Drop spindles relocate the "axle" centerline lower in reference to the upper and lower balljoints. If you install 2" lowering springs together with 2" drop spindles, you'll have somewhere in the neighborhood of 4" of drop. They can be used in conjunction with one another but it is not a must and usually its one or the other used.Anybody happen to know if I'll need what are known as "drop spindles" for UMI 2" springs? I keep seeing mention of them but I thought these just swapped in for stock.