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ReStackor User Manual

Finally computer software to tune a shim stack

ReStackor Calculation Outputs

ReStackor runs in the familiar graphical environment of a spreadsheet allowing inputs to be easily created, outputs manipulated, modified and plotted to investigate the performance of your suspension. Basic operation of the ReStackor spreadsheet is shown below:

  • Run Button:

    • Writes the spreadsheet inputs to a file and launches the 12,000 lines of ReStackor code.

  • Load Output Button: 

    • Loads stack deflection calculation results into the "stack" tab and damping performance results into the "ReStackor" tab.

    • All plots in the spreadsheet are updated with the current calculation results whenever you hit the "Load_Output" button.

  • Edit Output Button:

    • Opens the ReStackor output file in notepad.

 

 

Simple inputs - thorough analysis - practical results. ReStackor introduces a new era in suspension tuning.

ReStackor produces simple, easily understood graphs allowing you to instantly understand the effect of shim stack changes on suspension performance. Simple inputs allow you to easily modify the shim stack, fluid viscosity, valve port geometry and bleed circuits to determine the effect of each component on your suspension performance and re-tune those components to obtain the damping profile you want.

Plots Produced By The Baseline Shim ReStackor Code

Shim ReStackor produces plots of stack deflection, stack edge lift and the fluid flow area at the valve face including both open and closed clicker bleed settings. These basic plots make it easy to answer the age old question "Is this stack stiffer or not?". Referencing shim stack stiffness in terms of clicker settings allows you to instantly recognize the effect of shim stack changes and use your real world riding experience to evaluate stacks and retune those stacks to get the damping profile you want.

Changes in stack taper or clamp diameter are easy to evaluate in Shim ReStackor. Clicker settings on the Stack Flow Area curve show you how many clicks stiffer or softer each stack is. Evaluating stacks in terms of clicker settings allows you evaluate stacks in terms of real world forces you can actually feel when you ride.

The point where crossover gaps close is easy to identify in the stack structure plot and the plots of stack edge lift and flow area.

Backing shims and gap shims can be tuned to control the point where the stack contacts the backer and the effective stiffness of the stack after contacting the backing shim.

The shim stack can be re-tuned to simultaneously match specific clicker settings at BOTH high speed and low speed through tuning of stack preload and stiffness.

The above plots from the baseline Shim ReStackor code show the flow area available through the suspension valve with the clickers set to the position specified by n.click in the input file as well as the wide open and closed clicker positions. This allows stack modifications to be evaluated in terms of how many clicks stiffer or softer the modified stack will be compared to your current stack. This simple notion of comparing stacks based on clicker settings allows you to instantly recognize how much stiffer or softer each stack will be compared to real world forces you can actually feel when you ride. The allows you to use your real world riding experience to evaluate stack modifications. Stack modifications that are stiffer than your current stack with the clickers fully closed can be immediately eliminated allowing you to quickly focus on the range of face shims, clamp shims and stack taper modifications that are within your range of interest. 

Plots Produced By ReStackor pro

ReStackor pro produces all of the Shim ReStackor plots shown above and takes the calculations a step further with the capability to compute fluid dynamic forces and flow losses through the suspension circuits. This gives ReStackor pro the capability to compute damping force as a function of suspension speed providing the capability to design shim stacks to produce specific damping forces at a specific suspension velocity.

A simple clicker map of your current suspension allows you to visualize the shocks damping force curve and understand the influence of various clicker settings on the ride, feel and behavior of the suspension across the entire range of suspension speeds. 

Crossover shims can be designed to control transition rates between low speed and high speed damping.

Port flow restrictions can be easily identified and ports resized to produce the desired damping profile.

Split shims or ring shims can be tuned to produce controlled values of stack preload and a controlled transition from low speed to high speed damping rates. Preload produced by a ring shim can be tuned by changes in the centering shim thickness, ring shim thickness, ring shim diameter or the position of the ring shim in the stack. The above example demonstrates the effect of moving the ring shim location in the stack.

The capability to relate bump height to suspension velocity and suspension velocity to the fluid flow rates and fluid dynamic forces in the circuits of a shock absorber allow damping forces to be computed as a function of bump height. This gives you the capability to design the stiffness of shim stacks, stack taper, clamp shims, crossover shims, backing shims, gaper shims, split ring shims, stack preload and stack float to achieve specific damping effects at specific suspension velocities. Add to that the capability to compute valve port flow restrictions and the valve ports can be designed to prevent the suspension from blowing through its stroke on big hits or evaluate potential benefits various after market valves. That capability combined with relentless tuning gives you the capability to develop a suspension that is soft enough to float through the whoops yet stiff enough to handle jump landings and a suspension that works over a broad range of conditions.

Definition Of ReStackor Output Parameters

The "stack" tab of the worksheet contains the data needed to produce the stack deflection plot on the main "Plots" tab of the spreadsheet. The stack deflection plot is computed for both Shim ReStackor and ReStackor pro calculations. Data on the "stack" tab is simply a table containing the deflection of each shim at all of the major force balance node points in the ReStackor FEA analysis of the stack. The table consists of:

  • d.n [=] The diameter for each node point for shim n. For the stack computed below ReStackor used 28 node points across the face shim and the data table goes out to column AB, well off the right hand side of the screen shot below.

  • y.n [=] The deflection height, in inches, of the shim n at the node point d.n.

The ReStackor force balance solves up to 5,000 simultaneous equations to balance all radial and axial forces within the stack. The force balance determines the overall stiffness of the stack as a function of edge lift height and the forces necessary to close any crossover gaps within the stack. The ReStackor force balance page details the stack structure force balance used in ReStackor calculations.

The numerical data itself is relatively uninteresting. It is far more interesting when viewed as a plot. Multiple ReStackor runs at progressively higher stack force levels produce the sequence of plots shown below. These plots help to visualize the stack structure and the effect of stack taper changes, clamp changes and the effect of crossover gaps and backing shims on the effective stiffness of the stack. 

 

Stack Face Flow Area

Data tables containing the stack edge lift and flow area for both Shim ReStackor and ReStackor pro are loaded onto the "ReStackor" tab of the spreadsheet whenever you hit the "Load_Output" macro button. The data for Shim ReStackor calculations contain the stack deflection as a function of force applied to the stack and the ReStackor pro results contain the stack deflection as a function of suspension velocity and the fluid dynamic forces applied to the stack.

Shim ReStackor Calculation Results:

Results of Shim ReStackor calculations are contained in columns A through E. Definition of each parameter is given below.

  • Force [=] The force applied to the face shim of the stack in [lbf].

  • Yport [=] The edge lift height of the stack face shim [inches].

  • Aclsd [=] The stack face flow area between the valve face and stack [square inches]. This measurement is taken with the clickers in the closed position. The flow area depends on the valve port seat perimeter defined by W.port and N.port, and the radial length of the valve seat defined by D.port. These parameters are defined in the input file.

  • Aclk [=] The stack face flow area [in2] as defined above plus the flow area available through the bleed clickers at the requested clicker position. From the ReStackor input file shown at the top of this thread the requested clicker position is 7 clicks.

  • Awo [=] The stack face flow area [in2] as defined above plus the clicker flow area at the wide open position. From the ReStackor input file shown at the top of this thread the wide open position is 20 clicks and the bleed port diameter is 3 mm.

The maximum force applied to the stack for this calculation was 3 lbf as defined by the F.max in the input file. The Shim ReStackor table above computes the stack deflection at progressively higher applied force levels up to the maximum value requested. The calculations increment the applied force using a logarithmic curve which focuses more points at low force levels to accurately describe cracking open of the stack.

ReStackor pro Calculation Results:

ReStackor pro results are shown in columns G through M. ReStackor pro includes all of the shim stack deflection calculations of Shim ReStackor and adds the capability to compute fluid dynamic forces and flow losses through the fluid circuits. This allows ReStackor pro to determine shock absorber damping force as a function of suspension velocity and gives you the capability to design shim stacks to produce specific damping forces at specific wheel velocities. 

  • Uclk [=] The suspension damper rod velocity [inches/sec] with the clickers set at the requested position. For this calculation the clickers were set to the 7 click position. Using this setting ReStackor pro calculations determine the flow split between the bleed circuit and valve, fluid dynamic forces on the stack face, shim stack deflection and the resulting fluid flow, pressure drop and damping force produced by the shock.

  • Uwo [=] The suspension damper rod velocity [inches/sec] with the clickers in the wide open position. The difference between Uclk and Uwo is the fluid flow rate through the clicker bleed circuit. With the clickers wide open a higher suspension velocity is needed to provide the additional flow through the clicker bleed circuit. 

  • Uclsd [=] The suspension damper rod velocity [inches/sec] with the  clickers in the closed position. The difference between Uclk and Uclsd is there is no flow through the bleed circuit. 

  • Gv [=] The fluid flow rate through the combined valve and bleed circuits with the clickers set at the requested position [liters/min].

  • Fstack [=] The fluid dynamic force applied to the shim stack face shim [lbf].

  • Force [=] The damping force produced by the shock absorber [ lbf].

  • Pressure [=] The pressure drop across the valve face [psi]. This is the pressure drop across the valve and does not include any compression pressure created by changes in the oil height. Oil height effects the spring forces of a shock but does not effect the damping force other than the influence of pressure on cavitation. 

  • C.clk [=] Damping coefficient with clickers set at the requested position. The damping coefficient is defined as the shock absorber damping force divided by the shaft velocity [lbf-sec/in]

  • C.wo [=] Damping coefficient with the clickers wide open. [lbf-sec/in]

  • C.clsd [=] Damping coefficient with the clickers closed. [lbf-sec/in]