advantages/disadvantages of a spring under

[beater_k20]

looking into how i'm going to lift the rear of my truck to match the front SAS conversion. i currently have an ORD shackle flip, which is a definite. so obviously i'm staying leaf sprung. what are the pros and cons of both spring over and spring under suspensions, using a flipped shackle? FWIW, the truck will rarely if ever see trail use, primarily a street driver, with the occasional mud/sand play. i'm going to try to stay with ~6" of lift if at all possible.

why am i building an SAS truck for a driver you ask? nobody around here has one. the very same reason i'm entertaining the idea of a spring under suspension... its different.

 

[vortec]

on over-the-axle setups, like chevy fullsize trucks, the ubolts hold the sping pack together and help keep it centered (along with the center pin, etc.). but, with the leaves suspended underneath, like the much lighter s10, the ubolts have to bear the full weight of that corner of the vehicle, putting much more stress on the bolt. i have no numbers or stress tests to back this up, but it seems logical to me.

 

[1979jimmy350]

it probley would help prevent some axle warp, I can see the reason for thinking about doing this, most SFA conversions have a good amount of lift in them with stock springs, The s-10 SFA im working on has like 8 inches with stock springs, spring under would be a nie way to add a sfa and not get all the height

 

[beater_k20]

i'm going spring over in the front, the only way to get the 6" i want out of a spring under setup in the front would require a taller lift spring than the 4" i'm planning on using, and would that would compromise ride quality. not only that, but i would run into problems with clearance of things like the frame and the oil pan.

 

[ntsqd]

Spring under is prefered in the desert b/c of the arc that remains in the spring at full bump. Can get more travel out of the spring for the same height of vehicle w/o the danger of going flat in the main leaf. That is, assuming you've got or made the clearence for the axle to come up that far.
Crawlers seem to get away with reverse arching a spring in bump far better than desert trucks do. So this may not be a consideration for you.