone,
and then, through the levering action, to the torsion bar.
The torsion bar then twists along it's axis
to provide the spring force.
These are more common on European cars,
and there's coil springs,
basically a heavy duty torsion bar coiled around on an axis.
These are the most common.
Anything above the springs
and supported by 'em on the vehicle is sprung mass.
Anything below the spring between the springs and the road,
like the wheels, for example, is unsprung mass.
Unsprung mass was my nickname in college,
or it was until that fateful night
three years ago in September.
Spring stiffness effects how the sprung mass responds
while the car's being driven.
Loosely sprung cars, such as luxury cars,
swallow bumps for a smooth ride,
but they're prone to dive and squat
during braking and acceleration,
and can have body sway, or roll during cornering.
Tightly sprung cars, like sports cars,
are less forgiving on bumpy roads,
but they minimize body motion
so they can be driven aggressively, even around corners.
(engine revving)
(ding)
But you can't use just springs, you silly goose.
Springs absorb energy
but they stink when it comes to dissipating it,
that's why you need dampers.
One common dampening structure is a shock absorber.
Shock absorbers slow down and reduce the magnitude
of vibratory motion
by turning the kinetic energy of suspension movement
into heat energy that can be dissipated
through hydraulic fluid.
A shock absorber's upper mount connects to the frame
and the lower mount connects to the axle.
In a twin tube design,
the upper mount is connected to a piston rod
which is connected to a piston
and sits in a tube filled with hydraulic fluid.
Feels like I said that.
The inner tube's known as the pressure tube,
and the outer tube is known as the reserve tube.
The reserve tube stores excess hydraulic fluid.
When a wheel hits a bump in the road
and causes the spring to coil and uncoil,
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 it to leak through
as the piston moves up and down in the pressure tube.
Because these 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 when the piston moves down
compressing the hydraulic fluid
in the chamber below the piston,
and the extension cycle,
when the piston moves toward the top of the pressure tube
compressing the fluid in the chamber above the piston.
All modern shock absorbers are velocity sensitive.
The faster the suspension moves,
the more resistance the shock absorber provides,
so they can adjust to road conditions
and control all the unwanted motion
that can occur in a moving vehicle,
including bounce, sway, ah, I hate that guy,
brake dive and accelerating squat.
Another common dampening structure is the strut.
Basically it's a shock absorber mounted
inside a coil spring.
Struts provide two jobs,
dampening function like the shock absorbers,
and structural support for the vehicle's suspension.
They do a bit more than shock absorbers,
which don't support vehicle weight,
they only control the speed
at which the weight is transferred in a car,
not the weight itself.
The Mac Daddy of struts
is the MacPherson strut invented by Earle S. MacPherson.
No one knows what the S stands for except for Wikipedia,
which says is stands for Steele, cool.
The MacPherson strut consists of a single control arm
in a strut assembly
which allows tire and wheel to move upward and downward.
Its design allows for a reduction in a number of parts,
lowering unsprung mass, as well as smooth driving comfort.
These are pretty small, not too complicated,
and not too expensive, so they're pretty common.
They don't take up much space horizontally,
so they're super common in front suspensions
on the front wheel drive vehicles.
They do take up a lot of space vertically, though.
Another common type of front independent suspension,
the double wishbone suspension or an A-arm,
doesn't take up as much space vertically,
but is a horizontal hog.
That one guy in the comment section.
While there's several different possible configurations,
this design typically uses two wishbone shaped arms
to balance the wheel.
Each wishbone, which has two mounting positions to the frame
and one at the wheel, has 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 wheel tilts in and out.
(car squeaking)
They also help to minimize roll and sway,
and they provide for more consistent steering feel.
That's why double wishbone suspension's so common
on the front wheels of larger cars.
(claps) Real quick,
let's look at a couple of rear suspensions
and a split second picture of my belly button.
These are usually a little simpler
'cause you don't need to integrate the steering
for a dependent rear suspension,
if a solid axle connects with the rear wheels of a car,
then it's pretty simple,
based either on a leaf spring or a coil spring.
Leaf springs clamp directly to the drive axle,
and the ends of the leaf springs
attach directly to the frame.
The shock absorber's attached at the clamp
that holds the spring to the axle.
You can have the same basic design with coil springs
but in this case, the spring and shock absorber
can be mounted as a single unit or as separate components.
When they're separate, the springs can be much smaller,
which reduces the amount of space
that the suspension takes up.
For independent rear suspensions,
if both the front and back suspensions are independent,
then all the wheels are mounted and sprung individually,
resulting in what some ads call
four wheel independent suspension.
Any suspension that can be used in the front of a car
can be used on the rear
and versions of the front independent systems
described in the previous section
can be found in rear axles.
Of course, the rear of the car, the steering rack,
the assembly that keeps everything together
and lets ya turn, well, it's not there,
so that means rear independent suspensions
can be simplified versions of the front ones,
but the basic principles are the same.
Suspensions!
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