Sway - Causes?

[SteveH]

What does Can-Am do to the vehicle to increase rear axle weight rating, cooling system capacity, transmission cooling capacity, and GVWR, etc.?

[MrUKToad]

Originally Posted by SteveH

What does Can-Am do to the vehicle to increase rear axle weight rating, cooling system capacity, transmission cooling capacity, and GVWR, etc.?

I can only speak about work done on my TV, which was limited to an additional transmission oil cooler. I don't exceed the axle weight ratings nor the GVWR so no enhancements were needed.

[mstephens]

Originally Posted by MrUKToad

I rambled on a bit there but essentially the Sienna, suitably set up, works well for me and plenty of other Can-Am customers.

The Can-Am name seems to come a lot when interesting tow rigs are discussed. Too bad they are so far from me. Although I enjoy my Suburban, I'd be intrigued to know if our V6 Ford Escape could be setup to tow the same TT? I suspect at a minimum my gas mileage would climb by 4 or 5 MPG. Man, that would be nice!

General call out - - does anyone know of people in the USA who do what Can-Am do?

[Inland RV Center, In]

Originally Posted by mstephens

I've been towing my rig over all kinds of Interstates, highways, byways and roads for almost a year. Rain, wind, sun. I've towed up and down long grades, flat runs, and through wind-swept prairies. I have had triple trailer rigs go roaring by. And through all this, I can't say that I have ever had any sway of any appreciable amount (such as where I would have to adjust the steering wheel). I have a simple WD hitch with friction sway control.

I am interested to look at what contributes to sway?

- Tires on the TV and Trailer (side wall roll or flex)
- Overhang on the TV - distance from rear axle to ball compared to wheel base
- Improper weight distribution on the TV
- Improper balance of the trailer

Of course we have various hitches to eliminate sway, but my question here is what can be done to stop sway from happening in the first place?

If sway is reduced at the source, how much sway control needs to be in the hitch?

Do different TV types perform better than others in sway? Van vs. PU? SUV vs. sedan?

Can you just change tires and reduce sway?

Follow a boat being towed.

The back end oscillates, to some degree.

The same basic thing happens to an RV, especially the Airstream shell shape
design.

The longer the trailer, the more it oscillates, to some degree.

That oscillation will be experienced if a person rides in the back of the trailer at about 60 MPH.

Once they feel that small sway (oscillation) they then will do something directed towards correction, instead of insisting that theirs doesn't sway.

Not what owners want to hear, but something they should all experience as a fact.

Andy

[barts]

That oscillation will be experienced if a person rides in the back of the trailer at about 60 MPH.

Once they feel that small sway (oscillation) they then will do something directed towards correction, instead of insisting that theirs doesn't sway.

A damped oscillation in response to transient road effects is completely normal, and is NOT a cause for concern. The thing we're concerned about is uncontrolled growing oscillations. Most times, the driver is an important part of causing those oscillations, and if he would stop trying to "correct" things would die down again. However, the stability equations for trailers DO indication some conditions when uncontrollable sway can occur, and the following factors most exacerbate this:

1) insufficient tongue weight
2) grossly excessive speed
3) trailers loaded with high polar moment of inertia.

There are others, as others have commented.

- Bart

[ROBERTSUNRUS]

Hi, almost everything tends to oscillate on our grooved freeways. Seems that most of the problems occur while driving down hill, going too fast, passing or being passed by a big rig, and with some side winds. [driver error]

[mstephens]

Sway vs. Fishtailing?

Hmmm? I am starting to wonder if there are two separate, but similar phenomena here.

First, if I imagine the ball tracing a straight line, but the TT rear end moving side to side, I would call that a harmless "fishtail." In the second case the ball is moving side to side AND the TT rear end is moving side to side in opposition, I would call that the dangerous "sway", which we are trying to eliminate.

This came to mind after reading Andy's post. His position was that sway exists all the time, whether driver knows it or not. His evidence was the tail end of the TT swinging side to side when view from behind (paraphrasing).

When I said in the O/P that I don't feel sway, I mean that I don't feel my TV moving. The TT might in fact have some side to side (Andy's motion), but my TV seems stiff enough to resist. I am not making any steering corrections when big semis blow by. (I use a friction style anti-sway).

It would be hard for a fishtail of the trailer alone (ball not moving) to amplify out of control, whereas it is easy for the "sway" (ball moving side to side) to amplify out of control. Driver over-correction would of course be common.

It would be easy to imagine some reasons that the TT might be fishtailing all the time. Road surface, axle or tire alignment, tire balance, to name a few. It is also easy to imagine that TVs have a wide range of resistance to side force at the ball. I've never seen any metrics on this. Like, how much side force would it take to move the ball 2" east to west? Just a thought.

[SteveH]

Originally Posted by MrUKToad

I can only speak about work done on my TV, which was limited to an additional transmission oil cooler. I don't exceed the axle weight ratings nor the GVWR so no enhancements were needed.

Have you actually weighed it loaded with the trailer hooked up and ready for travel to be sure? Or, are you just trusting Can Am to know more about your Toyota than Toyota does?

Seems odd to me that a 1/2 ton pickup truck normally does not have enough RAWR to carry a trailer as large as yours, but a minivan does?

[perryg114]

I can't get the link to work. It just gives a link to a pdf converter not the paper.

Perry

Originally Posted by mstephens

If anyone is interested in the SAE paper aforementioned, it can be read here for no charge: download/delphi__com pdf techpapers 2008 01 1228.pdf « download article pdf. There may be other sites too, but this is the one I found.

[perryg114]

Yep the driver is usually the destabilizing force. When the conditions are such that the driver is perturbing a poorly damped system then bad things happen. Sway control is what keeps the system from becoming unstable when the driver and other forces perturb the system. When the trailer is swaying a lot slow down. I have found rutted highways are the most troublesome because the trailer is wider than the two vehicles and it wants to be in a different part of the rut than the tow vehicle.

Sway can happen even without a trailer. I lost control of my truck in the rain. The road was very slick with an oil film, there was nothing in the back of my truck, and one rear tire was overinflated since it had just been patched and I had not let some air out of it. I changed lanes and the truck started fish tailing to the point there it was yawing 180 degrees and my front bumper caved in the door of the truck next to me. I finally locked up the brakes and stopped the oscillations and almost ran off the mountain in the process. If the truck had a hand brake to pull the truck straight I could have gotten out of it. Steering into the skid made it worse because I was out of phase and was making it worse.

Perry

Originally Posted by barts

A damped oscillation in response to transient road effects is completely normal, and is NOT a cause for concern. The thing we're concerned about is uncontrolled growing oscillations. Most times, the driver is an important part of causing those oscillations, and if he would stop trying to "correct" things would die down again. However, the stability equations for trailers DO indication some conditions when uncontrollable sway can occur, and the following factors most exacerbate this:

1) insufficient tongue weight
2) grossly excessive speed
3) trailers loaded with high polar moment of inertia.

There are others, as others have commented.

- Bart

[idroba]

The best articles I have seen on trailer towing dynamics and sway are the ones by Colin Rivers pointed out in this thread by Rednax.

http://www.airforums.com/forums/f238...ics-88681.html

[GinMame]

Originally Posted by SteveH

I definately agree with that statement, and I'll stick my neck out and say any travel trailer will sway, if it's towed fast enough.

Additionally, I'll state that not all travel trailers tow the same, and what's more, not all Airstreams tow the same.

As an example, we had a 23' Airstream that we towed a lot, and NEVER had a swaying event. But, later had a 25' that was a bear to tow, wanted to sway all the time, and only stopped after I switched to a ProPride hitch. Interesting also this same trailer wore tires very rapidly, so I suspect that axle alignment contributed to the tendency to sway.

These statements are from my expereince towing trailers, not from an engineering viewpoint as I am not a mechanical engineer.

So is this something with all the longer Airstreams? I've seen a number of pictures on the net with 23' & small being towed by a 1/2 ton pickup and parked in the ditch next to the road because of what the drivers reported as sway. I had thought that the 25' and longer were perhaps more stable when being towed. The wife and I are considering a 25' or 27' to be towed by a 3/4 ton pickup and I am just curious about what I can expect.

Cheers,
Rion

[ROBERTSUNRUS]

Originally Posted by GinMame

So is this something with all the longer Airstreams? I've seen a number of pictures on the net with 23' & small being towed by a 1/2 ton pickup and parked in the ditch next to the road because of what the drivers reported as sway. I had thought that the 25' and longer were perhaps more stable when being towed. The wife and I are considering a 25' or 27' to be towed by a 3/4 ton pickup and I am just curious about what I can expect.

Cheers,
Rion

Hi, you can expect to have many-a-great-time with your trailer. The list is too long, but with driver ability, the truck and trailer combination that you mentioned, both vehicles maintained and loaded properly, and a proper hitch set-up you should be fine.

"My trailer is eight years old. It has been in 13 Western States and in three Provinces. Towed in all kinds of weather, in heat, cold, wind, rain, snow, and even ice. My Alaska trip alone was over 10,000 miles. And with all of this, my trailer has only swayed, violently out of control once; It was parked in my driveway during a 5.0 Earth Quake."

[Kosm1o]

Mr UKToad - what kind of gas mileage are you getting with the Sienna?

[SteveH]

Originally Posted by GinMame

So is this something with all the longer Airstreams? I've seen a number of pictures on the net with 23' & small being towed by a 1/2 ton pickup and parked in the ditch next to the road because of what the drivers reported as sway. I had thought that the 25' and longer were perhaps more stable when being towed. The wife and I are considering a 25' or 27' to be towed by a 3/4 ton pickup and I am just curious about what I can expect.

Cheers,
Rion

Rion, Sway is not a normal happening with an Airstream if everything is setup right. Since I had those troubles with the 25', I've owned two other trailers, a 28', and now a 31', and neither have had any sway issues.

And, as far as length goes, I once towed a friend's 34' when his truck broke down, and the 34 was far more stable than any other trailer I've ever towed. I suspect that is because of the three axles.

As ROBERTSUNRUS said, you won't have any troubles. Just get an expereinced Airstreamer to help you set up the hitch, and no most dealers are NOT good at setting up a hitch. They just want you out the door after they have collected the money.

[Inland RV Center, In]

Originally Posted by SteveH

Rion, Sway is not a normal happening with an Airstream if everything is setup right. Since I had those troubles with the 25', I've owned two other trailers, a 28', and now a 31', and neither have had any sway issues.

And, as far as length goes, I once towed a friend's 34' when his truck broke down, and the 34 was far more stable than any other trailer I've ever towed. I suspect that is because of the three axles.

As ROBERTSUNRUS said, you won't have any troubles. Just get an expereinced Airstreamer to help you set up the hitch, and no most dealers are NOT good at setting up a hitch. They just want you out the door after they have collected the money.

Sway can happen with any size Airtstream.

I settled a claim for the trailer, with a family that lost their mother and father
in a loss of control accident caused by a sway, that resulted in a roll over.

The tow vehicle was a 1/2 ton truck.

The trailer?

A 17 foot Caravel.

No load equalizing hitch, or sway control was in use.

Andy

[Inland RV Center, In]

Sway can very easily be caused by a mother nature gust of wind, and/or by a large passing or oncoming vehicle.

Wind speed tests were made in 1970, and filmed.

Andy

[perryg114]

Here is a link to a sway simulator that can be a useful tool in understanding sway. Sway can be initiated by anything, wind, the driver, a bump in the road etc. If you run the game/simulation you will see that as your speed increases the sway gets worse and takes longer to go away. At a certain speed anything can cause you to lose control. The higher the speed the closer you get the natural frequency of the system. You can slow down, change the way the trailer is loaded, or add damping or some combination of the three. Running at high speeds with no sway control and an improperly loaded trailer is trouble waiting to happen. Your trailer and tow vehicle are a mass spring system and there are certain combinations that are unstable. By unstable, I mean that you disturb the system and the oscillations get worse and you wreck. A stable system is one where the oscillations get smaller and damp out. You can tell when the system is on the edge. Just a little steering input will cause the trailer to sway. This means SLOW DOWN. Act like a sheep die like a sheep. Pay attention to how your trailer is behaving and you won't have problems. Learn to hitch properly and use sway control.

http://www.towingstabilitystudies.co...udies-game.php

Perry

[mstephens]

That's a nice simulation Perry. Thanks for that link.

[perryg114]

I stole the link from another post but I thought it was a useful tool.