not sure if you will be able to understand my jibberish, but when a leaf spring is under more load than usual (bump) it flatens out right, well this also makes the eye to eye measurement more than the static 64in. and when the truck is under less load than usual (droop) the eye to eye measurement is slightly less.
I thought the spring measured 64" along the arc so would be less than 64" at static ? [question...not statement]
and when the shackle (on a standard 180 degree flip) is moving from droop to bump or whatever, it is moving in a arch. so when the leaf setup is at full droop, the shackle flops down, and allows that eye to eye measurement to decrease. while the opposite is true for bump. the shackle moves more vertical. which allows the leaf to have a longer eye to eye measurement.
make sense?
yes
the usual rule of thumb on a shackle flip is to have the shackle 90 degree's from the angle of the main leaf near the leaf eye (that joins with the shackle). this helps keep the shackle angle in the "sweet spot" for best droop and bump!
I agree