Re: [A/S] tow hitches...FREAKED OUT!

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

Jay, Sway is not more important than load distribution. The tow vehicles
in common use (anything but a semi tractor) are NOT made to have a lot
of load out behind the back bumper. So when there is a load applied
there it squashes the back springs and lifts the front. Loosing down
pressure on the front tires leads to multiple problems. First the
headlights are in the sky even on low beam. Second there's far less tire
contact with the road and that leads to poor steering control and
terrible braking because the brakes are proportioned by cylinder size to
emphasize braking on the front. That brake emphasis on the front is to
the point that the fronts when loaded normally (no tail load) the front
wheels will lock up first in a really hard stop. While that takes away
steering control, it makes the vehicle stop straight. If the back brakes
lock up first then the greater grab of the front tires will make the
vehicle turn end for end. That gets a panic stop overly exciting. Having
the tail loaded down by a load at the bumper makes the front brakes lock
up prematurely.

A load distributing hitch has nothing to do with the load distribution
in the trailer (which needs to have about 10% on the tongue or the
trailer stability is drastically reduced, probably because the hitch
doesn't stick tight to the ball with lighter hitch loads) it has all to
do with transferring load from the back bumper to the front tires to
keep the tow vehicle nearly level, and to make the steering and front
brakes work more normally. Having positive steering by having full
weight on the front wheels will do a great deal to improve sway
characteristics but steering and braking are the primary reasons for a
load equalizing hitch.

Sway dampers do nothing for damping up and down motion. You can't
eliminate such motion and have the 6 or 8 wheels follow the surface of
the road. You can isolate the passenger compartment somewhat by the
suspension but not completely.

I don't think the simple passing of a truck causes all that much problem
with sway if the driver avoids over correction for the shock waves of
the truck. If the driver starts trying to correct dynamically all gets
lost quickly because the driver is too slow and ends up adding to the
sway instead of correcting for it.

By the way, its the law in Iowa that both load equalizing and anti sway
devices be used with the RV. I don't know how to do either on a 5th
wheel hookup. Since the load point of a 5th wheel trailer is over the
rear axle, the load doesn't have the lever arm for either load or sway
that the bumper region hitch has, but since that hitch is significantly
above the rear axle, seems to me that acceleration of the tow vehicle is
going to cause the tow vehicle nose to rise and braking when primarily
the tow vehicle is going to cause the tow vehicle nose to fall far more
than the tow vehicle would on its own. As there is a need for a load
equalizing hitch that doesn't exist. This is probably also the case for
semi tractors. Notice how their lights bob going down the road as the
trailer axles hit road surface changes (cracks and misaligned slabs)
that cause the trailer to jerk on the tractor.

Gerald J.