Penske Racing Shocks 7300 Series - Manual (Page 8)

A Guide To Damper Tuning
The ultimate purpose of a shock is to work together with the spring to keep the tire on the track. In compression (bump) to
help control the movement of the wheel and in rebound to help absorb the stored energy of the compressed spring.
Breaking down the shaft speeds to chassis movement can be done from the data taken from on board acquisition and/or
actual test sessions.
Where we find the biggest advantages with low speed adjusters is looking at the chassis in the plane of the four wheels in
relation to chassis movement in roll and pitch and how quickly weight is transferred to each corner in order to load the tire
sooner or later, depending on track conditions.
Usually in low grip situations allowing more bleed or less low speed damping is desirable to delay tire loading upon initial
roll.
In high grip conditions adding damping or restricting bleed will load the tire sooner upon initial roll increasing platform
stability.
In pitch situations on smooth surfaces under braking, increasing low speed damping or restricting bleed will help load the
tires for entry or mid corner. If the tire begins bouncing under braking usually an increase in high speed compression will
calm this down.
If the chassis feels like it is moving around too much between the plane of the wheels, increasing low speed damping or
restricting bleed, will overall, firm up the chassis and give it a crisp feel or a better sense of feel in the car. This is why most
drivers like this adjustment; as increasing low speed compression seems to give the driver better or quicker feedback from
the chassis, resulting in a higher confidence in the car.
A car with too much low speed damping will usually lack grip in change of directions, cannot put power down in slower
corners (wheel spin) and lack overall grip after initial turn in.
If traction is a problem coming off corners, reducing low speed damping or more bleed will help weight transfer at the rear
thus increasing traction.
The range of adjustments will have a relationship to high or low shaft velocity, depending on what main piston is
being used:
1) Linear Piston 1° - adjustment through range
2) Linear Piston 2° - greater change in low speed adjustment
3) Velocity Dependent Piston - adjustment through range with greater change in low speed
3) Digressive Piston - range primarily in low speed
Also 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 pressure 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.
Rebound adjustments are usually indicated by the driver asking for more stability. By increasing low speed damping,
stability will be enhanced; decreasing damping will allow more movement in the car, but will result in a little better tire wear.
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 car 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 compression 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 com-
pensate. 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 requires lower compression and higher
rebound. A softer spring requires higher compression and lower rebound.
FORCE FORCE
VELOCITY (SHAFT SPEED)
LOW SPEED HIGH SPEED
VELOCITY (SHAFT SPEED)
LOW SPEED HIGH SPEED
Large Amplitude Change
Small Amplitude Change Large Amplitude Change
Small Amplitude Change
LOW SPEED ADJUSTMENT EXAMPLE
(BLEED)
HIGH SPEED ADJUSTMENT EXAMPLE
(SHIM)