What is sway? - Fiberglass RV


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Old 06-17-2007, 03:23 PM   #1
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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
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Old 06-17-2007, 04:36 PM   #2
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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.
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Old 06-17-2007, 05:10 PM   #3
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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
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Old 06-17-2007, 05:18 PM   #4
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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......
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Old 06-17-2007, 05:50 PM   #5
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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.
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Old 06-17-2007, 06:13 PM   #6
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HAH!

I blamed in on the dog!

Talk about loss of control
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Old 06-17-2007, 07:52 PM   #7
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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
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Old 06-17-2007, 09:18 PM   #8
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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
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Old 06-17-2007, 09:30 PM   #9
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"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
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Old 06-18-2007, 10:10 AM   #10
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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
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Old 06-18-2007, 11:19 AM   #11
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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
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Old 06-18-2007, 11:39 AM   #12
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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.
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Old 06-18-2007, 02:27 PM   #13
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Quote:
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.

Quote:
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.
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Old 06-18-2007, 02:32 PM   #14
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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
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