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

["Harvey Barlow" <harveybarlow@xxxxxxxxxxxxxxxx>]

Jim and Oliver have made some interesting observations which are certainly,
as Oliver stated, not in the mainstream of ideas related to trailer towing
but are interesting to discuss.

I use and recommend an equalizing hitch because the hitch reduces and almost
eliminates the dynamic up and down and side to side forces that occur
constantly while towing.  The equalizer hitch increases stability and safety
when towing heavy and long trailers.  However, "3/4" and "one ton" trucks
are designed and built to carry large loads in the bed or on the hitch in
continuous service.  A typical heavy-duty 3/4 or one ton truck carries
around 60% to 65% of its static unloaded weight on its front axle and 40% to
45% on the rear axle.  Light trucks with turbodiesel engines carry even a
higher percentage of vehicle gross weight on the front axle because of the
weight of the engine.  Until recently, when sophisticated ABS and electronic
brake proportioning valves were added, these trucks were tricky to drive on
wet or slippery roads because firm application of the service brakes would
cause the lightly loaded rear  wheels to slide and directional stability was
challenged.  Ditto driving traction in mud or on snow or ice covered roads.
Adding weight to the rear of light trucks has always increased traction and
control.  These trucks have a typical carrying capacity of 2000 to 3500
pounds.  When a full rated load is added to the bed or a heavy load to the
hitch, the gross weight of the truck can be distributed approximately
equally between front and rear axles.  (Very heavy loads on the hitch ball
will tend to unload the front wheels due to the fulcrum effect)  If
anything, adding the entire tongue weight of an Airstream to the hitch ball
merely increases and redistributes the truck's gross weight to approximately
55% front and 45% rear which improves stability.  Hauling a vintage A/S
behind a Dodge-Cummins as Jim Smith does hardly provides a noticeable load.
His truck alone weighs approximately 6500 # which exceeds his trailer
weight!  (My Dodge dually weighs 7660 # with fiberglass camper shell, small
tool box, spare A/S wheel and tire, my old female German Shepherd, and a
full tank of fuel)

The warning by an earlier writer about the use of overload springs may be
true if he was referring to adding aftermarket overload springs to a car,
SUV, or light-duty pickup (i.e. S-10, Ranger, Nissan, Toyota, etc.) but is
definitely not true and is misleading when applied to light trucks in
general.  Many 3/4 ton pickups and most if not all one ton and heavier-rated
trucks are designed and factory-equipped with overload springs.  (Some heavy
trucks and busses use air bags in-lieu of steel leaf springs.)  Those that
don't have add-on overload springs typically have progressive-rate rear leaf
springs.  With progressive-rate springs, as load increases and springs
depress, resistance to further depression increases.  Standard overload
springs are simply an extra spring leaf or leafs that do not perform any
work until the rear axle of the truck is heavily loaded and the standard
spring pack is depressed far enough for frame-mounted pads to make contact
with the overload springs.  This design allows the manufacturer to install
softer springs for unloaded driving but still provide adequate springs for
the rated load of the truck.  The rear axle assemblies, wheels, and tires of
a heavy-duty 3/4 or one ton truck are rated to support, on a full-time
basis, the gross axle and gross vehicle weight of the truck.  On the other
hand, adding aftermarket overload springs to a passenger car or light duty
pickup could allow overloading the frame, rear axle, wheels, tires, brakes,
and could cause a dangerous instability situation.

The use of overload shock absorbers or air shocks is risky at best unless
the vehicle was factory-equipped with such devices.  A shock absorber is
typically attached to the frame of the vehicle by a 3/8" diameter bolt at
top and bottom.  The mounting is intended to dampen rebound, not support the
weight of the vehicle.  If the shock is inflated to a point where the shock
is carrying static weight, the mounting bolt will bend or eventually fail
under the stress it was not designed to carry.

Dropping the approximately 1000 pound tongue weight of my 31' A/S on the
hitch ball of my Dodge dually barely depresses the rear springs.  I
occasionally tow across town without taking the time to hook up the
equalizer bars when moving the trailer to prepare for a trip and have
noticed no instability whatsoever.

Anyone who has traveled the interstates of our country in recent years has
probably noticed the thousands of Ford-Powerstroke and Dodge-Cummins trucks
hauling huge multi-horse trailers, triple-axle enclosed cargo trailers, huge
commercial loads in hot-shot service, or hauling two or three cars on
car-hauler trailers.  Many of these rigs use fifth-wheel or gooseneck type
hitches but many are traditional tongue-pull trailers.  Few of them use
equalizing hitches because the trucks are capable of hauling the load
without additional equipment.

The point made by the earlier writer about maintaining 60% of gross vehicle
weight of the puller on the rear axle is not incorrect in concept, but
oversimplifies the issues and is only applicable to cars or SUVs.  It is not
possible or practical when a truck is used as the puller.  To shift from 60%
on the front wheels to 60% of the weight on the rear wheels would require
addition of weight beyond the capacity of the truck.  While I agree that
adding aftermarket overload springs or overload shock absorbers to an
under-rated tow vehicle to allow it to carry additional loads is
questionable, most light trucks have overload springs as part of their
factory-installed equipment.  Light truck owners should not fear their
equipment is unsafe because the design of their trucks includes overload
springs.

What I have written is only my opinion based on what I believe to be
correct.  It is worth only what a reader pays for it.  As Jim succinctly
stated, ask any 10 trailer enthusiasts and you will get at least 10
differing answers.

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