Some time ago, I introduced the classification and basic principles of shock absorption. Today, we will talk about the advanced knowledge of motorcycle shock absorption. If you like to study it, you can have a look.

Today, rear center damping is almost the most common, but you can still see the traditional double damping setting, mainly used on retro cars. Since the emergence of longer-range rear suspensions in 1974, single shock absorption has become easier to achieve. Why develop shock absorption technology? For decades, American motorcycles still use a rigid frame structure, which is what we call a hard tail. But with the improvement of the highway and the increase in speed, the rear suspension becomes a necessary condition for providing chassis stability. Let the spring bump up and down to protect the rider and chassis from interference.

Rear damping provides two basic functions: the spring rigidly supports the weight of the rear of the motorcycle car, and controls the up and down vibration of the suspension by providing damping. Damping is controlled friction. Its role is to absorb energy in the movement of the suspension. If there is no damper, the spring will continue to bounce after each impact.

In the early days, dampers worked by dry friction, but their piston motion was unstable. The work of modern dampers is linear, since they consist of a cylinder filled with oil and a movable piston connected to the suspension. The suspension motion drives the piston, which pumps oil back and forth through the restriction orifice. This converts the energy of the suspension motion into a rapid circulation of damping fluid to dissipate heat. The temperature brought about by the rear compression movement in use is the energy consumed by the suspension movement.

When the damper piston moves, the pressure in front of it is high, but the low pressure behind it will pull the damper oil apart or cause it to cavitate. In order to prevent the formation of negative pressure in the cavitation area, the damping oil is pressurized by the gas behind the accumulator piston. The cylinder is the "xx grip" of the most common damper design today ".

A simple fixed damping hole, the size of which can work at low speeds, quickly becomes difficult to compress or even rigid as the vehicle speed and the speed of the damper piston movement increase. This is because the pressure required to push the fluid through a fixed orifice rises with the square of the velocity. This means that if a given hole provides proper damping at a pace of 3 mph, then the speed doubles and the resistance will increase four times, and at 60 mph, the damper will become stiff. This sharp increase in resistance is referred to as "orifice restriction".

In order to avoid orifice restrictions, variable orifices were invented, which became larger as the pressure between them increased. There is a simple method, which is to drill multiple holes in the damping piston, cover them with a thin washer, and then cushion the washer with a spring. As the piston moves faster through the fluid, the rising fluid pressure will force the washer more and more against its spring, slowing the rate at which the damping force increases with piston speed. The variable orifice allows the resistance to remain approximately proportional to the piston speed.

The most common solution today is to use a steel gasket, covering the hole through a piston or valve body. It is clamped on its inner or outer diameter, and the fluid pressure driven by the damper piston deflects the gasket into a slightly conical shape, allowing flow to flow out from under the free edge of the gasket. By stacking a sequence of other washers and shims onto the washer, various damping-force-velocity curves can be generated. This is the most important gasket stack, sometimes called shim stack, so this is often mentioned in suspension design. The damping force must be proportional to the impact spring stiffness. Otherwise, the stiff spring will affect the damping, and vice versa.

The two directions of suspension motion are: compression and tension, and rebound occurs when the suspension extends after compression. For many years, the damper provides little damping force when compressed, because the orifice-restricted compression valve can easily support the motorcycle upward during impact compression, thereby reducing the loss of tire grip during impact. When engineers learned about "smooth" compression damping after 1978, it became practical and easy to use.