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Compression damping, the control of oil as suspension is
compressed through its travel, is traditionally handled by oil flowing
through a valve. The flow of that oil is usually governed by a stack of
thin shims, the fluctuation and deflection of which determine (in addition
to the size of the valve and the viscosity of the oil) the level of
damping in a given component. Thicker shims are harder to displace, and
tend to make for stiffer damping, thinner do the opposite.
Now, with the introduction of SPV (the genesis of
which can be found in Curnutt's work with three-foot travel desert race
trucks), that compression shim stack has been replaced with a pair of
overlapping aluminium cups. They fit into one another, and the resultant
atmospheric pressure trapped in between causes them to naturally push
apart, no springs, no shims. They are mounted on the compression side of
the damper valve. In static state, at the top of a suspension's travel,
the cups are held closed against the valve/piston by air pressure on the
oil in the damper, preventing oil flow. Depending on the level of air
pressure, it's possible to tune out low amplitude forces, like
pedal-induced bob, and create a breakaway threshold from which the shaft
begins moving through its travel. More air pressure on the oil will make
for a higher breakaway threshold, less air will make for a plusher initial
state, but with more resultant pedal bob.
1. High Speed Compression
The high speed compression is the traditional port and
needle design, the further you wind it in the more it restricts the flow
of oil through the compression port. This will slow the movement of the
downward stroke, wind it in for a firm ride,
out for to make it smoother over bumps.
2. Low Speed Compression
The low speed compression adjuster is a spring loaded
valve, tension is set by winding in or out, the spring causes resistance
in the compression circuit which aids to cancel out low frequency inputs
on the system, high pressure caused by impact loading will overcome the
spring acting in a blow by fashion......the low speed restriction will
reduce shock sensitivity over small bumps.
3. Bottom Out Resistance
Bottom out resistance is controlled by adjusting the
volume of air behind the floating piston, a shock needs to compensate for
the change in volume caused by the shaft entering the body, so too causing
the floating piston to travel  in the same fashion, by increasing pressure you also
increase the resistance of the shaft moving into the shock, air ramps up
quickly in a significantly reduced chamber and by the time the shock shaft
is three quarters through its compression stroke the air has multiplied
its initial pressure and bottom out pressure is obtained almost directly
afterwards.
4. Pre-Load
Spring pre-load is straight forward, spring collars are
for holding the spring in place, to wind more pre-load onto your coil
spring will not prevent bottom out but will eliminate usable travel
causing coil bind before the shock has completed its compression stroke,
if you are bottoming your shock increase the weight of your coil
spring.
5. Rebound
Rebound is a needle and port adjustment, the port shown at
5a, the needle runs the full length of the shaft 5b, housed in the centre
and adjusted through the rebound knob. Rebound slows the travel of the
shock shaft on its return and keeps the coil springs return movement
constant, no pogo.
6. Platform
Valve
All shocks compensate for the change in internal oil
volume caused when the shocks shaft moves in and out of the damper body (
displacement ) Since oil is relatively incompressible this is achieved by
an air chamber separated from the oil by a
floating piston ( some rear damper units utilize a rubber bladder ) The
Manitou and Fifth Element platform valve consists of two cups that fit
together to trap air, and is located behind the main damping piston
assembly, static, the valve is extended and the trapped air is
uncompressed, as the shaft moves into the damper body pressure increases
behind the floating piston ( air ) which also compresses the trapped air
inside the valve, in turn the outer ring of the valve moves under pressure
to close off the ports in the piston. When load is applied to the shock it
results in a difference in pressure between the front and rear damping
system. If the load is large enough, or sudden, it results in a pressure
spike in front of the piston which opens the valve. The more pressure
behind the floating piston the greater the resistance to the valve
opening, this aids to tune out low frequency inputs or low speed
compression forces such as those generated by pedalling. If there is no
pressure then the oil flow is restricted and there is no
damping.
BENEFITS OF SPV
TECHNOLOGY
1.Creates an efficient, firm platform for
pedaling that eliminates bobbing.
2.Manages ride, attitude and cornering
stability for greatly improved cornering, precision and speed.
Improves overall stability.
3.“Bump Dump” high velocity bump absorption
allows for greater oil flow, virtually eliminating
compression “spikes”.
4.Position-sensitive compression damping allows
for light initial damping and much heavier damping at
full compression.
5.Low-resonance threshold damping eliminates
much of the unwanted rider induced suspension motion.
Improved traction.
6.Externally adjustable damping that allows for
any rider to achieve the optimum set up for any bike, trail
conditions, rider weight in minutes with no
disassembly.
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