PDA

View Full Version : Suspension Setup Part 1



Raven
20th November 2005, 18:05
I've stolen the following but seeing as how it was freely available on the web what the heck


Suspension Setup

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 analyse 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 it's 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 a 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 it's 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 raise.
Without damping to control the spring, it would be free to continue moving the force backwards and forwards along it's 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!
Over the next few issues we'll break down basic bike set-up and give you at least a starting point for you and your motorcycle.
Good luck with your riding.
(Author Steve Brouggy is the owner of the Australian Superbike School on tel 03-9792 1322.)


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 downwards under pressure. Give way. Hang loosely - so we are in affect measuring the "curve downwards 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 it's 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.

See part 2

HDTboy
19th April 2006, 15:29
These three threads need to be merged and made sticky

Fishy
19th April 2006, 15:31
Is this the info from Sportrider.com?

bugjuice
19th April 2006, 15:49
someone already posted this all up in 3 parts..