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.
Good luck with your riding...