Below are graphs of each kind of bushing (OE rubber, polyurethane & the Delrin/SST solid) showing the force required to actuate the shock over a range of linear speeds. Please see the notes that accompany each plot for further explanation.
To help demonstrate this deflection, below are links to some videos of a Penske adjustable shock that was run on a shock dyno with the stock rubber bushings and then the Delrin & stainless steel bushings. Just watch to see the difference.
PIN TOP SHOCK MOUNTS
This product is the first and only truly correct mount for "pin top" shocks. They are CNC billet machined DuPont Delrin and stainless steel, allowing your shocks to have correct damping without rubber bushings while allowing angular deflection of the shock as it goes through its motion with virtually zero side load on the shock. Unlike some others, this mount is spherical on the top and bottom so it works with stock leaf springs or coil-over shocks.
A solid shock mount, as opposed to rubber or urethane, is important so that your shock, especially if they’re adjustable, are the only things that are damping the motion of the car. Rubber and urethane are both compressible and as such under heavy load can deflect as the shock compresses or extends. When the rubber or urethane deflects it changes the overall damping rate of the shock system, usually in an unpredictable and unrepeatable way. This deflection allows your shocks to operate within a window of varying damping rates, rather than at the single anticipated damping rate. By removing this deflection your shock will operate at the rate you expect.