Mountain Biking - Fork internals

Hi all

Went to the Lbs today to fork out some forks :D:D.
Anyway. They had the MXproETA there and i liked it A LOT. They didnt have the Z1 series but they had a DirtjumperII which is exactly the same as the Z1 in terms of appearance/crown/stanchions/sliders. I have to confess that the new Z1/DJ crown is veeeeery different to the pics i have seen so far...very beefy ...and i am a bit undecided on if i like it or hate it. Anyway....my first look shocked me a bit and i lean towards the Mxpro stuff. I would like to know in detail if anyone knows about the internals of the MXproETA. I have downloaded manual from marzocchi site but no details there. I cannot understand the coil/air concept at all. Anyone can explain me in nice mechanical/engineering terms how does this work and maybe a brief description of it's schematic. Thanks All

Go here Marzocchi (http://www.marzocchi.com/eng/spa/default.asp) , you wont be abble to get much more in detail then what they will tell you.

:beer:

Thank dirtbikedude...but i come straight from there....having disassembled totally my manitou fork i became a bit hungry and eager to understand exactly the internals and how it works my new to be fork.

Here is a little something that should be helpful. It pertains to motorcycle forks but the good mtb forks now use the same technology

"Conventional damper-rod forks provide spring damping by forcing oil through holes in a damper rod, located inside the fork tube. The problem with this arrangement is that the resistance of oil forced through these holes varies as the square of the velocity of the oil. Which means the damping can be set up just right for slow bumps but will nearly lock up over sharp ones. This phenomenon can't be detected by bouncing on the bike, but it's obvious when riding on a rough road.

Damping can be adjusted by varying oil weight, but that doesn't help with the sharp bumps.

Manufacturers of high-end forks solved this problem by eliminating the holes. Cartridge forks feature one-way valves comprised of a stack of shims held closed by a spring. Fork compression forces oil past these shims against the force of the spring - the amount of damping is determined by the number of the shims lifted off their seats by the oil pressure. Cartridge forks can be adjusted for good low- and high-speed damping.

For bikes (like my SV650) with damper-rod forks, there's a solution. Race Tech makes the Cartridge Emulator, which has a shim stack and spring just like in a cartridge fork. The original compression damping holes are drilled out to a much larger size, so they don't do anything, and compression damping is handled by the shim stack and its spring. The cartridge emulator sits on top of the damper rod, inside the fork tube.

Cartridge emulators have two advantages: improved high-speed compression damping, and the separation of compression and rebound damping adjustments. Rebound damping is set simply by changing the weight of the fork oil (same damping holes for rebound), then the compression damping is set by adjusting the spring on the shim stack.

This allows stiffer rebound damping with softer compression damping - which, as mentioned, works for both low and high speed bumps."

thanks mate

More fork internal questions
I just got a new Trek 7300 and the shocks are not stiff enough and are bottomed out all the time. I weigh 275lbs and I have the preload turned up all the way. From an engineering standpoint I should increase the spring contant so that the natural frequency of the shock with me on stays the same. Since I weigh 60 percent more than the average rider I should have a spring with a a 60% higher spring constant. When I search the internet for springs it seems that no one just buys springs, they buy whole forks and put up with what ever spring constant and damping factor they get. I would think the fanatics would know that a shocks should have a natual frequency of say 5 HZ and a damping factor of .6 or what ever is optimal and choose the springs and damping to achieve this goal. What is optimal? This info is not in the Trek manuals. In fact the Trek manauls say little about the shocks.

Closed, over a year old.