Looking for volunteers to install a shock revalve and provide feedback

[jjy130]

I'd be curious to see what actual shaft speeds are achieved while riding. Rebound certainly will never be in the 70 ips range.

[455]

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You said you have changed these springs may times and noticed a difference. But it sounds like those were KYB. The KYB adjusters are stiffer.

.

Yes tested the spring in KYB's. Only did the spring, didnt open up the shock other than to remove the adjuster to install the spring. Then rode the shock back to back.

[kevinstillwell]

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We are still looking at the 2 cadj springs. Test 1465 is the stk spring, test 1466 is the fc spring.

Quick Summary:

A. Here's another look at the "compression adjuster only" numbers for these two tests (we removed all the midvalve piston shims).

-- The tests were run at default clicker settings: lc10, hc2, r10

-- We concluded that this test didn't show much of a difference between these two springs, but we have to take into account the speeds we are testing at, and the fact that this is the 'high speed adjuster'.

B. Here are the actual pressures, and the calculated p.diff (pressure difference) between the chambers for test 1465.

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Here is a table that shows how the p.diff increased with the stiffer cadj spring.

-- Remember, the difference is in psi (pounds per square inch).

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The next step is to separate the 'compression force' into it's four parts (components).

1. mv comp force (lbs)

2. cadj comp force (lbs)

3. gas force (lbs)

4. drag force (lbs)

This shows where all the compression force is coming from. Once you know that, you can tune each indivudual component to achieve your goal. We will be doing that later.

Finally, we can compare each of the four components to determine what has changed.

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Next, we can start testing complete valve stacks.

Edited December 11, 2012 by kevinstillwell

[kevinstillwell]

I'd be curious to see what actual shaft speeds are achieved while riding. Rebound certainly will never be in the 70 ips range.

We figure rebound to be 40 ips, maybe a bit more.

That would put a Shock Clock to good use. Go out on the track and find the velocities for various bumps. You could test different size woops, jump faces, g-outs, square edge, braking bumps, and the velocites slamming into berms. Of course you won't find one velocity for each obstical, but a range. Once you new this range, you would be able to make more accurate valving changes, provided you had a way to measure and compare the shock.

Edited December 11, 2012 by kevinstillwell

[kevinstillwell]

I my case I did not felt any difference [in the stk cadj spring and the fc spring]

That's interesting to know. But when we start testing your stacks, we'll keep using the fc spring. So when I suggest a setup, it will be with the stiffer, fc cadj spring.

Edited December 11, 2012 by kevinstillwell

[racerfmx450]

We figure rebound to be 40 ips, maybe a bit more.

That would put a Shock Clock to good use. Go out on the track and find the velocities for various bumps. You could test different size woops, jump faces, g-outs, square edge, braking bumps, and the velocites slamming into berms. Of course you won't find one velocity for each obstical, but a range. Once you new this range, you would be able to make more accurate valving changes, provided you had a way to measure and compare the shock.

Thats one of the most important parts for tuning the suspension

Also the position of the strocke.

Both, fork and shock are positions sensitive.

We have a airspring and bottomingg cone on the fork

And a bumper and progressive linkage on the shockk.

So the rider says it's to stiff on bracking bumps i like it to make

A hi speed video to see the position .

It can be ride to low or to high.

The dyno data makes it perfekt to see wich part of the

Needs a change.

( lo or high speed. Slope, bleed, etc.)

[kawamaha]

I'd be curious to see what actual shaft speeds are achieved while riding. Rebound certainly will never be in the 70 ips range.

the pure shock can reach up to 100ips - but yes, I guess while riding it's far from that...

just a shock at 2.4m/s = 95 ips

https://www.thumpertalk.com/topic/842778-shock-rebound-speed/

[kevinstillwell]

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Time to look at the stacks provided by rdmx151.

But first, we need to look at the stock compression stack for the 2013 KXF 250, test 1467. Notice on the spec sheet that we're using the fc cadj spring, and the mv piston preload is '0002 cvx stk' (preload is actually negative, which we refer to as convex, measured in inches).

Next is a table that shows the compression forces for the stock stack.

-- 'co wgas' column shows the overall compression forces as measured by the dyno's load cell.

-- 'c force' (compression force) is the force from the mv piston.

-- 'ca force' (cadj force) is the force from the cadj piston.

-- 'gas force' is the gas force from the nitrogen charge.

-- 'drag' is the seal drag from the piston band, shaft seal and bushing.

The seal drag and gas force will always be about the same. To keep it simple, we'll start looking at only the 'cforce' and 'ca force' compression numbers.

-- This table represents the stock shock at the default settings of lc-10, hc-2, r-10.

-- We are leaving out the 'gas force' and 'drag'.

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The stock stack is test 1467, the first mod stack is test 1469.

Here is the compression stack (1469) tried by rdmx151.

This table shows the compression numbers comparing 1467 and 1469 (not including gas force and drag).

-- Obviously, the difference in the numbers are due to the compression stack, as the cadj remains the same for both tests.

-- This mod stack is softer initially, and stiffer at the higher velocities.

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Now we have dyno tested two valve stacks and can see the difference in the compression damping. All we need is the rider feedback.

-- I'll paraphrase what rdmx151 said, but he can fill us in on more details.

-- rdmx151 said "This was the first stack I tried but It seemed to hard on the comp and was too stiff. If I went softer on the clicker, then it kind of blow thru".

So let's see what happens when the low speed compression is turned out. This table shows the compression numbers for: lc-18, hc-2, r-10.

WAIT A MINUTE. . . . This is lc-18, and it gets stiffer starting at 50 ips. This must be a mistake.

-- Lets look at the two stacks side-by-side.

rdmx151 said the stack felt like it blew thru the stroke when he turned the compression clicker out. This would explain why it felt like that. Turning the compression out softened it initially, but then it actually stiffened the compression later in the stroke.

-- I'm sure the first question will be, is this info accurate. . . Answer, yes.

Looking at the pressures will show us whats going on.

-- This table compares the pressures between the two clicker settings. The pressures are lower for lc-18. That's what the adjuster does. It increases the bleed area and reduces the pressure created when the shaft enters the body.

This graph shows how the pressures in the body are reduced. The green and red graph lines are for lc-10, and the turquoise and purple lines are lc-18. The graph lines for lc-18 are lower, indicating a reduction in the internal pressures, but it's the pressure difference (p.diff) that determines the damping force.

-- In this case, the p.diff increased when the low speed compression was turned out.

-- But we also have to consider the cadj pressures. I didn't put them here because it cluttered up the graph, but you can see these pressures in the numbers below.

Finally, by looking at the numbers, we can see that the 'c force' increased and the 'ca force' decreased at lc-18 (we would expect the ca force to go down). But we have to add these numbers together to get the overall compression force. And, its this total that indicates the compression increased at lc-18.

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Next we'll test rdmx151's second shock setup.

Edited December 15, 2012 by kevinstillwell

[racerfmx450]

Kevin!

would you say the crossover gap plays a rule up to ~ 15 IPS on the second stack?

and it' possible at 1 IPS The shimstack it's still closed , only the bleed of the reb setting works?

i am curiouse about the real lo-speed,influence bleed vs shimstack and what does the crossover...

[mog]

I'm amazed the hs increased with the comp at 18, learn something new every day!

[kevinstillwell]

would you say the crossover gap plays a rule up to ~ 15 IPS on the second stack?

i am curiouse about the real lo-speed,influence bleed vs shimstack and what does the crossover...

No, the crossover does not work that way. We'll get into it more when we start analyzing the next stack.

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and it' possible at 1 IPS The shimstack it's still closed , only the bleed of the reb setting works?

Yes, we've seen that at 1ips the majority of the fluid flows thru the rebound bleed. At 2ips, the shims are starting to come into play. You will notice that 2ips is highlighted. We refer to this as the opening speed (os). It's a good number to look at to see how much initial tension is on the stack. This initial tension can be from preload, for example, or just a stiff stack.

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Edited December 15, 2012 by kevinstillwell

[kevinstillwell]

I'm amazed the hs increased with the comp at 18, learn something new every day!

It surprised us as well. It has to do with the balance between the mv shim stack and the stiffness of the cadj. Now, with the pressure sensors, we can see exactly what's going on, and are getting a new understanding of how all the forces and components in the shock interact.

[kevinstillwell]

I'd like to thank rdmx151 for supplying his stack. Without it, we wouldn't have found this oddity with the low speed clicker.

That's one of the reasons we like getting stacks from riders and tuners. They come up with stacks that we never would have tried.

Edited December 15, 2012 by kevinstillwell

[Vietze]

Great stuff guys, thank you!

Does anyone have a clue why the damping force increased with the clicker more out?

Pressure has been mentioned but I'm searching for a more detailed answer here (I guess most of us do after reading that...)

[Clicked]

Kevin!

would you say the crossover gap plays a rule up to ~ 15 IPS on the second stack?

and it' possible at 1 IPS The shimstack it's still closed , only the bleed of the reb setting works?

i am curiouse about the real lo-speed,influence bleed vs shimstack and what does the crossover...

I think the easiest way to figure out where the shim stack cracks open and the crossover comes into play is to plot the damping coefficient. The damping coefficient is the damping force divided by the shaft velocity. To get the damping force you have to subtract off the reservoir pressure gas force and the seal drag force. For the ValvingLogic data Kevin is posting all of that was measured in the pressure tap shock he is testing - normally you have to guess what the seal drag was.

For this case the shim stack cracked open at 3 in/sec. The downward slope from 3 to 10 in/sec tells you the shim stack opened slowly, probably because it had a bunch of preload on it. The thing that is missing on the plot is a step-up in the damping coefficient in the 20 to 30 in/sec range where the crossover closes.There isn't any.

The missing step-up in damping force when the crossover closes and the behavior of the clickers might have something to do with the odd shape of the pressure curves measured in the rebound chamber.

Is the compression stack cavitating? Hopefully Kevin will talk more about that when he gets around to tuning this thing.

Edited December 15, 2012 by Clicked

[kevinstillwell]

Does anyone have a clue why the damping force increased with the clicker more out?

Pressure has been mentioned but I'm searching for a more detailed answer here (I guess most of us do after reading that...)

That's difficult to explain.

It's one thing to picture something in your head, but another to put it in words. When we come up with a better explaination, perhaps with animation, we'll put it up.

But for now, the answer can be found in the pressure data.

You can't see it in the actual pressures, but when comparing lc-10 vs. lc-18, if you look at the force in pounds for 'c force' (column 4), you see that the numbers start to increase at 40 ips, but at the same time the numbers for 'ca force' (column 5) decrease. The overall compresson force (column 3) is from c force + ca force. It's in column 3 that we see the overall numbers start increasing at 50 ips. . . The 'c force' and 'ca force' are the results of the pressure differences in column 1 and 2.

So the issue arrises when the pressure difference of P.c - P.r starts to proportionatly increase more than the pressure difference of P.c - P.ca decrease. Now we have to picture what's going on in the shock. Basically, the mv stack is to stiff, and there is no longer enough 'back pressure' from the stiff cadj to force the fluid thru the mv shims. This increases the pressure in P.c, decreases the pressure in P.r, resulting in a bigger pressure difference, which translates to higher compression numbers. So the simple answer might be that the mv stack is to stiff.

Edited December 16, 2012 by kevinstillwell

[kevinstillwell]

might have something to do with the odd shape of the pressure curves measured in the rebound chamber.

Is the compression stack cavitating?

No, that odd hitch in the rebound side curve is not from cavitation. It is from the compression adjuster. That is one way to determine the 'relationship' between the mv stack and compression stack. The shape here tells you if the mv stack is to soft/stiff in proportion to the compression adjuster.

Edited December 16, 2012 by kevinstillwell

[kevinstillwell]

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We have tested the 2nd stack rdmx151 tried on his 2013 KXF 250.

The first mod stack was test 1469, this test is 1470.

This table shows the 'c force' and 'ca force' for these two stacks (gas and seal drag are removed as they will stay about the same for these tests).

-- A side note: we tested this stack at lowcomp-18, and the compression was softer at all velocities.

-- The numbers below show this stack is softer than the previous.

But we need a better understanding of how these forces have changed.

This new table shows the same stacks, but we've included the 'percent difference' (% diff).

-- Just looking at the lb difference in the force numbers can be deceiving. By looking at the percentage of change, we get a better understanding of how much the low speed and mid speed changed, and in what way (proportion or ratio).

-- Looking at the overall compression force (co wgas), we see the low speed was reduced by 8%, and the mid speed was reduced by 23%.

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There is still something missing.

It's nice to have numbers to compare, but they have to have some meaning. In other words, if the force at 2 ips has changed from 128 - 120 lbs, what does that mean. Same with 5 ips. What's the significance between 177 and 163 lbs.

We have dyno tested hundreds of stacks, and always look at the compression numbers for patterns. We have seen that all the shocks we've tested have compression numbers that fit within certain ranges. In other words, the numbers for woods stacks all fit within a specified range, and the numbers for MX all fit in another. And it turns out that all Japanese big bike shocks tested fall within these range of numbers, regardless of the manufacturer. In other words, the KYB_46 has basically the same compression force numbers as the Showa 50. More on that later.

First we'll assign some generic names like 'low speed' and 'mid speed' to the velocities.

We now have three velocities to watch.

-- os (opening speed)

-- ls (low speed)

-- ms (mid speed)

When making valving changes, our goal is to influence the numbers at any or all of these velocities. For example, we may want to increase the force at low speed, but minimize any increase at mid speed. More on that later.

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Lets look at tests 1469 and 1470 again.

-- Opening speed force wasn't changed much (6% softer), and the low speed only dropped by 8%. The big change was mid speed. It was reduced by 23%.

-- There are several ways to interpret this change.

-- This is one way:

-- -- If stack 1469 was proportionally to soft at the lower velocities, it might blow thru the stroke and hit hard later in the travel. Stack 1470 actually decreased low speed a bit, and it could still blow thru the initial part of the stroke, it just wouldn't hit as hard, and could feel smoother.

We have tested many different shocks and valving configurations. As a general rule, the opening speed, low speed and mid speed numbers always fall withing a certain range. The lower numbers are for woods riding, and the higher numbers for MX.

Compression forces for Showa 50 mm shocks fall within these ranges:

-- opening speeds = 115 - 140 lbs.

-- low speed = 155 - 205 lbs.

-- mid speed = 560 - 810 lbs.

We can compare the numbers from stack 1469 to see how they fit into these ranges.

-- Looking at the yellow highlights, you can see that proportionally, the mid speed is quite a bit stiffer than low speed. This would indicate that, compared to all the stacks we have tested, this stack has a bunch more mid speed damping force. Now, this isn't immediately saying this stack is no good. But it does give the rider/tuner a good idea of what to look for.

Now let's compare the numbers from 1470 to the range.

Test 1470 doesn't seem to be so far out of proportion.

The specific ranges we've listed here are not set in stone. We aren't saying that test 1470 would be perfect if the force at 50 ips = 610 lbs. This simply indicates one of the many ways the dyno data can be evaluated.

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Edited December 16, 2012 by kevinstillwell

[kawamaha]

Great stuff guys, thank you!

Does anyone have a clue why the damping force increased with the clicker more out?

Pressure has been mentioned but I'm searching for a more detailed answer here (I guess most of us do after reading that...)

kevin, you tested another stack. did you test it also with two different lc numbers?

[455]

You dont want to show us the 1470 stack?

Feel free to show and dyno the stack I gave you if you want?