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Dual
Suspension
It is imperative that dual suspension bikes are set up
correctly, both front and rear suspension units require balanced tuning if
bump absorption, traction and pedal efficiency are to perform in
harmony.
Follow manufacturers guidelines for your make/model of
fork or shock, set up accordingly keeping in mind that fine tuning will be
necessary, and it pays to be cautious on your first ride as suspension
settings at slow speed are not necassarily going to effect high speed test
runs. e.g. you over the bars due to too fast rebound :-(
Consider distribution of body weight when on the bike,
weight transfer as you hover over the bike when dealing with trail
obstacles, or your position on the bike when cornering, and take note
of how weight transfer, going up or down trails effects the
suspension.
Propedal, SPV etc is not designed to
inhibit the "trampoline" effect caused by cycling using your body mass to
propel you forward, when seated sit still and use your leg muscles when
riding dual suspension bikes, find a smooth pedalling style that promotes
a full circle of each crank stroke, if you need to pedal up to speed as in
a sprint situation, try rocking the bike side to side rather than throwing
your body weight into each pedal stroke.
Aggressive riding styles will always
torture test suspension design, most Pro’s are efficient when it concerns
forward motion on the bike, leaving bump absorption and traction the
ultimatum.
Rely on your suspension to absorb bumps and
reduce rider fatigue, make your actions smooth but deliberate and be
patient, it takes a few months for the body to slowly adjust to the
effects of springs at each end of your bike, in time you will
become more efficient on a dual sprung rig.
Consider fork and rear shock break in periods, most rear
suspension units show little performance change during run in, where as
some front suspension units will improve noticeably after time, and often
a re-tune is necessary.
If you expect high performance from your suspension ( and
you should ) have a regular inspection and service routine, preventative
maintenance avoids costly failures.
Suspension Set Up
 1. If your rear shock has a
Schrader valve for the IFP ( internal floating piston ) set this to a
minimum pressure of 80 psi, or use the shock manufacturers guide lines for
the correct pressure for your body weight, you can fine tune those
settings later. If your fork has SPV set the recommended
pressures for your body weight.
See
- Curnutt XTD * Fox Boost Valve *
Manitou SPV
Note: Sufficient pressure is
required at all times in SPV front suspension units and all
rear shocks, to maintain correct operation - regardless of riders personal
set up.
Caution ! If your rear shock does not
have a Schrader valve do not attempt to adjust pressure.
2. Start with the correct spring rate - Your bike settles into approximately 20 -
30% of its travel with you on it.
Air sprung forks and shocks require sufficient pressure (
introduced by the bike rider ) for correct operation, air pressure is
specific to rider weight and style, and the amount of pressure is relevant
to the amount of sag.
Mechanical springs such as steel coils require replacing
if the spring rate is not correct e.g. too much or too little
sag.
See - rear coil spring rate * fork
coil spring rates *
air shock pressures * air fork pressures
Spring Rate
Spring rate is described by force, in pounds or kilograms,
needed to compress the spring one inch or centimetre.
3. Set the sag according to your weight and
riding style - your bike settles into
approximately a third of its travel with you on it, Downhill bikes
should have suspension sag set on a gradient.
See
- fork sag * rear
shock sag
Sag
This term refers to number of millimetres that the forks
or shock sag with the rider on the bike ( in full riding gear )This is
essential to correct suspension tuning but is often overlooked or
adjusted incorrectly.
4. If the fork or shock has air assist platforms & bottom
out.
See
- Curnutt XTD * Fox Boost Valve *
Manitou SPV
Note: Sufficient pressure is
required at all times in SPV front suspension units, and all
rear shocks, to maintain correct operation - regardless of riders personal
set up.
Set the correct pressure according to the manufacturers
guidelines, Rock Shox Motion Control & Mission
Control damping platform utilizes internal pressure and requires
( external ) manual adjustment only. ( Rock
Shox air springs require air pressure adjustment via Schrader valves
)
5. Adjust the rebound dial on both fork & rear
shocks so that the suspension is just noticeably slower than full fast,
this is achieved with you on the bike. You can fine tune rebound once on
the trail.
( Rebound adjustment knobs are normally red in colour
with the exception of Manitou forks & shocks )
Rebound Damping
The damping circuit that effects the stored energy release
of the compressed spring in order to reduce the return speed of the damper
shaft.
Caution is advised, apart
from the performance effects of damper adjustments, rebound speed of
the rear damper, if not set up correctly could cause serious injury due to
too fast a rebound, the speed of a returning spring after being compressed
is such that it could catapult the bike rider over the bars....take it
easy!
A few rear shock designs incorporate adjustable rebound
beginning stroke ( Rock Shox Vivid, Cane Creek Double Barrel ) or are
designed in such a way that the damper shaft slows considerably on the
return stroke ( Curnutt )
6. If your fork or shock has compression adjustment, leave it on
the softest, or fastest setting for now, again, compression can be fined
tuned once on the trail.
( Compression adjustment knobs are normally blue in colour with
the exception of Manitou forks & shocks )
Compression
Damping
The damping circuit that absorbs the energy of compression
forces on the damper.
High Speed Compression
Damping
High Speed Compression damping is the damping
circuit in the shock absorber or suspension fork that is tuned to provide
suspension travel control at high speed over square edged bumps. Too low
of HSC damping will cause excessive bottoming out in rough terrain. Too
high of HSC damping will minimize suspension travel in rough terrain and
cause loss of traction.
Low Speed Compression
Damping
Low Speed Compression damping is the damping circuit in
the shock absorber or suspension fork that is tuned to provide suspension
travel control at low damper speed conditions. Too low of LSC damping will
cause the excessive travel use, brake dive and wallowing of the bike on
small bump terrain. Too high of LSC damping will cause loss of traction on
small bump terrain.
note: that both rebound and
compression damping will change with an increase in bike speed,
and/or various types of impacts.
7. If your rear
shock has externally adjusable propedal adjust this to its softest
setting - you can adjust pedal efficiency once suspension/bump
absorption is tuned.
see propedal
Suspension feel at both
ends should be similar, taking weight bias ( 40/60%) into consideration,
both fork and shock should absorb bumps and track in the same manner. If
the rear shock is set up too firm it will force the suspension fork
to work harder as weight transfer will shift towards the softer end of the
bike first. This causes all sorts of unwanted situations including changes
to geometry, which you will notice along with unbalanced suspension
control. With DH bikes consider operating the suspension fork slightly
firmer than recommendations.
If the bike is primarily for
descents then weight transfer is always going to effect the front end, and
of course the weight bias is no longer 40/60%, its something to consider
but not necessarily correct......until you put it into practise that
is.
Hard Tails
Where hard tails are concerned you have only the
suspension fork to set up, apparently your legs are suitable suspension
for the rear but I disagree with that ( common ) belief, your legs are
still the same on a dual suspension bike but the shock absorbers do a far
better job, not too mention I’ve never noticed the extra travel that our
legs are supposed to allow us when riding dual suspension. I agree we have
give in our limbs but its not suspension and the legs are not connected to
the wheels, the springs and dampers are.
Hard tails are relatively simple to set up, and even a
feeble attempt at set up can go unnoticed, but add just a bit more effort
into correct tuning and your ride will improve by 50%, follow the fork
manufactures guide lines and most often the end result is correct ( with
the exception of a few Marzocchi 66 ATA forks :-)
From personal experience I run my
hard tail forks slightly firmer than recommendations, my belief being that
as the fork cycles through its travel it pivots off the back axel, much
like a door hinge. Geometry changes are more severe as there’s nothing in
the rear end to squat....a hard tail will sag but only at one
end.
Cock pit set up becomes more
important on a HT too, although having said this I don’t expect any of you
reading this to go tearing off out to your 'flavour of the month hard
tail' and start confusing yourselves with assumptions, you have most
likely just spent months adapting to your current set up, if its working
fine then leave it alone.
Go out and ride, tune your senses to what the bikes suspension is
doing, sometimes you feel the bike isnt handling quite right, for
example, it may be hard to tell whether the problem is too little rebound
damping or too much compression damping. Sometimes the difference in
"feel" is subtle.
Some of the distictions are minute, if the damping doesnt
feel quite right, make your best guess as to what might help, then try it.
If handling doesnt improve then make another change in the opposite
direction. Keep experimenting like this untill the ride feels
best.
It is common practise for the bike rider to "test" shock
absorber damping by pushing down on the saddle or bars to observe shock
response, this test is useful but very limited. This test only involves
low speed damping and tells you nothing about shock response at medium or
high shaft speeds.
Low-speed vs. high-speed
damping
The terms 'low-speed' and 'high-speed' are tossed around
rather liberally when it comes to discussions on suspension dampers, but
it should be noted that those descriptors are in reference to the speed of
the damper shaft, not the rider's speed. In this sense, it is often the
shape of the impact itself that determines whether an input force can be
categorized at low-speed or high-speed, rather than its size.
If you were to hit a curb head-on at 20km/h, the curb (or
any square-edged impact, for that matter) would produce a relatively
high-speed compression force since the fork has to absorb the impact over
a much shorter distance. In comparison, a mound of dirt ( same
height as the curb at 20km/h ) would be classified as a relatively
low-speed impact since the fork has more time to react, and hence produces
a slower damper shaft velocity. Longer travel forks tend to see more
inhospitable terrain, higher speeds, and more aggressive use, and
therefore are more likely to encounter higher damper shaft velocities than
purely XC forks.
Once you determine whether a particular input force is
low-speed or high-speed, it becomes much easier to adjust the compression
damper to filter them out accordingly. Brake dive, for example, is a
low-speed event: if there's too much of it, simply increase the low-speed
compression damping to resist the movement. If a section of washboard or
ripples feels uncharacteristically harsh (also known as 'spiking'), the
compression damper likely isn't able to displace enough oil volume at high
shaft velocities..... decrease the high-speed compression damping to allow
more oil flow at high shaft speeds.
For many purpose-built forks, a wide range of low-speed
and high-speed adjustments may not be needed. However, in the case of
long-travel single crown forks, just about anything is possible so a
suitably wide range of adjustment is critical for maintaining good
performance across the full spectrum of riding conditions.
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