Shock absorber and suspension

Analysis and role of the spring / amorto-tector

All information about its maintenance

Responsible for maintaining contact between the ground and the wheel while ensuring the comfort of the rider and passenger, the combined shock absorber spring plays a leading role in the motorcycle's behavior and performance. So let's take a little look at who is following us this way.

Talking about a shock absorber is an abuse of language. Indeed, under this word we usually refer to spring / shock absorber combinationwhich combines two functions. On the one hand, the suspension, which is entrusted to the spring, on the other hand, the damping itself, which falls very naturally on the shock absorber itself.

Therefore, as a good biker, we will talk about 2 items, as they are closely related.

Suspense

Therefore, it is the spring that hangs you in the air, thereby preventing the motorcycle from collapsing at its stops. The spring is usually metallic and helical. There should be motorcycles in history equipped with torsion suspensions and other leaf springs commonly used in automobiles, but these are marginal technologies. The spring can also be pneumatic.

The metal springs are made of steel and very rarely titanium like here, 40% lighter but extremely expensive!

The spring is often linear, that is, constant stiffness. This means that from the very beginning to the end of his race he offers the same resistance for the same flooding. For every additional millimeter of lowering, it will react with the same opposite thrust, for example 8 kg. In contrast, a progressive spring will respond to 7 kg / mm at the start of a race, for example finishing at 8 kg / mm at the end of a race. This allows for flexible suspension while sitting on the bike, but this usually does not follow a lot of effort. This progressiveness can also be achieved by multiplying the suspension itself (tilver / tilge system, also linear or not).

In addition to its extreme lightness, the air source offers a very interesting natural progressiveness. The deeper it is pushed, the more it hardens. This makes it very easy to reconcile great attack comfort without the risk of excessive roll as it hardens considerably at the end of the race. The quality that makes it the king of great tourism and also makes it very interesting on low suspension motorcycles.

Mono or 2 shock absorbers?

Let's end the generalizations by pointing out that you can have one or two shock absorbers. The single shock absorber, which became widespread in the early 1980s, originally provided more sophisticated automotive shock absorber technology. Thanks to the tilt and crank systems, the engineers had more architectural freedom in positioning the rear suspension, as here on the Ducati Panigale.

The single shock also allowed the tube to be brought closer to the center of the bike to better center the weight without wasting too much shock travel. Indeed, the damping is in accordance with the force / speed law. The less races a shock absorber has, the slower it goes and the easier it is to control suspension travel. Thus, so-called "direct attack" systems mounted on a pivot arm, without rods or cantilevers, are certainly more economical than crank systems, but much less efficient.

Finally, thanks to the single rod shock absorber, it is possible to introduce a progressiveness between the relative wheel offset and the shock absorber travel to have a progressive suspension. But this is not fundamental. In fact, if it's interesting for road comfort, it should be avoided on a track where you prefer a suspension that's not progressive.

Damping: Reducing the amality of the mechanical assembly

Here we are at the heart of the case. Damping means reducing the vibration amplitude in a mechanical assembly. Without damping, your bike bounced from impact to impact like a cover. Damping is deceleration of movement. If this was done by friction systems in the distant past, then today we use the passage of fluid through calibrated holes.

The oil is pushed into the cylinder, the damper housing, forcing it to pass through small holes and / or to lift the more or less rigid valves.

But beyond this basic principle, there are many technical challenges that have led manufacturers to develop increasingly sophisticated technologies. Indeed, when the shock absorber sinks, the volume available in the cylinder is reduced to the length and part of the rod that penetrates it. In fact, the shock absorber cannot be filled with 100% oil as it is incompressible. Therefore, it is necessary to provide the volume of air to compensate for the volume of the rod. And this is where some of the difference between good and bad shock absorbers has already been made. Basically, air is present directly in the shock absorber housing, mixed with oil. This is not ideal, you can imagine, because when heated and stirred, we get an emulsion that no longer has the same viscosity properties when it passes through the valves. Really hot, emulsion shock absorber has everything from a bike pump!

The first solution is to separate oil and air with a mobile piston. It is called gas amortizer... The performance is becoming more and more stable.

The expansion volume can also be contained in an outer shell that surrounds the shock absorber. It is called amortizer Bitube... Technology pervasive (EMC, Koni, Bitubo, aptly named, Öhlins TTX, etc.). The moving piston can also be pulled out of the shock housing and placed in a separate reservoir.

If the cylinder is attached directly to the shock body, it is called the “piggy bank” model. The advantage of a cylinder over a built-in piston is that you can take advantage of the passage of oil through a calibrated orifice ... to have adjustment ...

Setting

Start by preloading

The first adjustment is usually in the spring rate. Let's start by twisting the neck towards a wrong conception: by increasing the preload, we are not hardening the suspension, we are just lifting the bike! Indeed, with the exception of the variable pitch spring, for the same amount of force the motorcycle will always sink at the same value. The only difference is that we start from above. In fact, for example preloading a spring into a duo, the risk of killing is effectively reduced as the spring will be proportionally more packed. However, the suspension will not be stiffer, since the stiffness is constant of the spring and never changes.

Moral, by preloading the spring, you are only adjusting the attitude of the motorcycle. However, it can be helpful for her to get in the best turn.

The main spring adjustment is to measure the backlash. To do this, we measure the height of the motorcycle's fully loosened suspensions and then do the same again once the motorcycle is placed on the wheels. The difference should be between 5 and 15 mm. Then we do the same again while sitting on the bike, and there it should go down from about 25 to 35 mm.

Once the correct spring and preload have been installed, the damping can be taken care of.

Relax and squeeze

The basic principle is to read the settings so you can always come back if you make a mistake. To do this, screw the dials down completely, counting the number of clicks or turns, and note the value.

In addition, the front and back are interacting, so the settings must be uniform. We always execute small keys (for example, 2 clicks) without changing too many parameters at a time so as not to get lost. If the bike seems unstable, sags on impacts during acceleration, does not fit well into the turn, release the trigger (at the bottom of the shock absorber as a whole). On the contrary, if he is unstable, bouncing and holding poorly, relaxation must be restored.

If, on the other hand, it seems too high and has no control over acceleration, it loses grip with sequences of impacts, releasing compression damping. On the other hand, if it seems too flexible to you, despite a good spring, sinks too much, looks unstable, close the compression a little.

Note that on a Fournalès air spring, when the pressure increases, which is equivalent to a changing spring, the damping is simultaneously hardened, which in fact remains well proportioned to the "suspension". In short, a kind of self-regulation. It's very easy!

Settings: low or high speed?

The increasingly sophisticated modern bikes often offer suspension settings that differ in speed. It's all about compromise here, but when you pick up your hands or back full throttle through the retarder, it's a pretty high speed. On the other hand, if your bike wobbles during the acceleration and deceleration phases, this time you will have to act more on the low speed settings.

However, be sure to walk slowly in any direction with the screwdriver to avoid getting lost.

Have a good trip!