Zombies dont care about shock fluid or spring type.

 

There's a reason for that.....

The extra weight flattens out the rear leaf spring some, and that changes the angle of the shackle.....usually from vertical to some angle below 45 deg away from vertical.....

This shackle angle change is a big part of the nicer ride.....that's why shackle relocation kits are so popular...they do the same thing without the extra weight.

There are other things that play in here, but a vertical shackle angle is a rough ride....