trailer shackles

[foreverfaster]

building a trailer 10 long x 74" wide plus tongue.
what is the proper angle to have the shackles.
I was thinking bottom bolt slightly forward of the upper bolt. If i'm explaining it right.
the thought is, as weight is on the trailer, the spring would expand and the shackle will then be straight, then transition into rearward angle.

any opinions.

 

[95 shaw]

Think of shackle as a variable spring rate,

As angle gets closer to 90 degrees from line drawn through spring eyes, rate increases.

Either side of 90 degrees, the spring rate softens.

Also, think about long shackle vs short shackle.

 

[flattop1]

You could look at one similar in size and go off that .
As 95shaw said straight up and down is max load / spring rate .