Re: [VACList] 2002 November 04 Monday

[James Clark <jec1938@xxxxxxxxxxxx>]

Hi out there....

We got into a heated discussion about this a while ago and a lot of people 
thought long and hard about what was going on with the truck and the trailer...

It is important to remember that the chains (flexible) can only pull 
down.... from none to the point where the spring bar fractures...

In the static mode..( standing still) the down pull of the chains is 
resisted by the ball and the axles of the trailer....ie the ball is pushing 
up and the ground is pushing up....but the lever arms are different... 
short to the ball and long to the wheels...

Net result is that increasing the pull of the chains always increases the 
weight on the ground and the weight on the ball....to keep all the forces 
in balance (nothing moving) the increase in the weight times the length of 
the lever arm (distance from wheels to point where the chain is pulling 
down has to equal the increase in the load on the ball times the short 
lever arm..(distance from the pull down point to the ball.)....one of the 
list members actually put a board across some bathroom scales and 
demonstrated that the weight goes up on both ends ( my 
recollection,)  there was a picture of the whole experiment in mid 
air...The fact that the hitch rises with increased pull on the chains is 
caused by the effect on the truck where weight is actually transferred to 
the front..It is a somewhat logical conclusion that if the hitch is coming 
up, the weight on the ball must be less, and if the bars were strong enough 
and the chains short enough the trailer would come off the ball 
altogether... obviously that is wrong...increasing the tension on the 
spring bars (shorter chain) always increases the weight on the wheels and 
the weight on the ball...

Looking at what is going on with the truck is more complex, but you can 
visualize that the weight of the truck with its load is balanced around 
some point... if you were to say that it is the middle of the truck, then 
the pulling up on the end of the spring bar would attempt to rotate the 
truck around the balance point... middle of the truck... and the stable 
condition dictates that the forces balance ... more push up from the ground 
on the front wheels and less on the back...(assuming the middle of the 
truck is between the front and back axle...

Why might all this make difference ???   If you were really reef up on a 
pair of 1200 # bars and your vintage hitch was marginal due to 30 years of 
wear on the ball socket, you might break it... or break it at the first 
bump... just something else to worry about..

If you still have any doubt about what is happening at the ball when the 
chains are made shorter, put a 6' plank on a pair of bathroom scales ( one 
at each end) and climb up on the plank about 1' from an end... The weight 
on each of the scales will go up...(the short end represents the ball and 
the long end the wheels)

I hope this gets the discussion started again...

Jim