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Discussion Starter · #1 ·
"Pull-behind" trailers are trailers that connect to the tow vehicle by
a ball (or other attaching arrangement) on the back of tow vehicle and
a trailer hitch on the tongue attached to the front of the frame of the
trailer. If the trailer is improperly-loaded into a tail-heavy
condition (in other words, the center of gravity is to the rear of the
center of the axles) arrangement, it will sway from side to side. But
why? Why would tail-heavy conditions cause such behavior? The weight on
the tongue would be negative, but I still can't understand the swaying
mechanism.
--
(||) Nehmo (||)
 
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Discussion Starter · #2 ·
Nehmo wrote:

> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> a ball (or other attaching arrangement) on the back of tow vehicle and
> a trailer hitch on the tongue attached to the front of the frame of the
> trailer. If the trailer is improperly-loaded into a tail-heavy
> condition (in other words, the center of gravity is to the rear of the
> center of the axles) arrangement, it will sway from side to side. But
> why? Why would tail-heavy conditions cause such behavior? The weight on
> the tongue would be negative, but I still can't understand the swaying
> mechanism.

My thoughts are that the CG is behind the tires, they become the
steering mechanism rather than the tung. The trailer axles do not have
caster / camber and tow in alignment to hold it steady. The increased
sway can be caused by wallowing of the tire, the more the wallow the
more the sway, and the more the sway the more the wallow.
One thing I do know, if you want to spread gravel just load it in the
back of the trailer and get it up to speed, but watch it, the sway will
be soon swaying the tow vehicle from bar ditch to bar ditch, do not try
this with any one around so the can see you. They might think it is a
stupid trick and it is. ;-)

--

BILL P.

2004, 2500 SLT Quad Cab, Dodge Ram,
SLT, SWB, 2WD,
5.9 HO Turbo Diesel, 48RE Auto Trans,
Anti-Spin 3.73 Dif.Rhino Liner,
Husky 16K. Voyager Controller
2005, 27RL Wildcat, DT/PC Wi-Fi.
Dual EU2000i Hondas
Just Me and Dog
 
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Discussion Starter · #3 ·
"Nehmo" <[email protected]> wrote in message
news:[email protected]
> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> a ball (or other attaching arrangement) on the back of tow vehicle and
> a trailer hitch on the tongue attached to the front of the frame of the
> trailer. If the trailer is improperly-loaded into a tail-heavy
> condition (in other words, the center of gravity is to the rear of the
> center of the axles) arrangement, it will sway from side to side. But
> why? Why would tail-heavy conditions cause such behavior? The weight on
> the tongue would be negative, but I still can't understand the swaying
> mechanism.
> --
> (||) Nehmo (||)
>

Nehmo, the reason this happens is due to the wind being able to catch the
underside of the trailer creating lift. It also happens because it can lift
the back of the truck up off the springs, even if it is a slight amount, it
will cause this problem. And then because the trailer is attached to the
very rear of the truck, it causes the rear axle to act like a pendulum and
causes the front of the truck to sway side to side. If the driver is
experienced in pulling a trailer, he can stop the sway action. You just have
to hold the steering wheel very straight, and not side to side to try to
counter the sway. And yes, balancing the load on a trailer is extremely
important, you dont want there to be any lift on the hitching device. This
can cause an improperly hitched trailer to come loose, and possibly come
completely free of the vehicle. Always use tow chains, criss-crossed under
the hitch (so as to look like they are going to catch the tongue if it comes
undone), and with enough slack that you can take hard corners without
stretching or getting the chains tight.
Happy towing,
Pk
 
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Discussion Starter · #4 ·
"Nehmo" <[email protected]> wrote in message
news:[email protected]
> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> a ball (or other attaching arrangement) on the back of tow vehicle and
> a trailer hitch on the tongue attached to the front of the frame of the
> trailer. If the trailer is improperly-loaded into a tail-heavy
> condition (in other words, the center of gravity is to the rear of the
> center of the axles) arrangement, it will sway from side to side. But
> why? Why would tail-heavy conditions cause such behavior? The weight on
> the tongue would be negative, but I still can't understand the swaying
> mechanism.


If the trailer is grossly unbalanced forth to aft, it can cause sway.
--
Jon
JPinOH
 
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Discussion Starter · #5 ·
Nehmo wrote:
> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> a ball (or other attaching arrangement) on the back of tow vehicle and
> a trailer hitch on the tongue attached to the front of the frame of the
> trailer. If the trailer is improperly-loaded into a tail-heavy
> condition (in other words, the center of gravity is to the rear of the
> center of the axles) arrangement, it will sway from side to side. But
> why? Why would tail-heavy conditions cause such behavior? The weight on
> the tongue would be negative, but I still can't understand the swaying
> mechanism.


If the CG is behind the pivot point 9 (axles) the trailer will try to
switch ends. This is the swaying. Much like an conventional gear
airplane. Most of the weight is behind the main wheels. They have a
tendency to try to switch ends.

Michelle
 
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Discussion Starter · #6 ·
Michelle writes:
If the CG is behind the pivot point 9 (axles) the trailer will try to
switch ends. This is the swaying. Much like an conventional gear
airplane. Most of the weight is behind the main wheels. They have a
tendency to try to switch ends.

Michelle

HUH?

Are you talking about the fact a dart flies straight because its weight
is forward and the tail feathers cause a little drag to keep it
straight? And, If you throw a dart backwards, it will automatically
switch ends and the heavy end will lead the way?

Hank <~~~don't know anything about airplanes
 
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Discussion Starter · #7 ·
"Nehmo" <[email protected]> wrote in message
news:[email protected]
: "Pull-behind" trailers are trailers that connect to the tow vehicle by
: a ball (or other attaching arrangement) on the back of tow vehicle and
: a trailer hitch on the tongue attached to the front of the frame of the
: trailer. If the trailer is improperly-loaded into a tail-heavy
: condition (in other words, the center of gravity is to the rear of the
: center of the axles) arrangement, it will sway from side to side. But
: why? Why would tail-heavy conditions cause such behavior? The weight on
: the tongue would be negative, but I still can't understand the swaying
: mechanism.


Because the majority of the weight is behind the center of gravity and it's
attempting to get to the front because it's smart enough to know that's
where it belongs :)
 
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Discussion Starter · #8 ·
Bob V wrote:
> "Nehmo" <[email protected]> wrote in message
> news:[email protected]
> : "Pull-behind" trailers are trailers that connect to the tow vehicle by
> : a ball (or other attaching arrangement) on the back of tow vehicle and
> : a trailer hitch on the tongue attached to the front of the frame of the
> : trailer. If the trailer is improperly-loaded into a tail-heavy
> : condition (in other words, the center of gravity is to the rear of the
> : center of the axles) arrangement, it will sway from side to side. But
> : why? Why would tail-heavy conditions cause such behavior? The weight on
> : the tongue would be negative, but I still can't understand the swaying
> : mechanism.
>
>
> Because the majority of the weight is behind the center of gravity and it's
> attempting to get to the front because it's smart enough to know that's
> where it belongs :)
>
>

thats what I was trying to say.....
Michelle
 
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Discussion Starter · #9 ·
"Nehmo" <[email protected]> wrote in message
news:[email protected]
> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> a ball (or other attaching arrangement) on the back of tow vehicle and
> a trailer hitch on the tongue attached to the front of the frame of the
> trailer. If the trailer is improperly-loaded into a tail-heavy
> condition (in other words, the center of gravity is to the rear of the
> center of the axles) arrangement, it will sway from side to side. But
> why? Why would tail-heavy conditions cause such behavior? The weight on
> the tongue would be negative, but I still can't understand the swaying
> mechanism.
> --
> (||) Nehmo (||)


Just having the weight behind the wheels in itself doesn't produce the sway.
It allows amplification.

Many things can get the sway started (wind, bumps in the road, passing
vehicles) and once going the weight unbalance makes it more difficult to
control.

The trailer is like a pendelum hanging out behind the tow vehicle. The
closer the weight is to the vehicle the easier it is to control. Try
holding a board with a weight on it out in the wind. It's a lot easier to
control if the weight is close in.

The weight and length of the tow vehicle also comes into play. When a tail
heavy pendelum starts to swing it will start controlling the tow vehicle.

The flex of the tires adds more amplificaton.


No matter what you do there is always possibility of sway. The amount of
weight you put on the hitch is a compromise.
Only total solution is to put all the weight on the tow vehicle and elimiate
the trailer.
 
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Discussion Starter · #10 ·
"Michelle" <[email protected]> wrote in message
news:[email protected]
> Bob V wrote:
>> "Nehmo" <[email protected]> wrote in message
>> news:[email protected]
>> : "Pull-behind" trailers are trailers that connect to the tow vehicle by
>> : a ball (or other attaching arrangement) on the back of tow vehicle and
>> : a trailer hitch on the tongue attached to the front of the frame of the
>> : trailer. If the trailer is improperly-loaded into a tail-heavy
>> : condition (in other words, the center of gravity is to the rear of the
>> : center of the axles) arrangement, it will sway from side to side. But
>> : why? Why would tail-heavy conditions cause such behavior? The weight on
>> : the tongue would be negative, but I still can't understand the swaying
>> : mechanism.
>>
>>
>> Because the majority of the weight is behind the center of gravity and
>> it's attempting to get to the front because it's smart enough to know
>> that's where it belongs :)

> thats what I was trying to say.....
> Michelle


Smart weight??? Where would one acquire such weight? I am sure I would
prefer it to dumb weight.
 
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Discussion Starter · #11 ·
"Rich256" <[email protected]> wrote in message
news:[email protected]
>
> "Nehmo" <[email protected]> wrote in message
> news:[email protected]
>> "Pull-behind" trailers are trailers that connect to the tow vehicle by
>> a ball (or other attaching arrangement) on the back of tow vehicle and
>> a trailer hitch on the tongue attached to the front of the frame of the
>> trailer. If the trailer is improperly-loaded into a tail-heavy
>> condition (in other words, the center of gravity is to the rear of the
>> center of the axles) arrangement, it will sway from side to side. But
>> why? Why would tail-heavy conditions cause such behavior? The weight on
>> the tongue would be negative, but I still can't understand the swaying
>> mechanism.
>> --
>> (||) Nehmo (||)

>
> Just having the weight behind the wheels in itself doesn't produce the
> sway.
> It allows amplification.
>
> Many things can get the sway started (wind, bumps in the road, passing
> vehicles) and once going the weight unbalance makes it more difficult to
> control.
>
> The trailer is like a pendelum hanging out behind the tow vehicle. The
> closer the weight is to the vehicle the easier it is to control. Try
> holding a board with a weight on it out in the wind. It's a lot easier to
> control if the weight is close in.
>
> The weight and length of the tow vehicle also comes into play. When a
> tail
> heavy pendelum starts to swing it will start controlling the tow vehicle.
>
> The flex of the tires adds more amplificaton.
>
>
> No matter what you do there is always possibility of sway. The amount of
> weight you put on the hitch is a compromise.
> Only total solution is to put all the weight on the tow vehicle and
> elimiate
> the trailer.
>
>


By The Way,

Amplification, this was the only reasonable response to your question...
 
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Discussion Starter · #12 ·
"351CJ" <[email protected]> wrote in message
news:[email protected]
>
> "Rich256" <[email protected]> wrote in message
> news:[email protected]
> >
> > "Nehmo" <[email protected]> wrote in message
> > news:[email protected]
> >> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> >> a ball (or other attaching arrangement) on the back of tow vehicle and
> >> a trailer hitch on the tongue attached to the front of the frame of the
> >> trailer. If the trailer is improperly-loaded into a tail-heavy
> >> condition (in other words, the center of gravity is to the rear of the
> >> center of the axles) arrangement, it will sway from side to side. But
> >> why? Why would tail-heavy conditions cause such behavior? The weight on
> >> the tongue would be negative, but I still can't understand the swaying
> >> mechanism.
> >> --
> >> (||) Nehmo (||)

> >
> > Just having the weight behind the wheels in itself doesn't produce the
> > sway.
> > It allows amplification.
> >
> > Many things can get the sway started (wind, bumps in the road, passing
> > vehicles) and once going the weight unbalance makes it more difficult to
> > control.
> >
> > The trailer is like a pendelum hanging out behind the tow vehicle. The
> > closer the weight is to the vehicle the easier it is to control. Try
> > holding a board with a weight on it out in the wind. It's a lot easier

to
> > control if the weight is close in.
> >
> > The weight and length of the tow vehicle also comes into play. When a
> > tail
> > heavy pendelum starts to swing it will start controlling the tow

vehicle.
> >
> > The flex of the tires adds more amplificaton.
> >
> >
> > No matter what you do there is always possibility of sway. The amount

of
> > weight you put on the hitch is a compromise.
> > Only total solution is to put all the weight on the tow vehicle and
> > elimiate
> > the trailer.
> >
> >

>
> By The Way,
>
> Amplification, this was the only reasonable response to your question...
>
>


Thinking about it a little more one could have a really long trailer that is
very heavily loaded in the rear and you could pull it at very high speeds,
with a short wheelbase vehicle, without any trouble. But only as long as
there is no wind, no bumps or anything else to get it into a sway condition.
But god help you if it begins to swing!!

Nothing more frightening than having the trailer begin to do the steering.
 
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Discussion Starter · #13 ·
Rich256 wrote:

> "351CJ" <[email protected]> wrote in message
> news:[email protected]
>
>>"Rich256" <[email protected]> wrote in message
>>news:[email protected]
>>
>>>"Nehmo" <[email protected]> wrote in message
>>>news:[email protected]
>>>
>>>>"Pull-behind" trailers are trailers that connect to the tow vehicle by
>>>>a ball (or other attaching arrangement) on the back of tow vehicle and
>>>>a trailer hitch on the tongue attached to the front of the frame of the
>>>>trailer. If the trailer is improperly-loaded into a tail-heavy
>>>>condition (in other words, the center of gravity is to the rear of the
>>>>center of the axles) arrangement, it will sway from side to side. But
>>>>why? Why would tail-heavy conditions cause such behavior? The weight on
>>>>the tongue would be negative, but I still can't understand the swaying
>>>>mechanism.
>>>>--
>>>> (||) Nehmo (||)
>>>
>>>Just having the weight behind the wheels in itself doesn't produce the
>>>sway.
>>>It allows amplification.
>>>
>>>Many things can get the sway started (wind, bumps in the road, passing
>>>vehicles) and once going the weight unbalance makes it more difficult to
>>>control.
>>>
>>>The trailer is like a pendelum hanging out behind the tow vehicle. The
>>>closer the weight is to the vehicle the easier it is to control. Try
>>>holding a board with a weight on it out in the wind. It's a lot easier

>
> to
>
>>>control if the weight is close in.
>>>
>>>The weight and length of the tow vehicle also comes into play. When a
>>>tail
>>>heavy pendelum starts to swing it will start controlling the tow

>
> vehicle.
>
>>>The flex of the tires adds more amplificaton.
>>>
>>>
>>>No matter what you do there is always possibility of sway. The amount

>
> of
>
>>>weight you put on the hitch is a compromise.
>>>Only total solution is to put all the weight on the tow vehicle and
>>>elimiate
>>>the trailer.
>>>
>>>

>>
>>By The Way,
>>
>>Amplification, this was the only reasonable response to your question...
>>
>>

>
>
> Thinking about it a little more one could have a really long trailer that is
> very heavily loaded in the rear and you could pull it at very high speeds,
> with a short wheelbase vehicle, without any trouble. But only as long as
> there is no wind, no bumps or anything else to get it into a sway condition.
> But god help you if it begins to swing!!
>
> Nothing more frightening than having the trailer begin to do the steering.
>
>

I think the only way to correct the swaying is to reload the trailer
properly.

--
Bill P.
just
Dog
&
ME

At this time in life all that
remains is left overs, some can
be cherished as good others bad,
but the only definite is that they
are all that remains, main course is
over.
 
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Discussion Starter · #14 ·
For simplicity, let's assume one axle and a flat deck trailer. My
experience has been the sway is dependent on the relationship of the
Center of Mass (CM) to the axle, in other words, if the CM is in front
or behind the axle.

Hitch - CM - Axle = stable
Hitch - Axle - CM = unstable

Trailers are self-correcting in terms of steering, like a caster on a
piece of furniture. If the wheel "steers" to the left like this \ , the
back and the front of the wheel touching the ground get resistance from
the ground. But the resistance on the back has more leverage in
relationship to the pivot, so the force is translated into a clockwise
turning moment about the pivot. This turning moment corrects the
orientation of the caster until it is pointed parallel to the direction
for travel, like this |.

So front-heavy trailers correct themselves regarding steering like the
caster, but the corrections are small. In tail-heavy trailers, the
steering corrections are large and they may even yank at the tow
vehicle.

I still don't understand it; I'm just restating the problem.
--
(||) Nehmo (||)
 
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Discussion Starter · #15 ·
"William Boyd" <[email protected]> wrote in message
news:[email protected].net...
> Rich256 wrote:
>
> > "351CJ" <[email protected]> wrote in message
> > news:[email protected]
> >
> >>"Rich256" <[email protected]> wrote in message
> >>news:[email protected]
> >>
> >>>"Nehmo" <[email protected]> wrote in message
> >>>news:[email protected]
> >>>
> >>>>"Pull-behind" trailers are trailers that connect to the tow vehicle by
> >>>>a ball (or other attaching arrangement) on the back of tow vehicle and
> >>>>a trailer hitch on the tongue attached to the front of the frame of

the
> >>>>trailer. If the trailer is improperly-loaded into a tail-heavy
> >>>>condition (in other words, the center of gravity is to the rear of the
> >>>>center of the axles) arrangement, it will sway from side to side. But
> >>>>why? Why would tail-heavy conditions cause such behavior? The weight

on
> >>>>the tongue would be negative, but I still can't understand the swaying
> >>>>mechanism.
> >>>>--
> >>>> (||) Nehmo (||)
> >>>
> >>>Just having the weight behind the wheels in itself doesn't produce the
> >>>sway.
> >>>It allows amplification.
> >>>
> >>>Many things can get the sway started (wind, bumps in the road, passing
> >>>vehicles) and once going the weight unbalance makes it more difficult

to
> >>>control.
> >>>
> >>>The trailer is like a pendelum hanging out behind the tow vehicle.

The
> >>>closer the weight is to the vehicle the easier it is to control. Try
> >>>holding a board with a weight on it out in the wind. It's a lot easier

> >
> > to
> >
> >>>control if the weight is close in.
> >>>
> >>>The weight and length of the tow vehicle also comes into play. When a
> >>>tail
> >>>heavy pendelum starts to swing it will start controlling the tow

> >
> > vehicle.
> >
> >>>The flex of the tires adds more amplificaton.
> >>>
> >>>
> >>>No matter what you do there is always possibility of sway. The amount

> >
> > of
> >
> >>>weight you put on the hitch is a compromise.
> >>>Only total solution is to put all the weight on the tow vehicle and
> >>>elimiate
> >>>the trailer.
> >>>
> >>>
> >>
> >>By The Way,
> >>
> >>Amplification, this was the only reasonable response to your question...
> >>
> >>

> >
> >
> > Thinking about it a little more one could have a really long trailer

that is
> > very heavily loaded in the rear and you could pull it at very high

speeds,
> > with a short wheelbase vehicle, without any trouble. But only as long

as
> > there is no wind, no bumps or anything else to get it into a sway

condition.
> > But god help you if it begins to swing!!
> >
> > Nothing more frightening than having the trailer begin to do the

steering.
> >
> >

> I think the only way to correct the swaying is to reload the trailer
> properly.
>
>


Not the only way but perhaps the most important. Even tires can contibute.
 
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Discussion Starter · #16 ·
I got really curious about this, and studied it for a long time (I'm an
engineer). There was a good thread on this at woodall's RV forum. I have
found no frank discussion of it by anybody who has broken it down into its
component forces. It's hard to explain it using ASCII here. But my opinion
is this:

First off, it's clear that trailers can amplify their swaying until you
crash. They don't do it all the time, but they can, and that's what
interests me. They have no power of their own to bring to the table. The
energy to do this comes from the tow vehicle. The trailer sways like a
pendulum, sort of (I admit the forces holding a trailer back are not exactly
like gravity in this analogy). A pendulum can be powered by a wide variety
of motions. One of those motions is moving the pendulum's pivot point side
to side. I think this is the motion we want.

The forces on the trailer come from its tires and the tow vehicle. I was not
interested in any other forces. "front loaded" trailers are trailers where
the center of gravity is in front of the tires. When the tires are pushing
the trailer sideways (during sway), the center of gravity is in front of
that force. Since the side force doesn't go exactly through the center of
gravity, the weight of the trailer pushes sideways on the tow vehicle.

The inertia of the swaying trailer pushes the tow vehicle from side to side.
The difference in loading is simply this. If the center of gravity is in
front of the wheels, it pushed the tow vehicle one way, and if it's behind
the wheels, it pushes the two vehicle the other way. One cancels the sway,
and the other amplifies it.

"Nehmo" <[email protected]> wrote in message
news:[email protected]
> "Pull-behind" trailers are trailers that connect to the tow vehicle by
> a ball (or other attaching arrangement) on the back of tow vehicle and
> a trailer hitch on the tongue attached to the front of the frame of the
> trailer. If the trailer is improperly-loaded into a tail-heavy
> condition (in other words, the center of gravity is to the rear of the
> center of the axles) arrangement, it will sway from side to side. But
> why? Why would tail-heavy conditions cause such behavior? The weight on
> the tongue would be negative, but I still can't understand the swaying
> mechanism.
> --
> (||) Nehmo (||)
>
 
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·
Discussion Starter · #17 ·
Joe wrote:
> I got really curious about this, and studied it for a long time (I'm an
> engineer). There was a good thread on this at woodall's RV forum. I have
> found no frank discussion of it by anybody who has broken it down into its
> component forces. It's hard to explain it using ASCII here. But my opinion
> is this:
>
> First off, it's clear that trailers can amplify their swaying until you
> crash. They don't do it all the time, but they can, and that's what
> interests me. They have no power of their own to bring to the table. The
> energy to do this comes from the tow vehicle. The trailer sways like a
> pendulum, sort of (I admit the forces holding a trailer back are not exactly
> like gravity in this analogy). A pendulum can be powered by a wide variety
> of motions. One of those motions is moving the pendulum's pivot point side
> to side. I think this is the motion we want.
>
> The forces on the trailer come from its tires and the tow vehicle. I was not
> interested in any other forces. "front loaded" trailers are trailers where
> the center of gravity is in front of the tires. When the tires are pushing
> the trailer sideways (during sway), the center of gravity is in front of
> that force. Since the side force doesn't go exactly through the center of
> gravity, the weight of the trailer pushes sideways on the tow vehicle.
>
> The inertia of the swaying trailer pushes the tow vehicle from side to side.
> The difference in loading is simply this. If the center of gravity is in
> front of the wheels, it pushed the tow vehicle one way, and if it's behind
> the wheels, it pushes the two vehicle the other way. One cancels the sway,
> and the other amplifies it.
>


I don't know if amplification is the correct term. Poor loading will
increase the sensitivity of a tow vehicle and trailer to winds and side
drafts from big trucks, but I don't understand how the forces could
actually be amplified. In my experience the side-to-side swaying is
amplified or increased by the driver trying to offset the swaying by
steering out of it.
 
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·
Discussion Starter · #18 ·
John S. wrote:
> Joe wrote:
>
>>I got really curious about this, and studied it for a long time (I'm an
>>engineer). There was a good thread on this at woodall's RV forum. I have
>>found no frank discussion of it by anybody who has broken it down into its
>>component forces. It's hard to explain it using ASCII here. But my opinion
>>is this:
>>
>>First off, it's clear that trailers can amplify their swaying until you
>>crash. They don't do it all the time, but they can, and that's what
>>interests me. They have no power of their own to bring to the table. The
>>energy to do this comes from the tow vehicle. The trailer sways like a
>>pendulum, sort of (I admit the forces holding a trailer back are not exactly
>>like gravity in this analogy). A pendulum can be powered by a wide variety
>>of motions. One of those motions is moving the pendulum's pivot point side
>>to side. I think this is the motion we want.
>>
>>The forces on the trailer come from its tires and the tow vehicle. I was not
>>interested in any other forces. "front loaded" trailers are trailers where
>>the center of gravity is in front of the tires. When the tires are pushing
>>the trailer sideways (during sway), the center of gravity is in front of
>>that force. Since the side force doesn't go exactly through the center of
>>gravity, the weight of the trailer pushes sideways on the tow vehicle.
>>
>>The inertia of the swaying trailer pushes the tow vehicle from side to side.
>>The difference in loading is simply this. If the center of gravity is in
>>front of the wheels, it pushed the tow vehicle one way, and if it's behind
>>the wheels, it pushes the two vehicle the other way. One cancels the sway,
>>and the other amplifies it.
>>

>
>
> I don't know if amplification is the correct term. Poor loading will
> increase the sensitivity of a tow vehicle and trailer to winds and side
> drafts from big trucks, but I don't understand how the forces could
> actually be amplified. In my experience the side-to-side swaying is
> amplified or increased by the driver trying to offset the swaying by
> steering out of it.
>


This is true and just about all trailer sway issue start with tow
vehicle stabilty issues. (tires and suspension not up to the extra load
on them)

--

-----------------
www.thesnoman.com
 
G

·
Discussion Starter · #19 ·
TheSnoMan wrote:

> John S. wrote:
>
>> Joe wrote:
>>
>>> I got really curious about this, and studied it for a long time (I'm an
>>> engineer). There was a good thread on this at woodall's RV forum. I have
>>> found no frank discussion of it by anybody who has broken it down
>>> into its
>>> component forces. It's hard to explain it using ASCII here. But my
>>> opinion
>>> is this:
>>>
>>> First off, it's clear that trailers can amplify their swaying until you
>>> crash. They don't do it all the time, but they can, and that's what
>>> interests me. They have no power of their own to bring to the table. The
>>> energy to do this comes from the tow vehicle. The trailer sways like a
>>> pendulum, sort of (I admit the forces holding a trailer back are not
>>> exactly
>>> like gravity in this analogy). A pendulum can be powered by a wide
>>> variety
>>> of motions. One of those motions is moving the pendulum's pivot point
>>> side
>>> to side. I think this is the motion we want.
>>>
>>> The forces on the trailer come from its tires and the tow vehicle. I
>>> was not
>>> interested in any other forces. "front loaded" trailers are trailers
>>> where
>>> the center of gravity is in front of the tires. When the tires are
>>> pushing
>>> the trailer sideways (during sway), the center of gravity is in front of
>>> that force. Since the side force doesn't go exactly through the
>>> center of
>>> gravity, the weight of the trailer pushes sideways on the tow vehicle.
>>>
>>> The inertia of the swaying trailer pushes the tow vehicle from side
>>> to side.
>>> The difference in loading is simply this. If the center of gravity is in
>>> front of the wheels, it pushed the tow vehicle one way, and if it's
>>> behind
>>> the wheels, it pushes the two vehicle the other way. One cancels the
>>> sway,
>>> and the other amplifies it.
>>>

>>
>>
>> I don't know if amplification is the correct term. Poor loading will
>> increase the sensitivity of a tow vehicle and trailer to winds and side
>> drafts from big trucks, but I don't understand how the forces could
>> actually be amplified. In my experience the side-to-side swaying is
>> amplified or increased by the driver trying to offset the swaying by
>> steering out of it.
>>

>
> This is true and just about all trailer sway issue start with tow
> vehicle stabilty issues. (tires and suspension not up to the extra load
> on them)
>

I do not agree. I think trailer sway issues start with proper loading.
I do agree that tow vehicle stability issues can be attributed to tire
and suspension problems. But they will not be the primary cause of sway,
the distribution of the load will be. Even a trailer that is grossly
over loaded may not sway if the CG is correct. But this is where the tow
vehicle suspension and tire pressure will show up more readily.
And I am no mechanical engineer or whatever scientist, but a retired
transportation superintendent with a lot of miles behind me. ;-)

--

BILL P.

2004, 2500 SLT Quad Cab, Dodge Ram,
SLT, SWB, 2WD,
5.9 HO Turbo Diesel, 48RE Auto Trans,
Anti-Spin 3.73 Dif.Rhino Liner,
Husky 16K. Voyager Controller
2005, 27RL Wildcat, DT/PC Wi-Fi.
Dual EU2000i Hondas
Just Me and Dog
 
G

·
Discussion Starter · #20 ·
William Boyd wrote:
> TheSnoMan wrote:
>
>> John S. wrote:
>>
>>> Joe wrote:
>>>
>>>> I got really curious about this, and studied it for a long time (I'm an
>>>> engineer). There was a good thread on this at woodall's RV forum. I
>>>> have
>>>> found no frank discussion of it by anybody who has broken it down
>>>> into its
>>>> component forces. It's hard to explain it using ASCII here. But my
>>>> opinion
>>>> is this:
>>>>
>>>> First off, it's clear that trailers can amplify their swaying until you
>>>> crash. They don't do it all the time, but they can, and that's what
>>>> interests me. They have no power of their own to bring to the table.
>>>> The
>>>> energy to do this comes from the tow vehicle. The trailer sways like a
>>>> pendulum, sort of (I admit the forces holding a trailer back are not
>>>> exactly
>>>> like gravity in this analogy). A pendulum can be powered by a wide
>>>> variety
>>>> of motions. One of those motions is moving the pendulum's pivot
>>>> point side
>>>> to side. I think this is the motion we want.
>>>>
>>>> The forces on the trailer come from its tires and the tow vehicle. I
>>>> was not
>>>> interested in any other forces. "front loaded" trailers are trailers
>>>> where
>>>> the center of gravity is in front of the tires. When the tires are
>>>> pushing
>>>> the trailer sideways (during sway), the center of gravity is in
>>>> front of
>>>> that force. Since the side force doesn't go exactly through the
>>>> center of
>>>> gravity, the weight of the trailer pushes sideways on the tow vehicle.
>>>>
>>>> The inertia of the swaying trailer pushes the tow vehicle from side
>>>> to side.
>>>> The difference in loading is simply this. If the center of gravity
>>>> is in
>>>> front of the wheels, it pushed the tow vehicle one way, and if it's
>>>> behind
>>>> the wheels, it pushes the two vehicle the other way. One cancels the
>>>> sway,
>>>> and the other amplifies it.
>>>>
>>>
>>>
>>> I don't know if amplification is the correct term. Poor loading will
>>> increase the sensitivity of a tow vehicle and trailer to winds and side
>>> drafts from big trucks, but I don't understand how the forces could
>>> actually be amplified. In my experience the side-to-side swaying is
>>> amplified or increased by the driver trying to offset the swaying by
>>> steering out of it.
>>>

>>
>> This is true and just about all trailer sway issue start with tow
>> vehicle stabilty issues. (tires and suspension not up to the extra
>> load on them)
>>

> I do not agree. I think trailer sway issues start with proper loading.
> I do agree that tow vehicle stability issues can be attributed to tire
> and suspension problems. But they will not be the primary cause of sway,
> the distribution of the load will be. Even a trailer that is grossly
> over loaded may not sway if the CG is correct. But this is where the tow
> vehicle suspension and tire pressure will show up more readily.
> And I am no mechanical engineer or whatever scientist, but a retired
> transportation superintendent with a lot of miles behind me. ;-)
>

CG is a factor but if your TV is not up to the load, it will be
unstable. Your TV has to effectively anchor the front of the trailer
where you want it to be and if trailer force easily deflect the TV's
controll of this, you will have sway. Correct CG on a poor TV can still
be quite unstable while even some CG error can do well if the TV is
stout enough.

--

-----------------
www.thesnoman.com
 
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