The following six part suspension set-up guide is copyright to Australian Motorcycle Trader and
reproduced here. These articles can also be found here
BikePoint.com.au
Suspension Set-up
Credits
The following six part suspension set-up guide is copyright to Australian Motorcycle Trader and
reproduced here. These articles can also be found here
BikePoint.com.au
Contents
Introduction
The following article was written by Steve Brouggy Proprietor / Head Instructor of the
Australian Superbike School,
former 'A' grade road racer and motorcycle shop proprietor, Steve Brouggy is the only person in the
world endorsed to teach Keith's format while he is not present. Steve's philosophy of results with his
students, ability to make the complex simple, as well as his undoubted riding skills, were all factors
in being awarded the only 'franchise' of Keith Codes enormously successful California Superbike School.
With a belief that the result at the end of the day is paramount, Steve's unique blend of experience
and enthusiasm has led him to put together a staff compliment devoid of 'name' riders, but full of
excellent instructors. "After all, students don't come to our school to see how good we can ride,
they come to learn how they can ride better."
Part 1 - Suspension - The Black Art
Welcome to part one of a six-part series on
suspension set-up, written by Steve Brouggy of the
Australian Superbike School, and published a couple of times over the
years by Australian Motorcycle Trader. All six articles are on this
site and you'll find this to be the best set-up guide around.
One of the most commonly asked about subjects at the Superbike School is suspension.
As with anything to do with riding motorcycles, there are usually simple explanations for
everything that happens, making it a matter of just taking the time to analyze each individual
action and the resulting consequence. To assist in making this process possible in the 'black art'
of suspension, I have enlisted the services of Melbourne based guru Rod Sharp
(Rod Sharp Cycleworks and technician / advisor with Team Ansett Air Freight Suzuki's superbike team).
Firstly let's discuss what suspension actually does. Simply put, the suspensions job is to keep the
wheels on the ground. (Giving you a nice comfortable ride is very much a secondary consideration!)
This means that how the suspension works will directly affect arguably the most important concern
when riding a motorcycle - traction.
We have already discussed how the way you ride can affect the suspensions operation,
simply by holding on too tightly and putting too much input into the bike, you are not allowing
the suspension to complete it's task. The end result of not allowing the suspension to fulfil its role,
is that traction is affected, and the bike will tend to run wide. It will also amplify any bumps
or deviations in road surface by transferring the force back and forth between your body and the bike.
(For more detailed information on this, either see "Keith's Corner" at the California Superbike School
web site -
www.superbikeschool.com - or read chapters 7 to 11 in "A Twist of the Wrist II" by
Keith Code.)
No amount of changes to the bike will overcome the problems associated with the rider doing
something to the motorcycle which interferes with the way the suspension is supposed to work.
So, riding problems aside, how does it all work?
There are several components to the suspension system of any motorcycle. Each one has specific
role and design parameters, and each will be effected in some degree by adjustments to the other
components. There are two major operations of any set of forks or shock absorber. They are; Springing;
and Damping.
The spring has two variables in its operation, one is pre-load, the other is the spring rate.
Preload is adjusted by changing the fitted length of the spring thereby changing the amount of
initial force needed to begin movement of the spring. Changing the preload also affects a very
important part of the basic set up which is 'static sag' (we'll talk a little more about that in the
next issue). The spring rate on the other hand can only be adjusted by changing the spring.
It determines the amount of force needed to keep the spring moving which can be lesser or greater
depending on the amount of coils and the thickness of material used for the spring.
The damping's job is simply to control the springs' speed of movement. There are two basic areas
of this; the first is compression damping, which deals with the rate at which the forks or shock can
compress or dive; and the rebound damping which deals with the rate at which the suspension can
extend or rise. Without damping to control the spring, it would be free to continue moving the force
backwards and forwards along its available travel, which would be substantially more than you want
on a motorcycle. (If you have ever jumped up and down on a pogo stick, you'll know what a spring
feels like without any damping!)
So, this means you have four totally different ways in which to change your suspension.
When you consider that most modern sport motorcycles have around 12 or more damping adjustments,
12 or more rebound adjustments, 'endless' preload front and rear, along with a plethora of different
rate replacement springs available, you now have literally thousands of possible combinations! Add to
this the fact that the front needs to be balanced with the rear, and it's no wonder most riders are
confused about what to do with the suspension!
Back to the top
Part 2 - Setting the sag
As mentioned in part one, setting the static sag of the motorcycle is the starting point to
getting your bike in the realm of using the suspension correctly. As you set the sag you will
uncover some basic flaws in your settings that can be arrived at no other way.
The static sag is set with the bike under it's own weight, and is backed up by two further tests;
the One G Test (with rider and normal weight load in place); and measuring the amount of suspension
travel used while riding. To get the springing rates correct for your motorcycle, this process must
be worked through in sequence. If you decide to miss one of the steps or allow the settings to fall
outside the guidelines given, you'll be missing at least one or more ingredients to getting your
suspension working the way it's designed to.
So, let's discuss exactly what the static sag is - Static: motionless, inactive. Pertaining to
bodies at rest or equilibrium. Sag: curve downward under pressure. Give way. Hang loosely - so we
are in affect measuring the "curve downward of a body at rest". The exact measurement for what to
set the static sag at will differ from bike to bike, rider to rider, and will vary depending on how
the bike is to be used. There are however some fairly stable guidelines on where to start.
First you need to know how much travel your suspension has by extending it fully and measuring
in the direction of travel. On the forks this is easy as you simply measure from the top part of
the lower fork leg, to the bottom of the triple clamp.
On the rear, you need to pick two points that are at each end of the travel. For example, the grab
rail and the axle. Unload the suspension fully by taking the weight off it and measure as shown in
pictures 1 and 2. This will give you the unloaded distance.
To get the fully extended length of the suspension it's important that you take any sag out by
lifting whichever end of the bike you are measuring. If possible it's best to actually lift the
wheel off the ground when doing so, to ensure you are getting accurate measurements. This can be
done by having someone balance the bike of the side stand (if a centre stand isn't fitted) while
you do the measuring. Once you have this distance, stand the bike upright, and allow it to sit under
it's own weight, measuring from the same points. It's best if you give the bike a couple of bounces
up and down, then allowing it to settle before measuring. This guarantees the suspension is settled
to its true sag. The difference between these two measurements is the static sag.
The rear sag should be somewhere between zero and 10 millimetres and the front between 20 and
30 millimetres. As mentioned earlier, there will be some differences from bike to bike and rider
to rider, depending on how you are using your bike, but it should always fall within this range.
For example, during racetrack use you will find that firmer is better (within reason), whereas
on the open road that is not always the case.
Back to the top
Part 3 - The One G Test
The One G Test backs up what we have already done in setting the static sag of the motorcycle,
and takes into account the particular weight load that is going to be carried and the way the bike
is going to be used. This is the part that most riders forget...so listen up!
To be effective, the measurements need to be done with the normal weight load (i.e. the rider)
in place. If you are a courier for example and carry a reasonable weight on the back of the bike
for a large percentage of the time, or you only ever ride with a pillion in place, it would be a
good idea to simulate that situation for the purpose of measuring. If you were planning a touring
trip with baggage, but still wanted the bike to handle at it's best for the roads you plan to ride,
you could reset the static sag to suit the weight load carried for that period of time, then change
it back to the way it was once the trip is over. To do this correctly you will need a measuring tape
and three helpers. Two to balance the bike with you in place, while a third person measures the sag.
First, you need to know how much travel your suspension has by extending it fully and measuring in
the direction of travel, just as we did to set the static sag. On the forks this is easy as you simply
measure from the top part of the lower fork leg, to the bottom of the triple clamp.
On the rear, you need to pick two points that are at each end of the travel. For example,
the grab rail and the axle. Unload the suspension fully by taking the weight off it and measure
as shown last issue. This will give you the unloaded distance.
Once you have this measurement, the rider (and any other normal weight load) should be put on
the bike as per the pictures shown, with helpers holding the bike front and rear. The rider should
then bounce the bike up and down a few times to free up the suspension and put it in the position
it would normally sit in with the rider in place. The designated 'measurer' should then measure
from the same points the first (unloaded) measurements were taken.
The difference between these two figures (the sag) should fall somewhere in the vicinity of
25-35mm front and rear. If you find your bike is either less or more than this, simply adjust
the preload either harder or softer using the preload adjuster, until it falls within this range.
Often time's bikes that have done a few kilometres will sag way beyond ideal settings, as will
new bikes sometimes. As a matter of fact I have measured brand new sport motorcycles that have never
been ridden and found they have more than 50mm sag front and rear! As you make adjustments you may
find that you get to one end or the other of the existing springs range. If this happens, it means
the next spring available (either heavier or softer) is probably going to be on your shopping list.
Often time's riders try to make up for a lack in one area of suspension by adjusting another.
In this example, if the bike were still too soft after the preload was adjusted fully, you could
turn up the compression damping to try and slow the speed of movement downwards. This would begin
complications that could severely effect the suspensions ability to function. If you were to arrive
at this point, speaking with an expert (as opposed to "pub experts") is really the only course of
action.
Back to the top
Part 4 - Measuring the travel
The final part of setting the springing (as we've been discussing the last two issues) on the
suspension is to measure the amount of travel used while riding. It's important to do this final
step rather than rely on how the bike feels. Often our perception of what the motorcycle is doing
is quite different from what is really happening.
This final step is probably the most simple of all. To measure how much travel the suspension
is using it's just a matter of putting a cable tie (sometimes referred to as a zip tie) on the shaft
of the forks and the shock. In this way you can see how much of the available travel is being used
by the location of your cable tie after the bike has been ridden.
To ensure accurate results, you should only measure the amount of travel being used after riding
in your normal environment. Meaning that if you do mostly ride days and sport riding, just going
around the block isn't going to give you a very accurate idea of what the suspension is actually
doing!
If you find your cable tie is pushed up against the end of the shaft, chances are your suspension
is too soft. On the other hand, if your cable tie is only half way along the suspensions travel,
chances are your suspension is now too hard. The ideal scene is to have the swept area
(the total amount of travel used) to be only slightly smaller than the total travel available.
By using the three measurements we have discussed over the last two issues of AMCT, you now have
the tools to set the springing correctly. As you change the preload to suit one of the settings,
you may find that it makes the suspension fall out of the ideal range in the other areas. This
tells you that your spring may not be the right one for your application. For example. Lets say
you did everything right in setting the sag and the one G test, but your suspension is bottoming
out (using too much of its available travel).
This would tell me that your style of riding requires a harder spring set with less preload.
This spring would require more force to use all its travel, but less to start it moving. Meaning
that you can still get the sag figures correct, while using the right amount of available travel.
There are far too many possible variations for us to cover in this short amount of time, but at
least now you should be able to recognise whether or not your suspension is working within the range
it was designed to work.
Back to the top
Part 5 - Damping
Now that we have the springing set correctly, it's time to control the spring movement with the
damping. Please note - if you haven't undertaken the process of setting the sag, doing the
"One G Test" and measuring the travel, you won't find the information on damping of much value.
If you've missed the AMCT issues with this information, copies are available by contacting the
Australian Superbike School, tel (03) 9792 1322, fax (03) 9792 1075.
Down to business... there are only two directions the suspension moves, up and down.
When the suspension is diving or compressing, it is termed the 'compression' and when it raises
or lifts it is called the 'rebound'. The damping's job is to control the speed of both the
compression and rebound of the suspension, thereby controlling the speed the wheel can move up and
down. This decides what sort of contact (if any) your wheel with have with the ground, thereby
affecting the tyre's traction to the road.
It accomplishes this hydraulically, by transferring oil from one
reservoir via a piston with a series of valves to another reservoir. By
adjusting the damping you are changing the amount of oil
that is able to go through the valves (the 'flow rate') thereby
changing how quickly the suspension
can move. The larger the hole in the valve the faster the suspension
will travel, the smaller the
hole in the valve the slower the suspension will travel. Similarly, the
thinner the oil in the
suspension, the faster the travel, the thicker the oil, the slower the
travel.
On most modern motorcycles there are adjustments for both the compression and rebound damping
both front and rear, along with the ability to change the oil weight. Before delving into the
specifics of setting up the damping, it is important to realise that both ends of the bike will
effect each other in their set up. Meaning your front forks may be set up perfectly, but if it is
mismatched to the rear in either the springing or the damping, it will be less effective.
The difficult thing when adjusting the damping is that there are no rule of thumb measurements
that are easily taken and compared like there is with the springing. In fact unless you have state
of the art data logging equipment and a shock dyno, the decision of how to change your bike will fall
somewhere between the observation of a technician (whoever you talk about suspension with) and the
feedback given by the rider (you). This is where riders get lost in trying to correct a handling
problem, and place the whole process of correcting suspension into the too hard basket.
The true difficulty here is that we now open up the whole subject to the different perspectives
given by each of these individuals. It is no surprise that when data logging
(sometimes referred to as telemetry) first appeared on racing motorcycles, the rider almost always
wanted to go the opposite direction in adjustments to what the data logging system suggested.
Showing conclusively what the experts have known all along...very few riders actually know what
their bikes are doing while they ride them! Racing has now become much more of a precise science
since the advent of such systems, to the point where a world championship level team wouldn't be
able to function effectively without it.
What this means to you and I is that we are now dealing with an area that requires some expertise
to get right, along with an ability to observe what the bike is doing while being ridden.
If you follow the guidelines and examples in the coming issues we can at least give you some idea
of what your bike may be doing, and hopefully help you chose a way in which to fix it.
Back to the top
Part 6 - Damping (continued - final of the series)
As mentioned in the last issue, there are no hard and fast measurements with which to set the
damping on the suspension. We also stated that most riders don't know what their bike is really doing
when they're riding it. So the question must be asked...how do you know when it's right?
And how do you know when it's wrong?
I've seen suspension technicians bounce a bike up and down and make a decision as to what
changes to make to the suspension. Mere mortals like ourselves may observe this and, seeing what
decision they arrive at, start to base similar decisions of our own on this information.
The problem is that we haven't had the technical training they have.
We probably haven't bounced a couple of thousand bikes up and down before, feeling for what
the suspension is doing either. Therefore, chances are we haven't gained a 'feel' for what good
damping should 'feel' like on a stationery motorcycle.
It should also be noted that this is usually not the only source of information that the technician
will base his decision on. As a matter of fact, to be as accurate as possible, they will use several
sources of information. So in combination with 'feeling' the bike by bouncing it up and down,
they will look at how the bike is wearing the tyres, if at all possible (especially in a racing
situation) the technician will try to observe for himself what the bike is doing, along with getting
the riders perspective.
Obviously if you are not racing and you come to a suspension expert, they will probably not be
able to observe what the bike is actually doing, and will have to base their decision on the other
factors. This should be enough for someone who has the skills to decipher the sometimes
incomprehensible babble that we (as riders) offer, and what he 'feels' the bike doing.
Our job as riders then is to give the technician accurate information. In other words we need to
observe what the bike is doing and report it. If you are going to be your own technician, that's fine,
just recognise the different roles you play. On the bike you are the rider, gaining the information
needed to base a decision on. Off the bike you are the technician and your job is to take that
information and base a decision on it. Don't expect every decision to be correct. Chances are
you'll have to repeat the process of changing these 'hats' more than once to get it right.
So...what exactly are we looking for? The damping can only be one of three things. Too hard.
Too soft. Or, just right! To help you understand what effect each of these have let's look at them
individually.
Too hard - as a rule, if the damping is too hard, the bike will feel unstable. If it's too hard
in the compression damping the suspension will not comply with bumps, as the transferring of the
force is too slow, meaning the wheel will tend to skip over the top of the bumps rather than follow
the contour of the road surface. If too hard in the rebound damping the bike will tend to 'pack down'
or 'squat'. This is caused by the suspension not allowing the bike to rise back up to its original
position quickly enough. The end result of this is sometimes referred too as suspension "chatter."
Although the bike will feel unstable, it will tend to feel quite 'stiff' or 'taught.'
Too soft - the interesting thing here is that if the damping is too soft, the bike will also feel
unstable. Only this time, rather than 'chattering' it will tend to feel 'sloppy,' and possibly
'wallow' in corners. (wallowing means that the suspension will oscillate without anything seeming
to start it off, like bumps for example) It may also feel a little like a pogo stick, continuing
to transfer the force up and down the length of the travel. This is particularly noticeable on
bikes that have done a lot of miles.
Just right! - if the damping is working correctly, you probably won't notice anything!
The suspension will keep the wheels moving up and down as required to keep the tyres on the ground
and the bike stable. Who was it that said "the more I know, the less I understand"?
The interesting thing about reading information on a technical subject like suspension is that it will
tend to raise more questions than it answers. I'm sure that over the last few issues we have been
focussing on the subject of suspension, that has happened for you. That's okay. In fact that's what's
supposed to happen.
It's now up to you to use this information and apply it. Doing so will answer some of your
questions, and the ones it doesn't need to be directed to someone who knows what they are talking
about. And...just in case you're wondering...that's probably not your brother in law or next door
neighbor...
Good luck with your riding.
(Author Steve Brouggy is the owner of the Australian Superbike School on tel 03-9792 1322.)
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