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Credit: http://www.gpsuspension.com
General Info:
This guide serves to provide some generic information about how to set up
your street motorcycle correctly given the OEM suspension you have. Not
all motorcycles come with fully adjustable suspension, so you may not have
some of the components that we talk about on this page. If you are lacking
those components, in some cases they can be added to the bike with the
acquisition of components/products and the use of a CNC machine to make
the third party parts fit and work. If you have any questions in regard to
this, please email us with them! |
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STEERING HEAD BEARINGS:
Each motorcycle has a manufacturers torque setting for the head bearings.
Do not exceed this or you will increase the wear on the bearings. Prior to
every track day and every race event, these bearings must be checked.
Loose head bearings will cause suspension issues, and may result in a lot
of time going in the wrong direction. If you are street riding – check
them once a month (or more frequently depending on what kind of street
riding you do). It is also advisable to check that the top and bottom head
bearings are packed with the correct type of grease! |
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FRONT WHEEL ALIGNMENT:
This will create a lot of questions. The only time this becomes applicable
is when you remove the forks to have them worked on, or you change the
height of forks in the triple clamp to increase/decrease the speed at
which the bike steers. Any time this is done, you must check that both
forks are exactly the same distance above the upper triple clamp. Using a
precision instrument will help with this but a metric ruler will work. Eye
balling the height will not work and will inevitably leave the front wheel
out of alignment. |
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CHAIN ALIGNMENT/ADJUSTMENT:
Prior to starting any suspension adjustment you must check that the chain
alignment and adjustment are correct, because not all stampings on the
swing arm will align the rear wheel correctly. You will need a string line
that is about 12 feet long.
Find the center of the string line and wrap that section around the rear
wheel twice (then tape it in place) and run the left and right ends of the
lines forward to two steady objects that must be beyond the front wheel
(jack stands work well). Tie the string ends off on the jack stands and
ensure that the line is just touching each edge of the side wall of the
rear tire. You then measure from the same point on either side of the
front wheel to the string line on both sides and compare measurements.
Adjust the rear wheel until such time as the distances from both sides of
the front wheel to the string line are the same. You need to reposition
the line after each adjustment prior to taking another measurement!
Chain adjustment is also critical. If the chain is too tight the shock
will not be able to function correctly as the chain will limit the
movement of the swing arm. To ensure that the chain is correctly adjusted,
sit on the bike and check there is an inch of play (half inch on top and
half inch below the normal position of the chain at rest). When
retightening the axle nut, use a rag or wrench and roll it physically
between the rear sprocket and the chain prior to actually tightening the
axle nut. Once set to the right torque, roll the wheel forward and remove
the rag/wrench.
NOTE: Both these tasks should be done simultaneously and once the rear
wheel is aligned, precise movement of both adjustments will ensure that
the rear wheel always stays in precise alignment.
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TIRES (track days & racing):
It is critical that the wheels are balanced correctly when tires are
installed. There is no substitute for time in getting this done right. It
is also important to ensure that the weights used stay on the wheel. We
recommend that you use duct tape to cover the weights, which should ensure
that they stay in place!
A lot of tire wear is blamed on suspension but in a significant number of
cases, it is due to the incorrect pressure in the tire. There are easy
ways to check that the tire pressure is correct, so that if there is a
suspension issue, it can be accurately identified. This really only
applies to track days/racing where speeds are consistently very high both
in corners and straight lines. When taking tire pressures, you need to use
a quality gauge and have that gauge calibrated so you know how to read the
gauge accurately (some will be + or – 1lb).
All manufacturers have recommended tire pressures that put you in the
ballpark for the day. However, these pressures do not reflect track or
ambient temperatures that change throughout the day. At the start of the
day when the tires are truly cold, set the tire pressure to the
recommended amount. When you go return from the ride (track or street),
immediately take the tire pressure. You should have a gain of 6-7lbs. If
you do not have that, then the tire pressure must be adjusted again, but
you have to wait until the tire is cold again to do this right
You make get the symptoms of the tire sliding as it is overheating and
therefore losing traction, and you may also see the tire “hot tearing”
as the rubber shreds in a band around the tire.
You make get the symptoms of the tire sliding as it is not reaching the
correct operating temperature and therefore losing traction, and you may
also see the tire “cold tearing” as the rubber shreds in a band around
the tire.
If you have a gain of more than 7lbs, then you have too little air in the
tire. You will need to increase tire pressure by half to one pound, and
then go ride the bike again. Once you come back in, immediately take the
tire pressure again. Adjust as necessary until you reach the correct gain.
If you have a gain of less than 6lbs, you have too much air in the tire.
Conversely you will need to decrease tire pressure by a half to one pound
and then go ride the bike again. Once you come back in, immediately take
the tire pressure again. Adjust as necessary until you reach the correct
gain.
Throughout the day whether at a track day or a race event the track
temperature and the ambient temperature will change, so at regular
intervals throughout the day, you will need to check both cold and hot
tire pressures and adjust accordingly. |
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Setting Sag:
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Forks:
This is essentially the difference between your suspension being fully
extended and then naturally compressed with you sitting on the bike. You
need 3 people to do this right, and you also need to be in full gear
(but not including helmet) whether that be weather suit or race
leathers, boots, gloves, back protector etc. Make sure that you have
paper and pen on hand before you start! |
| In order to set the SAG
properly, the motorcycle cannot be on any front or rear stand as it must
have both wheels on the ground. To set the correct SAG on the forks, 2
people must hold a handlebar each and lift the front end in order to
extend the forks to their maximum length (figure 1). The person
measuring (metric tape measure is easier) must pick a point to measure
from (traditional forks should be measured from the base of the triple
clamp to the shoulder of the lower fork leg leg, and upside down forks
should be measured from the shoulder of the upper leg to the end of the
chrome tube where it enters the axle casting-figure 2). |
Figure 1
Figure 2 |
ONCE YOU HAVE PICKED THE POINTS
TO MEASURE FROM, DO NOT CHANGE !
Once the measurement for the forks at full extension has been recorded,
the rider is then required to sit on the bike. The rider climbs aboard
with feet on the ground until the person holding the bike upright at the
rear (using whatever is solid on the rear of the motorcycle) has a firm
grip. The person holding the bike then instructs the rider to put his
feet on the pegs and pull on the front brake lever to keep the bike
stationary. The person doing the measuring compresses the front
suspension by pulling down on the handlebars and then lets the bike
settle. The second measurement is taken using the same two points used
previously, and that number is recorded (figure 3). Simple math of the
larger minus the smaller number will provide you with the SAG number. |
Figure 3 |
| As a general principle, the
front fork SAG should be approximately 32 to 38mm. If there is more than
38mm, preload (if available, see figure 4) can be added. Turns clockwise
add preload. If all the available preload is added and the resulting
number is still greater than 38mm, then the fork springs are too soft
and need to be replaced. |
Figure 4 |
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| Shocks: |
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| To set the correct SAG on the
shock, 1 person must grab the sub frame and lift the rear end in order
to extend the shock to its maximum length. The person measuring (metric
tape measure is easier) must pick a point to measure from the center of
the rear axle to a point on the plastic (using contour lines, edges of
decals etc helps). This measurement must be as straight a vertical line
as possible! |
Figure 5
Figure 6 |
ONCE YOU HAVE PICKED THE POINTS
TO MEASURE FROM, DO NOT CHANGE !
Once the measurement for the shock at full extension has been recorded,
the rider is required to sit on the bike. The rider climbs aboard with
feet on the ground until the person holding the bike at the front (using
the upper triple clamp is easiest) has a firm grip. The person holding
the bike then instructs the rider to put his feet on the pegs and pull
on the front brake lever to keep the bike stationary. The person doing
the measuring compresses the rear suspension by pushing down on the rear
of the bike and then lets the bike settle. The second measurement is
taken using the same two points used previously, and that number is
recorded (figure 7). Simple math of the larger minus the smaller number
will provide you with the SAG number. |
Figure 7 |
| As a general principle, the rear SAG should
be approximately 28 to 32mm. If there is more than 32mm, preload (if
available) can be added using the appropriate tool(s). Those shocks with
ramp adjusters (eg: Yamaha R6 OEM shock) have limited preload, whereas
some with lock rings (Penske, Fox, Ohlins, WP) have a great deal more
adjustment. If you add more than 5 turns of preload on a rear spring the
spring will become harsh, so that is a good indication that you have the
wrong spring on the bike. |
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Note:
Also note that some springs are straight rate (have the same rate
throughout their range of movement), whereas others are progressive
rates (where the rate increases during the shock travel). It is better
to have a straight rate spring if you are considering racing. |
Tuning Forks
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Note:
Not all forks share the same adjustment characteristics, so please
take a look at the forks to see what adjustment you have. |
PRELOAD:
This adjustment is always found on the top of the forks. Clockwise
increases preload, counter clockwise decreases it. The adjusters are
usually integrated into the fork cap and are sometimes differentiated by
color. The preload adjuster may have adjustment lines machined into it
so that you can compare to check that they are even.
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| Preload is initially used when setting SAG. Preload can
be added if the rider experiences the forks “diving” under hard
braking. A more accurate way of assessing “dive” is to attach a thin
zip tie on the slider tube (make sure that it slides easily but is not
sloppy), or place an appropriately sized rubber “o” ring on the tube
that slides into the fork leg (using an O- ring will require one fork
being removed). |
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| The zip tie/O-ring will allow you to see how
much of the fork travel you are using. If the zip tie/O-ring is firmly
against the dust scraper or on an inverted fork, the axle casting, then
the fork is bottoming out. In that case you need to add more preload,
and then check the zip tie/O-ring again. If the zip tie/O-ring rests 5mm
prior to the dust scraper or axle casting, this indicates that you are
using almost all of the available travel. |
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REBOUND:
The rebound adjuster is usually located in the center of the preload
adjuster, and commonly requires a flat head screwdriver to be used for
making adjustments (there are exceptions like Ohlins which require Allen
wrenches). Sometimes the adjustments are measured in “clicks”, other
times in degrees of turn. Usually OEM settings are in the middle of
adjustment.
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First, turn the rebound adjusters all the way
in on both forks and write down how many turns/clicks there were. Then
take the rebound adjustment all the way out on both forks so that you
know how much total adjustment there is. With the adjustment all the way
out, hold the front brake on to lock the wheel and then push down
vigorously on the forks. As the forks begin their upstroke, let them
move naturally and observe the action of the fork. The stroke may come
back and then return into the downward motion once more, and may even
return again on the upstroke (do not let go of the front brake while
doing this!!).
Then adjust the rebound all the way in on both forks, repeat the pumping
action with the front brake fully engaged and observe the difference in
the range of motion –the forks will rise back up slowly. What you are
trying to achieve is the fork rising back almost to the top of the first
rebound stroke and staying there. You will need to work the adjusters so
that they are always the same on both legs until you have the rebound
action set correctly. |
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COMPRESSION:
These adjusters are usually found on the underside of the fork
or close to the brake calipers at the bottom of the fork facing the
rider. They commonly require a flat head screwdriver to be used for
making adjustments (there are exceptions like Ohlins which require Allen
wrenches). Sometimes the adjustments are measured in “clicks”, other
times in degrees of turn. Usually OEM settings are in the middle of
adjustment.
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First, turn the compression adjusters all the
way in on both forks and write down how many turns/clicks there were.
Then take the compression adjustment all the way out on both forks so
that you know how much total adjustment there is. With the adjustment
all the way out, hold the front brake on to lock the wheel and then push
down vigorously on the forks. You will be able to feel the way in which
the forks move through the downward/compression stroke, which will be
fairly easily (do not let go of the front brake while doing this!!).
Then adjust the compression all the way in on both forks, repeat the
pumping action with the front brake fully engaged and observe/feel the
difference in the range of motion –the forks will compress more
quickly and will not travel as far on the compression stroke up. What
you are trying to achieve is the compression stroke allowing the fork to
move without restricting the amount of travel in the fork, which causes
the sensation of “packing”. You will need to work the adjusters so
that they are always the same on both legs until you have the
compression action set correctly. |
| NOTE: compression adjustment is very subjective compared
to the rebound adjustment because the compression adjuster is usually
difficult to see. It takes a lot more "feel" when making
adjustments, which will take time to acquire. Also note that compression
can be used in tandem with preload adjustment to help prevent the forks
bottoming out. This is not the right solution to the bottoming issue,
but one that helps in the interim. |
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Shocks:
Not all shocks share the same adjustment characteristics, so please take
a look at the shock to see what adjustment you have. Also note the shock
can come with no oil/nitrogen reservoir (eg: SV 650), with a piggy back
oil/nitrogen reservoir built into the shock (eg: GSXR’s) or with a
remote reservoir (eg: Penske, Fox, Ohlins)
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PRELOAD:
In the SV650 and R6, it is a simple ramp adjuster that can be moved
using the OEM tool. Clockwise increases preload, anti clockwise
decreases it.
Other shocks may have two rings, the upper serving as a lock ring. The
lock ring can be moved using the OEM tool and the second ring can be
moved clockwise or counter clockwise to adjust preload accordingly.
Should the OEM tool be missing the trusty mallet and flat blade
screwdriver will work to loosen the lock ring and adjust the second
ring. Spray some lubricant onto the threads on the shock body to ease
movement (eg: WD 40).
Some shocks require the use of a specific tool (eg: Penske) that must be
present for any preload adjustments to take place.
Preload is initially used when setting SAG. Preload can be added if the
rider experiences front forks becoming light or getting a
“headshake” under hard acceleration. This causes the bike to squat
on the rear wheel and alters the weight distribution on the front and
rear wheels. Preload can be added to reduce this problem. |
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REBOUND:
The rebound adjuster is usually located in the center of the hasp
locating the shock to the rear suspension linkage, and commonly requires
a flat head screwdriver to be used for making adjustments. Sometimes the
adjustments are measured in “clicks”, other times in degrees of
turn. Usually OEM settings are in the middle of adjustment. Other
rebound adjusters are rings at the bottom of the shock shaft that turn
clockwise and anti-clockwise. Check to see what system you have! |
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| First, turn the rebound
adjusters all the way in and write down how many turns/clicks there
were. Then take the rebound adjustment all the way out so that you know
how much total adjustment there is. With the adjustment all the way out
and the bike comfortably balanced between your legs, compress the shock
vigorously by bouncing on the seat and applying all your weight to this
motion. As the shock begins the upstroke, let it move naturally and
observe the action. The rebound stroke may come back very quickly to
cause the shock to top out (maintain the balance of the bike while doing
this!!). |
| Adjust the rebound all the way
in, repeat the same action with the bike comfortably balanced between
your legs and observe the difference in the range of motion –the shock
will rise back up slowly. What you are trying to achieve is the shock
rising back to the top of the first rebound stroke naturally, not
quickly or not too slow (or the rear end will “pack” in causing
removal of weight from the front wheel) and staying there. You will need
to work the adjuster until you have the rebound action set correctly. |
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COMPRESSION:
This adjuster is usually found on the upper section of the shock and it
commonly requires a flat head screwdriver to be used for making
adjustments. Sometimes the adjustments are measured in “clicks”,
other times in degrees of turn. Usually OEM settings are in the middle
of adjustment. |
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| Firstly turn the compression
adjuster all the way in and write down how many turns/clicks there were.
Then take the compression adjustment all the way out so that you know
how much total adjustment there is. With the adjustment all the way out
sit on the bike and balance it between your legs, then push down
vigorously compress the shock. You will be able to feel the way in which
the shock moves through the downward/compression stroke, which will be
fairly easily (keep the bike balanced while doing this!!). |
| Then adjust the compression all
the way in, repeat the compressing action with the bike balanced between
your legs and observe/feel the difference in the range of motion –the
shock will compress more quickly and will not travel as far on the
compression stroke. What you are trying to achieve is the compression
stroke allowing the shock to move without restricting the amount of
travel of the shock shaft, which causes the sensation of “packing”.
You will need to work the adjusters until you have the rebound action
set correctly. |
| NOTE: compression adjustment is
very subjective compared to the rebound adjustment which is very easy to
see. It takes a lot more feel when making adjustments, which will take
time to acquire. |
EXCEPTIONS:
For shocks with remote reservoirs, there are differing ways to adjust
compression. Some have high and low speed circuits separated by
different controls, or one control mechanism. In instances such as
these, you may want to refer to the manual provided by the manufacturer,
or contact the manufacturer for guidance. If all else fails you can
email us here and we can help you! |
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