Re: [A/S] Re: Overload Devices On Tow Vehicles

["Harvey Barlow" <harveybarlow@xxxxxxxxxxxxxxxx>]

Nick,

I don't know the answer to your question regarding weight transfer to the
front axle.  Discussions of first order and second order levers have
apparently faded from my memory.

Weight distribution would seem to be controlled by rear overhang (distance
between rear axle and hitch ball) (fulcrum point to end of lever), truck
wheelbase length, and stiffness of front and rear springs of the puller.

With four links dropped on a set of 1000 bars and a measured 660 pounds of
tongue weight transferred, you have probably distributed approximately 3/4s
of the tongue weight to the puller.  Did you happen to weigh your trailer
tongue in a static, disconnected condition?  As you suggested, that amount
of tension on the equalizer bars can present dangerous forces to handle when
hooking up and unhooking.  Of course, numbers of links dropped is a relative
measurement because the count can depend more on the angle of the hitch head
from the vertical (angle +/- 90 degrees between hitch draw bar and hitch
ball) rather than actual weights but the actual measured weight you cited,
660#, indicates the bars are tensioned significantly.  I think the hitch
head is supposed to be installed with a five degree slant from the vertical.
When standing on the driver's side of the truck and observing the hitch
assembly, the hitch head should be rotated approximately 5 degrees
clockwise.  Another way of explaining is that the  bottom of the hitch head
should be slightly closer to the truck than the top of the hitch head.

I don't load my equalizer bars as hard as you.  I haven't measured the axle
and tongue weights before and after as you did, but my equalizer bars
probably distribute only about three or four hundred pounds of static weight
out of an estimated total 900 -1000#.  My truck likes the extra weight and I
prefer to leave them lightly loaded under static conditions.  The bars to
compensate for dynamic weight shifts such as when the truck and trailer
cross uneven road surfaces like dips in the road.  When the rear wheels of
the truck enter a dip in the road surface causing the rear of the truck and
front of the trailer to dip, the bars will absorb and distribute
considerable dynamic forces and dampen reactions.

I think it will be very difficult to achieve the 66% weight transfer
referred to in Airstream literature.  I may be wrong but I think Airstream's
research on this issue may date from the '50s and '60s when trailers were
lighter and more owners were pulling with cars and 1/2 ton pickups,
Suburbans and similar vehicles from other manufacturers.

There could be 100 reasons why the Argosy you saw was rolled over and none
of the reasons may be relative to your equipment.  What tow vehicle was
attached to the rolled over Argosy?  Three years ago my wife and I were
traveling in Wisconsin.  As we topped a grade and started down the other
side a traffic tie up at the bottom of the hill caught my attention.  We
slowed and navigated the hazard and took a quick glance as we passed.  It
was a late model 1/2 ton Chevy p/u towing about a 31' SOB trailer.  Both
were lying on their right side, still connected, and neither appeared to
have suffered damage beyond their right sides.  I didn't have time or
opportunity to observe the hitch equipment without obstructing traffic.  My
guess is the driver experienced trailer sway as he descended the grade and
lost control.  The sway could have resulted from underinflated (passenger
car type) tires, lack of sway control, application of truck brakes without
adequate trailer braking, driver inattention resulting in dropping the right
side tires off the edge of the pavement, or a myriad of other reasons
including driver fatigue or sudden driver illness.

From your description, you have a comfortable margin of truck capacity above
and beyond the minimum required for a 25' A/S.

It is an interesting discussion whether we learn anything new or not.

Harvey Barlow
Lubbock, TX
'01 Dodge-Cummins 3500
'84 Airstream Excella 31'
'66 Airstream Safari 22'