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.