sportbike suspension tuning, MX suspension tuning or dirt bike suspension tuning is a much easier task using the physics based numerical dyno of Shim ReStackor.

Relentless Tuning 

You can purchase a basic suspension setup from any shop. Weight scaling a generic shim stack setup developed from the feedback of multiple riders will give a good starting point. After developing some confidence in the setup your riding skills will evolve and that generic setup will require tuning. Suspensions can't be setup once-and-for-all, you can see that trackside at any national level race with teams frantically searching for workable race setup.

One of the hardest aspects of suspension tuning, a skill professional tuners spend years developing, is the capability to guess the combination of shim stack changes needed to achieve a specific effect. 

Crossover shim stack configurations for tuning a woods bike suspension setup.

ReStackor uses fundamental physics to compute the stiffness of shim stacks and relate shim stack changes to clicker settings giving you the capability to confidently tune complex shim stacks and achieve specific effects to fine tune your suspension far beyond the limits previously possible. 

Shock Absorber Basics

 MX suspension setup for a twin chamber fork configuration with a custom ICS spring rate.Damping force produced by a shock is the result of controlled fluid dynamic flow losses through the fluid circuits. Flow losses are controlled by the stiffness of the shim stack on the shock absorber valve. At low speed the shim stack is barely cracked open resulting in high jet velocities, high flow losses and a high damping force. As shaft speeds increase fluid pressure forces the stack to further deflect producing progressively larger flow areas and controlled changes in damping force from the shock. 

Tuning the shim stack stiffness changes the fluid flow area, the resulting flow losses and shock damping force. Modeling that process in ReStackor requires a multi-physics simulation combining the fundamentals of structure mechanics with fluid dynamics to  numerically model shim stack stiffness, the resulting fluid dynamic flow losses. That gives you the capability to create customized shock absorber damping profiles.

A trail bike suspension setup needs shim stack taper changes to retune the low speed damping.

Models developed on basic physics make the calculations of ReStackor equally applicable to the tuning of motorcycle suspensions, automotive racing shocks, trophy trucks or the setup and tuning of mountain bike suspensions.

Take the guesswork out of suspension tuning

Woods suspension configuration with custom shim stack taper modifications and crossover shims to setup the suspension for race conditions.

The fundamentals of structure mechanics and fluid dynamics give ReStackor the capability to compute damping force as a function of shim stack structure, valve port geometry and clicker settings. Clicker settings let you use your real world riding experience to tune the shim stack in terms of forces you can actually feel when you ride and fine tune suspension setups in terms of two clicks stiffer at low speed or three clicks softer at high speed. The graphical environment and spreadsheet interface allow calculations to be easily run and results visually compared across the entire range of suspension velocities. ReStackor takes the guess work out of shim stack tuning so that you can focus on the art of suspension tuning.

Simple Inputs - Thorough Analysis - Practical Results

ReStackor uses simple geometric inputs that you can easily measure in your garage. Each parameter represents a geometric dimension that can be tuned and modified to control the shape of the damping force curve and refine the suspension setup across the entire range of suspension velocities. 

GP race suspension setups use shim stack configurations with ring shims to preload the stack and valve bleed ports to customize the low speed damping stiffness. 

ReStackor uses simple geometric inputs you can easily measure in your garage to setup the calculations for anything from a mountainbike to an MX suspension setup. ( User Manual )

The above snap shot of the ReStackor spreadsheet shows the entire input file, there are four sections:

  • Stack configuration: Lists the diameter and thickness of each shim in the stack.For a woods ride the valve port setup of a motocross bike requires modification to get the right suspension response.

  • Damper configuration: The shock absorber valve and damper rod diameter.

  • Valve geometry: Eight parameters describing the valve port and bleed circuit dimensions.

  • Settings: The shock absorber shaft speed, clicker setting and oil viscosity.

Test, experiment, tune and modify each feature of the shock. Learn the influence of each shim in the stack on damping performance and tune the shim stack to control the shape and magnitude of damping across the entire range of suspension velocities. Graphical outputs make it easy to understand the effect of each modification and make it easy to tune the shock to optimize performance. Evaluating the effect of modifications over the entire range of suspension velocities helps to eliminate unexpected side effects causing the suspension to suddenly become overly stiff at high speed or blow through its stroke on large hits ( download demo ).Getting the low speed suspension compliance needed for a trail bike suspension setup requires shim stack modifications to the stack clamp diameter and crossover shim position to get the suspension performance of a good enduro suspension setup.

  • Simple geometric inputs.

  • Intuitive graphical outputs.

  • Tune the shim stack in terms of clicker settings and forces you can actually feel when riding.

  • Test, tune, learn, experiment and modify ALL of the tunable features of your shock.

Simple inputs - thorough analysis - practical results. The graphical spreadsheet environment of ReStackor gives you the capability to setup, tune and refine your suspension far beyond the limits previously possible.

Thorough Analysis 

Shim ReStackor Calculations

The 14,000 lines of the basic Shim ReStackor code have been specifically designed to accurately evaluate the stiffness of complex shim stack structures and accurately compute shock absorber damping performance using simple geometric dimensions of the shim stack and valve port configuration. The ReStackor FEA force balance solves 5,000 simultaneous equations to resolve the axial and radial forces in the stack structure, determine the stack bend profile and the flow area at the shim stack face. Shim ReStackor computes the stiffness of complex shim stack structures with multiple crossover gaps, backing shims, stack taper and accounts of variations in shim thickness through the stack. 

Grip under slick riding conditions for a woods suspension race setup requires tuning of crossover shim stack configurations to provide adequate low speed compliance while maintaining good bottoming resistance.

Effects of adding shims to the stack are easy to compute with Shim ReSackor. Referencing stack stiffness in terms of clicker settings provides an instant intuitive reference for tuning the stack in terms of forces you can actually feel when you ride.


ReStackor pro Calculations

 The physics based fluid dynamic models of ReStackor pro account for entrance losses, valve port turning losses, skin friction, stack face jet impingement, valve port exit loss, stack edge loss, viscous flow losses at low suspension speeds and jet turning losses at high speed. The basic fluid dynamics gives ReStackor pro the capability to tune valve port geometries, compute damping force as a function of wheel speed, evaluate the effects of oil viscosity changes on low speed damping and tune stack preload on digressive suspension valves with predictable results. ReStackor pro can tune shim stacks to produce a specific damping force, design valve port flow restrictions to control damping at a specific suspension velocity and tune crossover gaps to close at a specific suspension velocity or match a specific clicker setting.

Getting the right dirt bike suspension setup requires tuning the shim stack taper and clamp shim diameter to get the suspension damping profile to match your speed, style and terrain.

The fluid dynamic calculations in ReStackor pro allow damping force to be directly computed as a function of wheel velocity.

Shim ReStackor application of basic FEA stack structure analysis and ReStackor pro application of basic fluid dynamics creates a set of suspension tuning tools that give you the capability to develop sophisticated suspension damping profiles and define a new era in suspension tuning.

Practical Results

Clicker Map: A simple clicker map will show you the damping force curve of your current suspension setup, the change in shape of the damping force curve with changes in clicker settings and the influence of basic tuning parameters on the ride, feel, performance and behavior of your suspension.

An important part of a trail bike ride setup is adjusting the clickers to get the damping profile shape that you want.

Crossover Gaps : Motocross suspensions are setup for landing big jumps on groomed tracks. Creating a trail bike or a good woods suspension setup out of a motocross bike requires softening the low speed damping to get compliance to roll over trail trash and gain traction under slick riding conditions. ReStackor quantifies the size, position, thickness and diameter of crossover shims needed to achieve a specific change in clicker settings at a specific suspension velocity.

Woods suspension tuning requires adjusting the size and location of crossover shims to get the low speed damping characteristics needed for suspension compliance and grip under slick riding conditions.

Valve Port Geometry: Taking an MX bike off the groomed tracks into the real world of desert riding requires opening the valve ports to get the high speed suspension action needed for a desert suspension setup. ReStackor pro computes the suspension velocity where the valve ports limit flow, the port flow area needed for a high speed suspension system and the shim stack modifications needed to maintain bottoming resistance while providing adequate whoop performance.

Converting an MX suspension setup into a good offroad bike suspension setup requires tuning of the valve ports to get the high speed suspension action needed for a desert suspension setup.

Stack Preload: Motards and GP suspension setups need stiff low speed damping to control chassis motions and provide the track feedback needed for high speed handling. ReStackor can tune the shim stack preload of valve face lips or ring shims to control the magnitude, width and transition into and out of the low speed damping region to tune the performance of the system. 

Sport bike suspension tuning requires adjusting the shim stack preload using ring shim to control low speed damping like the setups used in GP race bikes.

Mid-Valve Tuning: The stack stiffness and float of mid-valve shim stacks can be tuned to control bottoming resistance. Stiff mid-valve stacks and low values of float can cause the rebound chamber to cavitate. The loss of rebound damping from cavitation allows the fork to pop back to the top of the stroke producing the effect of riding "high in the stroke". Cavitation is a feature until the loss of damping causes the bike to head shake on a high speed corner exit.

MX suspension tuning of compression damping with a mid-valve setup requires balancing the ICS spring pressure with the cavitation limits of a twin chamber fork.  

Relentless tuning

Whether your suspension was setup on a dyno; tuned by a professional stack guru; or the old school method of cut and try; performance all comes down to how it rides. After months of "butt dyno" testing you may find your bike turns better with 10 wt oil gooing up the bleed circuits but the clickers then need to be four clicks out to handle whoops and you loose the low speed damping improvement. ReStackor takes this real world info and quantifies the fine tuning shim stack changes needed to keep the features and eliminate the unwanted side effects. The capability to relate clicker settings to stack stiffness gives you the capability to test and develop the suspension in-situ on the actual terrain, speed and conditions that you ride and fully account for all of the dynamic interactions of the chassis and suspension in fine tuning the shim stack configuration. 

Supercross suspension tuning requires relentless fine tuning of the shim stack setup to match the riders style and continuous fine tuning of damping rates based on the clicker settings.

Shim stack retuned to match SAE 10wt oil at low speed and whoop damping at high speed.

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. Tuning in software gives you the capability to evaluate stack changes over the entire range of suspension speeds and avoid unexpected surprises after the stack is installed in the system. Relating stack stiffness and damping force to clicker settings gives you the capability to implement single click changes to modify only the low speed or only high speed damping and confidently modify the shim stack configuration. Your capability to perfect your suspension is now only limited by your ability to complain about it. For some this may be nearly unlimited.

Develop An Initial Bike Setup or Fine Tuning a Suspension You Have Ridden For Years

Damping of a stock suspension setup is designed around the weight and spring rate of the phantom stock factory rider. Changing the suspension spring rate to get your sag right requires the damping to be changed to restore the ride, feel, handling and suspension response the manufacture intended for your bike. For many riders the basic exercise of weight scaling the stock setup to correct damping for a change in spring rate is enough to create a personalized "custom" setup. 

Motorcycle suspension tuning can be as simple as weight scaling stock damping rates to match the spring rate and rider weight to produce a custom shim stack configuration for a specific suspension setup.

Weight scaling uses the fundamentals of spring-mass-damper theory to scale the suspension response and performance of the stock suspension to correct for a change in weight and spring rate.

The capabilities of ReStackor go far beyond the basics of weight scaling. You can exchange stacks through web forums and weight scale the stack to your spring rate and weight so that you can test and feel the suspension response of the rider that originally developed the stack. Shim stacks can be fine tuned in terms of clicker settings allowing you to relentlessly pursue refinement of the suspension setup. Effects of 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 helps prevent wasting your time installing and testing stacks that are way too stiff or changes that are so slight they make no real difference. 

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 giving you the capability to accurately tune complex shim stacks and confidently refine and fine tune your suspension far beyond the limits previously possible.

Shim ReStackor    Buy Now     ReStackor pro