shim changes and damping curves, based on dyno testing

Kevin.

can a flipped springseat ( the steel part ) make a difference like this?

if this part flipped the spring works against the 18mm shims instead the 11mm.

for sure not on this adjuster, but do you think the difference would be 100lbs?

Here's a thought: could this one be functioning correct and you have a sealing issue with your other one? The oring in that adjuster assembly is annoyingly fragile.

I'd the same idea as Mike.

I would do a test without spring; with adjusters without the individual spring.

 

Missing the proper knowledge of interpreting these charts, however, I have the feeling that the hs spring alone can not make such a big difference...

Edited by Vietze

What would be really cool to see (in a properly functioning assembly) would be a collection of plots of the HSC adjuster at 1 through 3 turns out (in half turn increments), both with the OEM spring, and something like the Factory Connection stiffer spring.  See the result in force of rate vs. preload on that adjuster.  I wonder if they overlap at all, or shift the range more dramatically.

I had read once about a small and hard to notice difference in these adjusters.On the piston there is the small shoulder where the shim stack and then the shaft clamps them down.On one piston that shoulder was flush to the outer surface and on the other it was slightly recessed into the piston.

 

The difference was hard to see until you lay a straight edge across it.That change would have an effect on how far the shims check and also effects the bleed they generate when closed.

 

That is a good point to check.  I think you are referring to the piston preload (at least that's what we call it). Here are a couple pictures showing the compression side of the cadj piston, with and without a straight edge.

 

Dsc03317_resized.jpg

 

 

Dsc03318_resized.jpg

- - - - - - - - - - - - -

 

The straight edge works good.  You just hold it up to the light and can get a good idea if anything radical is going on.  But if the 'preload' is small, it can be hard to see.  We also measure the preload on a comparator stand.  Here are a couple pictures showing the piston on the stand.

- - The dial gauge is accurate to .0001 inch  ( .0025 mm).

- - The first picture shows the dial caliper on the outer edge of the piston.  It is zero at this point.

- - The second picture shows the dial caliper at the center of the piston.  The gauge reads.0010 inch at this point.  This indicates this piston has .0010 inch  negative preload. 

 

Dsc03320_resized.jpg

 

 

 

Dsc03322_resized.jpg

 

- - - - - - - - - - - - -

 

"Negative preload" ??? What the heck is that. 

- - Here is a diagram this is easier to understand.

 

01_kybsh_cadj_stk_pist24_prel_beed_01.pn

- - - - - - - - - - - - -

 

So anyway, that was an excellent idea.  In this case, both pistons actually had the same -.0010 preload, so that was not the problem. 

But we also need to look at the proportion of things.  In other words, if this preload was radically different,  how much would it effect the compression force. 

- - I'm sure we've measured it at some point in time, but can't seem to find the exact results at the moment.  If I recall, it would not amount to more that a couple pounds of force.

 

 

- - - - - - - - - - - - -

 

Edited by kevinstillwell

Very cool info Kevin!

 

  Gatta be the spring.

 

The spring is a possibility, but it would have to be a super major difference. The stock cadj spring rate is somewhere around 8 - 9 kg/mm. The funky adjuster would need about a 3000 kg/mm spring to account for this difference (that's a bit of an exaggeration, but it would take a big difference).

Here is some actual data showing how much the spring influences the compression numbers.

- - This table shows the compression force for a normal adjuster at hc-2 turn out vs. hc-closed.

- - So turning the hs nut all the way in only increases the forces by about 20 lbs.

 

1579_07.png

- - - - - - - - - - - - -

Edited by kevinstillwell

can a flipped springseat ( the steel part ) make a difference like this?

if this part flipped the spring works against the 18mm shims instead the 11mm.

for sure not on this adjuster, but do you think the difference would be 100lbs?

 

 

Here's a thought: could this one be functioning correct and you have a sealing issue with your other one? The oring in that adjuster assembly is annoyingly fragile.

 

 

I'd the same idea as Mike.

I would do a test without spring; with adjusters without the individual spring.

Missing the proper knowledge of interpreting these charts, however, I have the feeling that the hs spring alone can not make such a big difference...

 

 

These are all good places to look.  As you can see, if you really wanted to know exactly what was up with this adjuster, you would have to test each and every possibility, one at a time.  Eventually, you'd either find the problem or die of old age, depending on how persistent you were. 

 

But now that we've brought up this 'bad seed' of an adjuster, it makes us want to figure it out, once and for all.  Perhaps in a few days, when we get caught up, we can run some more tests.

 

 

 

- - - - - - - - - - - - -

Edited by kevinstillwell

What would be really cool to see (in a properly functioning assembly) would be a collection of plots of the HSC adjuster at 1 through 3 turns out (in half turn increments), both with the OEM spring, and something like the Factory Connection stiffer spring.  See the result in force of rate vs. preload on that adjuster.  I wonder if they overlap at all, or shift the range more dramatically.

 

We usually run a complete series of tests for each shock.  The default test is at clickers

 - - lc10

 - - hc1

 - - r10

 

We also run a low compression click range:

 - - lc18

 - - lc10.

 - - lc6

 - - lc0

 

Then we run a high compression click range:

 - - hc2

 - - hc1

 - - hc0

 

Then reb run a rebound click range:

 - - reb14

 - - reb10

 - - reb6

 - - reb0

 

This gives us a good idea of what is going on.  The drawback is, it takes about 3 hours to run this complete series.  But it definitely tells you exactly what's going on in the shock.

 

 

 

-----

Edited by kevinstillwell

Clicked,  I like your idea of the damping coefficient.  I haven't spent much time looking at the numbers in this format, so they don't have as much meaning as the format we are used to using. 

 

IMO, damping coefficient is a far better way to look at this data, for a variety of reasons.  For one, differences in low speed damping get lost when you use damping force, because of the large force range required (you could use a log scale, but I can't believe that would truly be sensible).  For another, most of the dynamic behavior that we care about (damping ratios, criticality, etc) is a function of the damping ratio and not the force, and therefore the damping coefficient curve better represents the way the shock will "feel."

Just a preference, but I feel the same way as Kyle. I've found that it's easier to reproduce the feel of a particular setup on another bike using the damping coefficient scale. It just seems more "sensitive" if that makes sense.

Ok so the spring is Out! thanks Kevin

If it's increasing the force right from the get go it's gotta be something with the ls needle. Don't these seal off an area behind the shimstack post and then bleed through an orifice in the alum part?

I know the needle taper goes toward the bore in the shimstack post but it only exits in an area in the blue part.

Just a thought as it's been awhile since I've had one apart that far.

Maybe something was blocking that exit and was forcing all of the fluid even at lower speeds over the hs stack. And maybe this also tells us how much the needle/orifice still flows even at 50 ips?

If it's increasing the force right from the get go it's gotta be something with the ls needle. Don't these seal off an area behind the shimstack post and then bleed through an orifice in the alum part?

I know the needle taper goes toward the bore in the shimstack post but it only exits in an area in the blue part.

Just a thought as it's been awhile since I've had one apart that far.

Maybe something was blocking that exit and was forcing all of the fluid even at lower speeds over the hs stack. And maybe this also tells us how much the needle/orifice still flows even at 50 ips?

The force curves shown are linear and not digressive in character...although, this a Microsoft Excel spreadsheet shown and not the actual dyno curve so I'm assuming there's some translation loss? I'm guessing that's why you also show 100lbs of force @ 0 velocity?

 

Almost 300lbs of force change @ 50ips via the external adjuster? If that's the case something is wrong. The force produced by a standard KYB adjuster is only 300lbs of total force so it shouldn't show up in the 600-900lb range. 

 

Darren

 

 

... there's some translation loss? I'm guessing that's why you also show 100lbs of force @ 0 velocity?

 

the shock is preloaded via the nitrogene pressure, that's why you have some pressure/force at 0 ips...

the shock is preloaded via the nitrogene pressure, that's why you have some pressure/force at 0 ips...

The rod certainly shouldn't be preloaded 100lbs if the gas pressure is only between 150-175psi! Also, when you dyno a shock or fork the machine runs a "gas test" prior to running the damper tests in order to isolate it from the equation. This allows you to view and manage the data from each independently. 

 

Darren

Darren,

Normally the dyno would run a “gas test” at the start of a run to zero out the initial reservoir pressure. Then you only have to “guess” the changes in reservoir temperatures over the course of the run to compensate for the changes in gas force. That can be quite a bit as you know.

 

Kevin is testing a pressure tapped shock. The pressure taps directly measure the gas force and the changes in gas force over the stroke. No guessing. The other cool thing is the measured pressure difference across the valves gives you the damping force contribution of each valve. With that, you can then back out the seal drag and how it changes over the range of stroke velocity.

 

So the bottom line is the gas force was not subtracted out of the force data. That is why the data has the 90 lbf offset. Works out to be about 190 psi of gas pressure and 15 lbf of seal drag.

Edited by Clicked

You raise a good point though.

At zero shaft velocity a shock is going to produce zero damping force. A straight statement of duh.

 

If anybody hands you dyno data and it starts off at anything other than zero you can immediately assume the low speed damping data is f’d up. You then have to add in some kind of correction for gas force and invent some other for seal drag.

 

After making up all of those corrections it’s reasonable to wonder what use the dyno data is since the corrections end up being on the order of the measured data in the first place.

Edited by Clicked

Here's a force curve of a rear shock from a 2014 YZF450. This test was performed on our Roehrig Engineering EMA and is gas force corrected. 

 

Specs:

LSC-10 Out

HSC-2 Turns Out

Reb-18 Out

Gas Pressure: 158psi

 

 

 

Darren

YZF Shock.jpg

Edited by Push Industries

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