Adjustment and maintenance of the chassis

Shock absorbers and telescopic forks are essential components on Chassis of all two-wheeler classes. Both are safety-relevant components whose functionality should be checked regularly. As standard, telescopic forks and shock absorbers usually consist of a combination of spring and damper. With pure gas pressure shock absorbers, the gas filling takes over the spring function. While the springs on which the vehicle is mounted to oscillate are intended to reduce unevenness in the road surface (shocks), the damper has the task of stopping these oscillations again promptly. The vibration energy is converted into heat by the damper. The shock absorber is therefore actually a "vibration damper".

If he does not complete his task properly, the vehicle will rock for a long time, for example. Shortly successive bumps, potholes and tight curves with bumps can lead to a further amplification of these vibrations, which make the scooter and moped increasingly difficult to control, which can ultimately lead to loss of ground contact and slipping of the wheels. While the shock absorbers are typically found as suspension struts on the rear axle of the scooter, they are usually found at the front in the form of the telescopic fork, which looks completely different, but fulfils exactly the same function. Rear and front suspension parts must be fully operational at all times.

Safety, comfort and cornering behaviour result to a large extent from the correct tuning of the chassis. But what is actually better - soft or hard damping? The suspension technology is complex and a chapter in itself, no matter which vehicle is involved. Whether the scooter buzzes over the asphalt better with a hard sports suspension or as a mobile sofa is sometimes a matter of taste and also depends on the driving style of the respective driver. Anyone who likes to drive fast and rush around bends will be more comfortable with a tight suspension. Those who prefer to do their shopping with the scooter will, on the other hand, attach more importance to appropriate driving comfort.

The good news for the second group of riders is that most scooters are equipped with a softer suspension that provides a high level of comfort. However, even this comfortable cushioning should not be left to its own devices. With increasing kilometres on the speedo clock, the damping capacity of shock absorbers and telescopic forks decreases. You don't even notice the deterioration, because you get used to the defective chassis and feel "normal" due to the slow process. A check of the complete suspension is therefore necessary from time to time, because otherwise it can become really dangerous in road traffic. But you can also be happy about a bonus after the effort of maintenance: The improvement is often noticed right away and you get a good portion of driving pleasure in addition to the new safe driving feeling. If, from a technical point of view, all suspension components are in order, some telescopic forks and shock absorbers offer various adjustment options that should also be used. After all, the scooter shouldn't bounce so much that it becomes a rocking horse, but it shouldn't lie so hard on the road that the rear wheel starts to jump.

Basic concepts of chassis technology and shock absorbers Setup

Stoßdämpfer YSS Mono PRO-X 285mm für Piaggio, Gilera

Not all shock absorbers offer all the adjustment options described below. Some very simple shock absorbers cannot be adjusted at all. These have to be taken (mostly) as they are. Some can at least be opened and adjusted to your personal needs with the damper oil. No matter which settings are made, two things have to be considered fundamentally: The values of the original setup should be noted down, because if the damper suddenly does not work as intended, you can simply return to the initial values.

Secondly, care should be taken to preserve the geometry of the chassis. This means that you should adjust the damping of both the telescopic fork and the rear suspension struts. Otherwise the ratio between the rear and front height of the scooter will change. If, for example, you only spice up the telescopic fork with stronger springs or longer distance sleeves, you should not be surprised if you feel that you are constantly driving uphill. However, the vehicle geometry can be played with a little bit: A raised front gives more driving stability, but also leads to slower handling. On the other hand, the braking behaviour improves, as the rear end comes up a little later due to the redistribution of weight. A raised rear makes the scooter an agile curve robber, which can be very dynamically meandered through city traffic. But you lose stability and have to get used to the changed braking dynamics.

Spring preload
Unlike a car, a scooter or moped reacts quite sensitively to minor weight changes. More payload allows the shock absorbers to continue to bounce and under certain circumstances to break through (suspension travel of the damper is fully exhausted and the inner piston strikes the end of the damper). In this case the spring preload should be increased. This shortens the spring travel from the outset, the tighter spring immediately offers more counterpressure and the scooter springs less strongly. If there is the possibility of adjustment, at the end of the damper spring you will find a rotating step adjustment with different locking points, which cannot be overlooked. With a special key you can turn this pre-tension ring. The same spring preload must be set on both sides of each axle. When the scooter is removed from the stand and the rider has taken a seat, a part of the total available spring travel is already used. This is the Nagativ spring travel, which should be about one third of the total travel when adjusted correctly. The length of the suspension travel from the rear of the frame to the rear edge of the swingarm is measured. If, for example, the suspension travel is 90 centimetres (total suspension travel) when the vehicle is jacked up, 60 centimetres should remain after the scooter has been removed from the stand and the rider has taken a seat on it. A helper may be useful for correct adjustment. The spring preload has no influence on how hard or soft the scooter springs, but only regulates the vehicle level. If the suspension is too soft for you, the compression and rebound damping is adjusted differently or, in case of doubt, you have to use harder springs or other shock absorbers.

Compression
A hydraulic shock absorber is subjected to tensile stress during spring deflection and compressive stress during compression. This is why damping is called rebound damping and compression damping. Since the wheels are not supposed to accelerate upwards with one blow when the road is uneven, etc., the spring deflection is braked by a damper. The strength of this braking process is called pressure stage. It is responsible for the feedback about the road conditions (fine impression). If the compression stage is too low, the wheel takes off briefly, if it is set too high, every blow on the road is passed on directly to the driver's spine, which then serves as a "damper". Technically the damping works via a bottom valve through which only a limited amount of oil can flow. This creates pressure resistance in the downward movement and dampens the movement. Handlebar hitting on uneven surfaces, especially in curves, indicates a too high pressure level. The compression stage is too low if the rear end still fails with a low load and already high spring preload, if cornering feels spongy and the rear end becomes restless.

Rebound
During spring deflection, the spring is hindered in the same way by a tensile resistance during relaxation. The spring deflection is thus delayed over time, resulting in the damping effect. If the rebound damping is set too low, the scooter will accelerate back too aggressively from the compression and the wheel will swing again after the first contact with the ground. If you like a real rodeo feeling and don't shy away from a drop, you don't need to fix this deficiency. If the rebound stage is too high, the effect is similar to that of a too strong compression stage. Even before the shock absorber has fully rebounded, new bumps etc. compress the shock absorber again and it can no longer absorb the shocks that follow each other quickly enough. This gives the rider a feeling of a rather hard vibration, especially when the bumps are quickly successive, combined with the feeling that the scooter is lowering more and more at the front and rear. Technically, similar processes take place as with pressure resistance. The upward movement is hindered by the fact that the damper oil can only flow in limited quantities through the bottom valve and the movement is slowed down by the resulting drag resistance. If you push the scooter downwards strongly at the rear, the starting position should be reached again in just under a second without any bangs. If this is the case, the rebound is always set correctly. If, on the other hand, there is a clearly audible sound, the rebound stage must be reduced. If the rebound lasts too long and the damping responds very sluggishly to a visual impact, the rebound stage must be increased.

Fork oil / Shock absorber oil
You shouldn't worry about the competing terms any further, because there are strictly speaking no differences between fork and shock absorber oil. Fork oil / Shock absorber oil is mainly available in viscosities SAE 5 / SAE 7,5 / SAE 10 / SAE 15 / SAE 20. The viscosity indicates how viscous an oil is. Thicker oil flows more heavily through the bottom valve of the damper, increasing rebound and compression. The higher the SAE value, the harder the suspension. Through the manufacturer, the internet or the workshop manual you can find out which oil belongs in the chassis parts of the scooter. The different viscosities can be mixed without problems, but the right ratio is not so easy to find. A mixture of fork oil SAE 5 and SAE 10 does not produce SAE 7.5 as expected because the viscosity does not change linearly. As a rule of thumb one can note that about 40% of the low and 60% of the high viscosity result in the mean value of both viscosities. If the amount of oil in both fork arms is correct and you are still not satisfied, you can adjust the damping in small steps up and down with other damper oil. Fork oil or damper oil ages with time. This means that it becomes thinner and thinner and loses its damping properties. Due to the high loads inside the damper parts, which are mainly made of aluminium, there is still considerable abrasion, which accumulates in the form of floating parts in the oil and also settles on the bottom of the shock absorber and telescopic fork. In addition to road dirt coming from outside, the aluminium particles promote leaks at every Simmerring / shaft seal of suspension strut and telescopic fork and lead to ever higher oil loss. As time goes by more and more of the damping agent gets lost and as a logical consequence the damping gets worse.

Gas bubble pressure for shock absorbers with expansion tank (nitrogen pressure)
Some shock absorbers also have a reservoir that is slightly smaller than the damper piston. The gas bubble inside is filled with nitrogen. Depending on the gas pressure, the response behaviour of the shock absorber can be regulated. More pressure makes the shock absorber harder overall (Attention: The ratio of rebound and compression stage also changes slightly), less pressure improves the starting behaviour and the scooter drives smoother over bumpy tracks due to the more responsive damper.

Shock absorber for sporty use: the Racingbros Bazooka 4.0

A prime example of an adjustable shock absorber is the Racingbros Bazooka 4.0, a premium product that is at home on scooter racetracks all over the world and can fully live out its qualities there. The Racing Planet racing team and other teams are already successfully using this lightweight shock absorber (about 550 grams) in the IDSM, EST and the Long Distance Cup. It is impossible to imagine the Asian racing series without this damper in road racing and off-road racing without it. The hydropneumatic damper is state of the art in suspension technology and not only a reliable partner on the track, but is also very popular with sporty, ambitious recreational drivers. There are no more adjustment possibilities:

Air Spring Pressure (freely variable spring rate / air spring pressure or selectable spring strength)
Wide-range rebound (rebound stage)
Compression (compression stage adjustable between high/low)
Ending Force Resistance (maximum immersion depth or The Bazooka 4.0 is in no way inferior to its little brother Bazooka 1.0 in terms of functionality and stability and additionally offers pressure stage adjustment and adjustable immersion depth. All settings can be done with the included tool "Bazooka Bomb".
maintenance and tuning of the teleghabel
The telescopic fork consists of two spars, which essentially consist of standpipe, immersion tube, spring, piston with valve and spacer sleeve / fitting sleeve. Their tuning is hardly less complex than that of the shock absorbers. Inside the tubes there is fork oil in the hydraulic telescopic forks, which can be filled in different viscosities like in the shock absorbers. Every 2 years the fork oil should be changed because of its aging processes, because the oil wears out and gets lost by the constant work of the chassis. The consequence for the front damping is a spongy driving feeling and the feeling of a bumpy front wheel when braking with very deep immersion of the fork rails.

Depending on the amount of oil filled in, a certain air cushion (which the manufacturer specifies exactly) remains in the fork spar. Air is compressible and serves as a progressive damper. By reducing the air cushion, the front suspension becomes firmer, and softer when enlarged. However, the cushion should not be reduced or enlarged more than 0.5 cm above the manufacturer's specification, otherwise driving becomes dangerous. After 15,000km it is not unusual for the air cushion to have increased by 1.0 to 1.5cm due to oil loss. The correct height of the air cushion is much more important than the filling quantity in millilitres. When filling, you should take your time and check both spars for the same filling by precise measurement. When Replacing the fork oil the oil seals or shaft seals should also be replaced. Even if the old ones still appear tight, they are also aged. A Simmerring does not cost a lot of money and how much you would get annoyed if everything else is new and 1000km later the old Simmerrings become leaky.

Scooter shock absorber

Adjustment and maintenance of the chassis

Basic concepts of chassis technology and shock absorbers Setup

Shock absorber for sporty use: the Racingbros Bazooka 4.0

maintenance and tuning of the teleghabel

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