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Old 03-25-2013, 10:01 PM   #15
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The idea behind the conventional sway (friction bar) is to increase the force required to move the trailer tongue in a horizontal direction. Thus preventing or at least reducing sway.
Which is logical for towing on straight roads.
But, when towing on curving mountain roads. The logic IMHO falls apart.
Look at it this way. On a straight road the friction type sway bar keeps the trailer straight behind you.
When on a curvy mountain road. You must steer hard enough to overcome the friction of the sway bar in order for the trailer to move out of the straight line to follow the curve of the road. Now the trailer has moved sideways to follow the curve of the road relative to the TV.
So now the sway bar wants to keep the trailer on that arc.
In order to straighten the rig out or go into the other half of a "S" curve. You have to steer hard enough to overcome the sway bar friction.
If there is enough friction in the sway bar mechanism to keep the trailer from moving sideways or swaying. There is enough friction to prevent the trailer moving back to a straight line behind you.
I believe any anti sway device places abnormal side wall pressure on the Trailer tires. Since their purpose is to keep the trailer from moving in an arc relative to the TV.
It would be akin to having a set of tires half way between your elbow and wrist. Then locking your elbow in a straight line. Now swing your arm in a horizontal arc from the shoulder. The tires are forced to slide side ways until the friction of the sway bar is overcome.
This force is the same when going into a curve or coming out of a curve.
The force required may be enough to affect the steering of the TV. Especially on gravel, wet or snow covered roads.
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Old 03-25-2013, 10:15 PM   #16
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If you're using the traditional anti-sway friction arm then advice to loosen it off in wet or icy conditions will be to do with the relative friction between the tires and the road on both sides of the friction arm (TV tires and trailer tires).

In order to overcome the forces of the friction arm when moving in anything other than a straight line, you're going to need the tires on both your TV and your trailer to be making good contact with the road. If there isn't sufficient contact, the friction arm forces won't be overcome and the TV, the trailer, or both, can be put into a situation where the tires prematurely lose contact with the road altogether and you're in a skid before you know it.

That said, I use two friction arms and have never loosened them at all in heavy rain and (thankfully) have never had a problem. Were the conditions obviously slick, like in snow or on ice, I may well get out and loosen the friction settings. I guess it's a bit like not using your cruise control in the wet.
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Old 03-25-2013, 10:21 PM   #17
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Torsion arm sway controls are always in use, without any adjustments, for sun, rain, or snow.

They always work.

Andy
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Old 03-26-2013, 07:06 PM   #18
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If you're using the traditional anti-sway friction arm then advice to loosen it off in wet or icy conditions will be to do with the relative friction between the tires and the road on both sides of the friction arm (TV tires and trailer tires).
It is correct that some friction sway bar manufacturers say to loosen the bar when towing in reduced-traction conditions.

The thing that puzzles me is -- why don't the Equal-i-zer and Dual Cam manufacturers give warnings about using theirt hitches in low-traction conditions? The EQ and DC generate several times as much resistance to straightening as does a friction sway bar. Therefore, if it is dangerous to tow in reduced-traction conditions with a friction bar, it should be several times more dangerous to tow with the EQ or DC.

It is correct that the bar will resist allowing the trailer to return to normal. However, I believe many people over estimate the magnitude of the effect.

The most commonly sold friction bar SC (FSC) is factory-set to produce a yaw-axis torque of about 500 lb-ft. A 25' TT will have a distance of about 18' from ball to axles. This means the FSC torque would equate to a lateral force of about 28# at the TT's tires. On dry pavement, if a 6,000# TT swings to an angle of 1 degree, its tires will develop a lateral restoring force of about 500#. The TT would need to have an "off tracking" angle of only about 0.06 degree to balance the FSC torque. On snow or ice, the angle might increase to about 0.2 degree.

For comparison, an angle of 0.06 degree would result in the rear end of a 25' TT being out of line by about 0.35".

Some people also over estimate the magnitude of added steering force required to overcome the torque generated by the FSC.

If the 500 lb-ft of torque is applied to a TV with a 120" (10') wheelbase, the front tires must generate a lateral force of 50# to counteract the torque. If the front axle is carrying 3000#, the tires must be turned about 0.15 degrees on dry pavement to generate a lateral force of 50#. Required increases in steering angle for other surface contitions might be: wet pavement = 0.2 degrees, packed snow and dry ice = 0.3 degrees, glare ice = 0.55 degrees.

So, yes, a friction bar SC can induce some "understeer". However, the added steering angle required to overcome the "understeer" is relatively small compared to the maximum tire slip-angle of 5-6 degrees at which the lateral force begins to plateau. The required added angle might be so small as to be undetected by the driver.

The "stiffening" effect of the FSC might be noticed when coming out of a curve. When not towing, the the camber and toe in of the TV's front suspension will tend to straighten the steering tires. When towing with a friction-based SC, the FSC torque will tend to oppose the camber and toe in effects and reduce the TV's self-straightening.

It might or might not be possible for the TV to self straighten. However, as long as the driver is aware that it might be necessary to provide some assistance in the straightening process, the FSC torque should not cause problems.

Ron
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Old 03-26-2013, 07:30 PM   #19
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I can tell you from personal experience that the anti sway bar which is bolted to the frame of my coach. Had a dramatic effect when driving on curvy mountain roads. So much in fact, that when I get on this type of road. I back the anti sway bar completely off.
Most of these roads have speed limits at or below 50mph. Because of the curves.
If your rig does not handle well at speeds below 50mph, sway bar or not. You have other problems.
I don't use the sway bar now that I have an Andersen system. Much better handling in the aforementioned conditions.
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Old 03-26-2013, 09:13 PM   #20
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It is correct that some friction sway bar manufacturers say to loosen the bar when towing in reduced-traction conditions.


Ron
Thanks Ron, what a great explanation! Without worrying too much about the math, I think it is a lot of people's experience that you don't have to loosen off the friction control, quite probably because as you say, not too much force is needed to counter the sway bar. I guess that manufacturers are covering their behinds with their advice.
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Old 03-27-2013, 06:07 AM   #21
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I can tell you from personal experience that the anti sway bar which is bolted to the frame of my coach. Had a dramatic effect when driving on curvy mountain roads. So much in fact, that when I get on this type of road. I back the anti sway bar completely off.
What effect were you noticing?
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Old 03-27-2013, 06:35 AM   #22
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Friction type anti-sway devices do not "know" where straight is. They simply dampen the swivel action of the the trailer frame relative to the hitch of the tow vehicle.

As mentioned above, the friction of tires on the ground must be greater than the friction of the anti-sway device or the wheels of the trailer, or perhaps even the TV, will slide and not allow the trailer to swing back behind the TV.

The trailer and TV will slide off the road, locked in the semi-jackknifed position by the friction of the anti-sway device.

On roads slick with water, ice, or snow there may not be enough traction to overcome the anti-sway device.

Again, this occurs because a friction device only resists movement, without regard to the position of the trailer or TV.

With cam type sway control the cams "know" when the trailer is straight behind the TV, and thus want to return to that position without the simple blind resistance of a friction type device.

They "know" when the trailer is straight behind because one adjusts them upon installation to be locked when the trailer and TV are in a straight line.

The cams only produce a "locking" type force when the trailer moves itself straight behind the TV.

My two cents.


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Old 03-27-2013, 10:03 AM   #23
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do I need a sway bar tv 1984 ford f 250 yes or no never used one.just tow with ball mount nothing else.
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Old 03-27-2013, 10:15 AM   #24
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do I need a sway bar tv 1984 ford f 250 yes or no never used one.just tow with ball mount nothing else.
You not only need a sway control, but you should also consider using a load equalizing hitch, for the sasfety of yourself, your passengers, and others that might be hurt when you lose control.

Safety, should never ever, be kicked to the curb, ignored, or decided, "NOT FOR ME".

Things happen, when we least expect it.

Being prepared, is the smartest thing a person can do, especially when towing an Airstream, since it offers little air resistance, therefore is much easier to lose control of it.

My background?

Settling over 1,000 (one thousand) loss of control accidents involving Airstream trailers, and establishing the cause in a little over 85 percent of the time.

Your setup, puts you in the head of the list as to "WHY".

Sorry, but you asked.

Apply safety as it should be. The innocent people that can be hurt, or worse, are dependent on your safety decisions, or not.

Your presently in the categorys of "WHEN" as well as "WHY".

Andy
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Old 03-27-2013, 02:23 PM   #25
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We always discussed it as being that the TT might get "stuck" when out-of-alignment with the TV on wet, cold roads. If it did, it would take some extra attention/ force/ input to correct the problem . . an uncomfortable time/distance problem (to go back to the 1960's).

Sort of like the brake controller problem of wet or broken surfaces . . something we didn't want to learn first-hand. Adjust, and go on albeit more slowly. As this TT type already exhibits best towing characteristics, slower speeds lessen the problem to almost nil, IMO. If worrisome, time for a long coffee break. After all, time is on the side of the well-prepared RV'er. Home is just a step away.
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Old 03-27-2013, 09:04 PM   #26
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So much of this (with the traditional bar type friction sway control) depends on the user determined adjustment on the nut at the back of the pressure apply plate. Back in the day when I used one, I kept the adjustment just barely over the pressure where I could get a third input when I purposely induced a sway on dry pavement. In other words, one motion out of straight and an immediate settling back on center....without a third "wag", if you will.

At this setting, I never loosened the handle on wet pavement and never felt any odd behavior. This setting usually required and additional 1/2 turn of the nut annually to compensate for wear of the friction material....at most.

I think if you really cranked that nut down excessively, you could...maybe...get odd behavior on wet roads.....maybe...IMO.
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Old 03-27-2013, 11:45 PM   #27
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Cha-ching ... listen to Andy; he is on the money as usual!
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