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  #71  
Old 04-07-2018
Terry Hay Terry Hay is offline
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YZ65 2018.jpg

YZ65 1 MPS.jpg

YZ65 Modified.jpg

There are certainly times when the dyno is a fantastic tool for diagnosis. It offers a snapshot into what is going on inside your shock / fork. Things that go beyond the norm. Here are some dyno runs of the latest bike from Yamaha, the YZ65.
The first attachment shows our multi point CVP run done a few weeks ago.

Ideally the trace of the curve will go as close as possible to overlaying. This will indicate similar behaviour of the shock absorber at the same velocities whilst both accelerating and slowing down.
You will note that the first 3 curves aren't bad but the gold curve (1000 MM/PS) has a bit of a blowout on rebound highlighting instability. The stock gas pressure was a little low for the demand placed upon it. This curve has been isolated on the second graph. The third graph shows the curve with increased gas pressure. Our next modification (not shown) involved modifying the compression adjuster to get the curve tighter again.
This is definitely a scenario that would not have been found and possibly completely mis-diagnosed through track testing. The dyno has saved a lot of time here.
Sorry about the brain Brentice.....I weld like a carpenter....
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  #72  
Old 06-07-2018
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Originally Posted by Terry Hay View Post
This is definitely a scenario that would not have been found and possibly completely mis-diagnosed through track testing. The dyno has saved a lot of time here.

Great result. Are you viewing these graphs with the gas force included?

I've been trying to find the time to reply in detail to your earlier posts, but it doesnt look like it is going to happen this week....too busy.
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  #73  
Old 06-07-2018
Terry Hay Terry Hay is offline
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Dave
We always test with gas force and seal drag included initially. This gives us the "Warts and all" perspective. If we are going to make a valving change, we will then isolate the forces to allow us to quantify the change more accurately.
If you look at the 2nd and 3rd graphs, the overall force has increased (due to gas pressure). It could well be that we would have to soften the damping a little to compensate. We took this bike off the showroom floor in order to gather as much info as possible. We measured the springs and did a Leverage Ratio Curve as well as dyno runs. All of this was to get springs on order ASAP. Existing valve kits are already suitable. I feel the YZ65 could be a turning point motorcycle. Japan has let KTM have its way with the mini bike market for too long. We test with a rider next week. The bike definitely has better suspension hardware than the KTM and certainly shows potential. Springs will be here in around 2 - 3 weeks....and in Yamaha Blue.....pretty...
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  #74  
Old 10-07-2018
Terry Hay Terry Hay is offline
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Dave
I think where you have become a little confused is in the curves as you see them. The dyno produces information in a sinusoidal waveform but the wave is reconstructed by the software for ease of viewing. When you look at the force vs displacement curve you see the curve almost as its meant to be. The rebound curve however has been folded back underneath the comp curve in order to best fit our screens. This now appears as an oval but that's far from reality.
When you are viewing other screens eg. comp closing / reb opening, its like the curve has been folded back on itself....for viewing purposes. This is like looking at a set of goal posts on a rugby field. From front on we get the full picture and see the gap between the posts, but from side on we only see the one post making everything appear in line.
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  #75  
Old 11-07-2018
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Terry,

I posted the graphs in answer to your comments about the dyno not being real world because it doesn't accelerate the fork or shock as fast as when being ridden. I've heard this many times before, but I'm yet to see anything that suggests this to be true.

I ran the tests with different strokes to make the shock accelerate and decelerate at different rates to reach the same peak velocity. The data shows that the shock with a faster acceleration rate produces the same damping at the same velocity.

If this pattern continues, then the real world application, even with faster acceleration rates, will still produce the same damping at the same velocities. This makes tuning the damping forces at given velocities on the dyno as real world as anything else.

Have you any data to suggest otherwise?
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  #76  
Old 12-07-2018
Terry Hay Terry Hay is offline
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C'mon.....that's suspension 101. Damping is velocity sensitive....hit the same velocity, you get the same damping....easy.
I have pointed that out all along.
The yawning gap here is the curve variation during the acceleration. Hit 500mm per second over 50mm displacement and 100mm, you will have the same peak force yet a very different curve. The nature of the force accumulation is wildly varied.
You posted a graph which you said had a near perfect overlay and then you said that they were at 2 different displacements allowing you to forecast behaviour at higher speeds through projection. That is why I urged you to look at a different screen which provided a more accurate and revealing view.
The graphs I posted of the YZ65 showed a fault manifesting itself at the fastest run speed yet the lower speeds looked quite acceptable. Imagine if I took it further. Or worse yet...imagine if I only tested at the lower speeds. You could not have projected a high speed outcome that was fault revealing if there was no sign of it a lower velocities.

Terry,

I posted the graphs in answer to your comments about the dyno not being real world because it doesn't accelerate the fork or shock as fast as when being ridden. I've heard this many times before, but I'm yet to see anything that suggests this to be true.


Dave
You don't even need data to know there is a difference here, just a simple understanding of the physics involved in both circumstances.
One is a controlled acceration and one is an impact....sometimes violent.
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  #77  
Old 13-07-2018
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Quote:
Originally Posted by Terry Hay View Post
Dave
You don't even need data to know there is a difference here, just a simple understanding of the physics involved in both circumstances.
One is a controlled acceration and one is an impact....sometimes violent.
Thats the thing Terry, the dyno has disproven more theories than it has proven. I'm questioning yours, mine and everyones "understanding of physics". I'm looking for measured data.

Being able to measure and quantify changes has made me the worlds biggest cynic. I dont believe anything anymore, not even things that I thought I knew.

I'm currently reading a Fluid Dynamics text book. A quote from the opening pages......"Fluid dynamics is more often observation than it is theory". A scientific text book admits that fluid dynamics is unable to be repeatedly calculated due to the complexities within a system and irregularities in the fluids behaviour.
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  #78  
Old 14-07-2018
Terry Hay Terry Hay is offline
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Dave
I don't see how you are proving anything if you aren't reading the data correctly.
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  #79  
Old 14-07-2018
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I reckon the some of world's best suspension techs are surely working in MotoGP. They can't even get it right every weekend. With all the data they look at. It's a never-ending search for perfection. Sometimes even the best can confuse themselves too.
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  #80  
Old 14-07-2018
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Terry, I appreciate your knowledge and your willingness to share it.
But you are kind of sounding like a bit of a jerk in the last day or so.
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