John S.

TheSnoMan wrote:
> John S. wrote:
> > Joe wrote:
> >
> >>I got really curious about this, and studied it for a long time (I'm an
> >>engineer). There was a good thread on this at woodall's RV forum. I have
> >>found no frank discussion of it by anybody who has broken it down into its
> >>component forces. It's hard to explain it using ASCII here. But my opinion
> >>is this:
> >>
> >>First off, it's clear that trailers can amplify their swaying until you
> >>crash. They don't do it all the time, but they can, and that's what
> >>interests me. They have no power of their own to bring to the table. The
> >>energy to do this comes from the tow vehicle. The trailer sways like a
> >>pendulum, sort of (I admit the forces holding a trailer back are not exactly
> >>like gravity in this analogy). A pendulum can be powered by a wide variety
> >>of motions. One of those motions is moving the pendulum's pivot point side
> >>to side. I think this is the motion we want.
> >>
> >>The forces on the trailer come from its tires and the tow vehicle. I was not
> >>interested in any other forces. "front loaded" trailers are trailers where
> >>the center of gravity is in front of the tires. When the tires are pushing
> >>the trailer sideways (during sway), the center of gravity is in front of
> >>that force. Since the side force doesn't go exactly through the center of
> >>gravity, the weight of the trailer pushes sideways on the tow vehicle.
> >>
> >>The inertia of the swaying trailer pushes the tow vehicle from side to side.
> >>The difference in loading is simply this. If the center of gravity is in
> >>front of the wheels, it pushed the tow vehicle one way, and if it's behind
> >>the wheels, it pushes the two vehicle the other way. One cancels the sway,
> >>and the other amplifies it.
> >>
> >
> >
> > I don't know if amplification is the correct term. Poor loading will
> > increase the sensitivity of a tow vehicle and trailer to winds and side
> > drafts from big trucks, but I don't understand how the forces could
> > actually be amplified. In my experience the side-to-side swaying is
> > amplified or increased by the driver trying to offset the swaying by
> > steering out of it.
> >
>
> This is true and just about all trailer sway issue start with tow
> vehicle stabilty issues. (tires and suspension not up to the extra load
> on them)
>

Yup...too big a trailer for the vehicle and an incorrest tow bar adds
up to the potential for big problems. Add to that the tendency for
inexperienced drivers to go too fast for conditions, especially on the
downhill and you have a recipe for a serious accident.

A family member was towing a large trailer with a Suburban and got
caught in a truck sidedraft when going too fast downhill on the way to
Wyoming. Rather than holding it steady he tried to compensate and
ended up flipping the trailer and spinning the truck round in traffic.
No injuries thanks to some fast thinking truckers.