[A/S] Re: [AS} dura torque

["Richard P. Kenan" <as5368@xxxxxxxxxxxxxx>]

> although really we should defer to Dick Kenan, our resident PHD 
Physicist.

Not really.  A Ph.D. is a research degree, and probably does not make 
one any more qualified for practical matters than a BS or other 
degree or no degree; an ME structural engineer would be my choice to 
analyze the statics of a hitch.
> 
> But here goes; it's as simple as this: the bars, when tensioned, 
create (1) a
> downward force on the A-frame members of the *trailer*; and (2) a 
lifting
> force on the *tow vehicle* hitch which is transmitted to the ball.  
The two
> forces meet and oppose each other precisely at the ball.  The 
increased stress
> on the ball is compressive, not shear or tensile, so my guess is 
that there is
> little concern for shortened life of the stem.  It just means you 
*really*
> need to keep the ball greased, which you ought to do anyway.

     I agree with this.  My view of the Reese hitch on my 1972 Safari 
is that it's like a spring toggle that wants to bend the rig at the 
ball and stand it on the trailer tires and the front tires of the tow 
vehicle.  Of course, that doesn't actually happen, but some of the 
tongue load is taken from the hitch platform and re-distributed to the 
trailer and tow-vehicle front tires.  The net result on the ball is an 
increase in compressive force, which is of little or no consequence.
     It is the loading on the hitch platform (receiver) that we should 
be worrying about.  It is subjected to a torque from the spring bars, 
but the carryied load is not increased; it may be decreased.  If the 
"load" on the ball were increased by 600# (the example offered 
earlier), we'd really be in trouble, as the load-carrying capacity of 
our hitches would be exceeded (it's typically 1000#; 12% or my 5000# 
loaded Safari would be another 600#).
     In short, the load distributing bars do little or nothing serious 
to the hitch ball or to the platform itself.  Of course, you should 
check the tightness of the ball, the torque on the hitch platform 
bolts, and look for cracks in the platform on a regular basis.  Use 
common sense, and all will be well.

- Dick
(5368)