Penske Racing Shocks 8900 Series - Manual (Page 10)

Guide to Damper Tuning
(cont’d)
Also, when making a big adjustment in high or low speed, the change will affect
the other in a small percentage. As an example, the high speed is set at (+4)
and the low speed at (-6). Now you want to set the low speed to (-2), this will
also increase a percentage of the high speed force figure. By dropping the high
speed from (+4) to (+3) would compensate for this low speed change so the
overall “damper curve” would remain intact. The more experience you have with
these the easier it will become to recognize what changes can occur in relation
to different valvings. The tendency of these circuits to “cross talk” is greatly re-
duced in our new digressive CD piston.
The rebound adjuster consists of a needle metering flow across a hole. This
metered flow bypasses the main piston/shim assembly until flow is choked off.
The shims then modulate the flow.
Depending on valving, there will be an affect on adjustment range. The softer
the valving (A - B), the less force range it will have. This is due to a lower pres-
sure required to blow the valves on the main piston. Obviously the heavier the
valving (C - E), the more effective the bleed becomes. On digressive pistons,
pre-load also affects the range of adjustment.
Also, the amount of rebound can have a great influence on weight transfer.
Less front rebound allows weight transfer to the rear under acceleration. Less
rebound in the rear allows for a greater amount of weight transfer to the front
under braking and turn in.
When a motorcycle is over damped in rebound it can pack down in a series of
bumps and a driver will recognize this as too stiff and usually will think it is com-
pression damping. Too much rebound can cause lack of grip on cornering.
When making a large spring change keep in mind where the rebound adjuster is
and do you have enough range to compensate. Sometimes a spring change will
bring a better balance to the damping values after the spring change. If the
spring/shock combination was balanced, the rule of thumb is a stiffer spring re-
quires lower compression and higher rebound. A softer spring requires higher
compression and lower rebound.
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