ReStackor Anchored To Real World Dyno Data
Dyno data for motorcycle suspension at www.supercross-online.de has measured effects of stack clamp diameter, crossover shims, stack taper and fluid viscosity on damping performance of motorcycle suspensions. Configurations as simple as flow through the clicker bleed circuits to complex mid-valve stack configurations have been tested and used to verify all aspects of ReStackor calculations. Dyno work of supercross-online has relentlessly pursued the fundamentals of suspension tuning and demonstrated those principals through dyno tests of actual suspension hardware.
Viscosity Effects Accurately Modeled By ReStackor
Supercross-online.de has measured the flow resistance and effects of fluid viscosity changes on simple orifice flows and the flow rates through suspension valves. ReStackor matches the dyno data over the entire range tested.
Viscosity relationships built into ReStackor pro accurately match dyno data measuring effects of fluid viscosity changes on suspension performance. Oil flow rates of 30 L/min are equivalent to a base valve velocity of 150 in/sec.
ReStackor pro accurately computes the effect of fluid viscosity changes on the flow resistance through suspension components. This allows you to test ride your bike using different oil viscosities and use that data to quantify specific shim stack configuration changes to reproduce those effects. You can tune the low speed stack to the performance of 2.5wt oil and the high speed stack to the performance of 10wt oil or visa-versa.
ReStackor uses the real world commercial suspension fluid viscosity data complied by Peter Verdone to establish the relationship of SAE wt to fluid viscosity. The Andrade [1] equation is used in ReStackor to determine temperature effects on oil viscosity; match published viscosity data at cSt@40c and cSt@100c; and accurately extended that data to subzero temperatures or the high fluid temperatures causing suspension fade under hard use.
[1] Reid, R.C., Prausnitz, J.M. and Sherwood, T.K.,”The Properties of Gases and Liquids”, McGraw-Hill 1977.
Bleed Circuit Flows
ReStackor accurately computes flow rates through the clicker bleed circuits. This allows you to evaluate shim stacks in terms of clicker settings and use your real world riding experience to reference stacks in terms of two clicks stiffer or three clicks softer.
Bleed circuit "clicker" flow rates computed by ReStackor pro accurately match dyno test data.
Flow rates through simple orifices have been measured by www.supercross-online.de. ReStackor matches this data. Industry places a huge importance on the capability to accurately meter fluids. Extensive development efforts have been spent to develop physics based fluid dynamic relationships capable of accurately computing flow rates through orifice metering circuits. These fluid dynamic relationships give ReStackor the capability to compute fluid flow rates at conditions far beyond those found in practical suspension systems.
ReStackor accurately computes the effect of crossover shims
The shim stack force balance in ReStackor has been specifically designed to accurately compute the effect of crossover gaps. This allows you to modify the crossover gap position, diameter or thickness and control the stack behavior and suspension damping rates. ReStackor graphically plots the stack deflection which allows you to easily identify the forces required to close the crossover gap. With ReStackor you can easily analyze complex stack configurations and accurately design the stack structure for control damping rates over the entire range of suspension speeds. These unique features gives you an unprecedented capability to tune a shim stack.
Stack deflection plots produced by ReStackor allow you to easily spot the influance of each shim in the stack and the point where crossover gaps close.
The above stack has been dyno tested by supercross-online.de. ReStackor calculations accurately match the supercross-online.de dyno data and accurately compute the effect of the crossover shim used in this stack.
ReStackor pro calculations accurately match dyno test data measured for crossover stack configuration.
The crossover gap reduces the initial stiffness of the stack. The gap closes at an applied force of 2.5 lbf which occurs at a wheel velocity of 5.3 in/sec. Due to the soft backing shims the crossover shim has little effect on the overall stiffness of the stack. The capability to compute that with ReStackor can save you a huge amount of time and keep you from wasting your time installing and testing stacks that have little effect on the overall performance. (more).
ReStackor calculations accurately compute shim stiffness
Simple straight stack configurations have been dyno tested by www.supercross-online.de. For anchoring ReStackor the straight stack tests remove the complexity of stack taper and isolate the ability of the code to accurately compute shim stiffness and its effect on flow area and flow resistance through the valve. For shim stiffness ReStackor uses the well known Belleville washer relationships and the extensions to adapt those equations to flat shims.
ReStackor computed stack structure for a simple straight stack configuration.
ReStackor calculations match the straight stack data of supercross-online.de dyno tests.
ReStackor pro accurately computes stack stiffness and flow resistance for simple straight stack configuration.
Whether you are designing a complex tapered stack structure with multiple crossover gaps or a simple straight stack, ReStackor calculations are capable of accurately computing the stiffness of each shim in the stack and the combined overall stiffness of the stack structure.
ReStackor accurately computes stack taper effects
Tuning the taper of a shim stack is a classic method for controlling stack stiffness. The FEA force balance in ReStackor is capable of accounting for effects of stack taper as well as changes in stack clamp diameter and variations in shim thickness through the stack. This gives you the capability to design the stack in software, implement multiple changes to the stack and accurately evaluate the stack stiffness for tuning of damping rates over the entire range of suspension speeds.
ReStackor calculations accurately compute stack struchure effects on damping rates produced by shock absorbers.
Dyno test at www.supercross-online.de have compared the differences in damping performance for straight and tapered stacks. ReStackor accurately match this data. These tests demonstrate the capability of ReStackor to accurately identify the subtle differences in performance between a straight and tapered stack.
Dyno tests of straight stack and tapered stacks tested by supercross-online.de demonstrate important fundamental design principals for ReStackor. The straight stack removes the uncertainty of complex stack structures and demonstrates the capability of the code to accurately compute compute shim stiffness and the effect of shim stiffness on valve flow resistance. The classic tapered stack configuration verifies ReStackor's capability to accurately compute the stack force balance and account for effects of stack taper and shim thickness variations on the structural stiffness and flow resistance of a shim stack.
High speed suspension motions and high stack deflections are accurately modeled in ReStackor
Modeling of shim stacks at high deflections is a frequent concern in suspension modeling. Belleville washers are limited to deflections of two to three shim thickness when used in spring applications. This limitation is due to edge wrinkling of the washer at high deflections. Once wrinkled, the edge of the washer is unevenly loaded by the points of the wrinkles randomly appearing along the shim edge resulting in unpredictable spring rates.
The situation at high edge lift is much difference for the shims used in suspension systems. Shims in a valve stack are loaded by the fluid jets. This loads the stack at discreet points allowing the shims to naturally deflect into the unloaded region between valve ports and relieve the tangential edge stress causing wrinkling in spring washers. This simple geometric effect allows the stiffness of shim stacks to be reliably computed at edge lifts far beyond the two to three shim thickness typically quoted for the application of Belleville springs.
Supercross-online.de tested a YZ250 fork mid-valve at velocities up to 250 in/sec. At these velocities the face shims have been deflected to thirty times the face shim thickness. The stack deflections computed by ReStackor at these test conditions are shown below.
Shim edge lift values computed by ReStackor at high suspension velocities have been verified through dyno tests.
The damping force computed by ReStackor matches the supercross-online.de dyno data and the data shows no evidence of shim wrinkling or any evidence of the stack behaving in an unusual way at high edge lift. These test demonstrate the ability of ReStackor to reliably compute damping performance at high suspension velocities and reliably compute the stack stiffness at edge lift values far beyond the limitation of two to three times the shim thickness typically quoted for Belleville spring applications..
Damping force measurements at high suspension velocities have been used to verify ReStackor calculations.
Dyno your suspension setup
Dyno data for your shock absorber setup provides a way to measure the relationship of damping force, spring rate and bike weight. That data and the fundamentals of spring-mass-damper theory provide a method to scale the suspension response zeta parameters of your current setup to your next bike and reproduce the ride, feel and handling of your current customized setup in the setup of your next bike.
www.valvinglogic.com provides an easy way to obtain accurate dyno data for the customized shim stack configuration you have developed for your current bike. Email your stack configuration to www.valvinglogic.com , they will install the stack in their suspension hardware and for about $60/stroke dyno test the stack and email the results back to you. No hardware shipping, no down time, no missed rides. Valving logic provides an easy method to obtain accurate dyno data for your suspension setup.
ReStackor calculations verified through dyno tests
Dyno tests performed by www.supercross-online.de have demonstrate the influence of fundamental stack design parameters on shock absorber damping performance. Stack taper, crossover shims, backing shims and stack float have been investigated in a systematic way to demonstrate the effect of each parameter on suspension performance. ReStackor calculations faithfully reproduce this data.
Computation of shock absorber damping force is a complex problem. Stack stiffness calculations are not a trivial. Variable shim diameters, variable shim thickness, crossover gaps and backing shims further complicate the problem requiring solution of 5,000 simultaneous equations to describe the stiffness and deflection of a shim stack.
Perfecting shim stack deflection calculations alone is insufficient to describe the damping force of a shock absorber. Fluid dynamic flow losses through the suspension circuits must be quantified with accurate calculation of entrance losses, flow turning losses, jet impingement pressures and dump losses at the valve exit must be quantified. ReStackor uses well anchored physics based relationships developed through years of effort by the fluid dynamics community to solve these practical fluid dynamic problems. Computation of damping force ultimately requires coupling of the fluid dynamic forces with the dynamically changing stack face flow area as the shims are progressively deflected with changes in suspension velocity. This requires accurate coupling of the fluid dynamic forces with the stack structure force balance. This interaction is further complicated by the flow split between the valve circuits and the clicker bleed circuits. All of these coupled phenomena must be accurately and simultaneously described to resolve the damping force produced by a shock absorber. Given the number of physical processes involved the capability of ReStackor to match the above dyno data is impressive.
Suspension Tuning
While the goal of ReStackor is to compute the damping force of shock absorbers based on direct application of first principals that goal is somewhat irrelevant in the application of suspension tuning. For suspension tuning, the fundamental application is to take your existing suspension setup and, based on the results of test rides, adjust the shim stack to produce slightly stiffer or slightly softer damping. Here, two clicks stiffer at low speed or three clicks softer at high speed are the relevant tuning parameters and the absolute value of damping force makes little difference. The above comparisons of ReStackor with dyno data indicate this capability is well within the capability of the code.
