ntsqd
Heretic Car Camper
I don't know that I do, I'm repeating what I *think* I was told some years ago by Eric @ Deaver Spring.
FWIW the longer shackle will travel in a smaller arc than a shorter shackle would. How this is significant is that the shackles need to be arranged so that they do not go over-center in their normal motion. Which means that the spring eye end of the shackle that has a motion component in the vertical plane. That effectively serves to reduce the spring rate.
Say 100 lbs-in spring sees 100 lbs load, but say the spring eye end of the shackle also moves up 1/4" If a centered spring pin then the suspension compressed 1.125" for that 100 lbs load. That makes it an 88.9 lbs-in effective spring rate at that point in the range of travel. As the suspension compresses more, the vertical motion component increases, so this effect is a non-linear falling spring rate which may or may not be offset by the spring's rising rate (if present).
The longer the shackle, the less of this phenomenon.
Probably splitting hairs, but worth mentioning for future ref.
FWIW the longer shackle will travel in a smaller arc than a shorter shackle would. How this is significant is that the shackles need to be arranged so that they do not go over-center in their normal motion. Which means that the spring eye end of the shackle that has a motion component in the vertical plane. That effectively serves to reduce the spring rate.
Say 100 lbs-in spring sees 100 lbs load, but say the spring eye end of the shackle also moves up 1/4" If a centered spring pin then the suspension compressed 1.125" for that 100 lbs load. That makes it an 88.9 lbs-in effective spring rate at that point in the range of travel. As the suspension compresses more, the vertical motion component increases, so this effect is a non-linear falling spring rate which may or may not be offset by the spring's rising rate (if present).
The longer the shackle, the less of this phenomenon.
Probably splitting hairs, but worth mentioning for future ref.
