ReStackor User Manual

Finally computer software to tune a shim stack

Mid-Valve Damper Tuning

The ReStackor-midvalve.xls spreadsheet makes tuning of MX mid-valve damping rates and control of cavitation limits in an ICS chambered fork easy. The spreadsheet determines the combined damping force of the base valve and mid-valve, the suspension velocity at the cavitation limit, the effectiveness of bladder or ICS systems in controlling cavitation and the severity of cavitation when the suspension is driven beyond the cavitation limits. There are three steps to setup and run the ReStackor spreadsheet:

Setup the base valve configuration: The BVc tab contains a standard ReStackor worksheet for specification of the base valve geometry and shim stack configuration. Enter the information and click the run/load output button.
Setup the mid-valve configuration: The MVc tab contains a standard ReStackor worksheet for the mid-valve. Enter the information and click the run/load output button.
Setup the bladder or ICS configuration: Enter the configuration of the ICS or bladder system on the the main "Plots" tab. Click the mv_Analysis button and ReStackor will compute the combined performance of the base and mid-valve including cavitation limits of the shock.

Outputs are loaded into the Mid-Valve-Calc tab of the spreadsheet.

ReStackor_midvalve.xls spreadsheet corrects for flow cavitation effects and combines base and mid-valve damping rates.

Input Parameters for ReStackor Mid-Valve Analysis

There are four section to the input block. The first section specifies operating conditions in the "Bump Height" input block. Lstroke specifies the suspension stroke depth and Rod Speed the suspension velocity.

Lstroke [=] The suspension stroke depth in inches. ReStackor will compute damping performance starting at the top of the suspension stroke to the stroke depth specified by Lstroke.

Rod Speed [=] The suspension velocity in inches/sec. ReStackor will compute damping performance starting at a suspension velocity of zero up to the value specified by Rod Speed.

Suspension velocity is also specified for the calculations in the BVc and MVc worksheets. When the shock is cavitating fluid velocities through the base valve can be much higher than the suspension velocity due to the flow surge produced by the cavitating mid-valve. The cavitation calculations begin with the flow velocities specified on the BVc and MVc worksheets. If cavitation drives fluid velocities beyond those initial values additional calculations are internally computed to establish the base valve fluid velocities necessary to match the suspension velocity specified by the Rod Speed input.

While these calculations occur automatically, you still need to run the BVc and MVc spreadsheets when setting up the calculation. Clicking the run button on the BVc and MVc spreadsheets writes the configuration files for use by the main calculation. If you change the base valve or mid-valve shim stack configuration you need to click the run button on that sheet to write the new configuration file.

Open-Office Spreadsheets: The insistence of SUN micro-systems to use links for loading data into open-office applications requires you to run the BVc and MVc sheets whenever you open up a spreadsheet. Otherwise those sheets will link to and load whatever data is laying around from your last calculation, which may have nothing to do with your current configuration.

ICS Configuration

The ICS configuration block specifies the spring stiffness, float and piston diameter in the ICS system. To run an ICS configuration all of the bladder inputs must be zeroed.

Kics [=] Stiffness of ICS spring; [ kg/mm].

Ncoil [=] Number of coils in the ICS spring. ReStackor uses the number of coils and wire diameter to estimate the spring coil bind length and available travel for the ICS piston. The fraction of ICS stroke used is reported in the ReStackor output as Nics.

Dwire [=] Wire diameter of ICS spring; [mm].

FLTics [=] ICS spring float at full suspension extension; [mm]. This parameter specifies the ICS piston motion necessary to engage the ICS spring.

Lics [=] ICS spring length; [mm].

Dics [=] ICS piston diameter; [mm].

ID.ics [=] Shaft hole diameter in ICS piston; [mm]. For a typical configuration the base valve support shaft passes through the ICS piston. This parameter specifics the shaft diameter and is used to determine the pressurized face area of the ICS piston.

Pzero [=] Fork bleed pressure at full extension of the suspension; [psig].

For a closed chamber ICS system the gas pressure above the ICS piston at full extension of the suspension is specified by the Pzero input in the Fork section. This initial value of Pzero is compressed as the ICS piston moves through its stroke. The value of Loil and Ltravel in the Fork section must be zero for a closed chamber ICS calculation.

For an open chamber ICS system the Loil and Ltravel parameters are used to compute the gas pressure acting on the ICS pistorn caused by gas compression in the fork chamber.

Bladder Configuration

The Baldder configuration block specifies the bladder configuration in the shock reservoir. To run a bladder configuration all of the Fork and ICS inputs must be zeroed.

P0.blad [=] Initial bladder pressure at full suspension extension; [psig].

L.blad [=] Bladder length; [mm].

OD.blad [=] Outside diameter of bladder; [mm].

ID.blad [=] For a bladder in a fork reservoir the bladder may have the base valve support shaft running through the bladder. This is the diameter of the shaft for use in computing the bladder volume; [mm].

Open Chamber Fork Inputs

For an open chamber fork the initial bleed pressure and oil height are entered in the "Fork" input block. To run an open chamber fork all ICS and Bladder inputs must be zeroed.

Pzero [=] Initial bleed pressure of fork at full extension of the suspension; [psig].

Loil [=] Oil height in fork from top of fork tube with the fork fully compressed; [in].

Ltravel [=] Length of fork travel; [in].

Additional Information

Definition of the output parameters from ReStackor mid-valve calculations are here.
Example plots from ReStackor mid-valve analysis are here.
Discussion of the physics of flow cavitation used in ReStackor calculations are here.