What is sway?

[Ron Davis]

I have read a bit about trailer pullin here and have to admit I am befuddled about something. What exactly is trailer sway?
Is it the oscillating yaw that one gets when they overload the back half a trailer? Theback and forth pendulum? That is deadly.
Or is it just one cycle of the yaw? You know.. a little kink and then back to center again without the pendulum effect... without oscillating?
Is sway the little buffeting you get when a truck passes? I get that sitin still on the side of the road sometimes.
I wash just wonderin what you all think is sway

RD

[CharlynnT]

Is it the oscillating yaw that one gets when they overload the back half a trailer? Theback and forth pendulum?

Yes, I think so. The side to side motion. We stopped at a parking lot, and put on the "sway bars" we got with the trailer. So that's what these are for! Stopped the swaying.

[Christi V.]

well thats one thing i do like about pulling the Scamp 5er No sway to deal with when trucks pass you..... towing the trailers made me to nervious!! ( not to say i am still not 100% comfortable pulling anything) LOL

[Gina D.]

You'll know a true sway without ever experiencing it before. I did once and managed to drive out of it.

The small stain on my drivers seat is a constant reminder......

[Chester Taje]

I had a major sway once.I loaded to much weight in the back.I was very lucky and managed to get control back.It was good that there was no on coming traffic.
PS
I sold that Tow Vehical with stain on seat.Gina kept hers.

[Gina D.]

HAH!

I blamed in on the dog!

Talk about loss of control

[Roger H]

Sway is an uncontrolled side-to-side oscillation of the towed trailer behind the tow vehicle. At speed, the oscillation will increase until the momentum that the trailer has in a side-to-side motion overcomes the ability of the rear tires of the tow vehicle to grip the road. As soon as that happens, you lose control and a rollover is frequently the result.

Sway is induced in a trailer from a variety of causes, some of which have nothing to do with the trailer itself. The same trailer can have severe sway problems behind one tow vehicle and have absolutely no problems behind another.

Sometimes the cause is in the tow vehicle's inability to keep the trailer tongue and hitch centered over the rear axle (known as rear axle steering). This can be countered with radius rods and body sway bar installation.

Tire pressure is also a significant contributor. Soft sidewalls, while making for a soft ride, also allow for lateral movement of the wheels over the tread. Make sure that your trailer tires are aired up to max or near max. Make sure also that your rear tires on your tow vehicle are at or near max pressure for the estimated load. The most likely single contributor to sway tendency is a light tongue weight; that is a tongue weight less than 10%-15% of the total trailer weight. Make sure also that your load is distributed evenly side-to-side in the trailer.

Once you've got each of those factors down, see if your trailer is still affected by external factors such as passing semis or going under overpasses on a really windy day. If, after all that you still experience a sway tendency, then sway control is probably in order.

Good luck!

Roger

[Ron Davis]

That is real real good advise.
One more question.
How do you know the difference between a normal "dip zig" when a big rig passes (like when you are parked by the side of the road) and sway? SOME feeling must be natural... like compression of the TV springs outboard.
Another way of saying it is: If I am driving down the road real nice and slow and feel a little wiggle as I go under a bridge or a big rig passes me, is that dangerous? just a wiggle? Is that going to start oscillating yaw?

Thanks a bunch

RD

[Roger H]

"Wiggles" aren't normal. If you're being moved by external forces, your trailer and tow vehicle should be moving together as a single unit, just as if wind were acting on your tow vehicle alone. They should move together and recover together. If each is being moved separately, then you have issues. Semis passing, driving in windy conditions and going under an underpass and then coming out, or any number of other conditions can induce a sway episode if your tow vehicle and trailer are being affected separately.

Roger

[Nancy Reeves]

Do you all have sway bars on the 13ft's? How does the straight hitch on the Uhaul trailer differ from pulling a Scamp? Thanks, We are still trying to figure out if we want a Scamp, Uhual or Burro.

Nancy

[Roger H]

Nancy, obviously I can't answer for "everyone", but I can give you some perspective. If I had to guess, I'd guess that few 13' trailer owners use sway control. Trailer sway only becomes a significant issue as the trailer weight approaches or exceeds the tow vehicle weight. The issue is whether or not the trailer can develop enough momentum to break the traction of the rear axle on the tow vehicle. For example, the likelihood of a 1200 lb 13' Scamp causing my 7,000 lb Excursion to roll, or even break the rear axle's traction is pretty slim. More than likely, there'd be a hitch failure and the trailer would break away from the truck rather than roll the Excursion.

Now, a 16' Scamp Custom Deluxe at 3,000 lbs towed behind a Toyota compact truck that weighs 3,500 lbs represents a much greater threat should it begin to sway. I didn't use friction sway control with MY 16' Scamp because of the weight of the tow vehicles I tow with. I DO use it with my Bigfoot 17', and I use a Reese Dual-Cam weight distributing hitch with my 25' Bigfoot.

So, again, once you've accounted for all of the causes of sway, a sway control is good insurance against the unexpected, but they're not a cure for all of the ills that cause sway. As a matter of fact, if you have a sway episode and don't cure the cause, the only thing a sway control device will accomplish for you is to mask the causes until they're REALLY bad and then you've REALLY got problems.

Roger

[Byron Kinnaman]

I have a 13' and don't use a sway bar. I'm pulling with a 4,200 lb SUV and 13' weighs 1,500 lb loaded. I do have electric brakes. From my point of view are there to keep the trailer behind the TV. One time I hit a break in the pavement that went across the road at an angle. The poor little trailer started bouncing from side to side, a quick application of the trailer brakes put a stop to that.

So in my case sway bar no, brakes yes.

[Brian B-P]

Do you all have sway bars on the 13ft's?

I'm going to put my regular plug in here for clear terminology...
"Sway bar" means many different things, to different people, in different contexts.

A device in the shape of a rectangular bar which connects one side of the trailer's tongue to one side of the tug's hitch is a [b]friction-type sway control device. It seems to be the one people are intending when they talk about a sway bar, singluar.

The springy steel bars which extend from each side of the tongue (or in one rare case, a single bar down the middle) to sockets in the hitch are the spring bars of a [b]weight distribution system. It seems to be the one people are sometimes intending when they talk about sway bars, plural.

While both affect yaw, and thus sway, they work entirely differently and are completely different things. By the way, my 17' trailer has neither.

How does the straight hitch on the Uhaul trailer differ from pulling a Scamp?

If you mean the tongue, the front part of the trailer structure... the tongue design should make no difference at all to vehicle behaviour. The details of mounting stuff do change, and if you were to use a weight-distribution (WD) system the required mounting hardware would be different, and the effect on roll (not yaw) of two-bar WD systems would be less with the narrower straight tongue.

[Ron Davis]

So, again, once you've accounted for all of the causes of sway, a sway control is good insurance against the unexpected, but they're not a cure for all of the ills that cause sway. As a matter of fact, if you have a sway episode and don't cure the cause, the only thing a sway control device will accomplish for you is to mask the causes until they're REALLY bad and then you've REALLY got problems.

Roger

I think "not a cure all" is an important concept. I pull a 3000lb trailer with a 7000 lb truck. I still get a little buffeting when a big rig passes but is no different than the buffeting (wiggle) I get without the tailer.

RD

[peterh]

Sway is an oscillation that gathers energy as you move the trailer forward. Here's how it happens: The trailer hits a bump -- even a small bump -- that transfers excess weight to one side of the trailer. Then the wheel on that side, which has energy because it is spinning, expends some of it's rotational velocity to push the extra weight back and eventually overcome the extra weight loading on that side. That sends the trailer swinging to the other side with just a little bit more energy than it came in with. Repeat this cycle a few times and you have a trailer that oscillates more wildly with each swing until the push from one side dumps the whole trailer over the wheel on the other side.

Avoiding the problem:

A swaying trailer is basically a heavy weight that is sways back over or behind the trailer axle. In order to get that trailer weight swinging, the trailer weight has to be located in a place that allows it to sway back and forth in the first place. A low center of gravity in your trailer means the weight will be shared more equally by the tires on either side at all times; a high center of gravity provides more weight that can be shifted from side-to-side. Load your trailer with the heaviest stuff on the floor and your trailer will be less likely to sway.

Also remember that trailers have three balance points: the hitch and the tires on either side. The hitch weight is weight you take off the tires and away from the amount of weight that can be shifted from side to side in a sway situation. If you look at manufacturer weights for their single-axle trailers you'll see that most of them put 10-20% of their total trailer weight on the hitch. (Scamp, for whatever reason, has weights a little lower, down to 7-1/2% of total weight, perhaps because they figure there just isn't that much weight to swing around in the first place.) Hitch weight is weight that will always pull your trailer down and center, so keep that in mind as you pack and load your trailer. (Remember not to exceed the hitch weight rating for your tow vehicle.)

Shocks (if your trailer has them) and tire inflation also play a role. Shock absorbers resist the movement of weight over one specific tire but allow that weight to move freely toward the center, taking energy out of the system as the trailer sways. Properly-inflated tires reduce sway the same way, resisting the addition of new weight to their side of the trailer and providing a more stable weight-bearing platform.

Using a brake controller's panic-switch to apply electric brakes on the trailer can help control sway. The brakes slow the wheels down so the pull of the tow vehicle becomes the major force pulling the trailer along, and the trailer has no choice but to follow in a more complacent manner.

Sway bars pull energy out of the system and dampen a trailer's tendency to sway by absorbing sway energy and transferring it to the tow vehicle. The down side of tow bars is that, if you have a badly loaded trailer, the trailer's tendency to sway can overwhelm the sway bar and tow vehicle's ability to take energy out of the system. In other words, they can help, but are no substitute for correct trailer loading and balance.

[I've made some changes to this post: My original post tried to explain some of the dynamics and physics involved in trailer sway based on a much more technical article I read last year and no longer have at my fingertips. On second reading I think I did a bad job of explaining things. Thanks to Brian B-P for pointing that out to me.]

[Brian B-P]

...Is it the oscillating yaw that one gets... The back and forth pendulum?

Sway is a really imprecise term, but if we are talking about sway as a problem, I think this is a good working definition: a continuing, even increasing, oscillation.

A single excursion and return to straight is not a sway problem, any more than a single up-and-down motion going over a bump is a ride problem. A vehicle which continues to bob up and down on the road after a bump is not properly controlled; a trailer which keeps swinging like a dog's tail repeatedly after a nudge (aerodynamic or otherwise) has a sway problem.

[CD Smith]

Sway is a really imprecise term, but if we are talking about sway as a problem, I think this is a good working definition: a continuing, even increasing, oscillation.

Technicaly: "...a continuing, even increasing, oscillation...", is an undamped oscillation.

The purpose of the 'sway control' is to provide a mechanism that turns the 'undamped' into a 'damped' oscillation.

[Ron Davis]

Technicaly: "...a continuing, even increasing, oscillation...", is an undamped oscillation.

The purpose of the 'sway control' is to provide a mechanism that turns the 'undamped' into a 'damped' oscillation.

Good info all! thanks.
According to Wikipedea anything that serves to reduce a the force of oscillation is "dampning".
I suppose that means if you roll your rig you are dampning the oscillation! hahahah

Thanks for all the input. It is making more sense now. I think some I have spoken too are talking about something other than oscillation when they talk about sway.

Thanks again.

RD

[Pete Dumbleton]

Here're my thoughts on sway, which I posted in the Files section of Yahoo Scampers. Some may disagree, but these are my thoughts based on experience and reading RV groups for more than a decade.

BTW, relative weight doesn't always do it -- I had a nearly uncontrollable sway incident on a curved, banked, wet gravel road in BC, where my 1700 lb Scamp 13 pulled my 4000 lb half-ton pickup around like they weighed the same.

QUOTE
Here are one person's thoughts on sway control, based on personal
experience and the experiences of others -- YMMV!


Below is a copy of the notes from a Reese friction sway control's
installation PDF

http://www.reeseprod.com/support/sup...fs/26660IN.pdf

Please read note No. 4 of the PDF -- How many folks actually stop
and pull over to the side of the road to disable their friction sway
control when driving in the rain or on gravel roads, etc., esp when
the rain first hits and the oils are starting to float on the road?
In fact, how many folks have even read Reese's note?

There are basically three kinds of sway that we encounter when towing:

A. That caused by a big truck's passing on a highway -- This, I believe,
is what most folks think about when sway is mentioned.

B. The reaction that the trailer has against the tow vehicle (TV)
when a change in direction happens, including a return from a change
in direction -- About the very worst is a turn while descending a
hill because the trailer is putting more weight on the TV rear and
lifting the TV front end while pushing to the side.

C. The reaction that the trailer has on the whole rig when its "speed
of instability" is reached and it starts to bounce and lurch from
side to side in ever-increasing distance.

The last two are the most dangerous, but sometimes vehicles are on
the very edge of the last one © when a big truck goes by -- The
resulting mess is blamed on the big truck, but that's really not
the base cause.

If the rig isn't balanced right (see Note No. 2 below about
first-line defense), then all the sway control does for you is
extend your "speed of instability" by a small margin and promote
a false sense of confidence, esp after a couple of big trucks
have passed by without incident.

If a friction sway control is set properly, at first it will resist
the trailer's tendency to sway and push the TV's rear to one side,
esp the momentary sway caused by encountering big trucks -- This
is why most folks have a sway control.

However, if the force is sufficient, as in a curve, the friction
sway control will slide to its new position -- It will now tend
to resist coming out of the turn with as much force as it used
going in -- If the road surface is slippery enuf, then either
going into the turn, or coming out, the sway control will not
allow the trailer to track properly and it will try to go into
a skid, yanking on the TV rear and possibly causing loss of control
-- Hence, the manufacturer's instructions to disconnect it in
slippery conditions.

In the case of major uncontrollable sway, as in C. above, the
friction control is tending to fight every steering correction
you try to make...

BTW, the Dual Cam and Equal-i-zer sway controls appear to be far
superior in this regard because they always try to straighten the
trailer behind the TV -- Unfortunately, they are only available with
weight distributing hitches (WDH).


QUOTE FROM THE REESE PDF FOR FRICTION SWAY CONTROL:

1.SWAY CONTROL CANNOT BE USED ON TRAILERS WITH SURGE BRAKES.

2.Trailer loading: Proper trailer loading is your first-line
defense against dangerous instability and sway. Heavy items
should be placed on the floor in front of the axle. The load
should be balanced side-to-side and secured to prevent shifting.
Tongue weight should be about 10-15 percent of gross trailer
weight for most trailers. Too low a percentage of tongue weight
can cause sway. Load the trailer heavier in front.

3. The handle (5) is an on/off device. The bolt (7) below is
for adjustment only.

4. When towing during slippery conditions such as wet, icy, or
snow-covered roads or on loose gravel, turn on/off handle (5)
counterclockwise until all tension is removed from unit. Failure
to do so could prevent tow vehicle and trailer from turning
properly.

5. Do not speed up if sway occurs. Sway increases with speed.
Do not continue to operate a swaying vehicle. Check trailer
loading, sway control adjustment, and all other equipment,
until the cause of sway has been determined and corrected.

6. Never paint or lubricate slide bar (6).
END QUOTE

Regarding front wheel drive (FWD), it's not sway controls that
are the question, it's a WDH to get the front wheels back down
on the ground properly to retain steering and control (and traction)
against the forces of sway -- This has to be offset, however,
by a serious look at the trailer frame because WDH takes the
weight off the rear of the TV and puts it on the front AND on
the trailer axle (and puts bending stresses on the frame in
the process).

However, if one had too light a front on FWD, one could
temporarily hide that condition from oneself by installing a
friction sway control >>> But only until the new limit of control
was reached...which will likely be at a higher speed with greater
consequences.

The bottom line on sway is to get your balances right, and stow
your heavy stuf as low and close to the axle as possible -- If
possible, do what you can to change your tow geometry -- Once
you have done all that, then add the anti-sway control for a
little insurance if you want.

On my Dodge D150 pickup, after towing for many tens of thousands
of miles, I had a near-miss on a descending curve on a wet gravel
road at slow speed -- My 1,700 91S13 slung my 4,500 lb truck like
I wouldn't have believed had I not experienced it -- Following that,
I rebalanced the load in truck itself to get more weight off the
rear and onto the front, modified the receiver hitch to move the
ball forward 2" and modified the ball mount to move it forward
another 2" -- Those things made a surprising improvement in
handling.

For those who don't already know this, here're some tow geometry
guidelines:

Long TV wheelbase is good
Short TV overhang (rear axle to ball) is good
Long trailer tongue (ball to trailer axle) is good
Short trailer overhang (trailer axle to bumper) is good

The worst possible things you can do are to have your tongue
weight too light and to put a lot of weight out on the trailer
bumper -- Installing a longer ball mount (aka stinger) is NOT
a good thing.

Pete D.

END QUOTE

[Pete Dumbleton]

Here's a post from a BulgeMoble Group:

QUOTE
======================
A trailer can sway for MANY reasons. Hensley, PullRite and 5th-
wheel hitches are vastly superior to conventional hitches but address
ONLY the level and direction of stresses the swaying trailer applies
to the tow vehicle, and better minimize the effects on the tow
vehicle. Trailerists concerned about stability would do well to use a
"good" hitch. But you must STILL pay attention to proper weight
balance, tire pressures, driving habits, and suspension conditions.
You CAN wreck your rig due to sway, no matter what hitch you use.
Here are some free tips:


BALANCE. TT's & utility trailers ought to have about 10-12% of their
weight on the tongue, fivers around 20% on the pin, and be more or
less equal side to side.


TIRES, both on trailer & tow vehicle, should be correctly inflated
for the actual load you're carrying. The best pressure is that shown
on the inflation chart for your actual measured weight. Absolute
precision is neither necessary or possible but don't over-inflate.


ALIGNMENT of both trailer and tow vehicle suspension as well as the
hitch is important. You can't expect a trailer to track straight if
the tow car is hunting back & forth or the hitch is off center.


HITCH TENSION is a factor: too much tension on the weight-
distributing bars takes too much weight off the rear wheels of the tow
vehicle and is potentially deadly in sudden braking; too little
squashes the rear suspension, unloads the front, and lets the trailer
nose down -- all three combine to decrease stability.


HIGH WINDS will move trailers around, some more than others,
Airstreams and Awards are a little less susceptible to crosswinds but
you will do will to park the dang thing on a real windy day.


TOW RATINGS have GOT to be conservatively applied if you expect a
safe, comfortable trip. I recommend you not exceed about 3/4 of the
max tow rating for your vehicle. You are a candidate for the Darwin
Award if you try to tow a 9,000 lb Airstream with an Intrepid or a
Winstar - no matter what some greedy sales loon tells you.


WHEELBASE. The right tow vehicle has a long wheelbase. It is
absolutely absurd to expect a Blazer, Jeep Cherokee, or Suzuki Samurai
to control a big TT. Those vehicles handle badly by themselves and
have all the confidence-building directional stability of a hockey
puck once a trailer is attached.


OVERHANG. The less the better for minimizing sway because the trailer
has less leverage to steer you. That is why the Hensley & PullRite
hitches feel as stable as a fifth-wheel setup. For years Suburbans
were considered a "good" tow vehicle but they have too much rear
overhang compared to some vans.


LOOSE PARTS on the hitch platform, the hitch itself, trailer frame, or
trailer suspension can cause havoc. Not common but a Big Deal if it
happens.


"SWAY CONTROL" gadgets are little more than bandaids, with minimal
effectiveness. If everything else is right they are unnecessary. At
best they introduce some small resistance to sway, and at worst they
can cause you a crisis under slippery conditions. I do NOT recommend
them. Instead, of you are serious about towing, check all the other
stuff and get a good hitch.


========================================


This lecture brought to you free by Will Sill KD3XR, who hopes you
are not offended by anything you read, inferred, assumed, presumed
or otherwise guessed I might have possibly meant as demeaning -
unless of course you are personally a humorless nitwit who WANTS
to be insulted. In which case be my guest.


Will Sill
The Curmudgeon of Sill Hill


END QUOTE