20 mm Open Bath Fork Specifications


Click on each icon to view details


This will make your fork feel like a completely different fork,
Low speed damping that’s firm but still blows-off to be plush on small bumps,
Reduced fork dive that eases the fork through the travel without harshness,
No more high speed compression spikes and no more bottoming with the ABS system.
Low speed compression and rebound adjusters help fine tune the valving as to how it transitions from low to mid and when the high speed kicks in,
Much more effective than the other dampers attempt to add high speed adjustment without the proper shim stack.


Hybrid coil/air cartridge conversion system options!





Examples of typical 20 mm cartridges

Marzocchi 66 RCV 20 mm Cartridge

Totem 20 mm Cartridge


Compression and rebound valves
Fork rebound caps
Abs Systems



• Replacement open bath maintenance free speed sensitive damper assembly, "set it and forget it"
• 20 mm ID damper tube with shimmed 4 port MX style compression and rebound valving pistons
• Available for 8 inch(200 mm) travel dual forks,single crown 180,170,160,150,140,130,120 mm travel forks
• Upper fork cap adjuster screw with 22 clicks of low speed rebound
• Base valve adjuster screw with 22 clicks of low speed compression adjustment
Hydraulic Anti-Bottoming System (ABS) for end of stroke bottoming resistance
• Speed sensitive multi-stage shimmed compression, midvalves and rebound valving
• Custom valved and set-up for each rider with printed set-up charts
• Fork spring and air pressure recomendations help us tune to to your weight riding style
Midvalve kit included with standard cartridge to prevent fork dive, adds low speed compression without harshness, optional midvalve revalving shim kit and set-up charts available
• Optional revalving kit for compression and rebound pistons, with revalving set-up charts
• Optional HSB compression blow-off system for the firmer feel with-out harshness
• Designed to be self-installed or send it to us for installation if you need us to do the install
• Weight approx. 300 grams

*Self install kit assumes good working knowledge of internals and service procedures.

Revalve Kit or Purchase Tools


Download: 20mm Cartridge Kit Revalving and Optional MidValve Procedure (53.2 MB)


Recommended oil: Golden Spectro 85/150 Cartridge Fork Fluid


Background as to why open bath and not a sealed damper as an upgrade

Since 1994 when
Suzuki introduced the twin chamber forks to the general public and by 1997 most the
high end MX forks replaced open bath dampers with twin chamberdampers.

These dampers are much more complicated than todays so called
sealed bladder dampers. The longer travel and larger diameters forced them to
create a pressurized upper chamber(rod displacement pressure spring IFP reservoir)
that created force on the damper oil in order to prevent cavitation at the
midvalve. The midvalve(back side of the rebound piston) had become the dominate
control of damping on longer travel forks because metering the rod displacement
thru the base valve became too crude and harsh at larger shaft displacements.
The current MTB bladder dampers are using the rod displacement to control damping
with base valves (on top but still referred to as the base valve) to meter and
control lock out with a high flow piston system and threshold damping created
by a rim loaded shim preloaded with a spring referred to as a high speed
adjuster. This simple damping design creates a large amount of resistance to
open the shims, but because of this it acts like a on/off light switch and creates
a harsh feeling until it blows off. Because the harshness is undesirable, the adjuster
is generally run all the way out to relieve this harshness, resulting in very little
damping in the system.

The Push H97 replaces the Trail/Lock part of this circuit
and simplifies the base valve to just a high speed threshold poppet valve and a
low speed adjuster needle. It does not add a midvalve or replace the rebound
piston system. The bladder design is still used to capture the displaced oil,
but is still not pressurized to prevent cavitation. The bladder design requires
that the damper rod be sealed, in fact this seal/seals has become the weak link
and still don’t prevent air ingestion into to damper oil, thus rendering the damper
useless until rebleed. The H97 also suffers from too much threshold as it also
creates a very harsh feel and most riders have to run very little high speed
preload to reduce the harshness resulting in very little to no damping
contribution. This results in more fork dive and reduced bottoming resistance
requiring over springing or adding too much progression to the spring leg.

The twin chamber forks are not actually sealed and contained
stanchion oil for lubrication and hydraulic bottom out. They are also self
bleeding and ingest small amounts of stanchion oil thru the damper rod lip seal
and the oil volume in the damper is reset by the ifp bleed off seal release
during full stroke compressions. This helps prevent accumulated air ingestion
from becoming an issue. This same type of self bleeding is also accomplished by
open bath systems in a very simple way by not completely sealing the damper oil
from the stanchion oil and allowing air to rise thru the rod bushing during use,
yes small amounts of air bubbles are trapped in the damper fluid causing a very
slight emulsion but with todays hydraulic fluids the foaming is almost eliminated.
This is easily account for in the valving. The air over oil creates a pressure
on the oil to prevent cavitation and further push out or shrink the air bubbles
to insignificant size thus creating a very consistent and simple damping system
that’s self bleeding. This pressure is also used to add ramp up to the fork resulting
in less tokens in the air side for a more linear midstroke air spring. The
pressure springs also add to the initial spring rate and preload of the initial
feel of the fork reducing the suppleness of the fork. MX bikes are much heavier
so this is not as noticeable. The new Grip and Rockshox RC dampers are using the
pressure spring system to replace the bladder design but are battling with spring rates and
preload to create a soft initial feel while still trying to reduce cavitation.

PinkBike Review of the Boxxer Cartridge

 e-mail at : techinfo@avalanchedownhillracing.com