Joined Feb 2012
8K Posts | 5K+
here
quick read for you guys, on the stuff behind it:
Suspension 101
this is not mine I forget where i got it, but good info:
Suspension 101.
Static sag without rider
Hold the bike upright on a flat surface. Independently lift front and
rear until the suspension is fully extended, the value should be
approximately:
Type Front sag Rear sag
Super Bike 20-30 mm 5-10 mm
Super Sport 20-30 mm 5-10 mm
RR 250 15-25 mm 0-5 mm
RR125 15-25 mm Just top out 0 mm
Static sag with rider
The accepted manner to adjust the spring ratio is to measure how much
stroke is used with the rider sitting on the bike in straight line
position (behind fairing) after you have set the correct static sag
without rider. Normally 1/3 of the full stroke is a good starting
point for all machines. This is only a guide line for the right spring
ratio. The final check must be done on the circuit.
Rebound damping:
*Rear suspension
Too much rebound damping can cause:
- The rear "jumps" on the bumps instead of following the surface.
- The rear "jitters" under braking.
- It holds the rear down with the result that the bike will understeer!
- It can cause overheating in the hydraulic system of the shock
absorber and make it fade, in other words, it will loose damping when
hot.
Too little rebound damping can cause:
- The rear "tops out" too fast under braking, causing the rear wheel to jump
- The bike feels unstable.
*Front suspension
Too much rebound damping can cause:
- Oversteering!
- It will give poor grip of the front tire.
- It feels like the front wheels will tuck under in corners.
Too little rebound damping can cause:
- Understeer!
- The front can feel unstable.
Compression damping
Rear suspension
Too much compression damping can cause:
- The rear wheel to slide under acceleration .
-It can give a harsh ride over bumps.
Too little compression damping can cause:
- The rear wheel start to bump sideways under acceleration out of the
corner. - The bike will squad too much (rear is too low), that will
cause the front to loose grip.
Front suspension
Too much compression damping can cause:
- Good result during braking.
- Feels harsh over the bumps.
Too little compression damping can cause:
- Strong diving of the front.
Adjustment advice:
Compression damping should be adjusted together with front fork oil level.
Spring ratio:
Rear
Too hard spring ratio:
- Gives easy turning into corners.
- Makes the rear feel harsh.
- Create poor rear wheel traction.
Too soft spring ratio:
- Gives good traction in acceleration.
- Creates understeer in entry of corner.
- Makes too much suspension travel which will make it difficult to
"flick" the bike from one side to the other in a chicane.
- Will give a light feeling in the front.
Front
Too hard spring ratio:
- Good under braking.
- Creates understeer.
- It feels harsh in the corners.
Too soft spring ratio:
- Gives easy turning into corners.
- Creates oversteer.
- Can cause front to tuck under.
- Bad under braking (diving).
Front fork oil level
First see manual. The modern front fork of cartridge type is very
sensitive for oil Level changes, because of the small air volume Air
inside the front fork works as a spring. The different level of oil
affects the spring ratio from the middle of the stroke and has a very
strong effect at the end of the stroke.
When the oil level is raised:
The air spring in the later half stage of travel is stronger, and thus
the front forks harder.
When the oil level is lowered:
The air spring in the later half stage of travel is lessened, and thus
the front forks are softer. The oil level works most effectively at
the end of the fork travel.
Note: Adjust the oil level according to your manual.
BASIC SETUP - Check the following first:
Forks/Rear Shock - Race sag 25-30 mm, 1 - 1 3/16 inch
Forks/Rear Shock - Street sag 30-35 mm, 1 3/16 - 1 3/8 inch
Check chain alignment. If not correct, sprocket wear is increased.
Proper tire balance and pressure. If out of balance, there will be
vibration in either wheel
Steering head bearings and torque specifications, If too loose, head
will shake at high speeds.
Front end alignment. Check wheel alignment with triple clamps. If out
of alignment, fork geometry will be incorrect and steering will
suffer.
Crash damage, check for proper frame geometry.
--------------------------------------------------------------------------------
TROUBLESHOOTING FORK DAMPING PROBLEMS
Fork Adjustment Locations:
Rebound adjustment (if applicable) is located near the top of the fork.
Compression adjustment (if applicable) is located near the bottom of the fork.
Spring preload adjustment (if applicable) is generally hex style and
located at the top of the fork.
Forks - Lack of Rebound:
Symptoms
Forks are plush, but increasing speed causes loss of control and traction.
The motorcycle wallows exiting the turn causing fading traction and
loss of control.
When taking a corner a speed, you experience front-end chatter, loss
of traction and control.
Aggressive input at speed lessons control and chassis attitude suffers.
Front end fails to recover after aggressive input over bumpy surfaces.
Solution
Insufficient rebound - Increase rebound "gradually" until control and
traction are optimized and chatter is gone.
Forks - Too Much Rebound:
Symptoms
Front end feels locked up resulting in harsh ride.
Suspension packs in and fails to return, giving a harsh ride.
Typically after the first bump, the bike will skip over subsequent bumps.
With acceleration, the front end will tank slap or shake violently due
to lack of front wheel tire contact.
Solution
Too much rebound - Decrease rebound "gradually" until control and
traction are optimized.
Forks - Lack of Compression:
Symptoms
Front-end dives severely, sometimes bottoming out over heavy bumps or
during aggressive breaking
Front feels soft or vague similar to lack of rebound.
When bottoming, a clunk is heard. This is due to reaching the bottom
of fork travel.
Solution
Insufficient compression - Increase "gradually" until control and
traction are optimized.
Forks - Too Much Compression:
Symptoms
Front end rides high through the corners, causing the bike to steer
wide. It should ride in the middle of suspension travel.
Front wheel bounces over bumps while ripples and bumps are felt
directly in the triple clamps and through the chassis.
Ride is generally hard, and gets even harder when braking or entering turns.
Solution
Too much compression - Decrease compression "gradually" until the bike
neither bottoms or rides high, and control and traction are optimized.
Symptom
Front end chatters or shakes entering turns. This is due to incorrect
oil height and/or too much low speed compression damping
Solution
First, verify that oil height is correct. If correct, then decrease
compression "gradually" until chattering and shaking ceases.
--------------------------------------------------------------------------------
TROUBLESHOOTING SHOCK DAMPING PROBLEMS
Shock Adjustment Locations:
Rebound adjustment (if applicable) is located at the bottom of the shock.
Compression adjustment (if applicable) is located at the top of the
shock or on the reservoir.
Spring preload is located at the top of the shock.
Shock - Lack of Rebound:
Symptoms
The ride will feel soft or vague and as speed increases, the rear end
will want to wallow and/or weave over bumpy surfaces and traction
suffers.
Loss of traction will cause rear end to pogo or chatter due to shock
returning too fast on exiting a corner.
Solution
Insufficient rebound - Increase rebound until wallowing and weaving
disappears and control and traction are optimized.
Shock - Too Much Rebound:
Symptoms
Ride is harsh, suspension control is limited and traction is lost.
Rear end will pack down, forcing the bike wide in corners, due to rear
squat. It will slow steering because front end is riding high.
When rear end packs in, tires generally will overheat and will skip over bumps.
When chopping throttle, rear end will tend to skip or hop on entries.
Solution
Too much rebound - Decrease rebound "gradually" until harsh ride is
gone and traction is regained. Decrease rebound to keep rear end from
packing.
Shock - Lack of Compression:
Symptoms
The bike will not turn in entering a turn.
With bottoming, control and traction are lost.
With excessive rear end squat, when accelerating out of corners, the
bike will tend to steer wide.
Solution
Insufficient compression - Increase compression "gradually until
traction and control is optimized and/or excessive rear end squat is
gone.
Shock - Too Much Compression:
Symptoms
Ride is harsh, but not as bad as too much rebound. As speed increases,
so does harshness.
There is very little rear end squat. This will cause loss of
traction/sliding. Tire will overheat.
Rear end will want to kick when going over medium to large bumps.
Solution
Too much compression - Decrease compression until harshness is gone.
Decrease compression until sliding stops and traction is regained.
Front Fork Problems
Possible Cure
Race sag too small -
Reduce preload.
Race sag too great -
Increase preload.
Forks compress too far on smooth turns -
Stiffer springs, increase preload.
Forks dive too far (bottom out) -
Stiffer springs, reduce air gap, possibly increase preload.
Always losing front end on corner entry -
Softer springs, adjust weight distribution.
Front end chatters coming out of corners - Softer rebound springs or
main springs, reduce damping.
Bike difficult to turn in -
Softer springs, reduce preload or compression damping, alter steering geometry
Front wheel skips on bumps -
Softer springs, reduce compression damping, increase air gap.
Forks judder when braking on a straight -
Reduce compression damping.
Forks dive too fast -
Increase compression damping.
Forks pump down on fast bumpy corners -
Reduce rebound damping.
Excessive pogo action through chicanes -
Slightly increase rebound damping.
Front end shakes (not chatters) in corners -
Increase rebound damping.
Front end shoots up too fast after braking -
Increase rebound damping.
--------------------------------------------------------------------------------
Rear Shock Problems
Possible Cure
Race sag too great -
Increase preload.
Race sag too small -
Reduce preload.
Rear squats on acceleration -
Stiffer spring, increase anti-squat angle, slightly increase
compression damping.
Very Harsh ride over ripples -
Reduce compression damping.
Bike wallows - Increase rebound damping.
Rear jacks up too fast on braking -
Increase rebound damping.
Rear end chatters exiting slow corners -
Increase rebound damping.
Bike kicks off ripples or bounces on bumps -
Increase rebound damping.
Rear end pumps down on bumpy corners -
Reduce rebound damping.
LACK OF COMPRESSION DAMPING ( Front Fork )
Front end dive while on the brakes becomes excessive.
Rear end of motorcycle wants to "come around" when using front brakes
aggressively.
Front suspension "bottoms out" with a solid hit under heavy braking
and after hitting bumps.
Front end has a mushy and semi-vague feeling, similar to lack of
rebound damping.
TOO MUCH COMPRESSION DAMPING ( Front Fork )
Overly harsh ride, especially right at the point when bumps and
ripples are contacted by the front wheel.
Bumps and ripples are felt directly - the initial hit is routed
through the chassis instantly, with big bumps bouncing the tire off
the pavement.
The bike's ride height is affected negatively - the front end winds up
riding too high in the corners.
Brake dive is reduced drastically, though the chassis is upset
significantly by bumps encountered during braking.
LACK OF REBOUND DAMPING ( Front Fork )
The fork offers a supremely plush ride, especially when riding
straight up. However, when the pace picks up the feeling of control is
lost. The fork feels mushy, and traction "feel" is poor.
After hitting bumps at speed, the front tire tends to chatter or bounce.
When flicking the bike into a corner at speed, the bike will tend to
"porpoise" or wallow a bit, before settling down. Getting aggressive
with the controls makes it worse. As speed increases and steering
inputs become more aggressive, chassis attitude and pitch become a
real problem, with the front traction feedback going numb after the
bike is countersteered hard into a turn.
TOO MUCH REBOUND DAMPING ( Front Fork )
The ride is quite harsh - just the opposite of the plush feet of too
little rebound. Rough pavement makes the forks feel as if they're
locking up with stiction and harshness.
Under hard acceleration exiting bumpy corners, the front end feels
like it wants to "wiggle" or "tankslap." The tire feels as if it isn't
staying in contact with the pavement when on the gas.
The harsh, unforgiving ride makes the bike hard to control when riding
through dips and rolling bumps at speed. The suspension's reluctance
to maintain tire traction through these sections erodes rider
confidence.
--------------------------------------------------------------------------------
LACK OF COMPRESSION DAMPING ( Rear Shock )
Too much rear end "squat" under acceleration - bike wants to steer
wide exiting corners (since chassis is riding rear-low/nose-high).
Hitting bumps at speed causes the rear to bottom, which upsets the chassis.
Chassis attitude affected too much by large dips and "G-outs" -
steering and control become difficult due to excessive suspension
movement.
TOO MUCH COMPRESSION DAMPING ( Rear Shock )
Ride is harsh, though not quite as bad as too much rebound - however,
the faster you go the worse it gets.
Harshness hurts rear tire traction over bumps, especially during deceleration.
There is very little rear end "squat" under acceleration.
Medium to large bumps are felt directly through the chassis - when hit
at speed, the rear end kicks up.
LACK OF REBOUND DAMPING ( Rear Shock )
The ride is plush at cruising speeds, but as the pace increases, the
chassis begins to wallow and weave through bumpy corners.
Poor traction over bumps under hard acceleration - rear tire starts to
chatter due to lack of wheel control.
Excessive chassis pitch through large bumps and dips at speed - rear
end rebounds too fast, upsetting chassis with a pogo-stick action.
TOO MUCH REBOUND DAMPING ( Rear Shock )
Very harsh ride - rear suspension compliance is poor and "feel" is vague.
Poor traction over bumps during hard acceleration (due to lack of
suspension compliance).
Bike wants to run wide in corners since the rear end is "packing down"
- this forces a nose-high chassis attitude, which slows down steering.
Rear end wants to hop and skip when the throttle is chopped during
aggressive corner entries
Part 2.
Suspension 101: Round 2, by Max McAllister (Traxxion Dynamics)
Do not be embarrassed if you are unfamiliar with the basics. Most
racers aren't. This is one reason some riders struggle as novices for
years and never improve. Some racers crash frequently and don't
understand why. If your bike isn't set up properly, it will frighten
you and you will assume that you are going as fast as you can safely.
In the meantime, some of your peers just continue to go faster while
you stagnate. You can change this. Sometimes it's as easy as turning a
couple of screws. Then you can be frightened because you're really
haulin' ...!!!!!!!
TERMINOLOGY:
Sag....Distance a motorcycle compresses with weight on it. There are
two types of sag we deal with. The first is "free" (static) sag, which
is the amount the springs compress under the weight of the bike. The
second is rider sag, which is the amount the springs compress with the
rider on board.
Preload....This is the amount a spring is compressed with no weight on it at all
Dampening....this is the primary function of your suspension. It
controls the movement of your springs as they encounter irregularities
in the pavement. Without dampening, you are riding a pogo stick. There
are two types we will address. The first is compression dampening,
which controls the downward movement of your motorcycle (upward
movement of the wheel). The second is rebound dampening. It controls
the upward movement of your motorcycle (extension of the suspension).
Rake....Angle of your steering axis.
Trail....Distance the contact patch of the front tire trails the
steering axis' imaginary point of contact with the ground. More trail
makes your bike more stable. Less trail makes it steer faster. Watch
the wheels of a grocery cart, they always fall in line behind the cart
when you push it forward. This self-aligning effect is the result of
trail.
Ride Height....distance the motorcycle rides above the ground. Can be
changed at the front or the rear (or both) to alter handling
characteristics.
Front Fork Problems
Possible Cure
Race sag too small -
Reduce preload.
Race sag too great -
Increase preload.
Forks compress too far on smooth turns -
Stiffer springs, increase preload.
Forks dive too far (bottom out) -
Stiffer springs, reduce air gap, possibly increase preload.
Always losing front end on corner entry -
Softer springs, adjust weight distribution.
Front end chatters coming out of corners - Softer rebound springs or
main springs, reduce damping.
Bike difficult to turn in -
Softer springs, reduce preload or compression damping, alter steering geometry
Front wheel skips on bumps -
Softer springs, reduce compression damping, increase air gap.
Forks judder when braking on a straight -
Reduce compression damping.
Forks dive too fast -
Increase compression damping.
Forks pump down on fast bumpy corners -
Reduce rebound damping.
Excessive pogo action through chicanes -
Slightly increase rebound damping.
Front end shakes (not chatters) in corners -
Increase rebound damping.
Front end shoots up too fast after braking -
Increase rebound damping.
--------------------------------------------------------------------------------
Rear Shock Problems
Possible Cure
Race sag too great -
Increase preload.
Race sag too small -
Reduce preload.
Rear squats on acceleration -
Stiffer spring, increase anti-squat angle, slightly increase
compression damping.
Very Harsh ride over ripples -
Reduce compression damping.
Bike wallows - Increase rebound damping.
Rear jacks up too fast on braking -
Increase rebound damping.
Rear end chatters exiting slow corners -
Increase rebound damping.
Bike kicks off ripples or bounces on bumps -
Increase rebound damping.
Rear end pumps down on bumpy corners -
Reduce rebound damping.
LACK OF COMPRESSION DAMPING ( Front Fork )
Front end dive while on the brakes becomes excessive.
Rear end of motorcycle wants to "come around" when using front brakes
aggressively.
Front suspension "bottoms out" with a solid hit under heavy braking
and after hitting bumps.
Front end has a mushy and semi-vague feeling, similar to lack of
rebound damping.
TOO MUCH COMPRESSION DAMPING ( Front Fork )
Overly harsh ride, especially right at the point when bumps and
ripples are contacted by the front wheel.
Bumps and ripples are felt directly - the initial hit is routed
through the chassis instantly, with big bumps bouncing the tire off
the pavement.
The bike's ride height is affected negatively - the front end winds up
riding too high in the corners.
Brake dive is reduced drastically, though the chassis is upset
significantly by bumps encountered during braking.
LACK OF REBOUND DAMPING ( Front Fork )
The fork offers a supremely plush ride, especially when riding
straight up. However, when the pace picks up the feeling of control is
lost. The fork feels mushy, and traction "feel" is poor.
After hitting bumps at speed, the front tire tends to chatter or bounce.
When flicking the bike into a corner at speed, the bike will tend to
"porpoise" or wallow a bit, before settling down. Getting aggressive
with the controls makes it worse. As speed increases and steering
inputs become more aggressive, chassis attitude and pitch become a
real problem, with the front traction feedback going numb after the
bike is countersteered hard into a turn.
TOO MUCH REBOUND DAMPING ( Front Fork )
The ride is quite harsh - just the opposite of the plush feet of too
little rebound. Rough pavement makes the forks feel as if they're
locking up with stiction and harshness.
Under hard acceleration exiting bumpy corners, the front end feels
like it wants to "wiggle" or "tankslap." The tire feels as if it isn't
staying in contact with the pavement when on the gas.
The harsh, unforgiving ride makes the bike hard to control when riding
through dips and rolling bumps at speed. The suspension's reluctance
to maintain tire traction through these sections erodes rider
confidence.
--------------------------------------------------------------------------------
LACK OF COMPRESSION DAMPING ( Rear Shock )
Too much rear end "squat" under acceleration - bike wants to steer
wide exiting corners (since chassis is riding rear-low/nose-high).
Hitting bumps at speed causes the rear to bottom, which upsets the chassis.
Chassis attitude affected too much by large dips and "G-outs" -
steering and control become difficult due to excessive suspension
movement.
TOO MUCH COMPRESSION DAMPING ( Rear Shock )
Ride is harsh, though not quite as bad as too much rebound - however,
the faster you go the worse it gets.
Harshness hurts rear tire traction over bumps, especially during deceleration.
There is very little rear end "squat" under acceleration.
Medium to large bumps are felt directly through the chassis - when hit
at speed, the rear end kicks up.
LACK OF REBOUND DAMPING ( Rear Shock )
The ride is plush at cruising speeds, but as the pace increases, the
chassis begins to wallow and weave through bumpy corners.
Poor traction over bumps under hard acceleration - rear tire starts to
chatter due to lack of wheel control.
Excessive chassis pitch through large bumps and dips at speed - rear
end rebounds too fast, upsetting chassis with a pogo-stick action.
TOO MUCH REBOUND DAMPING ( Rear Shock )
Very harsh ride - rear suspension compliance is poor and "feel" is vague.
Poor traction over bumps during hard acceleration (due to lack of
suspension compliance).
Bike wants to run wide in corners since the rear end is "packing down"
- this forces a nose-high chassis attitude, which slows down steering.
Rear end wants to hop and skip when the throttle is chopped during
aggressive corner entries
Part 2.
Suspension 101: Round 2, by Max McAllister (Traxxion Dynamics)
Do not be embarrassed if you are unfamiliar with the basics. Most
racers aren't. This is one reason some riders struggle as novices for
years and never improve. Some racers crash frequently and don't
understand why. If your bike isn't set up properly, it will frighten
you and you will assume that you are going as fast as you can safely.
In the meantime, some of your peers just continue to go faster while
you stagnate. You can change this. Sometimes it's as easy as turning a
couple of screws. Then you can be frightened because you're really
haulin' ...!!!!!!!
TERMINOLOGY:
Sag....Distance a motorcycle compresses with weight on it. There are
two types of sag we deal with. The first is "free" (static) sag, which
is the amount the springs compress under the weight of the bike. The
second is rider sag, which is the amount the springs compress with the
rider on board.
Preload....This is the amount a spring is compressed with no weight on it at all
Dampening....this is the primary function of your suspension. It
controls the movement of your springs as they encounter irregularities
in the pavement. Without dampening, you are riding a pogo stick. There
are two types we will address. The first is compression dampening,
which controls the downward movement of your motorcycle (upward
movement of the wheel). The second is rebound dampening. It controls
the upward movement of your motorcycle (extension of the suspension).
Rake....Angle of your steering axis.
Trail....Distance the contact patch of the front tire trails the
steering axis' imaginary point of contact with the ground. More trail
makes your bike more stable. Less trail makes it steer faster. Watch
the wheels of a grocery cart, they always fall in line behind the cart
when you push it forward. This self-aligning effect is the result of
trail.
Ride Height....distance the motorcycle rides above the ground. Can be
changed at the front or the rear (or both) to alter handling
characteristics.
A quick visual inspection of the components of your chassis will make
sure that your chassis will be able to be adjusted into the ballpark.
You'll need to look closely at the following areas.
Rear shock....Look for external physical damage to the shock itself.
The main thing to look for though, is oil leaking around the shaft.
Turn the rebound adjuster in all the way and push on the seat. You
want to see a very slow return action. Turn the compression adjuster
in (if so equipped), and the shock should feel stiffer.
Front fork....Look for misalignment, nicks in the tubes, and damage to
the sliders. Again your primary concern is oil leaking around the
seals. Turn the rebound adjuster in all the way (if your bike has one)
and look for very slow action. Turn the compression adjuster in (if so
equipped), and the forks should feel stiffer.
Tires....Look for irregular wear patterns. This can tell you a lot
about the function of your chassis. They should be smooth and clean
with no major visible irregularities.
Wheels....These should be round, no dents, cracks (2mm of run out is
the service limit, up and down, and side to side) inspect the wheel
bearings anytime you remove the wheels.
Brakes....Check for fluid leaks by pulling hard on the lever and
keeping pressure on it for a minute or so. There should be no fluid
escape at all. Use a high boiling point racing DOT 3 or 4 fluid. Look
closely at your rotors and be cognizant of their wear.
Chain and Sprockets....This is simply the most commonly screwed up
service item on motorcycles. Most people have their chains too tight.
It should have slop in it even when you sit on the bike. A worn chain
is the recipe for disaster. Don't mess around with a worn chain.
Steering head....An improperly adjusted steering head is simply
dangerous. If it's too loose, the bike will wobble and wallow. If it's
too tight, the bike will "track" (go where it wants to on the
straights) and not steer properly. Try and find an expert mechanic to
assist you with this
BASELINE SETUP
At this point, we're finally going to do some measuring and adjusting.
We will use a known working baseline to set up your chassis. Then the
next time you practice, you will be able to analyze how it works and
fine tune it to work even better. All suspension adjustments made by
pushing or bouncing on the bike should be made with the bike off the
stands, on level ground, and with the bike in neutral.
Rear Shock....The first and most basic adjustment is to set the sag on
the shock. When you make these measurements, accuracy is important. If
at all possible, use a metric tape measure with millimeter increments.
If you use an S.A.E. tape, then measure to the sixteenth of an inch
(1" = 25.4mm). You need to pick two fixed points on the rear of your
bike for this. One on the rear of the swingarm (like a stand spool or
the axle), and one on the sub frame (like one of the bolts that holds
the rear passenger pegs on. never use the bodywork since it can sag
when the rider gets on). Before you can measure the sag, you must
first find the fully extended measurement between your two points.
Have a friend help you by pulling up on the footpegs to fully extend
the rear suspension. Your bike may be fully extended already. If it
is, this is not a problem. Record the distance at "full extension" on
your log sheet. Now have your friend balance the bike for you and push
down on the seat several times to settle the suspension. Now measure
and record the distance between your two points again. This is your
static sag. There should definitely be a little static sag on the rear
shock. Most expert race bikes have 5-10mm static sag. Your next
measurement is rider sag. Have a friend stand at the front of your
bike and balance it by the ends of the handlebars. Sit on the bike
like you would ride it and bounce down on it three times to settle the
suspension. Now have another friend measure between your two points
for you and log the measurement in the log. This is your rider sag.
Next you need to subtract your rider sag measurement from your full
extension measurement. This is your rear sag measurement. You should
have 30mm of sag. This is your baseline setting and can be adjusted
after your test ride. If your spring tops out the bike, you will need
a stiffer spring.
Now we need to adjust the dampening. The object is to get the
suspension to respond as quickly as possible to irregularities in the
pavement. Dampening is required to control the movement of the wheel
and the spring. Set your rebound dampening adjuster first. It is
difficult to explain how it should appear in words, but as you push on
the seat, it should return quickly, but not instantaneously. It should
take approximately one second for it to return to the top from a hard
push. You should be able to watch the seat rise. If it just pops back
up right away, you need to add rebound. If it drags up slowly, loosen
it up. If you have a compression adjuster, sit it up in the middle.
You can determine how to adjust it after your initial test ride, too
hard loosen it up, and to soft add.
Front Forks....Start here by setting the sag on the fork the same way
you did on the shock. First you need a fully extended measurement.
Only way to get consistency is to have two guys pick up on the
handlebars until the front wheel leaves the ground slightly. Measure
the exposed area of the fork slider. On a conventional fork, this will
be from the bottom of the lower triple tree to the top of the dust
seal on the slider. For an inverted fork, this will be from the dust
seal down to the top edge of the aluminum axle clamp. Record this
measurement on your log sheet. Push down on the fork hard three times,
to settle the suspension. Now measure the static sag. Finally, get on
the bike and push down three more times, while a friend balances the
bike. Have your friend with the tape take the final measurement. The
measurement you are looking for on the front fork is 35mm. If your
spring is of the correct rate, the free sag should be about 65 percent
of the rider sag, or about 20mm. The front fork has to have a great
deal of free sag so that the front wheel may move down into a hole as
well as over a bump. If your fork has too much sag turn the preload
adjuster in. If you don't have preload adjusters, then you will have
to remove your fork spacers and cut longer preload spacers. Adjust in
10mm increments. When you get close, you can go to 5mm increments.
Next is the dampening adjustment. The fork needs to move much faster
by comparison than the shock. Again, you should be able to watch it
rebound, but not as slowly as the shock. Grab the front brake and push
down on the front of the bike as hard as you can. Don't release the
brake and don't resist the rising action of the fork. Observe the
action. You want it to rise back as quickly as possible without
topping out and settling back down again. Loosen the rebound until the
bike does want to settle back after topping out, and then dial in just
enough rebound to make that settling tendency go away.
The compression adjuster should be set as softly as possible, but
prevent the fork from bottoming over severe bumps or under hard
braking.
If you do not have these adjusters available to you externally, then
you must change your fork oil weight to adjust the dampening. Thicker
oil affects both compression and rebound dampening.
If your forks works properly over bumps, but bottoms under hard
braking, you can add more oil, or "raise the level" to help prevent
bottoming. This reduces the air cushion you fork has above the oil.
Steering Dampener....This is primarily a safety device and should be
thought of as such and treated with great respect. Anyone racing
without one might as well not wear leathers or a helmet. It's very
dangerous. It should not be used to mask a bad handling motorcycle.
When you go out to test your suspension, have the dampener set so that
is barely drags when you sweep the wheel from side to side. It should
not make your bike difficult to steer in the pits. Test ride the bike
and analyze what it's doing before you crank up the dampener. A
dampener that is too stiff will make the bike track from side to side
and will be difficult to steer. After you make changes always return
to this base setting, and then adjust.
Jockey check....quick test method. Have a friend balance the bike
while you get on and assume your riding position. Lift up off the seat
slightly and bounce down on the bike. It should compress and rebound
in a balanced fashion from front to rear evenly. If your bike isn't
balanced, it won't work right. Your initial adjustments are only to
get to this simple test. If the bike isn't acting balanced, adjust it
until it does regardless of the initial adjustments you made. Balance
is the single most important facet of chassis setup. A bike that is
too soft or too stiff is still easier to go fast on than one that is
out of balance. If you bounce lightly, it should act balanced, as well
as if you bounce with great force.
PERFORMANCE ANALYSIS/DIAL IN
Now that you have a good baseline set-up, it's time for a test ride.
Ensure that your tires have the correct pressure in them, and head to
the track or your testing grounds. In order to make an assessment of
your bike's chassis, you need to be conscious of what's going on while
you are riding it. Someday when your a racing god, you'll have data
acquisition equipment to tell your chassis engineers what to adjust.
But until then, you are the only suspension sensor on your motorcycle.
This is actually the best way to learn. There are several things you
need to analyze as you ride.
High speed stability.....this should be self explanatory, and the
easiest to analyze. Go fast in a straight line and your bike should
never scare you. If it does, you have some adjusting to do.
Performance under braking....Is the bike stable? Does it squirm
underneath you? Does the front wheel bounce? Does the rear wheel
bounce? Does the forks bottom? How does the bike behave trail braking?
Performance in the corners....This needs to be analyzed in three
segments: Turn in, mid corner, and exit. Be conscious of these things
within each of these segments: Overall stability, steering effort,
ground clearance, front wheel action, and rear wheel action. That's a
bunch of stuff to think about, especially when you're just trying to
circulate and learn to ride. If any of these things are out of whack,
they'll usually let you know, consistently, in most turns. Here is an
explanation of what to look for.
Overall stability....The main thing to look for here is wallowing
action. There should not be any. Wallow indicates a need for more
spring.
Steering effort....Does the bike track well in the corners? Do you
have to fight to keep it on the racing/riding line? Are your arms
completely worn out after riding/practice?
Ground clearance....If you have anything dragging the ground, you have
a problem that could result in injury. Some guys think they're cool
because they drag stuff around the track/road. These people are a
hazard to themselves and others. If you have anything dragging, fix
it! Raise your footpegs, bend your pipe in, or
whatever it takes. If you lean in hard enough on a bike that's
scraping the ground you will lift a tire off the ground, and then you
will immediately take its place on the pavement; this is serious
business. If you are happy with the way your chassis works, then don't
alter your ride height to stop things from dragging. Just get
the dragging stuff up and out of the way. Changing ride height alters
the bike's handling characteristics.
Front wheel action....The wheel should roll smoothly through the
corner and inspire confidence. Does the wheel bounce? If it does, you
need to pay close attention to the way it bounces. If the wheel is
bouncing and you can't really feel it in the bars, then this is a lack
of rebound dampening. If the handlebars are jarring you, then
you may have too much spring preload or compression dampening.
Use rebound dampening carefully. Too much rebound dampening creates a
situation where the fork is packing down. This means your forks has
collapsed and is not re-extending fast enough. This is a VERY
DANGEROUS situation. A fork that has packed down has no suspension
travel left. A crash is eminent. You need to
speed up your rebound dampening. You may also need a higher fork oil
level, or more compression dampening to keep the forks from bottoming.
This situation is usually set up by hard braking that compresses the
fork followed by trail braking into the turn which never lets the
forks recover. Some additional spring may help this too.
Rear wheel action....Your rear wheel can exhibit many of the same
symptoms as the front wheel. If your bike feels like a pogo stick then
this is typically an all around lack of dampening. This condition will
also cause a bunch of wheelspin on exit and tear up your tire.
Wheelspin also fools riders into believing that they are going fast;
that is until some novice on a GS500E goes railing around the outside
of them in a turn. Too much rebound will cause the rear wheel to
"swim" under the bike side to side under hard straight line braking.
This is because the shock is packing up and the rear wheel is hanging
in the air instead of returning to the ground to keep you pointed
straight.
A lack of compression dampening will cause the bike to pogo while
under acceleration. This will be a vertical "sawing" motion; vertical
relative to the bike even though it is still leaned over. Too much
compression dampening will make the bike "buck" or kick you in the
butt over sharp bumps. This can also cause excessive wheelspin. The
shock should be soft enough to let the bike squat some. This transfer
of weight helps give the tire more grip.
When you notice a flaw in your suspension, note where it occurred in
the turn. Was it as you rolled into the turn, was it in the middle of
the turn, or was it as you accelerated out of the turn? This is
critical information to help you (and a suspension tuner) decide what
the correct changes should be.
Chassis geometry....If your bike's chassis is soaking bumps properly,
but your bike isn't steering around the track properly, then you need
to adjust the "attitude" or "geometry" of your bike. This will affect
it all the way around the track.
The variables you have to work with are the fork height, and the
swingarm angle. Here's what each does.
Fork angle....Will increase or decrease your trail. Moving the nose of
the bike lower (forks higher in the clamps) will make it steer faster,
but will be less stable. Moving the nose of the bike higher (forks
lower in the clamps) will require more steering effort, and will
increase stability. Most expert riders say this increases "feel" at
extreme lean angles.
For most novice riders, will find it the easiest way to evaluate this
is to ride through a high speed sweeper and evaluate how the bike
steers into the turn and notice how much effort it takes to make it
steer to the apex of the turn. In other words, "How does it hold a
line?"
If the bike is too low in the front, it will steer dramatically, and
try and drive off the inside of the track. It will be unstable all the
way through a turn, and sometimes even on the straight-aways.
If the bike is too high in the front, it will steer in slowly and
require that you pull on the bars to hold it down to get it to the
apex. This condition will make it very difficult to steer the bike to
the apex. It will fatigue your arms and they will feel tired after
riding.
Swingarm angle....tunes the way the bike reacts to acceleration. Your
motorcycle wants to "squat" under acceleration due to the rearward
weight transfer.
If the swingarm is too flat, the bike will squat too much, and the
bike will sit back and the front will extend like a "chopper". This
will make the bike want to "run wide" or run off the edge of the
track. The front end will feel light and dance about as you are
leaving a turn. The result is that you have to wait to get on the
throttle. You should raise the rear of the bike to correct this.
If the swingarm angle is too steep, then the bike will not squat
enough, and the result will be poor traction. This is "wheelspin" If
you can whack the gas, and the wheel spins up, then you need to lower
the back of the bike.
Here's where it gets more complicated. Changing one end of the bike
affects the other. There is a simple way to figure it out. If your
problem occurs from steer-in to mid-corner, then change the front. If
your problem
occurs from mid-corner to the exit, then change the rear. Although
there is no way to accurately mathematically describe what happens
when you make a change, here is a VERY crude way to think about it.
Changing the front ride height has an effect of "5" on the front and
an effect of "1" on the rear. Changing the rear has an effect of "5"
on the rear, and an effect of "1" on the front.
A common example of where riders improperly change their bikes comes
when the bike steers in too slowly. Many confused riders and tuners
will raise the back of the bike. This makes the nose steeper, and the
bike will steer more sharply. But remember, in order to get an effect
of "1" on the front of the bike, you have now make an effect of "5" on
the rear. Your bike may now turn in better, but you will get less
traction, more wheelspin, and more tendency to high-side. This is not
what you wanted... The correct change is to lower the nose of the
bike. This affects the turn in "5 (front)" and the exit "1 (rear)".
Much better!!!!
If you have no idea where to start with your geometry, look around the
pits or ask a suspension tuner. There is no correct answer or magic
formula for what you personally want your bike to do. Your personal
style of riding will dictate to you what to do with the bike. You will
find that most production bikes are way off of what's is generally
"good" Find a range of "good" seems to be for your model of bike and
start on the "safe" or "stable" side of the range
Suspension 101
this is not mine I forget where i got it, but good info:
Suspension 101.
Static sag without rider
Hold the bike upright on a flat surface. Independently lift front and
rear until the suspension is fully extended, the value should be
approximately:
Type Front sag Rear sag
Super Bike 20-30 mm 5-10 mm
Super Sport 20-30 mm 5-10 mm
RR 250 15-25 mm 0-5 mm
RR125 15-25 mm Just top out 0 mm
Static sag with rider
The accepted manner to adjust the spring ratio is to measure how much
stroke is used with the rider sitting on the bike in straight line
position (behind fairing) after you have set the correct static sag
without rider. Normally 1/3 of the full stroke is a good starting
point for all machines. This is only a guide line for the right spring
ratio. The final check must be done on the circuit.
Rebound damping:
*Rear suspension
Too much rebound damping can cause:
- The rear "jumps" on the bumps instead of following the surface.
- The rear "jitters" under braking.
- It holds the rear down with the result that the bike will understeer!
- It can cause overheating in the hydraulic system of the shock
absorber and make it fade, in other words, it will loose damping when
hot.
Too little rebound damping can cause:
- The rear "tops out" too fast under braking, causing the rear wheel to jump
- The bike feels unstable.
*Front suspension
Too much rebound damping can cause:
- Oversteering!
- It will give poor grip of the front tire.
- It feels like the front wheels will tuck under in corners.
Too little rebound damping can cause:
- Understeer!
- The front can feel unstable.
Compression damping
Rear suspension
Too much compression damping can cause:
- The rear wheel to slide under acceleration .
-It can give a harsh ride over bumps.
Too little compression damping can cause:
- The rear wheel start to bump sideways under acceleration out of the
corner. - The bike will squad too much (rear is too low), that will
cause the front to loose grip.
Front suspension
Too much compression damping can cause:
- Good result during braking.
- Feels harsh over the bumps.
Too little compression damping can cause:
- Strong diving of the front.
Adjustment advice:
Compression damping should be adjusted together with front fork oil level.
Spring ratio:
Rear
Too hard spring ratio:
- Gives easy turning into corners.
- Makes the rear feel harsh.
- Create poor rear wheel traction.
Too soft spring ratio:
- Gives good traction in acceleration.
- Creates understeer in entry of corner.
- Makes too much suspension travel which will make it difficult to
"flick" the bike from one side to the other in a chicane.
- Will give a light feeling in the front.
Front
Too hard spring ratio:
- Good under braking.
- Creates understeer.
- It feels harsh in the corners.
Too soft spring ratio:
- Gives easy turning into corners.
- Creates oversteer.
- Can cause front to tuck under.
- Bad under braking (diving).
Front fork oil level
First see manual. The modern front fork of cartridge type is very
sensitive for oil Level changes, because of the small air volume Air
inside the front fork works as a spring. The different level of oil
affects the spring ratio from the middle of the stroke and has a very
strong effect at the end of the stroke.
When the oil level is raised:
The air spring in the later half stage of travel is stronger, and thus
the front forks harder.
When the oil level is lowered:
The air spring in the later half stage of travel is lessened, and thus
the front forks are softer. The oil level works most effectively at
the end of the fork travel.
Note: Adjust the oil level according to your manual.
BASIC SETUP - Check the following first:
Forks/Rear Shock - Race sag 25-30 mm, 1 - 1 3/16 inch
Forks/Rear Shock - Street sag 30-35 mm, 1 3/16 - 1 3/8 inch
Check chain alignment. If not correct, sprocket wear is increased.
Proper tire balance and pressure. If out of balance, there will be
vibration in either wheel
Steering head bearings and torque specifications, If too loose, head
will shake at high speeds.
Front end alignment. Check wheel alignment with triple clamps. If out
of alignment, fork geometry will be incorrect and steering will
suffer.
Crash damage, check for proper frame geometry.
--------------------------------------------------------------------------------
TROUBLESHOOTING FORK DAMPING PROBLEMS
Fork Adjustment Locations:
Rebound adjustment (if applicable) is located near the top of the fork.
Compression adjustment (if applicable) is located near the bottom of the fork.
Spring preload adjustment (if applicable) is generally hex style and
located at the top of the fork.
Forks - Lack of Rebound:
Symptoms
Forks are plush, but increasing speed causes loss of control and traction.
The motorcycle wallows exiting the turn causing fading traction and
loss of control.
When taking a corner a speed, you experience front-end chatter, loss
of traction and control.
Aggressive input at speed lessons control and chassis attitude suffers.
Front end fails to recover after aggressive input over bumpy surfaces.
Solution
Insufficient rebound - Increase rebound "gradually" until control and
traction are optimized and chatter is gone.
Forks - Too Much Rebound:
Symptoms
Front end feels locked up resulting in harsh ride.
Suspension packs in and fails to return, giving a harsh ride.
Typically after the first bump, the bike will skip over subsequent bumps.
With acceleration, the front end will tank slap or shake violently due
to lack of front wheel tire contact.
Solution
Too much rebound - Decrease rebound "gradually" until control and
traction are optimized.
Forks - Lack of Compression:
Symptoms
Front-end dives severely, sometimes bottoming out over heavy bumps or
during aggressive breaking
Front feels soft or vague similar to lack of rebound.
When bottoming, a clunk is heard. This is due to reaching the bottom
of fork travel.
Solution
Insufficient compression - Increase "gradually" until control and
traction are optimized.
Forks - Too Much Compression:
Symptoms
Front end rides high through the corners, causing the bike to steer
wide. It should ride in the middle of suspension travel.
Front wheel bounces over bumps while ripples and bumps are felt
directly in the triple clamps and through the chassis.
Ride is generally hard, and gets even harder when braking or entering turns.
Solution
Too much compression - Decrease compression "gradually" until the bike
neither bottoms or rides high, and control and traction are optimized.
Symptom
Front end chatters or shakes entering turns. This is due to incorrect
oil height and/or too much low speed compression damping
Solution
First, verify that oil height is correct. If correct, then decrease
compression "gradually" until chattering and shaking ceases.
--------------------------------------------------------------------------------
TROUBLESHOOTING SHOCK DAMPING PROBLEMS
Shock Adjustment Locations:
Rebound adjustment (if applicable) is located at the bottom of the shock.
Compression adjustment (if applicable) is located at the top of the
shock or on the reservoir.
Spring preload is located at the top of the shock.
Shock - Lack of Rebound:
Symptoms
The ride will feel soft or vague and as speed increases, the rear end
will want to wallow and/or weave over bumpy surfaces and traction
suffers.
Loss of traction will cause rear end to pogo or chatter due to shock
returning too fast on exiting a corner.
Solution
Insufficient rebound - Increase rebound until wallowing and weaving
disappears and control and traction are optimized.
Shock - Too Much Rebound:
Symptoms
Ride is harsh, suspension control is limited and traction is lost.
Rear end will pack down, forcing the bike wide in corners, due to rear
squat. It will slow steering because front end is riding high.
When rear end packs in, tires generally will overheat and will skip over bumps.
When chopping throttle, rear end will tend to skip or hop on entries.
Solution
Too much rebound - Decrease rebound "gradually" until harsh ride is
gone and traction is regained. Decrease rebound to keep rear end from
packing.
Shock - Lack of Compression:
Symptoms
The bike will not turn in entering a turn.
With bottoming, control and traction are lost.
With excessive rear end squat, when accelerating out of corners, the
bike will tend to steer wide.
Solution
Insufficient compression - Increase compression "gradually until
traction and control is optimized and/or excessive rear end squat is
gone.
Shock - Too Much Compression:
Symptoms
Ride is harsh, but not as bad as too much rebound. As speed increases,
so does harshness.
There is very little rear end squat. This will cause loss of
traction/sliding. Tire will overheat.
Rear end will want to kick when going over medium to large bumps.
Solution
Too much compression - Decrease compression until harshness is gone.
Decrease compression until sliding stops and traction is regained.
Front Fork Problems
Possible Cure
Race sag too small -
Reduce preload.
Race sag too great -
Increase preload.
Forks compress too far on smooth turns -
Stiffer springs, increase preload.
Forks dive too far (bottom out) -
Stiffer springs, reduce air gap, possibly increase preload.
Always losing front end on corner entry -
Softer springs, adjust weight distribution.
Front end chatters coming out of corners - Softer rebound springs or
main springs, reduce damping.
Bike difficult to turn in -
Softer springs, reduce preload or compression damping, alter steering geometry
Front wheel skips on bumps -
Softer springs, reduce compression damping, increase air gap.
Forks judder when braking on a straight -
Reduce compression damping.
Forks dive too fast -
Increase compression damping.
Forks pump down on fast bumpy corners -
Reduce rebound damping.
Excessive pogo action through chicanes -
Slightly increase rebound damping.
Front end shakes (not chatters) in corners -
Increase rebound damping.
Front end shoots up too fast after braking -
Increase rebound damping.
--------------------------------------------------------------------------------
Rear Shock Problems
Possible Cure
Race sag too great -
Increase preload.
Race sag too small -
Reduce preload.
Rear squats on acceleration -
Stiffer spring, increase anti-squat angle, slightly increase
compression damping.
Very Harsh ride over ripples -
Reduce compression damping.
Bike wallows - Increase rebound damping.
Rear jacks up too fast on braking -
Increase rebound damping.
Rear end chatters exiting slow corners -
Increase rebound damping.
Bike kicks off ripples or bounces on bumps -
Increase rebound damping.
Rear end pumps down on bumpy corners -
Reduce rebound damping.
LACK OF COMPRESSION DAMPING ( Front Fork )
Front end dive while on the brakes becomes excessive.
Rear end of motorcycle wants to "come around" when using front brakes
aggressively.
Front suspension "bottoms out" with a solid hit under heavy braking
and after hitting bumps.
Front end has a mushy and semi-vague feeling, similar to lack of
rebound damping.
TOO MUCH COMPRESSION DAMPING ( Front Fork )
Overly harsh ride, especially right at the point when bumps and
ripples are contacted by the front wheel.
Bumps and ripples are felt directly - the initial hit is routed
through the chassis instantly, with big bumps bouncing the tire off
the pavement.
The bike's ride height is affected negatively - the front end winds up
riding too high in the corners.
Brake dive is reduced drastically, though the chassis is upset
significantly by bumps encountered during braking.
LACK OF REBOUND DAMPING ( Front Fork )
The fork offers a supremely plush ride, especially when riding
straight up. However, when the pace picks up the feeling of control is
lost. The fork feels mushy, and traction "feel" is poor.
After hitting bumps at speed, the front tire tends to chatter or bounce.
When flicking the bike into a corner at speed, the bike will tend to
"porpoise" or wallow a bit, before settling down. Getting aggressive
with the controls makes it worse. As speed increases and steering
inputs become more aggressive, chassis attitude and pitch become a
real problem, with the front traction feedback going numb after the
bike is countersteered hard into a turn.
TOO MUCH REBOUND DAMPING ( Front Fork )
The ride is quite harsh - just the opposite of the plush feet of too
little rebound. Rough pavement makes the forks feel as if they're
locking up with stiction and harshness.
Under hard acceleration exiting bumpy corners, the front end feels
like it wants to "wiggle" or "tankslap." The tire feels as if it isn't
staying in contact with the pavement when on the gas.
The harsh, unforgiving ride makes the bike hard to control when riding
through dips and rolling bumps at speed. The suspension's reluctance
to maintain tire traction through these sections erodes rider
confidence.
--------------------------------------------------------------------------------
LACK OF COMPRESSION DAMPING ( Rear Shock )
Too much rear end "squat" under acceleration - bike wants to steer
wide exiting corners (since chassis is riding rear-low/nose-high).
Hitting bumps at speed causes the rear to bottom, which upsets the chassis.
Chassis attitude affected too much by large dips and "G-outs" -
steering and control become difficult due to excessive suspension
movement.
TOO MUCH COMPRESSION DAMPING ( Rear Shock )
Ride is harsh, though not quite as bad as too much rebound - however,
the faster you go the worse it gets.
Harshness hurts rear tire traction over bumps, especially during deceleration.
There is very little rear end "squat" under acceleration.
Medium to large bumps are felt directly through the chassis - when hit
at speed, the rear end kicks up.
LACK OF REBOUND DAMPING ( Rear Shock )
The ride is plush at cruising speeds, but as the pace increases, the
chassis begins to wallow and weave through bumpy corners.
Poor traction over bumps under hard acceleration - rear tire starts to
chatter due to lack of wheel control.
Excessive chassis pitch through large bumps and dips at speed - rear
end rebounds too fast, upsetting chassis with a pogo-stick action.
TOO MUCH REBOUND DAMPING ( Rear Shock )
Very harsh ride - rear suspension compliance is poor and "feel" is vague.
Poor traction over bumps during hard acceleration (due to lack of
suspension compliance).
Bike wants to run wide in corners since the rear end is "packing down"
- this forces a nose-high chassis attitude, which slows down steering.
Rear end wants to hop and skip when the throttle is chopped during
aggressive corner entries
Part 2.
Suspension 101: Round 2, by Max McAllister (Traxxion Dynamics)
Do not be embarrassed if you are unfamiliar with the basics. Most
racers aren't. This is one reason some riders struggle as novices for
years and never improve. Some racers crash frequently and don't
understand why. If your bike isn't set up properly, it will frighten
you and you will assume that you are going as fast as you can safely.
In the meantime, some of your peers just continue to go faster while
you stagnate. You can change this. Sometimes it's as easy as turning a
couple of screws. Then you can be frightened because you're really
haulin' ...!!!!!!!
TERMINOLOGY:
Sag....Distance a motorcycle compresses with weight on it. There are
two types of sag we deal with. The first is "free" (static) sag, which
is the amount the springs compress under the weight of the bike. The
second is rider sag, which is the amount the springs compress with the
rider on board.
Preload....This is the amount a spring is compressed with no weight on it at all
Dampening....this is the primary function of your suspension. It
controls the movement of your springs as they encounter irregularities
in the pavement. Without dampening, you are riding a pogo stick. There
are two types we will address. The first is compression dampening,
which controls the downward movement of your motorcycle (upward
movement of the wheel). The second is rebound dampening. It controls
the upward movement of your motorcycle (extension of the suspension).
Rake....Angle of your steering axis.
Trail....Distance the contact patch of the front tire trails the
steering axis' imaginary point of contact with the ground. More trail
makes your bike more stable. Less trail makes it steer faster. Watch
the wheels of a grocery cart, they always fall in line behind the cart
when you push it forward. This self-aligning effect is the result of
trail.
Ride Height....distance the motorcycle rides above the ground. Can be
changed at the front or the rear (or both) to alter handling
characteristics.
Front Fork Problems
Possible Cure
Race sag too small -
Reduce preload.
Race sag too great -
Increase preload.
Forks compress too far on smooth turns -
Stiffer springs, increase preload.
Forks dive too far (bottom out) -
Stiffer springs, reduce air gap, possibly increase preload.
Always losing front end on corner entry -
Softer springs, adjust weight distribution.
Front end chatters coming out of corners - Softer rebound springs or
main springs, reduce damping.
Bike difficult to turn in -
Softer springs, reduce preload or compression damping, alter steering geometry
Front wheel skips on bumps -
Softer springs, reduce compression damping, increase air gap.
Forks judder when braking on a straight -
Reduce compression damping.
Forks dive too fast -
Increase compression damping.
Forks pump down on fast bumpy corners -
Reduce rebound damping.
Excessive pogo action through chicanes -
Slightly increase rebound damping.
Front end shakes (not chatters) in corners -
Increase rebound damping.
Front end shoots up too fast after braking -
Increase rebound damping.
--------------------------------------------------------------------------------
Rear Shock Problems
Possible Cure
Race sag too great -
Increase preload.
Race sag too small -
Reduce preload.
Rear squats on acceleration -
Stiffer spring, increase anti-squat angle, slightly increase
compression damping.
Very Harsh ride over ripples -
Reduce compression damping.
Bike wallows - Increase rebound damping.
Rear jacks up too fast on braking -
Increase rebound damping.
Rear end chatters exiting slow corners -
Increase rebound damping.
Bike kicks off ripples or bounces on bumps -
Increase rebound damping.
Rear end pumps down on bumpy corners -
Reduce rebound damping.
LACK OF COMPRESSION DAMPING ( Front Fork )
Front end dive while on the brakes becomes excessive.
Rear end of motorcycle wants to "come around" when using front brakes
aggressively.
Front suspension "bottoms out" with a solid hit under heavy braking
and after hitting bumps.
Front end has a mushy and semi-vague feeling, similar to lack of
rebound damping.
TOO MUCH COMPRESSION DAMPING ( Front Fork )
Overly harsh ride, especially right at the point when bumps and
ripples are contacted by the front wheel.
Bumps and ripples are felt directly - the initial hit is routed
through the chassis instantly, with big bumps bouncing the tire off
the pavement.
The bike's ride height is affected negatively - the front end winds up
riding too high in the corners.
Brake dive is reduced drastically, though the chassis is upset
significantly by bumps encountered during braking.
LACK OF REBOUND DAMPING ( Front Fork )
The fork offers a supremely plush ride, especially when riding
straight up. However, when the pace picks up the feeling of control is
lost. The fork feels mushy, and traction "feel" is poor.
After hitting bumps at speed, the front tire tends to chatter or bounce.
When flicking the bike into a corner at speed, the bike will tend to
"porpoise" or wallow a bit, before settling down. Getting aggressive
with the controls makes it worse. As speed increases and steering
inputs become more aggressive, chassis attitude and pitch become a
real problem, with the front traction feedback going numb after the
bike is countersteered hard into a turn.
TOO MUCH REBOUND DAMPING ( Front Fork )
The ride is quite harsh - just the opposite of the plush feet of too
little rebound. Rough pavement makes the forks feel as if they're
locking up with stiction and harshness.
Under hard acceleration exiting bumpy corners, the front end feels
like it wants to "wiggle" or "tankslap." The tire feels as if it isn't
staying in contact with the pavement when on the gas.
The harsh, unforgiving ride makes the bike hard to control when riding
through dips and rolling bumps at speed. The suspension's reluctance
to maintain tire traction through these sections erodes rider
confidence.
--------------------------------------------------------------------------------
LACK OF COMPRESSION DAMPING ( Rear Shock )
Too much rear end "squat" under acceleration - bike wants to steer
wide exiting corners (since chassis is riding rear-low/nose-high).
Hitting bumps at speed causes the rear to bottom, which upsets the chassis.
Chassis attitude affected too much by large dips and "G-outs" -
steering and control become difficult due to excessive suspension
movement.
TOO MUCH COMPRESSION DAMPING ( Rear Shock )
Ride is harsh, though not quite as bad as too much rebound - however,
the faster you go the worse it gets.
Harshness hurts rear tire traction over bumps, especially during deceleration.
There is very little rear end "squat" under acceleration.
Medium to large bumps are felt directly through the chassis - when hit
at speed, the rear end kicks up.
LACK OF REBOUND DAMPING ( Rear Shock )
The ride is plush at cruising speeds, but as the pace increases, the
chassis begins to wallow and weave through bumpy corners.
Poor traction over bumps under hard acceleration - rear tire starts to
chatter due to lack of wheel control.
Excessive chassis pitch through large bumps and dips at speed - rear
end rebounds too fast, upsetting chassis with a pogo-stick action.
TOO MUCH REBOUND DAMPING ( Rear Shock )
Very harsh ride - rear suspension compliance is poor and "feel" is vague.
Poor traction over bumps during hard acceleration (due to lack of
suspension compliance).
Bike wants to run wide in corners since the rear end is "packing down"
- this forces a nose-high chassis attitude, which slows down steering.
Rear end wants to hop and skip when the throttle is chopped during
aggressive corner entries
Part 2.
Suspension 101: Round 2, by Max McAllister (Traxxion Dynamics)
Do not be embarrassed if you are unfamiliar with the basics. Most
racers aren't. This is one reason some riders struggle as novices for
years and never improve. Some racers crash frequently and don't
understand why. If your bike isn't set up properly, it will frighten
you and you will assume that you are going as fast as you can safely.
In the meantime, some of your peers just continue to go faster while
you stagnate. You can change this. Sometimes it's as easy as turning a
couple of screws. Then you can be frightened because you're really
haulin' ...!!!!!!!
TERMINOLOGY:
Sag....Distance a motorcycle compresses with weight on it. There are
two types of sag we deal with. The first is "free" (static) sag, which
is the amount the springs compress under the weight of the bike. The
second is rider sag, which is the amount the springs compress with the
rider on board.
Preload....This is the amount a spring is compressed with no weight on it at all
Dampening....this is the primary function of your suspension. It
controls the movement of your springs as they encounter irregularities
in the pavement. Without dampening, you are riding a pogo stick. There
are two types we will address. The first is compression dampening,
which controls the downward movement of your motorcycle (upward
movement of the wheel). The second is rebound dampening. It controls
the upward movement of your motorcycle (extension of the suspension).
Rake....Angle of your steering axis.
Trail....Distance the contact patch of the front tire trails the
steering axis' imaginary point of contact with the ground. More trail
makes your bike more stable. Less trail makes it steer faster. Watch
the wheels of a grocery cart, they always fall in line behind the cart
when you push it forward. This self-aligning effect is the result of
trail.
Ride Height....distance the motorcycle rides above the ground. Can be
changed at the front or the rear (or both) to alter handling
characteristics.
A quick visual inspection of the components of your chassis will make
sure that your chassis will be able to be adjusted into the ballpark.
You'll need to look closely at the following areas.
Rear shock....Look for external physical damage to the shock itself.
The main thing to look for though, is oil leaking around the shaft.
Turn the rebound adjuster in all the way and push on the seat. You
want to see a very slow return action. Turn the compression adjuster
in (if so equipped), and the shock should feel stiffer.
Front fork....Look for misalignment, nicks in the tubes, and damage to
the sliders. Again your primary concern is oil leaking around the
seals. Turn the rebound adjuster in all the way (if your bike has one)
and look for very slow action. Turn the compression adjuster in (if so
equipped), and the forks should feel stiffer.
Tires....Look for irregular wear patterns. This can tell you a lot
about the function of your chassis. They should be smooth and clean
with no major visible irregularities.
Wheels....These should be round, no dents, cracks (2mm of run out is
the service limit, up and down, and side to side) inspect the wheel
bearings anytime you remove the wheels.
Brakes....Check for fluid leaks by pulling hard on the lever and
keeping pressure on it for a minute or so. There should be no fluid
escape at all. Use a high boiling point racing DOT 3 or 4 fluid. Look
closely at your rotors and be cognizant of their wear.
Chain and Sprockets....This is simply the most commonly screwed up
service item on motorcycles. Most people have their chains too tight.
It should have slop in it even when you sit on the bike. A worn chain
is the recipe for disaster. Don't mess around with a worn chain.
Steering head....An improperly adjusted steering head is simply
dangerous. If it's too loose, the bike will wobble and wallow. If it's
too tight, the bike will "track" (go where it wants to on the
straights) and not steer properly. Try and find an expert mechanic to
assist you with this
BASELINE SETUP
At this point, we're finally going to do some measuring and adjusting.
We will use a known working baseline to set up your chassis. Then the
next time you practice, you will be able to analyze how it works and
fine tune it to work even better. All suspension adjustments made by
pushing or bouncing on the bike should be made with the bike off the
stands, on level ground, and with the bike in neutral.
Rear Shock....The first and most basic adjustment is to set the sag on
the shock. When you make these measurements, accuracy is important. If
at all possible, use a metric tape measure with millimeter increments.
If you use an S.A.E. tape, then measure to the sixteenth of an inch
(1" = 25.4mm). You need to pick two fixed points on the rear of your
bike for this. One on the rear of the swingarm (like a stand spool or
the axle), and one on the sub frame (like one of the bolts that holds
the rear passenger pegs on. never use the bodywork since it can sag
when the rider gets on). Before you can measure the sag, you must
first find the fully extended measurement between your two points.
Have a friend help you by pulling up on the footpegs to fully extend
the rear suspension. Your bike may be fully extended already. If it
is, this is not a problem. Record the distance at "full extension" on
your log sheet. Now have your friend balance the bike for you and push
down on the seat several times to settle the suspension. Now measure
and record the distance between your two points again. This is your
static sag. There should definitely be a little static sag on the rear
shock. Most expert race bikes have 5-10mm static sag. Your next
measurement is rider sag. Have a friend stand at the front of your
bike and balance it by the ends of the handlebars. Sit on the bike
like you would ride it and bounce down on it three times to settle the
suspension. Now have another friend measure between your two points
for you and log the measurement in the log. This is your rider sag.
Next you need to subtract your rider sag measurement from your full
extension measurement. This is your rear sag measurement. You should
have 30mm of sag. This is your baseline setting and can be adjusted
after your test ride. If your spring tops out the bike, you will need
a stiffer spring.
Now we need to adjust the dampening. The object is to get the
suspension to respond as quickly as possible to irregularities in the
pavement. Dampening is required to control the movement of the wheel
and the spring. Set your rebound dampening adjuster first. It is
difficult to explain how it should appear in words, but as you push on
the seat, it should return quickly, but not instantaneously. It should
take approximately one second for it to return to the top from a hard
push. You should be able to watch the seat rise. If it just pops back
up right away, you need to add rebound. If it drags up slowly, loosen
it up. If you have a compression adjuster, sit it up in the middle.
You can determine how to adjust it after your initial test ride, too
hard loosen it up, and to soft add.
Front Forks....Start here by setting the sag on the fork the same way
you did on the shock. First you need a fully extended measurement.
Only way to get consistency is to have two guys pick up on the
handlebars until the front wheel leaves the ground slightly. Measure
the exposed area of the fork slider. On a conventional fork, this will
be from the bottom of the lower triple tree to the top of the dust
seal on the slider. For an inverted fork, this will be from the dust
seal down to the top edge of the aluminum axle clamp. Record this
measurement on your log sheet. Push down on the fork hard three times,
to settle the suspension. Now measure the static sag. Finally, get on
the bike and push down three more times, while a friend balances the
bike. Have your friend with the tape take the final measurement. The
measurement you are looking for on the front fork is 35mm. If your
spring is of the correct rate, the free sag should be about 65 percent
of the rider sag, or about 20mm. The front fork has to have a great
deal of free sag so that the front wheel may move down into a hole as
well as over a bump. If your fork has too much sag turn the preload
adjuster in. If you don't have preload adjusters, then you will have
to remove your fork spacers and cut longer preload spacers. Adjust in
10mm increments. When you get close, you can go to 5mm increments.
Next is the dampening adjustment. The fork needs to move much faster
by comparison than the shock. Again, you should be able to watch it
rebound, but not as slowly as the shock. Grab the front brake and push
down on the front of the bike as hard as you can. Don't release the
brake and don't resist the rising action of the fork. Observe the
action. You want it to rise back as quickly as possible without
topping out and settling back down again. Loosen the rebound until the
bike does want to settle back after topping out, and then dial in just
enough rebound to make that settling tendency go away.
The compression adjuster should be set as softly as possible, but
prevent the fork from bottoming over severe bumps or under hard
braking.
If you do not have these adjusters available to you externally, then
you must change your fork oil weight to adjust the dampening. Thicker
oil affects both compression and rebound dampening.
If your forks works properly over bumps, but bottoms under hard
braking, you can add more oil, or "raise the level" to help prevent
bottoming. This reduces the air cushion you fork has above the oil.
Steering Dampener....This is primarily a safety device and should be
thought of as such and treated with great respect. Anyone racing
without one might as well not wear leathers or a helmet. It's very
dangerous. It should not be used to mask a bad handling motorcycle.
When you go out to test your suspension, have the dampener set so that
is barely drags when you sweep the wheel from side to side. It should
not make your bike difficult to steer in the pits. Test ride the bike
and analyze what it's doing before you crank up the dampener. A
dampener that is too stiff will make the bike track from side to side
and will be difficult to steer. After you make changes always return
to this base setting, and then adjust.
Jockey check....quick test method. Have a friend balance the bike
while you get on and assume your riding position. Lift up off the seat
slightly and bounce down on the bike. It should compress and rebound
in a balanced fashion from front to rear evenly. If your bike isn't
balanced, it won't work right. Your initial adjustments are only to
get to this simple test. If the bike isn't acting balanced, adjust it
until it does regardless of the initial adjustments you made. Balance
is the single most important facet of chassis setup. A bike that is
too soft or too stiff is still easier to go fast on than one that is
out of balance. If you bounce lightly, it should act balanced, as well
as if you bounce with great force.
PERFORMANCE ANALYSIS/DIAL IN
Now that you have a good baseline set-up, it's time for a test ride.
Ensure that your tires have the correct pressure in them, and head to
the track or your testing grounds. In order to make an assessment of
your bike's chassis, you need to be conscious of what's going on while
you are riding it. Someday when your a racing god, you'll have data
acquisition equipment to tell your chassis engineers what to adjust.
But until then, you are the only suspension sensor on your motorcycle.
This is actually the best way to learn. There are several things you
need to analyze as you ride.
High speed stability.....this should be self explanatory, and the
easiest to analyze. Go fast in a straight line and your bike should
never scare you. If it does, you have some adjusting to do.
Performance under braking....Is the bike stable? Does it squirm
underneath you? Does the front wheel bounce? Does the rear wheel
bounce? Does the forks bottom? How does the bike behave trail braking?
Performance in the corners....This needs to be analyzed in three
segments: Turn in, mid corner, and exit. Be conscious of these things
within each of these segments: Overall stability, steering effort,
ground clearance, front wheel action, and rear wheel action. That's a
bunch of stuff to think about, especially when you're just trying to
circulate and learn to ride. If any of these things are out of whack,
they'll usually let you know, consistently, in most turns. Here is an
explanation of what to look for.
Overall stability....The main thing to look for here is wallowing
action. There should not be any. Wallow indicates a need for more
spring.
Steering effort....Does the bike track well in the corners? Do you
have to fight to keep it on the racing/riding line? Are your arms
completely worn out after riding/practice?
Ground clearance....If you have anything dragging the ground, you have
a problem that could result in injury. Some guys think they're cool
because they drag stuff around the track/road. These people are a
hazard to themselves and others. If you have anything dragging, fix
it! Raise your footpegs, bend your pipe in, or
whatever it takes. If you lean in hard enough on a bike that's
scraping the ground you will lift a tire off the ground, and then you
will immediately take its place on the pavement; this is serious
business. If you are happy with the way your chassis works, then don't
alter your ride height to stop things from dragging. Just get
the dragging stuff up and out of the way. Changing ride height alters
the bike's handling characteristics.
Front wheel action....The wheel should roll smoothly through the
corner and inspire confidence. Does the wheel bounce? If it does, you
need to pay close attention to the way it bounces. If the wheel is
bouncing and you can't really feel it in the bars, then this is a lack
of rebound dampening. If the handlebars are jarring you, then
you may have too much spring preload or compression dampening.
Use rebound dampening carefully. Too much rebound dampening creates a
situation where the fork is packing down. This means your forks has
collapsed and is not re-extending fast enough. This is a VERY
DANGEROUS situation. A fork that has packed down has no suspension
travel left. A crash is eminent. You need to
speed up your rebound dampening. You may also need a higher fork oil
level, or more compression dampening to keep the forks from bottoming.
This situation is usually set up by hard braking that compresses the
fork followed by trail braking into the turn which never lets the
forks recover. Some additional spring may help this too.
Rear wheel action....Your rear wheel can exhibit many of the same
symptoms as the front wheel. If your bike feels like a pogo stick then
this is typically an all around lack of dampening. This condition will
also cause a bunch of wheelspin on exit and tear up your tire.
Wheelspin also fools riders into believing that they are going fast;
that is until some novice on a GS500E goes railing around the outside
of them in a turn. Too much rebound will cause the rear wheel to
"swim" under the bike side to side under hard straight line braking.
This is because the shock is packing up and the rear wheel is hanging
in the air instead of returning to the ground to keep you pointed
straight.
A lack of compression dampening will cause the bike to pogo while
under acceleration. This will be a vertical "sawing" motion; vertical
relative to the bike even though it is still leaned over. Too much
compression dampening will make the bike "buck" or kick you in the
butt over sharp bumps. This can also cause excessive wheelspin. The
shock should be soft enough to let the bike squat some. This transfer
of weight helps give the tire more grip.
When you notice a flaw in your suspension, note where it occurred in
the turn. Was it as you rolled into the turn, was it in the middle of
the turn, or was it as you accelerated out of the turn? This is
critical information to help you (and a suspension tuner) decide what
the correct changes should be.
Chassis geometry....If your bike's chassis is soaking bumps properly,
but your bike isn't steering around the track properly, then you need
to adjust the "attitude" or "geometry" of your bike. This will affect
it all the way around the track.
The variables you have to work with are the fork height, and the
swingarm angle. Here's what each does.
Fork angle....Will increase or decrease your trail. Moving the nose of
the bike lower (forks higher in the clamps) will make it steer faster,
but will be less stable. Moving the nose of the bike higher (forks
lower in the clamps) will require more steering effort, and will
increase stability. Most expert riders say this increases "feel" at
extreme lean angles.
For most novice riders, will find it the easiest way to evaluate this
is to ride through a high speed sweeper and evaluate how the bike
steers into the turn and notice how much effort it takes to make it
steer to the apex of the turn. In other words, "How does it hold a
line?"
If the bike is too low in the front, it will steer dramatically, and
try and drive off the inside of the track. It will be unstable all the
way through a turn, and sometimes even on the straight-aways.
If the bike is too high in the front, it will steer in slowly and
require that you pull on the bars to hold it down to get it to the
apex. This condition will make it very difficult to steer the bike to
the apex. It will fatigue your arms and they will feel tired after
riding.
Swingarm angle....tunes the way the bike reacts to acceleration. Your
motorcycle wants to "squat" under acceleration due to the rearward
weight transfer.
If the swingarm is too flat, the bike will squat too much, and the
bike will sit back and the front will extend like a "chopper". This
will make the bike want to "run wide" or run off the edge of the
track. The front end will feel light and dance about as you are
leaving a turn. The result is that you have to wait to get on the
throttle. You should raise the rear of the bike to correct this.
If the swingarm angle is too steep, then the bike will not squat
enough, and the result will be poor traction. This is "wheelspin" If
you can whack the gas, and the wheel spins up, then you need to lower
the back of the bike.
Here's where it gets more complicated. Changing one end of the bike
affects the other. There is a simple way to figure it out. If your
problem occurs from steer-in to mid-corner, then change the front. If
your problem
occurs from mid-corner to the exit, then change the rear. Although
there is no way to accurately mathematically describe what happens
when you make a change, here is a VERY crude way to think about it.
Changing the front ride height has an effect of "5" on the front and
an effect of "1" on the rear. Changing the rear has an effect of "5"
on the rear, and an effect of "1" on the front.
A common example of where riders improperly change their bikes comes
when the bike steers in too slowly. Many confused riders and tuners
will raise the back of the bike. This makes the nose steeper, and the
bike will steer more sharply. But remember, in order to get an effect
of "1" on the front of the bike, you have now make an effect of "5" on
the rear. Your bike may now turn in better, but you will get less
traction, more wheelspin, and more tendency to high-side. This is not
what you wanted... The correct change is to lower the nose of the
bike. This affects the turn in "5 (front)" and the exit "1 (rear)".
Much better!!!!
If you have no idea where to start with your geometry, look around the
pits or ask a suspension tuner. There is no correct answer or magic
formula for what you personally want your bike to do. Your personal
style of riding will dictate to you what to do with the bike. You will
find that most production bikes are way off of what's is generally
"good" Find a range of "good" seems to be for your model of bike and
start on the "safe" or "stable" side of the range
