Shim ReStackor Input File Setup

Shock Compression Valve Calculation

ReStackor has been designed to be easy to use and operate with the minimum information need to adequately describe the shock absorber flow circuits. ReStackor runs through an excel interface. Macros within excel write the input file, run the code, load the calculation outputs and automatically refresh all of the plots within the ReStackor spreadsheet. The entire input file for the crf450r shock compression valve is shown below. There are four sections that describe different features of the suspension system.

Stack configuration
Damper configuration
Valve geometry
Operating conditions

The values input in each of these sections are discussed below. After filling out the input file, clicking the run button in the upper left hand corner executes the 11,000 lines of the ReStackor code. The Load_Output button loads the calculations outputs back into the excel workbook. As the output file is loaded all of the plots in the ReStackor spreadsheet are updated with the new calculation results.

Stack Configuration Inputs

The stack configuration in columns C and D is simply a list of the diameter and thickness for each shim in the stack starting with the first shim on the valve face. Up to 50 shims can be used. The 35 shims used in the shock crf450 stack run off the bottom of the page above. The inside diameter for all shims in the stack is entered in the cell (c6). Stack float is entered in cell (d6). Shim stack preload used in digressive valve configurations can be modeled using a negative value of float. All dimensions are in millimeters.

Plots of the stack deflection generated by ReStackor shows the stack structure and the thickness of each shim in the stack. This plot helps to insure the stack parameters are entered correctly. If you miss type a shim diameter or thickness it will show up as a disruption of the stack structure.

Damper Configuration

There are two types of valves used in suspension systems. Mid-valves and base-valves. Base valves are generally located on the opposite end of the shock from the rod entrance. As the damper rod is forced into the shock body, fluid is forced out of the shock through the base valve. Typically a base valve is used for compression damping. Since the damper rod is a small diameter the fluid flow rate through the base valve is generally low.

The mid-valve is located on the end of the damper rod. As the damper rod is forced into the shock fluid flows through the face of the mid valve and fills the annuls behind the mid-valve. On compression the entire face of the mid-valve is pressurized. On rebound only the annulus between the outside diameter of the valve and rod diameter is pressurized. Due to this difference in pressurized area the forces generated by a mid-valve are different under compression or rebound.

The type of valve to be analyzed in a ReStackor calculation is specified through the Vspec keyword in the input file:

BVc: Base valve compression
MVc: Mid-valve compression
MVr: Mid-valve rebound an

The crf450r shock compression valve is a mid-valve so the keyword Vspec is set to MVc. D.rod is the diameter of the damper rod, D.valve is the valve outside diameter. All dimensions are in millimeters. The definition of w.seat is discussed below.

Valve Geometry

Damping rates produced by suspension systems are strongly influenced by the valve geometry. If you mistakenly input overly large or overly restrictive valve ports ReStackor will compute those inputs with impunity and your damping rates will be off. It is important to get the valve geometry right in the ReStackor inputs.

r.port defines the inner radius where forces from the valve ports are applied to the shim stack face. d.port and w.port define the perimeter of the valve port seat. ReStackor uses these seat perimeter measurements to determine the available flow area between the valve face and shim stack. A larger perimeter provides more flow area and less flow resistance. w.seat defines the valve port seat width and is entered in the damper configuration block above.

N.port defines the number of valve ports. For the crf450r there are four compression ports and four rebound ports. D.bleed defines the diameter of the clicker bleed port through the suspension valve. If the flow path of the bleed port has a smaller diameter flow restriction somewhere within the bleed port you need to use that diameter. N.clicks defines the total number of adjuster clicks from full open to closed. Full open is defined as the position where the tip of the needle enters the bleed port. If there are a bunch of clicks beyond that point they do nothing to effect damping and should not be used in the value of N.clicks.

The D.thrt and N.thrt parameters are not needed for the crf450r calculations. The definition of these parameters are given in the input file description.

Operating Conditions

The final input block "Settings" define the operating conditions.

n.clicks defines the clicker setting, zero is closed. SAEwt defines the oil viscosity and T.oil defines the oil temperature in degrees Fahrenheit. With these inputs you can quickly change the clicker setting or the oil viscosity, click the run button, and see the effect of each parameter on the performance of the suspension.

F.max defines the maximum force to be applied to the shim stack. The calculations compute approximately 20 points between zero and the input value of F.max. The stack deflection plot, shown on the right, is computed at the input value of F.max.

u.wheel defines the maximum suspension velocity for use in ReStackor pro calculations. The relationship of bump height, bike speed and suspension velocity is given in the ReStackor user manual.

Simple parametric calculations

After setting up the input file parametric calculations with the ReStackor codes is easy. You can change the value of n.clicks to see the damping forces generated at different clicker settings. Change the SAE wt oil viscosity to see how many clicks stiffer or softer that would make your suspension. Or modify the shim stack configurations to compare damping rates for different shim stacks compared to the stock configuration.