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Has anyone ever looked at shock dyno graphs wondered what the tell you?
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Can you spot the slack (hysteresis) in this damper indicated in the dyno graph?

This is a linear valving.

Force to absolute velocity graph.

 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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So. There is always hysteresis in a non-conservative system. Damping produces heat, heat is energy loss.
The f-v curves also change when the fluid heats up as the kinematic viscosity of the oil changes.

Most smart folk would split the difference between the hysteresis, intersect the rebound and compression at 0,0 and get on with life. If you plot the data using the 1st and 3rd quadrants, you can easily see what I'm talking about. You'd also be able to visualize the fundamental hysteresis loop a whole lot better. One typically doesn't tune the damper response due to hysteresis, you tune it for the average value, then you go by your data to tell you if you went faster or slower due to the changes.

What is TDC and BDC of a damper? Most shock dynos do not go full stroke when producing data. They are just run on a simple sine wave or even a sawtooth wave at around 1-2" of total stroke. This means the zero velocity data is when the dyno changes direction.
Zero on the "y -axis" means zero velocity, there is no position indicated. By definition, using a basic equation of motion, the damping coefficient is multiplied by velocity, hence, with no velocity, there is no damping force. Since the shock dyno is not theoretical, you get the hysteresis due to the latency in one shim stack closing and the other shim stack opening, the frequency of the dyno (to achieve the target fastest velocity) and the the recording frequency of the dyno's data system.

By the posted graph, if you are trying to tune this damper at less than 1 inch/sec, you are wasting your time.

Get the rest of the data for every two clicks of added rebound and compression, and even slow speed compression and then you will really understand how the shock is tuned.
 
Posts: 81 | Location: behind this screen | Registered: July 30, 2015Reply With QuoteReport This Post
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BDC of "1 - 2 of total stroke" and TDC of "1 - 2 of total stroke".
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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So, in reading the copy n paste "Rick injected, there's a lot of subjective notions implied which will actually be useful in dissecting.

So we will start with the claim "there's always slack (hysteresis) in a damper because of heat.

For one, this is the measure of a dampers capacity to operate in extreme conditions (high shaft speeds over many racing miles).

There's no reason for heat in a drag racing damper unless you just towed 500 miles and didn't tie the car down properly so the damper isn't cycling.

If you have a high end damper with the capacity to have very little hysteresis over 100's of miles in extreme racing environments, you have a high technology shock no hysteresis (slack) drag racing a 1/4 mile. This is the example which can be reasoned, in regards to the differences in the levels of damper / shock technology.
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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It's obvious you don't know how a shock dyno works so you should type "shock dyno graphs" in your search bar and pay attention to the very few folks who actually can explain the hysteresis in the compression and rebound damping curves. One of them even tells you what he did to minimize hysteresis. If you look real careful-like at the graphs between -1inch/second and 1inch/second, you'll see even his tuned dampers still have hysteresis in the force range of your original post. These are high end dampers so there might be a common theme that I previously stated that hysteresis is inherent in all hydraulic and MR dampers.

McAmis and Bell put on a nice series of simple videos to help you understand shocks and finally how to tune them to track conditions. Pay special attention to the peak velocities they talk to and how many clicks and sweeps to go when attempting to make noticeable changes.
Afco has a simple tech tips sheet to guide adjustments for common car reactions.
Most astute racers know how to turn the knobs on their shocks for bias ply slicks; add compression and reduce rebound or reduce compression and add rebound, depending on track conditions, assuming all other variables have been addressed appropriately. Having the shock dyno graph gives a quick reference to how much force was rearranged so it could be entered in a log book. The racers with shock sensors and data acq will be far ahead of those without it.
Your graph is incomplete at best.

Here is what a racer really needs:

shock dyno graphs showing responses to adjustments

Once you do all the above, and then design and tune dampers and buffers for around 25 years, maybe we can talk about this on the same level.
 
Posts: 81 | Location: behind this screen | Registered: July 30, 2015Reply With QuoteReport This Post
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LoL!!!

Where is the hysteresis indicated in the graph, from the link you provided?

This message has been edited. Last edited by: Mike Rietow,
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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The schrader valve tells you it's a high pressure design. Leaks a little so pickup a guage and tank from quarter max, when you go to the track with these.

 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post



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quote:
Originally posted by Rick!:
Afco has a simple tech tips sheet to guide adjustments for common car reactions.


Found it HERE, Thanks !
 
Posts: 2543 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
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Alright, so we have a graph above from a link Rick provided no hysteresis, and a generic linear graph I found online indicating hysteresis (slack) below.

No hysteresis


hysteresis
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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Alright so a lot of opinions have entered into this already including

"One typically doesn't tune the damper response due to hysteresis, you tune it for the average value"

For an average value you'd use the Average force vs absolute velocity option.

Most people, depending on who you talk to, believe because these graphs clean everything up quite a bit, they're more used as a sales gimmick.

Same valving, the graph on the right is average force vs absolute velocity.

There's hysteresis indicated in both but the average makes it appear to be less.

This message has been edited. Last edited by: Mike Rietow,
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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