Motorcycle Suspension Settings

Racing motorbikes, and more frequently, street motorcycles, are equipped with suspensions that allow you to change their functional behavior.

The main reason for having adjusters on our suspension is that suspension producers must manufacture a vast number of equal components, e.g., front forks, rear shock absorbers, and steering dampers, which lots of customers can use.

How can suspension manufacturers reach this target?

Before answering, it is a good idea to describe a suspension’s main purposes briefly.

The suspension is the mechanical component that connects the parts in contact with the ground, usually the tires and wheels, and all of the other masses not in contact with the ground, called, in fact, suspended masses. Sprung masses include the frame, engine and, of course, the rider.

Support function: The springs maintain the ideal setup of a motorcycle. The springs also allow for achieving the best position for a rider during all of the riding phases, from the hardest braking to a full gas acceleration. In simpler terms, the springs support all of the weight placed on the suspension.

Damping function: A fluid, usually oil, is moved through the inner passages of the suspension, generating viscous friction and a pressure drop. The energy dissipated by the friction results from the movement on the suspension caused by the roughness of the ground

being driven on or by the movement of the suspended mass during the riding phases. The energy dissipation is also called damping. You can easily check the damping by touching a suspension after its up and down movement; if it is hotter than at the beginning of the experiment, it means the damping worked correctly, turning the displaced energy, or kinetic energy, into heat.

Picture I: here is a pin which allows the section variation. The adjusters move the pin.

Picture II: shim stacks are metallic discs, used in tuning the correct way lubricant flows through the piston and valve holes.

Picture III: The separating piston is moved up and down during the suspension motion. Holes and pockets allow the flow of the lubricant between inner chambers. 

All the parts, shown on the pictures, are important and fundamental to set the correct damping behavior of a suspension.

What suspension adjustments are there?

Settings allow us to change the behavior of a suspension, adapting it to our needs.

Spring setting: the variation of spring preload allows to sustain different weights. For example, a 70 kg rider lends their motorcycle to their 100 kg friend. If they do not vary the spring preload properly, the motorcycle will squash down due to the heavier weight. In addition, the suspension will risk reaching its stroke limit during the braking and acceleration phases.

A suspension reaches its stroke limit when it can no longer move the upper in the rebound phase or the lower in the compression phase. A critical situation will occur when it happens: It will be like riding without any suspension! Without a suspension, there are no other parts that can dampen. Consequently, the roughness of the ground will not be properly absorbed, and losing control will be unavoidable! This is the physical reason behind the front tire understeering, or front closure, with a crash resulting after this quick and unpredictable movement, which we can sometimes see, for example, during MotoGP and SBK races.

However, moving back to the example. If, after changing the spring preload for the 100 kg rider, the 70 kg rider starts riding the motorbike without resetting the preload to the initial values, then riding in the absence of suspension will appear again. This second “no suspension” situation appears because the force, generated by the spring preload, limits, or worse, locks the displacement (stroke) of the front fork or rear shock absorber. So, it will be the opposite of what was described in the first case. 

FOCUS ON: K Value of springs

The K value of a spring, also called spring stiffness, is one of the main mechanical characteristics for determining a spring. By maintaining the preload value, a spring with a higher K [60 N/mm] can sustain more weight than one with a lower K [50 N/mm]. Therefore, by combining the correct values of stiffness and preload, you will have the desired stroke, avoiding the two bad situations previously described.

Hydraulic settings: the famous clicks, we hear when we vary the configuration of the suspension, are used to recognize what is happening by rotating the adjusters.

There are two main types of registers: one for compression and one for the rebound.

The compression register affects the damping and, therefore, the suspension’s displacement velocity in the squashing phase. Finally, the rebound register allows setting how fast the suspension will move back to its initial position.

In simpler terms, by moving the position of the two described registers, they change the section the oil must pass through during the suspension’s movements. For example, this section becomes smaller when you close the register (commonly, clockwise rotation). In this way, the suspension will generate more damping, and the rider will feel it harder. 

On the opposite side, if the register is turned anti-clockwise, the section will become bigger. As a result, the rider will have a softer setting that will generate less damping.

TRICKY QUESTION TIME

At this point, there is usually some confusion around the meaning of the hard/soft referred to in the spring and hydraulic settings.

Therefore, let us do another example:

If during the braking phase, the front fork moves down too quickly, it means:

A) There is a soft spring with insufficient stiffness and/or less preload than needed.

B) There is a soft compression setting.

If your answer was B, then you are correct!

To understand if you should modify the hydraulic settings or the springs, it is important to define if the suspension is moving down too much or too fast.

In the first case, you have to focus primarily on the springs, changing the preload, or choosing another spring with a different K value.

It is a good suggestion to change the compression register and close it in the second case.

INSIDE A MOTOGP TEAM

When you speak to a rider who rides GP prototypes, it is common to receive extremely interesting information and feedback, sometimes apparently crazy stuff, about their motorcycle settings compared to one of their teammates or the ones of their competitors with other motorbike models. For example, if we start with a simple situation of two riders who ride the same prototype and with the same weight when they are fully equipped for a track session, the setup data of their motorcycles will have differences in 100% of situations. So let us explore the reasons behind these apparently nonsense differences.

• The two examined riders have a different distribution of their body weight. So, for example, you could have a tall person with less muscle mass, or they could be short with a lot of muscle mass.
• Pro riders have developed an incredible sensibility thanks to their natural predisposition and the huge amount of time they spend riding extreme motorbikes and training themselves. Their superhuman sensibility allows them to recognize the smallest variation of riding conditions caused by the tires wearing or, for example, if they are riding among other riders or alone in first position during a race. They can also feel and determine, in real-time and at every point of a track, the differences of speed, a slight variation of the lean angle in a corner, or again the minimum variation of riding lines and path, from one lap to another. Compared to the telemetry data, all this feeling data shows an incredible precision and connection between what the rider says and what the data says! Such an extraordinary ability!
• The riding style and the rider’s position change the vehicle’s behavior significantly during every single phase. The minimum detail becomes relevant when riding at the limits of the vehicle and the grip. Quality and performance are in the details!
• Different tires are used for the race and the qualifying practice/time attack.
• Different configurations of components connected to the suspension, especially the rear shock absorber. Linkage elements are particularly important when you want to obtain a different ratio between the suspension stroke and wheel travel or between the force generated by the springs and the force that pushes the tire down on the asphalt to generate the correct grip.

The synergy between the rider and the people who work on their motorcycle must be absolute for the reasons described above, together with the reasons connected with the rider’s feeling and psychological sphere. Until the information from the riders and telemetric data are in the same direction, engineers can usually set the motorcycles as desired by their riders. The situation becomes more difficult when, after some laps, the rider who was following a competitor with a motorcycle of other constructors, says:

• The other rider’s motorcycle was more precise entering the corner because their rear tire was stabler and always connected with the asphalt.
• Exiting the corner, the competitor was faster because they opened the throttle quicker after reaching the apex without going out of the ideal riding line.
• What people watch on TV is extremely different from reality. Therefore, engineers must avoid watching videos; they must focus on what the rider says!

CONCLUSION

There is much possibility to customize the settings of your suspension. First, however, they need to be well assembled, checked, and serviced according to the safety and maintenance instructions to do a good job.

Therefore, remember one of the most important tips: you should know and write down the beginning conditions and settings before every setting variation. This way, you can quickly move back if the change does not match your requirements.

Always have fun and remember there is real pleasure only when there is consciousness that, with determined input, you will have the desired result!

Enjoy your ride!!!