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  #61  
Old 02-07-2018
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LS vs HS

I'm going to chop up your reply and quote it over several replies. I hope this provides better reading and keeps the flow of the conversation. I hope we can continue this discussion for some time, as this isnt something most people talk about and I'm always happy to learn more.


Quote:
Originally Posted by Terry Hay View Post
Dave
You certainly went a long way without eluding to an actual answer to the question.
Sorry, but I didnt mean to elude the question, I was waiting for you to narrow your questions some, but I'll answer it generally instead.


Quote:
Originally Posted by Terry Hay View Post
I believe there is a mistaken theory that "Low Speed" is separated from "High Speed" by a simple 0.1mm crossover shim.
This is certainly where tuners have chosen to affix these labels over the years but as you have pointed out....you are seeing changes to the force curve at relatively low speeds when you alter the (perceived) high speed stack.
This is the way that I always viewed it. After all, it makes good sense to view the low speed stack creating the low speed damping and the high speed stack producing the high speed damping.
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  #62  
Old 02-07-2018
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Velocity

After my findings of how low in the velocity scale that our tuning variables (shims stacks) come into effect, I concluded that we dont always need to test at the upper end of the velocity range.

I've attached a screenshot showing the same shock tested at a little over 0.5m/s and and again at 1.25m/s. If we multiple this by the leverage ratio, that equates to approx 1.5m/s and 3.75m/s. So by no means is this near our peak, but well into our mean velocities.

As you can see, the graphs overlay near perfectly. There is nothing new happening beyond the lower test velocity. If you want to know how much damping is happening at a higher velocity, we could simply extrapolate the data. The only exception to this is orrifice style damping IF the ports every become a restriction.


Quote:
Originally Posted by Terry Hay View Post
2 metres per second was considered quite slow by the guys at Showa, hence their investment. (their dyno is EMA)
The guys at Race Tech also have an EMA dyno that will read in excess of 5 metres and they utilise Showa's for higher demands. There is so much to be seen above 5 metres.
As I've never seen any real world data at these velocities, what can you see above 5m/s that you can't see at say, 1 or 2m/s? More importantly, how can you tune at those velocities?




Quote:
Originally Posted by Terry Hay View Post
There is certainly useful information in the lower speeds but it pertains more to moments of traction and force indicators.
From what I have read, right or wrong, I think I value the lower speed values more than you. My view is that everytime we hit a bump and the suspension changes direction, whether it be reaching a low or high peak velocities, the suspension always starts from a stationary position and accelerates through the lower velocities. In other words, the suspension always goes through 50mm/s whether the max velocity is 0.1m/s or 10m/s.



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Originally Posted by Terry Hay View Post
The problems you have experienced with shock speeds on your dyno are precisely the reason I opted for the more powerful unit. If you want to see higher speeds more accurately....you need power....
I agree with reducing / eliminating rebound force in order to see greater compression speeds but you are still limited to the capability of the machine itself.
I have never had an issue with reaching maximum velocity on my normal test stroke. It was only when I was doing some experimenting with much longer strokes and higher velocities that my dyno failed to pull the shock fast enough. So this isn't an issue for me every day.
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  #63  
Old 02-07-2018
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Quote:
Originally Posted by Tom68 View Post
I like the tutorial answers, since I don't have that much shock experience.
And that was the reason for my long winded reply. It wasn't meant as an education for Terry (he's been around long enough), but more for the 8000 other readers of this thread.


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Originally Posted by Tom68 View Post
There must be a lot of data for MX and SX shock and fork speeds logged ?

Any wwweb sources of the above out there ?
You'd think there would be plenty of data, but I'm assuming its all closely guarded secrets as its not something I've seen much of. I've got some Shock Clock data from a couple of sections on a MX track. Its not my data to share, but its only a screen capture and doesnt show peak velocities.
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  #64  
Old 02-07-2018
Terry Hay Terry Hay is offline
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Dave
First of all, if I have taken your reply as being directed at me rather than the forum base, you will have to forgive the assumption. After all you were directly quoting me at the time.

In order to avoid the maths, lets speak in terms of actual speeds or for easy visualisation, that of forks
I don't disregard the information at low speeds. As I said it has value in pertaining to traction, force etc. But 50mm per second (vertical wheel speed) is not something that is about to produce too many issues in the real world.....even slow people walk at over 1 metre per second. I know that wheel radius vs bump height will expand this figure but it is still slow. As you know we track test almost every day....the most difficult rider to test with is the guy that sits down everywhere and rides at a very low pace. This is because he is not riding fast enough to either break traction or to get the wheels to leave the ground....no fault is obvious to the eye and you are forced to rely on feedback. Testing at higher speeds will see traction yeild and wheel movements become apparent.
Your curves in the snapshot do overlay...and they should. The scale you have chosen is "Force vs Velocity". You are naturally getting the same force at the same velocity. As the velocity increases, the force increases. Try displaying the 2 curves in "Force vs Displacement".

This is for everyone...
The dyno tells a story but it is not intelligent. The load cell only knows it is experiencing a force and displays what it feels. Unfortunately a Scotch yoke dyno builds force in a very calm manner and can in no way replicate impact. Not only that, the force is created in the same fashion over the entire speed range.
The dyno starts at BDC and rotates the pin through a very controlled circular motion. This builds speed over 90 degrees of rotation and slows over the same distance.
The real world is a completely different story. The moment of impact sees a rapid acceleration of the suspension component that is meeting immediate resistance and slows to the point where acceleration force is equalled by that resistance. Next the stored energy in the springs will force the component to extend.....meeting immediate resistance through damping, friction etc.
Smaller square bumps (50mm paver) will see a very easy movement of the forks due to wheel diameter but larger, square bumps (150mm gutter) will see a much more rapid and aggressive movement. Not just due to size but also force vectors. This wont be replicated on the dyno. Increase the size of the square bump to where it is larger than the wheel radius and you are going over the bars.
The dyno is a great tool and I would rather have one than not have one.....but its not real world.
Dave
As for high speed vs low speed....sure it makes sense to differentiate at the crossover but as you have found.....it doesn't work out that way. We could measure shim deflection but that will vary with port area and port area growth rates. The biggest issue with higher speeds is that we may well reach a point where the midvalve outpaces the base valve. This is where real troubles start to raise their heads and pressure balance becomes a major issue. This is a big problem for the 4cs. I have begun making fork cartridge tubes out of acrylic with amazing results. I have a set of Ohlins 30mm NIX cartridges (Road bike ) and they absolutely drop their lunch at 1 MPS but are perfectly fine at 200 mm ps. Road bikes will see nearly 3 MPS. I am currently making a set for WP open chamber forks and for the Xplore. I will post a video of the NIX forks on our facebook page this week.
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  #65  
Old 03-07-2018
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Quote:
Originally Posted by Terry Hay View Post
Dave
First of all, if I have taken your reply as being directed at me rather than the forum base, you will have to forgive the assumption. After all you were directly quoting me at the time.
No need to aplogise Terry. I can enjoy a healthy conversation without being offended. Besides, its always good to remind ourselves of the basics from time to time. Even for me, typing it out is a great excercise because it makes me think of it in a clear precise manner that the other readers can understand.


Quote:
Originally Posted by Terry Hay View Post
I don't disregard the information at low speeds. As I said it has value in pertaining to traction, force etc. But 50mm per second (vertical wheel speed) is not something that is about to produce too many issues in the real world
What velocities do you think issues are noticeable to the rider? At what velocities do you collect data?

Quote:
Originally Posted by Terry Hay View Post
As you know we track test almost every day....the most difficult rider to test with is the guy that sits down everywhere and rides at a very low pace. This is because he is not riding fast enough to either break traction or to get the wheels to leave the ground....no fault is obvious to the eye and you are forced to rely on feedback.
Sounds like a good example of where the dyno might provide you data that the rider or your eye can not.



Quote:
Originally Posted by Terry Hay View Post
Your curves in the snapshot do overlay...and they should. The scale you have chosen is "Force vs Velocity". You are naturally getting the same force at the same velocity. As the velocity increases, the force increases. Try displaying the 2 curves in "Force vs Displacement".
Viewing in the FvD graph would not produce comparable results because the two tests were run with different strokes.



Quote:
Originally Posted by Terry Hay View Post
This is for everyone...
The dyno tells a story but it is not intelligent. The load cell only knows it is experiencing a force and displays what it feels. Unfortunately a Scotch yoke dyno builds force in a very calm manner and can in no way replicate impact. Not only that, the force is created in the same fashion over the entire speed range.
The dyno starts at BDC and rotates the pin through a very controlled circular motion. This builds speed over 90 degrees of rotation and slows over the same distance.
The real world is a completely different story. The moment of impact sees a rapid acceleration of the suspension component that is meeting immediate resistance and slows to the point where acceleration force is equalled by that resistance. Next the stored energy in the springs will force the component to extend.....meeting immediate resistance through damping, friction etc.
Great explantion. It would be great to be able to replicate true acceleration and velocities. I wonder how much different it would actually be? The graphs I attached previously were the same shock (untouched between runs) with different strokes. The longer stroke allowed the shock to reach higher velocity which means it will have a higher acceleration rate. So even with the three differences, they still tested the same up to 3.75m/s at the rear wheel. Do you care to guess at what velocities we would start to see a change?


Quote:
Originally Posted by Terry Hay View Post
The dyno is a great tool and I would rather have one than not have one.....but its not real world.
Its no less "real world" than a measuring tape is to a builder. Arguably his most valueable tool....or a maybe a hammer .


Quote:
Originally Posted by Terry Hay View Post
As for high speed vs low speed....sure it makes sense to differentiate at the crossover but as you have found.....it doesn't work out that way. We could measure shim deflection but that will vary with port area and port area growth rates.
At the end of the day, it probably doesnt matter where you or I decide to split and label the velocity scale. As long as we differentiate when we are talking to each other so that we understand each other.

I'm not real fond of your previous suggestion to use the lower half of the peak velocity range for LS and the upper half for HS, as everyones peak is different. This would make it hard when comparing a slow trailrider setting to a Finke or SX setting. Unless you split the highest ever peak in half and gave those splits to everyone.

I think it would be better to split it where we see changes in the graph. There is no point having all the change happen in the first half and then have the other half stable without change.


Quote:
Originally Posted by Terry Hay View Post
I have begun making fork cartridge tubes out of acrylic with amazing results. I have a set of Ohlins 30mm NIX cartridges (Road bike ) and they absolutely drop their lunch at 1 MPS but are perfectly fine at 200 mm ps. Road bikes will see nearly 3 MPS. I am currently making a set for WP open chamber forks and for the Xplore. I will post a video of the NIX forks on our facebook page this week.
Sounds very interesting. Being able to connect the dots between the visual issues in the damper and the data on the graph will be great.
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  #66  
Old 03-07-2018
Terry Hay Terry Hay is offline
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Dave
Re velocities....
We test from low speeds as well. As I said there is value here even though it may not be causing / revealing any issues. I would test a shock typically at 4 points
100, 250, 500 and 1000 mm per second.
Forks are double these speeds. We will naturally go slower for road bikes.

Re good example of a situation where a dyno might help.....even better time to listen to your customer. He's here for a reason and more likely in this case it is comfort and confidence. Some guys will benefit more from a few helpful riding tips than a dyno run.

Re the wrong graph / field and different velocities shhh.....I think they bought it.....
Try a multi point CVP and display in force vs displacement. You will find what you are looking for.

Tape measure....doesn't get much more real world than that. It's relevant, repeatable and will even tell you how long a piece of string is.

Re high vs low...You're right. Our opinion doesn't matter to the end result but the more you get into the data the more you realise that where the average guy is making a judgement based on shimstack construction is not so cut and dry.
If we look at a car, much more time would be spent below 60 than above 100 but most wouldn't consider 100 "high speed" (in the 100 zone).

Time for dinner......
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  #67  
Old 03-07-2018
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Terry, thanks for taking the time to reply.

Quote:
Originally Posted by Terry Hay View Post
Try a multi point CVP and display in force vs displacement. You will find what you are looking for.
I've attached a force vs displacement graph as suggested for three separate tests. I've matched the velocities to your test speeds.

Let me explain the graph for the others.

The purple graph is a test using 25mm stroke with 100mm/s, 250mm/s and 500mm/s test speeds. I can not reach 1000mm/s with this length stroke on my dyno. This isn't because I run out of power, but the invertor is limited to a maximum frequency.

The blue graph is the same shock tested with a 75mm stroke and 100, 250, 500 & 1000mm/s test speeds.

The green graph is the same shock again tested with a 100mm stroke and the same 100, 250, 500 & 1000mm/s test speeds.

The shorter stroke (purple graph) does not engage the secondary piston and cup. The longer strokes do and that's why they have the big "bump" in the top right corner. The "bump" starts earlier on the green graph because it has a longer stroke and the "bump" is bigger because the shock is moving faster and therefore creating more damping.

The force values align very closely in both comp and rebound for all three tests at 100, 250 & 500mm/s velocities even though they have different strokes and acceleration rates. The force values line up well on the two longer stroke tests at 1000mm/s.


Anything I've missed here Terry?
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File Type: jpg MCR FvD.JPG (118.9 KB, 30 views)
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  #68  
Old 04-07-2018
Terry Hay Terry Hay is offline
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David
The force values will always line up at the same velocity.....that's the point. You could skip any two out of the three tests and you get a clear indication of force vs velocity within the same shock over the same distance. Apples and apples.
Your previous comment about the curve overlay gets put to rest in any one of these runs. Eliminate any two of the tests and you clearly see the lack of overlay in the remainder.
Look at the purple one as a sole entity. Every speed creates a completely different curve......no overlay. This details a very different force accumulation within the same shock over the same displacement. Add extra velocity and the curve will grow evermore. This lays waste to your comment re extrapilation and prediction. There is a very good reason people pay extraordinary money for more capable test equipment.
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  #69  
Old 04-07-2018
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This is a good thread. But...in so many areas of my working life I've seen incredible knowlege and experience disappear into the ether on retirement.

2T tuning is one. If Dave at TSP had worked under Tony Hatton or Ross McWatters imagine the knowlege transfer.

Paul Thede has put a lot (but conspicuously not all...) of his knowlege out there in books. It's be great if Terry, Rossi, etc did the same.

Young LV and MC mechanics come out of their trade with SFA suspension expertise, largely because texts are almost impossible to source. Food for thought.
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  #70  
Old 04-07-2018
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I can hit metal things with big hammers, loosen and tighten bolts and weld stuff to other stuff.
All this intellect stuff hurts whats left of my brain
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