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Poppet Damping Dyno Curves Thread.

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Dougal

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Discussion starter · #1 · (Edited)
This is a thread to discuss the dyno curves possible with Poppet dampers.

Several have claimed lately that Poppet dampers can be adjusted to provide digressive, linear or progressive. I would certainly like to see evidence of this.

Poppets typically run flat (i.e. not speed sensitive) with two quadratics.
1. A quadratic into it from leakage and LSC bypass through fixed sized orifices.
2. A quadratic after the poppet has popped from the fixed restriction of piston orifices.

Image
 
#2 ·
Yes, Id like to see the claims from Push substantiated. I have some thoughts as to why they may be saying it, cant easily describe on my phone here, but the curves would show it. The dyno curves and even this latest info earlier from Push would have helped immensely earlier. There are plenty of “trust the mfr and dont ask questions” types, but thats been going on too long with suspension IMO.
 
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#3 ·
Dougal said:
...
Poppets typically run flat (i.e. not speed sensitive) with two quadratics.
1. A quadratic into it from leakage and LSC bypass through fixed sized orifices.
2. A quadratic after the poppet has popped from the fixed restriction of piston orifices.

View attachment 2089714
Click to expand...
What would this poppet damping feel like? It's a relatively flat compression force after the poppet opens based off that curve, does that mean you're blowing through suspension travel on the bigger hits as you're only reliant on the spring forces from a particular shaft speed onwards? Can you rely on a progressive spring from then onwards to not blow trough travel with the drawback that it is uncontrolled (to some extent) suspension movement?
 
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Discussion starter · #4 ·
meschenbruch said:
What would this poppet damping feel like? It's a relatively flat compression force after the poppet opens based off that curve, does that mean you're blowing through suspension travel on the bigger hits as you're only reliant on the spring forces from a particular shaft speed onwards? Can you rely on a progressive spring from then onwards to not blow trough travel with the drawback that it is uncontrolled (to some extent) suspension movement?
Click to expand...
You feel the peak in that graph, too much initial damping and then not enough later on.
So feels like lots of support for chassis movements, harsh on chatter, then not enough support for bigger hits.

There are all sorts of work-arounds to help individual events. But they all have trade-offs.
 
#5 ·
meschenbruch said:
What would this poppet damping feel like? It's a relatively flat compression force after the poppet opens based off that curve, does that mean you're blowing through suspension travel on the bigger hits as you're only reliant on the spring forces from a particular shaft speed onwards? Can you rely on a progressive spring from then onwards to not blow trough travel with the drawback that it is uncontrolled (to some extent) suspension movement?
Click to expand...
You're best off not asking people who don't fully understand the valves and tuning intricacies.
It's sort of like saying that a shimmed piston valve has just one profile: flat with drilled holes and a cheap spring washer closing it. But really the shape of the ports, convex or concave dishes and everything else plays a huge part.

Notice comments like this "Poppets typically run flat (i.e. not speed sensitive) with two quadratics." which immediately make the general reader think he is saying they run flat.... He's not. Because he knows it is possible for them not to.
While it is typical, the more advanced ones don't and there is no reason beyond simplicity of design that the valve has to "run flat", and infact it can be speed sensitive (which Dougal has conveniently implied it can't, while also not denying that it can).

That's pretty much all I have for this thread.
I opened his eyes with two advantages that they can provide over disc shim valves that he obviously was unaware of. That alone should tell you the level of knowledge he has about poppet valves in suspension.
 
#7 ·
Yup
 
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#9 ·
Poppets use springs to open, shims are springs in themselves. So I would propose that a poppet that has a spring rate and little preload would open progressively (based on the valve geometry) rather than being an on/off valve, as your assumtion is. As it is not more than a spring loaded, un-bendable shim. So the difference would be shim is not part of the spring system... There are other high performance tuners that swear by poppet style dampers, with great success.
 
#11 ·
hssp said:
Poppets use springs to open, shims are springs in themselves. So I would propose that a poppet that has a spring rate and little preload would open progressively (based on the valve geometry) rather than being an on/off valve, as your assumtion is. As it is not more than a spring loaded, un-bendable shim. So the difference would be shim is not part of the spring system... There are other high performance tuners that swear by poppet style dampers, with great success.
Click to expand...
I cant make any long replies for a few days, so it might get covered before I get back to this, but Im not sure thats true, you have a fixed orifice and all you do is add preload to the spring. Although both use a “spring”, I believe the spring profile in a poppet valve is fixed at basically stacked shims of the same size. Changing the spring rating is like changing all the flat shims to thicker shims.
 
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#12 ·
Jayem said:
I cant make any long replies for a few days, so it might get covered before I get back to this, but Im not sure thats true, you have a fixed orifice and all you do is add preload to the spring. Although both use a “spring”, I believe the spring profile in a poppet valve is fixed at basically stacked shims of the same size. Changing the spring rating is like changing all the flat shims to thicker shims.
Click to expand...
If I remember right, Dougal has said in the past that poppets valves can work well provided various weight springs are available for the valve. However, they virtually never are.
 
#13 · (Edited)
#14 · (Edited)
I'm not sure we can really dive into poppets and their advantages without discussing the underlying architecture that they are operating within. What I (think) I learned from the HC97, is that there are nuances to poppet valves being the majority of the system that determines compression damping that I did not jive with. From that experience, it's left me thinking that they can still be quite effective, but really need to be the method of external adjustment when used up stream and in tandem with a proper main piston valving or base/mid valve strategy... which likely involved a shim stack. I really know just barely enough to be significantly dangerous... but it seems that they are a means of bleed/bypass which is very tricky to utilize correctly in a 1/1 leverage scenario like a fork. This is the reason that I wanted to know the specific arrangement of the damper design in the Nine.One thread as I had a hunch that it was a much more nuanced and advanced architecture then what I experienced in the HC97. Obviously, the biggest advantage and reason why a mfg would chose to stop modifying other products and start over with a clean sheet design of their own.

There was a comment made in the other thread about significant amounts of motorsports dampers using poppets. I'm aware of plenty of spool valves being used in high end motorcycle forks (which are a variation of a poppet) however I am not aware of any of those that do so without a mid valve and/or base valve that utilize as shimmed piston. Granted, I am about 1 generation behind of what WP is using in their top end closed cartridge SX forks at the moment. That being said, I'd refrain from motorsports references in general as I am well versed in cars and motorcycle suspension... and my experience is the bulk of the performance products in those avenues are using pretty heavily double digressive damping setups. I have yet to have a completely satisfactory experience with damping setups on a mountain bike that are as aggressively digressive as I experienced on the motorsports side.
 
#16 ·
#17 ·
KoolGrandWizardLuke said:
...

Notice comments like this "Poppets typically run flat (i.e. not speed sensitive) with two quadratics." which immediately make the general reader think he is saying they run flat.... He's not. Because he knows it is possible for them not to.
While it is typical, the more advanced ones don't and there is no reason beyond simplicity of design that the valve has to "run flat", and infact it can be speed sensitive (which Dougal has conveniently implied it can't, while also not denying that it can).

...
Click to expand...
can you describe this aspect of poppet valves? is it something that can realistically be sized for mtb applications, not just chucking an industrial applications onto a bike?
 
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Discussion starter · #18 ·
jsma09 said:
Straight from the suspension lab IG post. Are these poppet valves?
View attachment 2089766
Click to expand...
Yes they are flat face poppet valves. Each piston has 4 round ports which are kept shut by the black valves and preloaded by the coil springs. The red parts wind up and down on the black mounts to change preload and the silver needles are your LSC adjust.

hssp said:
Poppets use springs to open, shims are springs in themselves. So I would propose that a poppet that has a spring rate and little preload would open progressively (based on the valve geometry) rather than being an on/off valve, as your assumtion is. As it is not more than a spring loaded, un-bendable shim. So the difference would be shim is not part of the spring system... There are other high performance tuners that swear by poppet style dampers, with great success.
Click to expand...
Shims open progressively and the rate of progression can be infinitely varied with different shim stacks. Poppets however open all the port area at once then greatly increase the curtain area with small changes in stroke. This is why they're a good pressure relief with little speed sensitivity.

Poppets are successfully used in the base-valve adjusters of rear shocks where the mid-valve piston with shim stacks carries the majority of the load.

This is however not the case with a fork. Forks run virtually all damping on base-valve.

l'oiseau said:
Instead of speculation, why don't one of you with a dyno find a customer who has a fork and convince them to let you test it, or buy one of your own and resell it after you measure?
Click to expand...
There's no speculation. I know what Poppet valves do. I want to see the marketing claims substantiated as they are in conflict with all the data and indeed the physics.

bad mechanic said:
If I remember right, Dougal has said in the past that poppets valves can work well provided various weight springs are available for the valve. However, they virtually never are.
Click to expand...
Yes you would need much firmer springs with very light preload but then it would only be less like a square cut-off and give some speed sensitivity.

minimusprime said:
I'm not sure we can really dive into poppets and their advantages without discussing the underlying architecture that they are operating within. What I (think) I learned from the HC97, is that there are nuances to poppet valves being the majority of the system that determines compression damping that I did not jive with. From that experience, it's left me thinking that they can still be quite effective, but really need to be the method of external adjustment when used up stream and in tandem with a proper main piston valving or base/mid valve strategy... which likely involved a shim stack. I really know just barely enough to be significantly dangerous... but it seems that they are a means of bleed/bypass which is very tricky to utilize correctly in a 1/1 leverage scenario like a fork. This is the reason that I wanted to know the specific arrangement of the damper design in the Nine.One thread as I had a hunch that it was a much more nuanced and advanced architecture then what I experienced in the HC97. Obviously, the biggest advantage and reason why a mfg would chose to stop modifying other products and start over with a clean sheet design of their own.

There was a comment made in the other thread about significant amounts of motorsports dampers using poppets. I'm aware of plenty of spool valves being used in high end motorcycle forks (which are a variation of a poppet) however I am not aware of any of those that do so without a mid valve and/or base valve that utilize as shimmed piston. Granted, I am about 1 generation behind of what WP is using in their top end closed cartridge SX forks at the moment. That being said, I'd refrain from motorsports references in general as I am well versed in cars and motorcycle suspension... and my experience is the bulk of the performance products in those avenues are using pretty heavily double digressive damping setups. I have yet to have a completely satisfactory experience with damping setups on a mountain bike that are as aggressively digressive as I experienced on the motorsports side.
Click to expand...
Indeed. What works for circuit racing is very different to MTB.

KoolGrandWizardLuke said:
You're best off not asking people who don't fully understand the valves and tuning intricacies.
It's sort of like saying that a shimmed piston valve has just one profile: flat with drilled holes and a cheap spring washer closing it. But really the shape of the ports, convex or concave dishes and everything else plays a huge part.

Notice comments like this "Poppets typically run flat (i.e. not speed sensitive) with two quadratics." which immediately make the general reader think he is saying they run flat.... He's not. Because he knows it is possible for them not to.
While it is typical, the more advanced ones don't and there is no reason beyond simplicity of design that the valve has to "run flat", and infact it can be speed sensitive (which Dougal has conveniently implied it can't, while also not denying that it can).

That's pretty much all I have for this thread.
I opened his eyes with two advantages that they can provide over disc shim valves that he obviously was unaware of. That alone should tell you the level of knowledge he has about poppet valves in suspension.
Click to expand...
ROFL. Got any linear dyno plots to open our eyes with?
 
Discussion starter · #19 ·
reo-fahrer said:
starting at page 23:
https://www.ohlinsusa.com/files/files/Inside_TTX_A4-Europe1.pdf
(yes, it's an automotive TTX, but it explains quite nicely what could be adjusted, external and internal and what the results are)
Click to expand...
Well worth a read, they're using hybrid valves with shims on the face of the poppets:
Ohlins TTX manual said:
Poppet valves preloaded by coil springs were picked to become the high speed valves, as they can be made very compact in size and precise in opening pressure. This type of valve very often gives an abrupt opening characteristic, resulting in a sharp ”knee” in the damping curve. To make the ”knee” more rounded and to be able to change its shape, some shims are added to the face of the poppet valves. By changing these shims, the shape of the ”knee” can be affected.
Click to expand...
 
#20 ·
On a (somewhat) related note. Isn't the cone valve used by WP a close variation of a poppet valve, but one that has less binary characteristics? In other words, it acts both as a bleed mechanism as well as a type of blow-off valve?
 
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