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HOW TO CORRECTLY PRESSURIZE YOUR SHOCK
To get the correct pressure in your shock it is important
to follow some guide lines. Thread the pump’s connector onto the Schrader
valve on the shock. Pump to the desired pressure. Quickly unthread the
connector from the Schrader valve until the connector breaks free. The
pressure you have in your shock is the one you pumped to. At this point do
not re-attach the pump to check your setting, as it will be inaccurate.
This is due to some of the shock’s air rushing into the pump’s hose,
making the reading wildly incorrect.
COMPRESSION DAMPING AND BOTTOM OUT RESISTANCE -
ITD
Compression Damping is your shock’s ability to absorb the
bumps and obstacles found on your trail ride, and is mostly set at the
factory to your specs. Optimum compression damping includes your shock
being able to use all of its travel (8”-9”) over the entire range of
obstacles and terrain found on a typical ride. Once you have broken-in
your bicycle, it is normal for your Curnutt to bottom once in a while
during a ride - this will not damage your shock. However, the repeated
bottoming of your shock during a ride is indicative of too little air
pressure, and will eventually damage the shock’s seal head and lead to
other maladies, such as the coil-binding of your spring and the
transmission of unwanted energies through your frame, increasing the
likelihood of stress cracks. Therefore, it is very important to maintain
the optimum air pressure inside your shock before each and every ride.
Controlling bottoming of your ITD rear suspension is
achieved by air pressure in your shock. Too little air pressure and your
shock will bottom too easily. Too much air pressure and your rear
suspension will not bottom, but it can become harsh and stiff. This is
because, as well as controlling resistance to bottoming (the last
one-fourth of your shock’s travel), air pressure can also affect damping
in the first three-fourths of the shock’s travel,
effectively reducing small bump compliance if used too
much. That is, as you increase your air pressure to control bottoming,
this will stiffen the shock over the entire stroke, to some degree.
The point is… there are diminishing
returns when you increase air pressure to control bottoming, and these
returns result in shock stiffness. The best air pressure is the least
amount of pressure that will yield consistent bottoming resistance. Foes
recommends an initial setting of 65 psi, yet, your optimum setting for
each course or trail will avail itself only by riding and testing
different pressures over each terrain. NEVER GO UNDER THE 50
PSI!
REBOUND DAMPING - ITD/XTD
Rebound Damping is your shock’s ability and speed to get
back into its neutral position (sag setting) to accept another compression
or bump. Rebound damping is sometimes more correctly referred to as
rebound speed, and is controlled by the red knob found at the bottom of
your shock. The knob has an ‘S’ for Slow and an ‘F’ for Fast etched into
its face. The knob has a range of 5 full turns. Turning the knob all the
way ‘in’ – clockwise – is the slowest setting. From this ‘seated’
position, turning the knob ‘out’ – counter clockwise – 5 complete turns
will put you at the fastest rebound setting. Dialling your rebound to a
medium setting (2 ½ turns from seated) is a good way to start. From there
you can test different settings (1/2 turn at a time) over the same set of
obstacles.
Please note that, by design, Curnutt shocks rebound
progressively more slowly than standard shocks as they reach the end of
the rebound stroke (neutral sag setting). So, in the first ½ of the stroke
rebound will be faster, and in the last ½ of the stroke the rebound will
progressively slow. This feature – impossible for standard shocks – makes
your ride incredibly smooth and mostly free from pedalling interruptions.
Your appropriate rebound speed setting is, basically, dependent on two
variables: 1) the contour of the terrain, and 2) the speed with which you
ride over this terrain. The faster you ride over obstacles, the faster
your rebound will have to be. If you find your rear wheel bouncing, you
should slow your rebound, as your shock is expanding back to its neutral
position too fast. If you find that your rear suspension is too harsh, it
may be that your rear wheel is not rebounding back into its neutral
position fast enough for the next consecutive bump. This is called
‘packing’, and it forces the shock to remain in, or near, the compressed
or ‘packed’ position, un-ready for the next obstacle. The correct setting
is the ‘fastest’ one that allows the rear wheel to neither bounce, nor
pack. Your correct rebound setting will become obvious by testing various
settings over the same set of obstacles at nearly identical
speeds.
SPRING RATE - RIDER WEIGHT CHART
SPRING RIDER
WEIGHT - w/GEAR
250 130-145
300
146-160
350
161-175
400
176-190
450
191-210
500
211-230
BOTTOMING CONTROL - XTD
If you have the optional Curnutt XTD Shock, and once you
have your ‘optimum’ air pressure introduced, you may fine tune your
bottoming control using your XTD Ramping Dial (see picture on page 7).
This dial, essentially, reduces the volume of air in your shock,
effectively increasing the air pressure without using your pump. There are
four full turns of adjustment in your Ramping Adjustment Knob. When
re-adjusting, if there is any doubt about where the adjustment is set,
turn the knob clockwise until it stops (the seated position), and then
back it out as necessary to a maximum of four counter- clockwise
revolutions from seated.
DO NOT FORCE PAST 4 TURNS FROM
SEATED – THIS CAN FORCE THE COMPENSATOR ACTUATOR OUT OF ITS PRESSED-IN
POSITION, AND WILL REQUIRE A FOES TECHNICIAN TO PRESS IT BACK
IN.
The Ramping Adjustment Knob controls how stiff the shock
gets in the last 25% of the shock’s stroke. If at 65 psi you are happy
with the overall ride and sensitivity, but are never using all of the
travel, turn the Ramping Adjustment Knob counter-clockwise 1 full turn at
a time. This will allow the XTD to use more of the stroke. If at 65 psi
you are bottoming out, turn the Ramping Adjustment Knob clockwise 1 turn
at a time to stiffen the last part of the shock’s stroke. If you are
bottoming consistently when the Ramping Knob is seated, then introduce
more air pres- sure using your hand pump -10 psi at a time. Then, re-test.
You will have to do some air pressure-ramping adjustment tests to get a
feel for the optimum adjustments for both.
Higher air pressures will result in improved pedalling
efficiency (anti-bob). DON’T MISTAKE THIS FOR STICTION – it is supposed to
ignore small bump or rider input. This is what makes ‘anti-bob’ possible.
EXCEEDING 100 psi COULD RESULT IN
SHOCK FAILURE... DON’T DO IT!
Once you find an acceptable setting, never think this is
the final adjustment. Some courses/terrain have more pedalling sections
(higher pressure), some may have ‘chatter’ bumps (lower pressure), and
some may have excessive big ‘hits’ and landings (higher pressure and more
Ramp). Consider the Curnutt XTD Shock and adjustments a tool easily
customized to meet your course needs.
For the break-in period Foes recommends that you introduce
a low pressure, like 65 psi, to start. This is a good setting to break-in
your shock, and will allow you to get a good feel for what this pressure
will do over a variety of terrain. Your Curnutt will break-in properly in
about 10 hours of ‘normal’ riding. This means that, much like a new motor,
the contact-moving surfaces of the shock will ‘seat’ better if they are
allowed to move throughout their entire range or stroke, without
introducing them to undue or violent spikes of energy (as in landing from
jumps). Once your shock has broken-in, you will be able to much more
accurately feel what the shock is doing with more or less air pressure.
Adjusting air pressure during the break-in period will be confusing at
best. That being said, if your shock repeatedly bottoms over normal trail
terrain during break-in, it is appropriate to introduce more air pressure
to compensate – 5 psi at a time. Additionally, it should be remembered
that proper break-in requires the shock to cycle through its entire stroke
or travel. If it appears that your shock is not using its entire stroke
(too stiff) – over normal riding conditions - then reducing its air
pressure would be an appropriate measure – BUT NEVER GO UNDER 50 PSI!.
Once your Curnutt ITD is broken-in, controlling bottoming
with proper air pressure will be more accurately achieved. BREAK-IN PERIOD
Since your Curnutt was actually built, valved, sprung and pre-loaded
according to your specific rider weight, skill level and type of riding
you mostly enjoy, your Curnutt shock is about 95% tuned to you right from
the factory. The other 5% will be the Bottoming Control, and tuning your
Rebound Damping. This section will speak to Bottoming Control and the air
pressure that affects it. Rebound Damping will be addressed in a following
section. Your Curnutt ITD/XTD Shock is a true fluid–damped, coil-over
shock which, uniquely, uses air pressure to control bottoming (as well as
reduce fluid foaming). The range of air pressure needed inside your
Curnutt ITD/XTD is between 65 and 100 psi. This means, between these
minimum and maximum pressures lies an ideal setting for the control of
bottoming the rear suspension over a given terrain. As said initially,
your shock’s compression damping is mostly set for you at the factory,
yet, adjusting the air pressure will tune your shock’s ability to resist
bottoming – an important feature for the life and longevity of your
Curnutt Shock and Foes Frame.
Do not exceed 100 psi or run the shock with less
than 50 psi! |
