ReStackor Home

 

Model Physics

  Stack Stiffness

  Fluid Dynamics

  Cavitation

  Spring mass damper

Dyno Data

 

User Manual

Sample Applications

Download demo

 

Buy Now

  Shim ReStackor

  ReStackor pro

Constact Us  

  info@ShimReStackor

 

Shim ReStackor

Finally computer software to tune a shock absorber shim stack

Damping forces produced by shock absorbers are the result of controlled fluid dynamic flow losses through the fluid circuits of the shock. The flow losses are controlled by the stiffness of the shim stack on the shock valve. At low shaft speeds the shim stack is barely cracked open resulting in high fluid jet velocities. As shaft speeds increase the pressure forces produced by the fluid flow force the shim stack to deflect and progressively increase the flow area. Tuning the stiffness of the shim stack changes the fluid flow area, the fluid jet velocity, flow losses and damping forces produced by the shock. Modeling the processes occurring within the shock using basic physics makes the calculations equally applicable to motorcycle suspension tuning, trophy trucks, automotive racing shocks or the setup and tuning of mountain bike suspensions.

ReStackor takes the guess work out of shim stack tuning

The 11,000 lines of ReStackor code have been specifically designed to accurately evaluate the stiffness of complex shim stack structures and accurately compute damping forces produced by shock absorbers using simple geometric descriptions of the valve port geometry and comprehensive modeling of the fluid dynamic flow losses. The thorough stack structure force balance in ReStackor solves 5,000 simultaneous equations to accurately balance forces within the stack structure and resolve the stack deflection following the principles of FEA analysis. This gives ReStackor the capability to accurately compute the stiffness of complex stack structures and account for multiple crossover gaps, backing shims, stack taper and shim thickness variations within the stack structure. 

ReStackor gives you the tools to confidently modify the stack structure for control of high speed and low speed damping rates and match specific clicker settings. 

Tune your suspension far beyond the limits previously possible

Modeling the shock absorber fluid circuits using the basic principles of fluid dynamics gives ReStakor the capability to compute damping forces as a function of stack stiffness and relate changes in damping force in terms of clicker settings. This gives you the capability to use your real world riding experience to evaluate changes to the shim stack stiffness, valve port geometry or oil viscosity in terms of damping forces being two clicks softer at low speed or three clicks stiffer at high speed. Evaluating suspension modifications in software gives you the capability to test potential modifications over the entire range of suspension velocities and eliminate unexpected side effects of the suspension suddenly becoming overly stiff at high speed or blowing through its stroke on large bumps. Whether you are working on initial bike setup or fine tuning a suspension you have ridden for years ReStackor gives you the capability to tune your suspension far beyond the limits previously possible.  ReStackor defines a new era in suspension tuning.

Motorcycle Suspension Setup and Tuning

Modern motorcycles use sophisticated suspensions with adjustable compression, rebound and high speed blow-off systems. Unfortunately, mass production force manufactures to build these systems around the spring rate and weight of the phantom stock factory rider. If you change the factory spring rate your damping rates are off.

Spring-mass-damper theory defines a specific relationship between weight, spring rate and damping force through the parameters tau and zeta. If two riders of different weight setup their suspensions to match the values of tau and zeta the suspensions will produce exactly the same travel, feel, response and performance when hitting the same bump at the same velocity. This fact is a direct result of fundamental physics (more).

Restore the suspension performance the factory intended for your bike

The suspension natural frequency (tau) is defined as the ratio of weight to spring rate. If you change the spring rate to match a specific suspension sag you are setting up your suspension to match the factory value of tau and the setup of the phantom shock factory rider. Restoring the suspension response and feel the factory intended your suspension to have requires modifying the shock damping coefficient (c) to restore the value of zeta used in the stock factory setup. ReStackor gives you the capability to determine the value of the stock factory damping coefficient and easily scale that value to your suspension setup. 

Weight scaling stock damping rates to correct for a spring rate change is a simple matter of retuning the shim stack to match a target stack stiffness.

With ReStackor calculation of the stock damping coefficient is a simple matter of entering the stock shim stack configuration. The change in damping coefficient (c) needed to restore the factory suspension performance is computed based on the spring rate used in your suspension setup. With that value Shim ReStackor computes a weight scaled target stack stiffness. Correcting damping rates to restore the factory suspension response and feel is a simple matter of modifying the stock shim stack configuration to match the target damping rate shown on the ReStackor plot (more).

Weight scale another riders stack to your suspension setup

The internet has revolutionized the ability of riders to setup and tune their bike. For the first time riders can exchange information on a world wide basis, trade local tuning tips and fact based information on aftermarket equipment. The setup and tuning of suspension systems is far behind the curve and with good reason. A desert setup perfected by a 140 lb desert rat is worthless to a 200 lb rider for the same reason that a Volkswagen shock is worthless on a Mac truck. ReStackor gives you the capability to weight scale the suspension setup of another rider to the spring rate and weight of your bike. ReStackor gives you the capability to test ride another riders stack under appropriately weight scaled conditions that maintain the suspension response, feel and performance tuned into the system by the original rider (more). 

Exchange stacks with another rider and weight scale the stack to your suspension setup with ReStackor pro.

The capability of ReStackor to tune your suspension goes far beyond these basic weight scaling functions. ReStackor gives you the capability to compare weight scaled stacks to the stack you are currently riding and relate the differences in performance in terms of clicker settings. That allows you to use your real world riding experience to identify the difference in feel and performance of the stack in terms of two clicks softer at low speed or three clicks stiffer at mid-speed. ReStackor gives you the capability to instantly recognize the differences between the stacks, intuitively evaluate the performance of the stack and decide if you want to install and test the modified configuration or not. 

Beyond these basic setup functions ReStackor gives you the capability to fine tune your existing setup. You can make the low speed damping two clicks softer and the mid-speed rates three clicks stiffer. Design a crossover gap to close on a specific bump height to allow the suspension to float over chop or retune the backer gap to increase bottoming resistance of the suspension on large hits.  ReStackor defines a new era in suspension tuning (more).

Accurately compute the stiffness and behavior of complex shim stack structures

The thorough stack structure force balance in ReStackor gives you the capability to modify complex shim stack structures and determine the combination of face shims, stack taper or clamp shim diameter needed to achieve a specific stack stiffness. Crossover gaps can be designed to close at a specific stack deflection. Backer shims tuned to control damping forces on large hits and gaper shims sized to adjust the point where the backer comes into play. These stack design features are easily tuned through the simple graphical interface of Shim ReStackor. 

ReStackor force balance solves up to 5,000 simultaneous equations to accurately resolve the stack structure and accurately compute the stiffness and deflection of complex stack structures.

These simple functions of ReStackor allow you to test, learn and understand the effect of each feature in the stack design and understand the effect of that feature on the performance of the specific shim stack configuration you are tuning. Graphical outputs allow you to easily spot the influence of each shim and modify the stack structure to control the stack stiffness across the entire range of suspension operation. 

Tune the shim stack to match specific clicker settings

Calculation of stack stiffness is necessary yet insufficient to tune a shock. Damping forces are controlled the fluid jet velocity and the jet velocity is controlled by the fluid flow area produced by the shim stack defelction. ReStackor carefully integrates the bend profile of the stack face shim to determine the flow area along the perimeter and edge of the valve port. The flow area is referenced to the clicker bleed circuit flow area. This simple reference allows you to instantly recognize the effect of stack modifications in terms of clicker settings and use your real world riding experience to evaluate the effect of shim stack modifications.

The baseline Shim ReStackor tool gives you the capability to compute stack deflections and compare stack modifications in terms of clicker settings.

ReStackor gives you the capability to tune the stack to be two clickers softer everywhere to take advantage of the full suspension travel or increase the high speed damping to be three clicks stiffer to control bottoming resistance while keeping the low speed damping the same. The capability of Shim ReStackor to relate shim stack stiffness to clicker settings creates an intuitive tuning process and helps to keep you from wasting your time installing and testing stacks that are too stiff or modifications that are so slight they make no real difference under actual riding conditions. Simple, intuitive and exact. ReStackor gives you the capability to tune your suspension far beyond the limits previously possible.

Shim ReStackor sample applications

Example applications using Shim ReStackor to solve practical suspension tuning problems.

Shim ReStackor defines a new era in suspension tuning

The capability of the baseline Shim ReStackor tool to accurately compute the stiffness of complex shim stack structures and relate stack stiffness to real world clicker settings allows you to tune your suspension far beyond levels previously possible. You can now design the stack to be two clicks softer at high speed -and- two clicks stiffer at low speed without spending months of seat-of-the-pants tuning reshuffling shims trying to stumble onto the magic combination that produces that result. Accurate, simple and intuitive. 

ReStackor anchored to real world suspension data

Tuning shim stacks in software can obviously save you a huge amount of time but the calculations mean nothing if they cannot reproduce the behavior of real suspension hardware. Dyno data for real suspension components demonstrating effects of shim stack changes on real suspension hardware have been dyno tested by www.supercross-online.de. ReStackor calculations have been demonstrated to accurately reproduce dyno data for straight stacks, tapered stacks and crossover configurations as well as the effects of oil viscosity changes. (more) .

ReStackor calculations have been anchored to dyno data for everything from bleed circuit orifice flows to complex crossover stack configurations.

ReStackor pro

ReStackor pro takes your ability to tune a shim stack to the next level

The advanced calculations of ReStackor pro include all of the stack stiffness and stack deflection calculations of Shim ReStackor and add the capability to compute fluid dynamic force and flow losses through the suspension circuits. This gives you the capability to relate bump height and suspension velocity to damping force. 

The physics based fluid dynamic models in ReStackor pro account for entrance losses, valve port turning losses, skin friction, stack face jet impingement, jet turning losses, valve port exit loss, stack edge loss, viscous flow losses at low suspension speeds as well as flow losses through the suspension bleed circuits. This gives you the capability to tune the valve port geometries, compute damping force as a function of wheel speed, evaluate the effects of oil viscosity changes on damping rates and tune the preload of digressive valve stacks with predictable results. ReStackor pro can tune shim stacks to produce specific damping forces, valve port flow restrictions can be tuned to control damping forces at a specific suspension velocity and crossover gaps designed to close on a specific bump height.

ReStackor pro calculations quantify the effect of oil viscosity on suspension performance

The fluid viscosity relationships built into ReStackor pro give you the capability to compute the effect of fluid viscosity on damping performance. This gives you the capability to test ride your bike with different oil viscosities and use those results to retune the shim stack. You can tune the stack to match light weight oil performance at low speed or the stiffer damping characteristics of 10wt oil. Oil viscosity temperature effects are built into ReStackor pro allows you to evaluate suspension fade at high temperature. 

Testing your suspension with different oil viscosities helps you tune the stack in ReStackor pro.

ReStackor pro calculations give you the capability to design crossover gaps to close at a specific suspension velocity

The capability of ReStackor pro to relate suspension velocity to the fluid dynamic forces acting on the shim stack give you the capability to compute shim stack deflections as a function of suspension velocity. This feature gives you the capability to design crossover gaps to close at a specific suspension velocity by tuning the crossover shim diameter and thickness. The damping force produced before and after the crossover closes can be tuned through changing the crossover position, the stack taper or tuning of the stack clamp diameter. The capability to do that in software gives you the capability to understand and tune the stack far beyond the limits previously possible.

ReStackor pro calculations provide the design tools you need to tune crossover gaps to close at a specific suspension velocity.

The fluid dynamic calculations of ReStackor pro give you the capability to identify suspension velocities where valve port flow restrictions are controlling damping performance. This gives you the capability to test modifications to the valve port flow area to tune performance or evaluate various after market valves to determine their effect on suspension  performance. Accurate fluid dynamic calculations give you the capability to scale suspension systems from one bike to another and correct for differences in the valve geometry and suspension oil flow rates. This gives you the capability to scale the custom stack configuration from your old bike, developed through years of tuning and testing, to your new bike and preserve the basic suspension characteristics and feel while correcting for valve geometry and necessary changes in spring rate when setting up the suspension on your new bike.

Practical applications

Application of ReStackor pro to practical suspension tuning problems are included in the sample applications link of the ReStackor web site.

Relentless tuning

Whether your suspension was setup on a dyno, tuned by a professional stack guru or the old school cut and try method it all comes down to how it rides. Over the coarse of months the "butt dyno" may show you your bike turns a little better with 10 wt oil gooing up the bleed circuits or the clickers need to be three clicks out to work in the rocks but two clicks in to handle whoops. ReStackor gives you the capability to take this real world clicker setting information and quantify the fine tuning changes needed to the shim stack to match these specific clicker settings. The capability of ReStackor to relate stack stiffness to clicker settings gives you the capability to test and develop the stack in-situ on the actual terrain, speed and riding conditions where the suspension is used. This gives you the capability to tune your suspension in an environment that fully accounts for dynamic interactions of the suspension components and fine tune the stack to compensate for those effects. 

The capability of ReStackor to accurately evaluate complex stack structures gives you the capability to tune the clamp shim diameter, stack taper and crossover shim to develop sophisticated damping profiles. The capability to do this in software gives you the ability to evaluate the stack over the entire range of suspension speeds and avoid unexpected surprises when the stack is installed in the suspension system. The capability of ReStackor to relate stack stiffness to clicker settings gives you the capability to confidently modify the stack and implement single click changes to modify only the low speed or high speed damping characteristics. This provides you the capability to confidently fine tune your suspensions far beyond levels previously possible. Your capability to tune your suspension is now only limited by your ability to complain about it. For some this may be nearly unlimited.  

Simple geometric based inputs used in the ReStackor codes

The entire input file to the 11,000 lines of ReStackor code is shown in the screen shot below. The inputs to ReStackor have been purposely streamlined requiring only simple geometric parameters you can easily measure in your garage while maintaining the detail necessary to adequately model all components of the shock absorber flow circuits. (more)

ReStackor uses simple geometric based inputs and has been demonstrated to accurately match suspension dyno data.

ReStackor helps you with the initial suspension setup or fine tuning of a suspension you have ridden for years

ReStackor gives you the capability to accurately tune your suspension with predictable results. The performance of your stock suspension, and the rider weight it was designed for, can be scaled too the weight of a heavier or lighter rider to establish an initial suspension setup. Effects of stack changes are evaluated in terms of clicker settings so you know how much stiffer of softer the modified stack will be. Stack taper changes can be evaluated across the entire range of wheel speeds and referenced to you current stack to quantify effects of the change. Crossover shims can be designed to close at specific suspension velocities on a specific bump height giving you the capability to develop sophisticated damping profiles. The capability to evaluate stack modifications in software before committing those changes to your bike prevents you from wasting your time installing and testing shim stacks that are way outside the range of modification intended .

Whether you are working on the initial suspension setup or fine tuning a suspension you have ridden for years ReStackor takes the guess work out of shim stack tuning and gives you the capability to accurately tune complex stack structures and confidently fine tune your suspension far beyond the limits previously possible.

Shim ReStackor    Buy Now    ReStackor pro