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  1. Clicked

    Real life shim stacks vs theory

    MXScandinavia put out some dyno data comparing thick versus thin face shims. Some argue the shorter stack you get using thicker face shims increase the dynamic response since there is less moving shim stack mass. Others argue thinner shims can be bent further before becoming deformed. That allows thinner shims to take a larger hit without permanently bending the shims and deforming the shim stack.
  2. There is the basic question of do you want your suspension stiffer or not. Once you get past that the next level is figuring out the effects of the shim stack clamp diameter, stack tapper, number of face shims and crossovers to get the suspension feel you want. Dyno tuners have measured the effects of various shim stack mods to figure out how to go about modifying the shock to get the damping force curve they want. Thanks to the efforts of MXScandinavia, ValvingLogic and Kawamaha dyno data measuring the effects of various shim stack mods is here on TT. I gathered up most of that data and put it in a thread here: “Dyno data and what it tells us....”
  3. Clicked

    Restackor and Oil Viscosity tuning

    On the “Plots” or “Res” tab in ReStackor spreadsheets you can input the oil viscosity and density. Getting the oil density right (“SG” – specific gravity) is a big deal when comparing performance of different oils.
  4. Clicked

    Baseline suspension setup

    Not a stupid question. The zokes valve port geometries are identical on the base and mid-valve so the oil volume flow limit is going to be the same. The mid-valve rebound circuit hits that flow limit around 110 in/sec and you can see that in the rebound curve with damping force kicking up when pushed beyond 110 in/sec. For the weight, spring rate and damping of the te610 the fork rebound speeds just clip that 110 in/sec limit. On the compression side speeds are way up there around 350 in/sec. So why doesn’t the compression damping curve show a big force increase when pushed beyond 110 in/sec? The reason is oil flow through the base valve is a whole lot less than the mid-valve. Oil flow is defined by the valve “swept area”. For the base valve that swept area is the damper rod area. For the mid-valve the swept area is the valve area minus the damper rod area. The ratio of swept areas on the zokes works out to about 4:1 meaning there is four times more oil flow through the mid-valve rebound circuit compared to the base valve compression circuit. So…. The mid-valve rebound circuit hits the oil volume flow limit around 110 in/sec. With a 4:1 volume flow ratio the base valve is going to hit that same limit at 440 in/sec. But peak compression speeds are around 350 in/sec so the base valve never hits that flow limit – and that’s a good thing.
  5. Clicked

    Baseline suspension setup

    Most shock valves use simple spoke like geometries. For those geometries the port entrance area is simply defined as h.deck*w.port. The flow geometry of this Showa valve throws a curve ball at that with the entrance deck width (w.deck) that is much wider than the port as oblisk photo shows. The photo is a bit twisted but as best as I can tell the entrance deck width is around 6.6mm. With the entrance deck at 1.5 mm that gives a flow area that is about 15% greater than the port flow area and an equivalent h.deck of 4mm for the 2.5mm rebound port width in the valve. There is no entrance port restriction for this Showa fork valve.
  6. Clicked

    Wp cc or dal soggio spheres

    But that stuff gives the same result every time. Can't say that for test....
  7. Clicked

    Wp cc or dal soggio spheres

    That right there is the basic problem with test. If you don't know why its better you don't know nothen. And, you have no way to transport that knowledge from one suspension setup to another.
  8. Clicked

    Baseline suspension setup

    obelisk, Based on clicker needles in other Showa forks I expected the needle geometries to be different. Just goes to show there is no way to know what is in your fork until you measure it. You and I are in the same boat. The Marzocchi fork I’m working on has too much bleed on the base valve and not enough on the mid-valve. Those miss-sized bleeds mess up performance. The bleed shim you put in the rebound stack looks about perfect: For the base valve an important target is getting the ratio of low speed rebound/compression damping to be 0.8:1. With rebound set at zeta values of 0.7 the suspension is under-damped (critical damping is zeta= 1.0). That means the suspension is going to return over center (race sag) and baby-buggy its way in. Setting low speed compression damping to be stiffer than rebound does two things: The stiff low speed compression damping catches the rebound overshoot and hold the suspension “high in the stroke” Stiff low speed compression slows the suspension approach back to race sag stopping the suspension baby-buggy motions The setup you have shows a low speed damping ratio around 1.2. To get more low speed compression damping I closed the base valve clickers down to 6 out and stiffen the base valve stack. That made high speed compression a little stiffer than I wanted so I increased the mid-valve compression float from 0.3 to 0.35 mm. Those changes bring the low speed damping ratio down to 0.8:1. The compression damping force in the 3 to 6 in/sec range is around 10 lbf. So that stiff low speed compression doesn’t make much difference in terms of “pounding the bars” but it makes a huge difference in ride by holding the suspension high in the stroke. With those changes the setup you have is close enough for a test ride. Being an mx bike it is likely that rm250 shock is tuned around an mx setting. On the test ride you are going to have to make a decision: Do you want to stiffen up the fork to match the shock – or – loosen up the shock to match the fork.
  9. Clicked

    Baseline suspension setup

    While you have the thing apart is the metering hole 2.0mm or a little bigger and different sizes for the base and mid-valve? Showa 97 RM125 2.0 - metering hole Nclk Dclk [mm] 0 2.0 - base of needle 24 1.6 - tip of needle
  10. Clicked

    Baseline suspension setup

    texasthierry: Yes, you have an older version. obelisk: Are you running the same clicker needle geometry in both the base and mid-valve?
  11. Clicked

    Baseline suspension setup

    Looks pretty good! Assume the post here is looking for some nit-picky feedback. There are two things: The target high speed compression damping “rule of thumb” sets the peak damping force to match the peak spring force. On the wheel bottoming stroke your setup produces a peak compression damping force that is nearly double the peak spring force. That stiff high speed compression forces the suspension to deflect off of high speed root and rock impacts. To get compression damping down to the target value you will probably have to back off on the mid-valve compression stack stiffness. The second target on the high speed wheel bottoming stroke is high speed rebound damping should also be approximately equal to the peak spring force. Softer rebound at high speed gives a faster wheel response and that improves suspension compliance over high speed chatter bumps. To get rebound to fall-off at high speed you need a digressive rebound curve. Your curve looks like it hooks up a bit at high speed. With the crossover you already have in the rebound stack getting a digressive rebound curve may be as simple as softening the high speed stack above the crossover. The more typical case requires hacking around on the crossover shim diameter as well. The goal here is to move the peak of the damping coefficient curve to the right with a softer high speed stack so damping falls-off at high speed. Something like the dashed line I drew above. To one-up the baseline tuning you should take a look at the showa fork setup you are currently running and compare that to the targets you are shooting for here. Based on that you may want to go up or down a spring rate to keep the same chassis bottoming velocity or fiddle with chassis compression damping based on a fast versus plush trade. BTW: Thanks for posting your setup details. That will help others trying to tune a showa fork. I am a little skeptical of the 24 lb wheel weight you are using. That weight needs to include the wheel weight, tire, tube, brake caliper, stanchion tube and everything else bouncing up and down with the wheel. My usual guess is 30 lbs. The best way to measure wheel weight is put a bathroom scale under the wheel with the bike on a stand and the fork caps loosened to take the spring preload off. That fork may well have 10 lbs of seal drag between the two fork legs and that can make getting a good weight measurement tricky.
  12. Clicked

    Baseline suspension setup

    Bottoming Code Mod The stock fork hits the bottoming cones like a ton of bricks. To soften bottoming I drilled a couple of vent holes to make the force from the bottoming cones more progressive. I put two 0.169 inch holes 1/3 of the way from the top. One 0.169 inch hole at 2/3 travel and one 0.120 inch hole at the bottom. The vent at the bottom keeps the fork from “sticking” at full travel while rebound is trying to suck the piston out of the bottoming cone. Those vent holes give 38% of the stock bottoming force through the first 1/3 of travel, 62% through the second third and 84% over the final 1/3 of travel. By fiddling with the hole size you can make the bottoming cone force profile any shape you want.
  13. Clicked

    What does cavitation feel like?

    On my Marzocchi fork compression speeds hit 350 in/sec on a 10 inch compression stroke, more info here. If the compression ports on your fork limit the flow at 110 in/sec you may have found your problem. Is that port flow limit from ReStackor? Are you sure the compression port is 69 mm2? Is the valve installed upside down? -happens sometimes.
  14. Clicked

    Baseline suspension setup

    Compression damping "feel" To get a consistent “feel” through the wheel bottoming stroke the peak compression damping force needs to be approximately equal to the peak spring force. That gives a nearly constant force over the wheel bottoming stroke where the compression damping force ramps down as the spring force ramps up deeper in the stroke. Getting those forces to match is the goal of the 3.5:1 damping ratio “rule of thumb”. Computing the force over stroke data shows the setup hits that target pretty closely. If you made compression damping stiffer the force at bump impact would be higher than the peak spring force. That produces a setup that is stiff at bump impact and gets softer as the suspension approaches the peak spring force at bottoming. Stiff but then blow through. If you made compression damping softer the suspension would produce a progressive force increase over the stroke. That makes the suspension softer at bump impact and get progressively stiffer deeper in the stroke as the spring force kicks in. Setups with a progressive force increase are plusher but bottom easier. The goal of the baseline setup is set the forces to be equal and fine tune it from there. Chassis bottoming occurs at a lower suspension velocity around 130 in/sec. At that lower speed the compression damping force is less and comes in around 1/3 of the peak spring force. That fraction is typical for an enduro setup. If you wanted more chassis bottoming resistance you would have to hack around on the compression shim stack crossover configuration, or add a ring shim to get some stack preload, to produce more damping force at the chassis bottoming velocity. That compression damping force needs to roll-off at high speed so the compression force matches the peak spring force on the high velocity wheel bottoming stroke. For an enduro setup chassis compression damping is set at 1/3 of the peak spring force. The modified compression shim stack hits that target pretty closely and can be fine tuned from there. Close enough for a test ride.