Penske Racing Shocks 7300 Series - Manual (Page 19)

Damping Adjustments
There are three major ways in which you can vary the damping produced by the main piston: Shim
stiffness, shim pre-load and the amount of bleed past the shims. These graphs help to visualize the
way in which the damping is affected by each of these changes.
Figure 1 shows the effect of changing the pre-load (on digressive or VDP pistons) or dish (on linear or
high flow pistons). Adding pre-load or dish will create a lot more low speed damping. In compression, it
will cause the tire to be loaded quicker and give a “snappy” feel. In rebound, it will help to tie the
vehicle down and let it take a set quicker.
Figure 2 shows the effect of increasing the stiffness of the shim stack. Increasing the thickness of
the shim stack (i.e., .004 to .010) stiffens the damping rate of the shock across the whole velocity
range. While the other two adjustments only affect the lower shaft speeds, the shim stiffness is
the best way to adjust damping at higher shaft speeds. The shims give the damping that chassis
dynamics require.
Figure 3 shows the effect of adding bleed to the piston or through the shaft. Bleed is simply a low
speed bypass for the shims and softens the shock at lower shaft speeds. This will improve the compli-
ance of the chassis to the ground under low amplitude movements which can improve grip. It will give
the driver a softer ride, but will let the chassis move more and take away support. (This is what the
driver feels)
Figure 1