How Does Valving Work by Too Tech Suspension

What is Compression and Rebound Damping?

When your suspension moves up and down, the movement is controlled by the spring and the shock.  When you first hit the bump, the suspension compresses.  We call this the Compression stroke.  The resistance to this compression stroke is created by the main spring and the hydraulic resistance created in the shock.  Hydraulic resistance in the compression direction is called compression damping.  

After your suspension has passed the bump and finished the compressed stroke, the compressed spring try's to return (rebound) to it's original position.  I.  To control the energy stored in the spring, the shock has to create enough rebound force to slow the springs return.  If there were no damping, it would return like a "pogo stick"  Hydraulic resistance in the rebound direction is called rebound damping.

The rebound damping is much greater than the compression damping because the rebound damping has to control all the energy stored in the compressed spring while the compression stroke is partially controlled by the main spring and doesn't require as much help from the hydraulics.  Typically rebound damping is about 3 times higher than compression damping.

Where Does Damping Come From?

Resistance to movement caused by a piston traveling through hydraulic fluid is called damping.  During shock movement, the piston moves through fluid in the bore.  Reed type valves at the end of the piston restrict the flow of oil through the piston.  Since the piston has to be pushed through the oil, more pressure is created in front of the piston than there is behind it.  This pressure differential creates the force used to resist  the movement of the piston.  This force become the damping force.  The damping force is controlled by how stiff the valves are that block the flow of oil,. how large the oil flow holes are, and how fast the piston is being pushed through the oil.  

What Is Valving

Valving is a general term for restricting oil flow.  In reality, the valve restrictions work together with the oil flow holes (orifices) to control the different shaft speeds.  Generally speaking, the stiffness of the valves determine how much low shaft speed damping there is and the orifice size determine how much high shaft speed damping there is.  The combination of  reed valve stiffness and orifice size combine to create different amounts of damping for different shaft speeds.  Manipulating the valves and the orifices allows the suspension tuner to "tailor" the damping forces at different shaft speeds.  The resulting damping levels at each shaft speed determines the damping curve of a suspension component.

How Do Different Types Of Valving Work?

A simple orifice valve generates a damping force which grows with the square of the velocity as shown in curve A of the graph below.  If a tuner choses a small enough orifice to control low speed suspension movements, the suspension would become too stiff and spike the rider on high speed (square edge) bumps.

The second type of valving comes from the reed valves covering the piston openings.  These valves restrict low speed movements by remaining closed until pressures are high enough to open the valves.  When they open they tend to "blow off" as shown in curve B of the graph below.  Note that curve B starts out high at low speeds but the damping forces rise slowly with faster shaft speeds.  These two type of damping complement each other since their characteristics are opposite of each other.  A good suspension tuner can achieve a typical overall damping curve like C which can offer enough low speed damping control without making the suspension spike on high speed bumps.


The curve C shown above could only be achieved with a much larger orifice than used to create curve A and a much less abrupt reed valve stack than shown in blow off stack B.  


If it was really this simple, more people would be able to fine tune there own bikes.  For instance the shock has a compression adjuster that directly affects the ability of the main piston orifices and valves to make compression pressure in the chamber.  After the adjuster there is bladder pressure that dictates the maximum damping pressure that can be achieved in the shock body.  And that pressure is a moving target as the bladder compresses from shock shaft intrusion.

The forks are even trickier.  Cartridge compression pressure is created as the rod assembly plunges into the cartridge body. This cartridge pressure is determined by the base valve and it's orifice sizes.  Additionally, pressure is built by a mid speed valve assembly.  If the mid speed is set too tight the valves may fatigue and permanently bend over time ruining the low speed performance.  The KYB uses a valve at the top of the cartridge that is prone to collecting debris and leaking.  The Showa Twin Chamber has an replaceable pressure spring that simulates the bladder pressure used in a shock and determines the maximum pressure that can be built up in the cartridge.   Add to this the fact that KYB forks really operate in an emulsion of oil and air which changes with speeds and temperatures and the black art of the whole system begins to raise it's head.  

It is challenging and fun, but no one gets it perfect for every rider every time.  This is why Too Tech Racing works closely with a wide variety of riders.  This is also why we specialize only in suspension - it is complicated  enough and I can't imagine cluttering my mind with other performance mods!