Raven
20th November 2005, 18:11
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 times 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 times 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.
Next issue we'll talk about the final point in getting the springing right in your suspension, and start to figure out what to do with the damping.
Good Luck with your riding...
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 it's 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.
Next issue: damping controlling the movement of the spring...
Good luck with your riding.
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.
See Part 3
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 times 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 times 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.
Next issue we'll talk about the final point in getting the springing right in your suspension, and start to figure out what to do with the damping.
Good Luck with your riding...
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 it's 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.
Next issue: damping controlling the movement of the spring...
Good luck with your riding.
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.
See Part 3