Cartridge forks, well, I don't know how many of you are actually familiar with this type of fork. So, I'll explain how it works and what's so good about it today.
When you disassemble cartridge forks, the damping mechanism comes out as *cartridge(piston/cylinder unit)*. You are not supposed to disassemble any further, so the manual does not tell you, or show you anything more.
Well, inside of this cartridge, there are two valves(damper pistons), one for compression damping, the other one for rebound damping. The valve has a ring of bleed holes, and on top of the valves are floppy thin wahers(shims) which act like a circular reed valves. When the suspension starts stroking, the shims deflect under the pressure of fork oil. And the pressure is in proportion to the speed (of suspension, not the bike's speed). Thus, the faster the fork strokes, the more the shims deflect, which means increase orifice area. (It is called variable orifice, as opposed to fixed orifice in the damper rod style forks.)
The first shim is the same diameter as the valve,with the following shims getting progressively smaller, forming a cone shape. Oil passes thruogh the holes of valve, forces the shims to flex, the faster it moves, the greater the pressure on the shims, causing more of them to deflect.
Shim's thickness, the number of shims,would change the rate of damping, It's possible to change the thickness of certain shims in the stack, so that only certain damping characeristics are altered. What does that mean ? Well , that means your fork's damping action can be tailor made to your aplication. Low/high speed damping, the point where it shifts from low speed setting to high speed setting,etc,etc all can be adjusted independently.
Incidentally, Penske shock's low / high speed damping adjustment is basically the same thing. Cartridge fork's valve system is fundamentally the same "shim-stuck "style as the one in the modern rear shock unit. The difference is, on Penske shock you can change high and low speed damping setting independently WITHOUT disassembling the shock. (You can do the same thing with your Fox shock, for example. But you're gonna have to take it apart. )
Damping control is there in your suspension system to keep the chassis stable, and it *must* be in proportion to spring rate. What this means is if you increase spring rate, you will have to increase damping, too. Cartridge fork makes it possible, you can create almost any kind of dumping curve you want. Which, greatly improves your bike's handling.
Well, so if you fit the cartidge forks to your GPz(or, Kz), how do you set it up? I' ll write my *personal* experience about this in my page.
Cartridge Emulators...everybody has heard the name, but in this group, (surprisingly) only one has tried it so far...
Well, how do I explain the way Emulator kit works just by words? Look at those pictures.
I already expained the way damper-rod forks work. (and how it creates undesirable dumping curve.)
Emulator kit works in an entirely different way. It sits on top of the damper rod(in other word, under the spring), and allows you to do damping adjustment, such as;
1) Damping curve change-- this can be changed by preload on *Emulator*'s spring.
2)High speed damping-- by Emulator's spring stiffness itself
3)low speed damping-- by bleed hole size
4)rebound damping--oil viscosity
This gives you tremendous control of damping curve. And they are(relatively) simple and easy to install.Well, to me, it is simple. IF you find it difficult to disassemble& re-assemble forks, you may want to have someone to do it for you..
What you would do is drilling out damping rod, so the rod no longer creates any compression daming. As forks get compressed, the oil goes through from those holes(that you just drilled out) and up the center of the damping rod. Up top of the damper rod is now caped by Emulator(it's held in place by fork spring's tension), where oil normally squirts up like a geyser. And the oil goes this way...
1) low speed damping; the oil goes through bleed hole (not the hole you drill. This is the small hole on Emulator itself.) So, the size of bleed hole controls damping force at this stage,... (up to the point it sees enough pressure builds to lift the spring loaded check plate off its seat. )
2)mid- to high speed damping; as suspension verocity increases, it creates enough pressure build behind the Emulator's check plate to overcome (Emulator's) spring preload, and the plate lifts off the seat. Emulator spring's stiffness itself control high speed damping. Preload on this spring moves the point where your suspention would switch from low speed damping characteristic to high speed damping characteristic.
3) On rebound stroke : it works in the same way as normal damper-rod forks, BUT, since you have all drilled out damper rod, the oil flows a lot more freely. This greatly reduce cavitation problem. (Meaning you can run higher viscosity oil, still you have to think about fade, though.)
The result is a damping curve that emulates the damping curve of a cartridge fork. Hence, "Cartridge Emulator"
This is probably the best investment you can do to your stock forks. Not only because it works, but also because this is turly a "bolt-on" kit. Having said that, it is true to install Emulator is more work than just throwing a pair of springs.(Also they cost a bit more.) I think this is the real reason why some people like to go progressive springs.