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Dirt bike suspension tuning by Mike Hobbs and Rick Johnson
Ρυθμίστε την αναρτηση σας (το περίφημο SAG)
Here's PART I of Too Tech's Suspension Tuning Tips.
Dialing in your bike's suspension: 7 easy steps.
The settings in this article are for a '97 YZ 250, GP Desert. Yours
may be different
STEP 1: Measure suspension "RACE SAG" (Most important
adjustment)
All measurements are made between the rear fender and the rear axle.
The first measurement is made with the bike on a center stand with
the rear wheel in the air.
The second measurement is made standing on the foot pegs with full
equipment. The difference between these two measurements must be
3-3/4" for Short track and Supercross, 3-7/8" Natural terrain
moto-cross, 4" Gran Prix and desert.
STEP 2: TUNE RACE SAG (The other "most important adjustment")
Adjust the forks to the standard height in the triple clamps before
starting any adjustments.
Increasing the preload on your rear spring will decrease the Race
sag.
This will raise the rear of your bike putting more weight on the
front wheel and reduce the front-end rake. This will always make the
bike turn sharper. However, if you tighten the spring too far it
will make the bike twitchy and promote headshake.
Decreasing the preload on the rear spring will increase the Race
sag. This will lower the rear of your bike, putting less weight on
the front wheel and causing it to ride like a "chopper". This will
reduce head shake, making the bike go straighter and be more secure
in high speed sections.
However, if you loosen the spring too far the bike will be harder to
turn.
To fine tune the spring preload (Race Sag), try tightening the rear
spring adjusting nut 1/2" turn at a time and mentally note how much
easier the front end will dive into a turn and hold the inside line.
Continue this spring tightening until the bike becomes twitchy and
unstable, or it feels like you're always pulling up on the
handlebars. Measure and record your Race Sag.
Then try loosening the rear preload 1/2 turn at a time and mentally
note how the rear end "Squats" down and traction increases as you
exit each turn. When you reach the point of excessive front-end lift
(wheelies) and loss of steering, or you begin to have trouble
holding a tight turn, the spring is too loose and you have too much
Race Sag.
Measure and compare these two extremes, then reach a compromise
between them that balances "stability" and "tight turning".
Tune the front-end ride height to match the rear end! If the Race
Sag compromise you determined above is close to the typical
measurements listed above, your fork height adjustment in the triple
clamps is probably about right. Raising the forks in the triple
clamps will lower the front end making the bike turn sharper but
will reduce high-speed stability. (Similar to increasing the rear
preload.)
Lowering the forks in the triple clamps will raise the front end
making the bike harder to turn, but will reduce high-speed
stability. (Similar to lowering the rear preload.)
NOTE: Once you have established the best overall ride height
front and rear, record these settings as your baseline. For added
stability on a Desert or Gran Prix track, I always push my forks
down about 1/8" to 1/4". For Moto-Cross I pull them back up to
improve turning. To further improve turning on a flat Supercross
style track, tighten the rear spring about 1 turn.
STEP 3: Break in the new suspension valves and oil
Leave the settings as received for at least 1/2 hour. Put the bike
on a center stand and release the accumulated air from the front
forks. Re-measure the rear shock sag to insure this critical
adjustment is still 4 inches. Ride once again concentrating on any
gross problems like suspension bottoming front or rear, definite
harshness.
STEP 4: Adjust compression damping for bottoming
Rear shock: Increasing your compression damping (the screw on
the shock reservoir), will slow down the compression stroke and
decrease rear end bottoming. Turn you compression adjuster "in"
(clockwise) to reduce bottoming. If you never bottom, try turning
your adjuster "out" (counter clockwise) to soften the compression
damping and use more travel.
Slight occasional bottoming is OK, but don't allow the bike to crash
down when bottoming.
Front Forks: Increase the compression damping (the screw at
the bottom of the forks) to slow the compression stroke and decrease
front end bottoming. Turn your compression adjuster "in" (clockwise)
to reduce bottoming. If you never bottom, try turning the adjuster
"out" to soften the compression damping and use more travel.
NOTE: Softer, screw "out", settings provide a plush mushy
feel which works well for cross country racers trying to go straight
and conserve energy.
Stiffer, clicker "in", settings hold the suspension up and out of
holes and provide more lift on jump take-offs. Additionally, body
English and throttle changes transfer directly into the dirt instead
of getting lost in a mush suspension.
STEP 5: Adjust compression damping front & rear
NOTE: Bring a small screwdriver with you and make adjustments
at your test track.
It is important to make all damping decisions with the suspension
hot and to immediately test the change.
Making damping decisions in the garage can lead to nasty surprises.
Letting your friends adjust your suspension is also a no - no.
If "bottoming" is noted at either end, the compression damping
should be adjusted "in" (clockwise) to reduce the compression
stroke. The front fork compression adjuster is the slotted screw at
the bottom of the fork. The rear compression adjuster is the screw
in the shock reservoir.
STEP 6: Adjust rebound damping front/rear. (Critical adjustment,
change slowly)
If either front or rear tends to kick up, (rebound), more than the
other after landing from a large jump, then more rebound damping is
needed at that end. Adjusting the rebound damper screw "in" or
"clockwise" causes more damping, which causes the suspension to
return more slowly to its original ride height.
If the front end bounces up after landing from a jump, turn the
slotted screw at the top of the forks "in" 1 click at a time to slow
their return. If the rear end kicks up after landings, or kicks up
side to side down high-speed straights, turn the slotted screw at
the bottom of the shock "in" 1 click at a time, to slow the rear
wheel return.
But remember, too slow a rebound setting causes "packing" because
the suspension does not have time to rebound to its original ride
height before you hit the next bump.
Rule Of Thumb: Run your rebound at both ends "faster" rather
than "slower". When the bike in on the verge of, but not quite,
kicking up after lands, the rebound is just about right.
STEP 7: Balance front end and rear end static rideheight.
If the rear end squats under acceleration along with too much
front-end lift and/or the bike doesn't want to turn sharp or easily
enough adjust your rear sage to 3 - 3/4 inches. If the front end
rides low, turns too sharp, and/or tends to Head Shake, try a
combination of lowering the front forks in the triple clamps and
adjust your rear sag to 4 - 1/4 inches.
PART II of Too Tech's Suspension Tuning Tips.
More 4 easy steps.
Let's pick up where we left in PART I: if "bottoming" is
noted at either end, the compression damping should be adjusted "in"
(clockwise) to reduce the compression stroke. Generally, the front
fork compression adjuster is the slotted screw at the bottom of the
fork. The rear compression adjuster is the screw in the shock
reservoir.
Remember this! Making damping decisions in the garage can lead to
nasty surprises.
Letting your friends adjust your suspension is also a no - no. Don't
forget this!
From PART I, the bike spring rates were dialed in and the rebound
and compression damping was adjusted.
Let's go further and fine tune the bike's suspension rebound and
compression settings.
STEP 1: Adjust rebound damping front/rear. (Critical adjustment,
change slowly)
If either front or rear tends to kick up, (rebound), more than the
other after landing from a large jump, then more rebound damping is
needed at that end. Adjusting the rebound damper screw "in" or
"clockwise" causes more damping. This causes the suspension to
return more slowly to its original ride height. If the front end
bounces up after landing from a jump, turn the slotted screw at the
top of the forks "in" 1 click at a time to slow their return. If the
rear end kicks up after landings, or kicks up side to side while
riding down high-speed straights, turn the slotted screw at the
bottom of the shock "in" 1 click at a time. This slows the rear
wheel return.
But remember, too slow a rebound setting causes "packing" because
the suspension does not have time to rebound to its original ride
height before you hit the next bump. Rule Of Thumb: Run your rebound
at both ends "faster" rather than "slower". When the bike in on the
verge of, but not quite, kicking up after lands, the rebound is set
just about right.
STEP 2: Adjust rebound damping and stability for jumping.
This adjustment is extremely important and must be fine tuned by the
rider very carefully. This adjustment determines how much time it
takes the rear wheel to return to its original position after
hitting a bump. In steps 1 & 2, (from PART I) you determined how
much compression travel will be used as you hit each bump. The
rebound damping must now be "tuned" to return the suspension to its
original ride height before contacting the next bump.
If the rebound is too fast, the bike will bounce up after landing
from a large jump, or kick sideways through rough sections. If the
rebound is too slow, the wheel will not have enough time to return
between bumps. This causes it to "pack down" becoming harsh and
bouncy. "Packing" can occur as soon as the second bump.
Experimentation is required to fine tune this adjustment. Stick a
small screwdriver in your boot so you can make track side
adjustments. Then ride and concentrate on the highest speed and most
aggressive portions of your test track.
Front Forks: Start by speeding up the front rebound by
turning the screw at the top of your forks "out" (counterclockwise)
2 clicks then ride your test track.
Continue turning the adjuster out until the bike kicks up after
landings or bounces up for no reason. Record this setting for
reference.
Then try turning the rebound "in" (clockwise) 2 clicks at a time
until the front end begins to get stiff or your arms seem to be
working harder.
These are signs of packing. Record setting. These settings define
your rebound working range.
Personally, I prefer to run my rebound on the fast side. "Fast fork
rebound will reduce headshake and arm pump."
Rear Shock: Start by speeding up the rear rebound by turning
the screw at the bottom of your shock "out" counterclockwise) 2
clicks then ride your test track.
Continue turning the adjuster out until the bike kicks up after
landings or kicks side to side. Record this setting for reference.
Then, try turning the rebound "in" (clockwise) 2 clicks at a time
until the rear end begins to pound and get stiff.
If may feel like you have a flat tire, the rear is riding low, or
like the rear is "dead". You will probably get tired faster.
These are signs of packing. Record the setting.
These settings define your rebound working range. I prefer to run my
rebound as fast as possible without it kicking up or sideways.
NOTE: "Faster rebound settings will help you clear double
jumps and ride aggressively." "Slower rebound settings conserve
energy in deep sand and desert whoops."
STEP 3: Balance front end and rear end static ride height.
If the rear end squats under acceleration along with too much
front-end lift, and/or the bike doesn't want to turn sharp or easily
enough: Adjust your rear sag to 3 - 3/4 inches. If the front end
rides low, turns too sharp, and/or tends to Head Shake, try a
combination of lowering the front forks in the triple clamps and
adjusting rear sag to 4 - 1/4 inches.
STEP 4: Balancing front and rear.
Regardless of personal preference on compression stiffness and
rebound speed, both ends must be balanced and work together.
Compression Balance: The front spring and compression
setting must coordinate with the rear spring and compression
setting. If the front forks are too soft and plow through a whoop,
but the rear end rides up over it, the bike will go into the "endo"
position. To cure this, you would try to stiffen the front to make
it ride up and over this bump to match the rear end. First, try a
combination of turning the fork compression adjuster screw in,
adding 1/4" fork oil, adding preload to the front fork springs, and
pulling the fork tubes down in the triple clamps. Also, try speeding
up the front rebound clicker "out" 1 or 2 clicks. This makes the
front end kick up after this bump. When you reach the limit on
making the front stiffer, you should try making the rear end softer.
Try a combination of turning the shock compression setting "out",
and reducing rear spring preload. Also try slowing the shock
rebound, clicker "in" 1 click, to make the rear stay down after the
bump. Reverse this logic if the fork is stiffer than the rear.
Rebound Balance: The front and rear rebound settings must
coordinate to throw the bike up level on jump take-offs. (First the
compression balance adjustments above must be made.)
If the front end continuously jumps higher than the rear, try a
combination of slowing the fork rebound, clicker "in" 1 click, and
speeding the rear rebound, clicker "out" 1 click.
GENERAL NOTE: Heavier riders, very aggressive riders, and
desert riders will usually prefer heavier spring rates.
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