How to adjust the suspension of a motorcycle
The suspensions are one of the most important points of our motorcycle. The good dynamic behavior of the whole bike depends on them. Do not think that it is something unimportant; on the contrary; it is something that you should not overlook.
A good adjustment of the suspension will improve the stability underway, ensure the best response of the bike, get the most out of it and also take care of your own safety.
To know how to tune the suspension of your bike it is essential that you know the elements, terms and basic concepts that influence the suspension, such as preload, extension and compression. Only when you have these ideas clear you understand why it is necessary to adjust their parameters and how to get the best behavior.
SAG: What is it?
On a motorcycle there are some measures that you have to take into account to adjust your suspension, both the front fork and the rear shock absorber. It is called SAG to the extent that it will indicate the preload that the suspensions of our motorcycle have on us. The preload of the suspensions can vary from one user to another; depending on their weight or even if we travel by motorcycle with a passenger.
The SAG marks the difference between what the extended suspension free of weight measure and what they measure once subjected to the weight of the motorcycle and its pilot. This difference will vary depending on the spring of the suspension and it’s preload, so we must act on the preload to get certain figures depending on the type of driving we are going to perform, whether sports circuit, sport, normal or comfort, as it can be in a motorcycle trip.
SAG: How is it calculated?
The procedure to calculate the SAG of our motorcycle requires a little time and the help of another person, but it is worth the effort to get the required adjustment. We are going to calculate the difference that there is in millimeters between the extended suspension without weight and the suspension compressed with the weight of the pilot, that is to say, what margin of movement we are going to leave it in march, and for it we will follow the following steps:
- With the help of another person, we extend the fork until the front wheel does not touch the ground. If the bicycle has a central support, it is simple if we load weight on the rear wheel, and if it only has one side leg, we will have to tilt it over until the front wheel is in the air.
- Once we have the fork fully extended, we will measure the distance from the upper point of the bottle to the lower point of the fork near the wheel axis. We enter that figure, for example, 365 mm.
- With the bike resting with the wheels on the ground we get on the seat and put our feet on the footrests, another person can help us to maintain balance, and it is convenient that we do it with all our equipment of biker positions, with the helmet included, so that our weight is as real as possible.
- We repeat step 2 and measure the fork length from the same points as before, but now compressed with the weight of the bike and the driver. We note that measure, for example, 330 mm.
Rear shock absorber
- We will do exactly the same as with the front fork in step 1 and we will take measures with the shock absorber extended in a position in which the rear wheel does not touch the ground. If we have a center stand it is enough to put weight on the front part of the bike, and if we only have a side leg we will have to tilt it over it until we leave the rear wheel in the air.
- At this moment we will take measurements, from the axis of the rear wheel to a fixed point of reference, such as for example some point of the subframe under the passenger seat, or an adhesive tape that we can glue for the occasion and take as point reference. We note the measurement, for example, 410 mm.
- As with the fork, now we will repeat this procedure but with the driver riding on the bike with all his clothing.
- Repeat the measurements taken in step 2 but this time with the pilot on the bike, and always measuring from the same points that we made in step 2. We note this new measure, for example, 370 mm.
Adjusting the ideal preload
After calculating the SAG, the difference between extended suspension and compressed suspension, we have a front measurement of 35 mm and a rear measurement of 40 mm. We can change these measures depending on the type of driving that we are going to carry out, following the recommendations as a guide:
- Sports driving: Front: 35 mm/Rear: 30 mm
- Normal driving: Front: 42 mm/Rear: 35 mm
- Comfort driving: Front: 48 mm/Rear: 40 mm
Example of adjustment
Once we have calculated the SAG of our motorcycle, we will act on the preload of both the fork and the rear shock absorber to achieve the desired figures.
If the SAG obtained, for example in the fork, it is 40 mm and the desired is 35 mm, it means that we must increase the preload to reduce those 5 mm difference. That is, we have to get the fork to sink only what is necessary, in this case 5 mm less, when we are on the bike. Normally in the fork each turn of preload screw usually means one millimeter of travel, so we will increase the preload by 5 turns and we will repeat the operation of measuring the length of the fork compressed with the weight of the pilot. If we have increased the preload now the fork will sink less and we will get closer to those 35 mm that we looked for at first. We will repeat this operation, both before and after, until we reach the desired figures.
It is possible that due to our low weight to our high weight the springs that our motorbike equips as standard are not able to reach the figures we need when we are on the bike. In this case, it is advisable to consult with specialized trustworthy workshop for a possible change of springs.
The perfect balance
Once we have the preload adjusted to our weight, both in the fork and in the rear shock absorber, we have the suspension of our bike balanced. Thus, therefore, we have the ideal preload fixed and will be the basis for the rest of the operations.
As we told you, there are two other parameters that can be modified in the suspension of our motorcycle: compression and extension.
Both depend on the behavior we demand of our motorcycle, the compression will control the speed at which the suspension will compress when we brake our motorcycle, accelerate or pass over potholes, and the extension the speed at which the suspension will extend when the spring tends to return to its natural position. We can vary one and the other depending on our needs, but it is important to know what the factory settings are to be able to return them always if we do it erroneously and worsen the behavior of our motorcycle.