[A/S] By, Maurice Riggins

["jfiredog_1" <jfiredog1@xxxxxxx>]

 I find this in our club files:TRAILER SWAY
Many things can cause the trailer to want to develop a sway behind 
the tow vehicle, where it swings back and forth, side to side, about 
its pivot point with the tow vehicle. A fast moving, large vehicle 
passing to the side has a pressure wave that pushes the rear of 
trailer away, and it's followed by a vacuum behind it, which sucks 
the rear of the trailer back in. This can cause the trailer to try to 
start swaying. A strong crosswind can cause the trailer to try to 
start swaying. Hard braking can cause the trailer to try to start 
swaying and trying to pass the tow vehicle on either side, if the tow 
vehicle is braking harder than the trailer brakes, or if the trailer 
brakes have locked up and its tires are skidding, especially on slick 
surfaces. If the angle of swing gets too great during trailer tire 
skidding, jack knifing can occur. Getting too close to the edge of 
the road and trailer tires dropping off the edge and climbing back 
onto the road can cause the trailer to try to start swaying. A flat, 
or low pressure tire can cause the trailer to try to start swaying. 
Having insufficient or improperly distributed tongue weight can cause 
the trailer to try to start swaying. If the driver is quick enough, 
judicious use of the trailer brake manual control will often put 
sufficient drag on the trailer to pull it back in line behind the 
unbraked tow vehicle. But this doesn't work if the trailer brakes are 
locked and its tires are skidding.

The effect of the sway of a bumper pull trailer on its tow vehicle is 
much greater than that of a similar fifth-wheel trailer. With the 
latter, a swaying trailer would be pivoting close to or above the tow 
vehicle's rear axle, and it would have little ability to move the 
rear of the tow vehicle side to side. The bumper pull trailer's pivot 
point is located considerably behind the rear axle, which gives it 
mechanical advantage over the rear axle. A bumper pull trailer with 
the ball located 50" behind the rear axle on a 150" wheelbase tow 
vehicle would have 33% more effect than a similar fifth-wheel trying 
to slide the rear axle of the same tow vehicle. You can see the 
importance of providing resistance and control the trailer's attempt 
to start swaying with a bumper-pull trailer.

 


FRICTION SWAY CONTROL
Friction-based sway control is the oldest and least desirable 
technology. When wet, the friction is dramatically reduced, at a time 
when you may need the sway control most. When dry, they not only 
oppose the trailer trying to move the tow vehicle, but also oppose 
the tow vehicle trying to turn the trailer. They continue to resist 
turning even at large angles at low speeds, such as parking and 
backing, where sway control isn't needed and their resistance isn't 
desired. Separate friction sway control devices can be used with 
regular weight distributing hitches. Equal-I-Zer makes a weight 
distributing hitch that combines the function of equalizer spring bar 
and friction sway control, however it still has the disadvantages of 
friction sway control. See http://www.equalizerhitch.com for more 
info. Other hitches combine weight-distribution and sway control 
using better methods.
 


CAM TYPE SWAY CONTROL HITCHES
These type sway control hitches use a cam on each side to resist an 
angle developing between the tow vehicle and trailer. Like the 
friction control, they oppose the tow vehicle trying to turn the 
trailer as much as they do the trailer trying to sway the tow 
vehicle. However, unlike the friction sway controls, once the angle 
between the tow vehicle and trailer reaches a certain point, the cam 
over-centers and all resistance to turning goes away. At large 
turning angles, speeds are low, and sway isn't an issue. So the anti-
sway resistance isn't needed, or desired. Cam type sway control 
hitches do not resist turning at large angles at low speeds, binding 
up when turning tight corners and backing like a friction sway 
control would if not disconnected or loosened. One problem with them 
is that the cam arm angles up forward from the rear of the equalizer 
spring bar toward the front of the tongue and sometimes needs to be 
anchored right where the LP gas bottle holder is located. If the 
holder can be unbolted and relocated, or modified, this can be worked 
around. However, some bottle mounts are welded to the tongue A-frame 
and can't be moved. Sometimes there's no interference at all. Reese 
and Draw-Tite make these type hitches. See http://www.reeseprod.com 
and http://www.draw-tite.com for more information.