[A/S] sway concepts summary

["bleipper" <k1cd@xxxxxxxxxxx>]

For those hypothesizing or worrying about sway or trying to figure out
how it might affect them, here is a summary of concepts that might be
of some use.

1) sway is not an oscillation in the classical physics sense. That
would require a return to center force. For example, if you parked
your rig with the tow vehicle and trailer at an angle to each other
on, say, slick ice, this means that the rig would tend to straighten
itself out all by itself. There is no 'return to straight' force to do
this so there is no classical physics (2nd order PDE type F=MA)
oscillation. (this has significant implications in the management of
sway events)

2) sway is not normally something that just happens unless there is an
emergency maneuver or other significant disturbance. Sway instability
can be felt and noticed by any good driver as a problem when it is
still just a minor nuisance. 

3) sway is an indicator of some deficiency in the rig. It can most
often be minimized by proper loading, good tires properly inflated,
using an appropriate suspension, and other methods.

4) a trailer braking system should allow panic stops without
aggravating or causing sway. If adjusted right, the trailer braking
system will stop the trailer at the same rate the tow vehicle is
braking or just a bit more aggresively. 

5) catastrophic sway is usually caused by some unexpected significant
event such as a severe crosswind (bow waves or zephyrs) or avoidance
maneuver that is improperly handled.

6) there are three common means to minimize sway problems. The first
is proper loading and configuration (see #3). The second is damping
(Reese DC or friction bar or Equal-i-zer). The third is by moving the
pivot point forward (Pullrite or HA or short overhang in tow vehicle).

7) sway is an inherent problem in automotive design and can create
problems in any vehicle depending upon conditions and events.

The fact that moving the hitch point forward is such a driver comfort
when coupled with the fact that sway is not an oscillation in the
classical physics sense implies that much of the problem with sway has
to deal with how the driver reacts to what sway causing events do to
the tow vehicle. This means that training and preparation are (as
always) critical components of safe driving. Some suggestions:

=> select, configure, equip, and maintain your rig for safety and good
handling.

=> avoid hasty maneuvers, especially when slowing or stopping or going
downhill.

=> stay off the road when conditions are poor (e.g. high winds) or the
road is not in good condition (e.g. snow and ice)

=> if you get hit with something, don't panic and don't over-react.
put your efforts to just staying in lane as much as possible rather
than in trying to maintain absolute straightness. know how to use the
trailer brake override in order to help straighten the rig back out
and slow down to gain control.

Also - don't take the discussion about catastrophy out of context and
get paranoid about driving trailers. These problems with sway in the
motorhome crowd usually involve shocks and steering dampers and such
rather than hitches but the odds of a catastrophic event are
equivalently small. So don't exagerate the risk. Drive safe, drive
confident (but not overconfident!). 

-- 
Bryan