There are many common misconceptions, stories and unfound truths surrounding the term "Revalve". At Factory Connection, the term "Revalve" means the modifying of the suspension component to improve the performance to better suit the riders skill set and needs.
Suspension both forks and shock on all dirt bikes; regardless if they have springs or air holding them up use oil hydraulics to create the damping forces necessary to make suspension what suspension is.
Forks come in many forms; Separate Function Forks -SFF, Speed Sensitive Suspension (which interestingly all suspension is speed sensitive) -SSS, 4 Chamber System -4CS, Twin Chamber or Open Cartridge all of which follow the same basic principles in different ways.
The following information is intended to provide a very basic understanding of how dirt bike forks and shock hydraulic control works.
When suspension compresses (compression stroke) a piston on the end of a rod travels through oil in a chamber. Four basic things are happening:
Oil is passing through the piston ports as it moves through the chamber, the flow of that oil is metered by a series of shims (referred to as the shim stack); shims are thin washers that bend under pressure to limit, or control the flow of oil. The size, thickness and number of shims in a stack helps create the action of the suspension and is commonly referred to as "The Setting" or "Valving". This shim stack is primarily what is changed in a suspension "Revalve". Factory Connection works very hard to utilize the OEM pistons in its performance modifications.
The rod (or shaft) entering the chamber is displacing oil. Because oil cannot be compressed the displaced oil must flow to a second chamber area. The flow of this oil is also metered (controlled) commonly by a piston with shims and so the modifying of the flow control to the secondary chamber is also part of the "Revalve" process.
In the secondary chamber there is also a need to allow the oil in, the entering oil needs somewhere to go; this means the secondary chamber volume must increase (expand). In a shock this is commonly achieved by having a bladder filled with nitrogen, as the oil comes in the nitrogen filled bladder is compressed. In a fork there are many ways this is done, the most common is a piston/spring system (Pressure Spring) the spring is compressed making the chamber bigger to accept the oil as it enters. Adjusting how the expansion of the secondary chamber happens is also part of the Revalve process.
In addition there is typically a small hole, or preloaded spring/shim set up that allows oil to bypass the metering of oil in one of these areas; the size of this hole or preload on the spring/shim is controlled by an external adjuster. That is how you have external control over the compression stroke. These external adjustments are only a fine tuning of the internal damping. For example if you have suspension set up for vet motocross the external adjusters are never going to make it an Enduro set up. The range of adjustment offered externally is not large enough to make that much of a change.
After the suspension has compressed it then extends again (rebound stroke). The rebound stroke is the same as the compression stroke but in reverse. The compression ports and holes seal and the rebound ports open up as the rod or shaft exits drawing the oil back into the main chamber again.
Suspension components; both forks and shocks all do these basics during the compression and rebound stroke – the metering of oil flow in each area is managed by some type of 'valve' system. For a suspension tuner the oil control in each area must be matched. When the restrictive forces generated in one area are changed the appropriate change has to be made in the other areas to maintain a well-balanced suspension system. As suspension has become more technical the balancing of forces within the metering systems; and ultimately the pressures generated in the separate oil volumes has become increasingly important.
As shaft speeds increase or decrease (the suspension is compressed quickly or slowly) the amount of oil needing to flow in each area changes dramatically. Most suspension systems have high and low speed control; the low speed portion is always working. As the amount of oil flowing through the low speed reaches its maximum the high speed portion comes into effect. The low speed / high speed control is achieved in many different ways, additionally modern suspension is adding external high and low speed adjustments in many cases. Our intent here is not to explain any systems operation just the basic theory that applies to all. The suspension tuner has to factor in multiple systems all working in conjunction with each other as shaft speeds increase and decrease.