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Old 01-15-08, 11:09 PM   #1
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How to read a shock dyno.

I was going over some older posts about coilovers and a usual thing that is said in those posts is"I want to see the dyno!". In the past, i have also asked "do you know what your even looking for when looking at the dyno?" and the answers I have gotten are completely wrong. Its a little more complex than an engine dyno...

So heres the deal. There is 3 types of curves associated with automotive dampers. A linear curve, a progressive and a digressive. One of these you don't want, the other is very common but outdated, and the last is what you want. But before I explain that, you should know what the dyno actually reports.

What the dyno shows is how a damper operates at a given force. This is shown as force Vs. velocity. Force is usually on the Y-axis and velocity on the X-axis. You can use common sense and figure out if a shock is frim or soft by looking at how much force it takes to move it. For instance, if it takes 600lbs to move the shock 1" over 2 seconds, clearly this is a VERY firm shock and not meant for any rx-7. It would take over 600lbs of force to move the suspension any noticeable amount. Just think what an average bump would feel like....

Bump (compression) is on the bottom half of the graph and rebound (expansion) is on the top. Of these, rebound is more important for good control. Because of this, most 1 way adjustable shocks only affect the rebound side.

Anyway, about the curves.

http://www.iammike.org/pictures/misc...front_dyno.gif

Take a look at this link, This is a buddy club racing spec damper probably for a honda since i found it on a honda page. We can see all 3 curves in play here so this is a good example.

First thing that we note is that the adjustments only change the rebound side and have virtually no effect on the bump side.

Progressive - you can see at zero clicks of adjustment (red and lt. blue line), the shock has a slightly progressive curve to it. That means the shock applies disproportionally more resistance as the force increases. Progressive shocks are bad for handling and ride. This is because they are very soft a low forces, and get exponentially firm as the force increases. So, what you feel as a driver is a shock thats soft and sloppy on smooth roads, and a ride that kicks your *** on rough and bumpy roads. Exactly what we dont want! Note that with this shock, the curve is so minor that it could be considered linear. The shock is probably bouncy at zero clicks.

This trend decrease until about 10 clicks (pinkish line), then the shock becomes fully linear. Liner isn't that good either, it has the same characteristics as the progressive curve, but with a little more control down in the low speed/force area. Its still too firm if you go over rough roads.

Finally at 15 clicks, which is probably all the adjustment this shock has, it goes into a digressive curve. Digressive is what you want. This is why: Digressive gives you lots of control and a firm ride on smooth roads. This is good because thats where you want it. This allows you to have good handling by having the shocks very firm when you want it to be; but its also great when the road becomes rough because as the force increases, the shock gets softer. So its the best of both worlds! The progressive and linear curve simply can not provide the level of control that a digressive curve has.

http://honda-tech.com/zerothread?id=1104049&page=1
lots more dyno graphs to look at on this page.

If you are smart, you might ask this question! "What causes the shock to produce a progressive/linear curve at the softest setting???" well, its because the adjustment **** that you control actually is moving a needle valve in and out of a hole on the piston. This hole bypasses the fancy main valve in the piston that gives the digressive curve...
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Old 01-15-08, 11:16 PM   #2
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we can really see how crappy the KYB AGX shock really is when we look at the dyno:

http://www.koni-na.com/presentations...ges/Slide8.JPG

You can see that it has virtually no difference between adjustments, and really does not have a significant digressive curve.
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Old 01-15-08, 11:17 PM   #3
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thank you for this post OC
that actually put alot of things together for me
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Old 01-16-08, 11:33 AM   #4
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Quote:
Originally Posted by OC_ View Post
If you are smart, you might ask this question! "What causes the shock to produce a progressive/linear curve at the softest setting???" well, its because the adjustment **** that you control actually is moving a needle valve in and out of a hole on the piston. This hole bypasses the fancy main valve in the piston that gives the digressive curve...
Be careful with generalizations...
It's true that the majority of adjustment systems is by a needle valve - not all of them are.

Also, you missed the point about endurance testing.
Dampers can look really good when they are "cold", but some of them change their characteristics radically when under long duration actuation.
Most of these tests do not mention under what procedures they used for testing, but it's practically useless to throw a "cold" damper on the dyno and punch out a result.

The KYB AGX graph does look pretty bad when analyzed by itself.
Try overlaying other dampers, and you might be surprised.
When I saw testing of Tokico Illuminas versus KYB AGX's, I was surprised what was actually "better".


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Old 01-16-08, 11:42 AM   #5
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Very interesting.

As a learning tool then, can someone give an example, of photoshop overlay, of what an extremely *ideal* dyno should look like for an FC? Even if the curve is unrealistic to something you might actually be able to make/buy, it would be good for expressing which areas of the graph should be where in terms of having an ideal digressive curve.
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Old 01-16-08, 12:03 PM   #6
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Apparently the ideal shock will have about 65% of critical damping up to about 3 in/sec (body motions like roll happen below this) and then as digressive as possible above that (for road irregularities). The values of force per velocity will vary on the corner weights and the spring rates.

There are other plot types that are important, like the circle plot which shows the force on the shock as it goes through a full cycle of extension and compression on the dyno. If you plot a number of cycles one on top of the other it can help show you if the shock fades and will help show if the shock is consistent from one sweep to the next. Monotubes are better at shedding heat and typically run at higher pressures than twin tubes, so are therefore typically more fade resistant,

There's also regular dyno plots that aren't corrected to center around zero, this is useful as some shocks (monotubes in particular) have a "nose force" on them from gas pressure or other things. This isn't so good, but we put up with it anyway, as the high pressure that can cause this cuts down on fade.

If you plot the full cycle then you can see the hysterisys of the shock, that is when the force on accel and decel are different. This is bad and should be minimal.
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Old 01-16-08, 04:02 PM   #7
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I think the suggested as been modified to 65% of critical from 0-3 in/sec, then a knee at 3 in/sec to 30% of critical all the way back (still digressive, of course).

Looking at the AGX dyno curve, I'd shoot for setting 3. But this is a good thing though! The reason why I've always liked Koni Yellows is that you could adjust rebound independently of compression to fine tune weight transfer. Apparently, you can do that on the AGX's as well, since compression adjustment is pretty much nil.

Any rear AGX dyno's?
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Well, when you say it like that, it sounds much more balanced. D-cups are easily worth paying thousands in interest.

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Old 01-16-08, 08:22 PM   #8
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Quote:
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I think the suggested as been modified to 65% of critical from 0-3 in/sec, then a knee at 3 in/sec to 30% of critical all the way back (still digressive, of course).

Looking at the AGX dyno curve, I'd shoot for setting 3. But this is a good thing though! The reason why I've always liked Koni Yellows is that you could adjust rebound independently of compression to fine tune weight transfer. Apparently, you can do that on the AGX's as well, since compression adjustment is pretty much nil.

Any rear AGX dyno's?
You bring up a good point about adjusting rebound independently. You actually dont want to adjust both sides (compression and rebound) with just one ****. By adjusting only rebound, you are still able to tune the car on a rough track. Where if you adjusted both sides, then the shocks might become to firm and decrease road contact on the rough stuff.

Theirs actually equations out their to figure out the optimal amount of damping needed for a given springrate. Any engineer that went though a vibration course should know!

Theres also equations to figure out where the digressive knee (the part of the graph where the shock gets soft) should happen for a given car! pretty neat stuff.
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Old 01-16-08, 08:34 PM   #9
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Quote:
Originally Posted by RETed View Post
Be careful with generalizations...
It's true that the majority of adjustment systems is by a needle valve - not all of them are.

Also, you missed the point about endurance testing.
Dampers can look really good when they are "cold", but some of them change their characteristics radically when under long duration actuation.
Most of these tests do not mention under what procedures they used for testing, but it's practically useless to throw a "cold" damper on the dyno and punch out a result.

The KYB AGX graph does look pretty bad when analyzed by itself.
Try overlaying other dampers, and you might be surprised.
When I saw testing of Tokico Illuminas versus KYB AGX's, I was surprised what was actually "better".


-Ted
Dont forget to take into consideration that these graphs are probably smoothed out. It looks like the AGX graph has very few samples taken... Its so easy to stretch the truth with a graph. Also, make sure when compairng 2 different graphs, that the units are the same on both!
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Old 01-16-08, 08:35 PM   #10
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From empirical testing, the knee should occur around 3 in/sec.

If I had the money, I wouldn't use shocks with adjusters anyway. I'd valve them based of histograms of the suspension movements, taken by my suspension position sensors. Then I'd just leave them there, since the valving would be ideal for all road surfaces.
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Well, when you say it like that, it sounds much more balanced. D-cups are easily worth paying thousands in interest.
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Old 01-16-08, 08:45 PM   #11
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Quote:
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From empirical testing, the knee should occur around 3 in/sec.

If I had the money, I wouldn't use shocks with adjusters anyway. I'd valve them based of histograms of the suspension movements, taken by my suspension position sensors. Then I'd just leave them there, since the valving would be ideal for all road surfaces.
What about the tuning the handling characteristics of the car? Somtimes I want a little more oversteer on turn-in. I can do this by adjusting my shocks!
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Old 01-16-08, 09:05 PM   #12
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You can, but the car drives fastest when it has the most grip in all situations. The key to driving fast with respect to an unfamiliar setting that produces more grip is adapting to the car, rather than adapting the car to you.
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Well, when you say it like that, it sounds much more balanced. D-cups are easily worth paying thousands in interest.
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Old 01-16-08, 10:08 PM   #13
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Remember, that graph of the AGX is taken from a presentation available on the Koni site, so they'll be a lot more critical of it than any uninterested party would be.
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Old 01-17-08, 06:56 PM   #14
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Quote:
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You can, but the car drives fastest when it has the most grip in all situations. The key to driving fast with respect to an unfamiliar setting that produces more grip is adapting to the car, rather than adapting the car to you.
The most grip in all situations??? what? Are you saying that theres a 'perfect' setup?
You can damp a given spring perfectly, but that that doesn't mean your going to get the most grip. All that means is that the spring is not boucing around.

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From empirical testing, the knee should occur around 3 in/sec.
Wait, for what car? FC's, FD'S?.. FB? If the car has leverage on the shock, like a car with upper and lower control arms, the raito of movement at the shock is going to be different from the wheel. So the knee would have to be at a different velocity.
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Old 01-17-08, 08:38 PM   #15
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3in/sec wheel velocity. Just as the force values will have to be scaled for the motion ratio, so will the velocity values.
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Old 01-17-08, 10:19 PM   #16
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WHO! sorry but I have to step in here....way to much misinformation for the general public. it appearers that OC is the one who has actually gotten it completely wrong.

I don't even recognize the dyno software you linked to...but its simply an average force vs velocity graph (not very useful)


OC. So heres the deal. There is 3 types of curves associated with automotive dampers. A linear curve, a progressive and a digressive. One of these you don't want, the other is very common but outdated, and the last is what you want. But before I explain that, you should know what the dyno actually reports.

SS. This a very broad statement not to mention untrue, there are times in which any one of these curve's may be desired most notably would be rebound. maybe thats why penske makes piston's for all of them.

OC .What the dyno shows is how a damper operates at a given force.

SS. No it shows what forces the damper generates at given velocity's.

OC. Bump (compression) is on the bottom half of the graph and rebound (expansion) is on the top. Of these, rebound is more important for good control. Because of this, most 1 way adjustable shocks only affect the rebound side.

SS. Bump is actually represented(by most manufactuers default such as SPA, Roehrig) on the top half...and just to be sure look at the force #s positive = compression, negative= rebound. so the adjustments depicted are actually in compression.

OC. First thing that we note is that the adjustments only change the rebound side and have virtually no effect on the bump side.

SS. again, no this is compression.

OC. Digressive is what you want. This is why: Digressive gives you lots of control and a firm ride on smooth roads. This is good because thats where you want it. This allows you to have good handling by having the shocks very firm when you want it to be; but its also great when the road becomes rough because as the force increases, the shock gets softer. So its the best of both worlds!

SS. a digressive comp. curve will tend do as you describe...however with the buddy clubs...you can clearly see you are increasing the hs portion of the curve nearly the same if not more than the LS...not going to give you the "best of both worlds"...not to mention not very digressive

OC. we can really see how crappy the KYB AGX shock really is when we look at the dyno:

SS. Um, actually this is a very nice range of adjustment to have....since you can increase LS compression with out increasing the hs portion..making for a more digressive compression curve thus giving you the ability to increase platform stiffness with increasing harshness.

if you would like to learn more on damper valving and dyno interpretation check out

roehrigengineering.com
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Old 01-17-08, 11:11 PM   #17
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SS. Bump is actually represented(by most manufactuers default such as SPA, Roehrig) on the top half...and just to be sure look at the force #s positive = compression, negative= rebound. so the adjustments depicted are actually in compression.

OC. First thing that we note is that the adjustments only change the rebound side and have virtually no effect on the bump side.

SS. again, no this is compression.
You'd be wrong on that one, whether it's positive or negative is basically arbitrary as it depends on the sign convention used and from what point of view we're talking about (shock vs dyno). The compression will almost always be the lower value, in this case on the bottom, and they're specifically rebound adjusters. In all cases that I'm aware of for off the shelf shocks, if there's one adjustment only it'll be rebound. Sometimes it's rebound and compression at the same time, but I'm not aware of any that are only compression, as that'd be stupid.
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Old 01-18-08, 12:55 AM   #18
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Quote:
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OC. So heres the deal. There is 3 types of curves associated with automotive d

SS. This a very broad statement not to mention untrue, there are times in which any one of these curve's may be desired most notably would be rebound. maybe thats why penske makes piston's for all of them.
Please tell me a situation where our cars are going to want something other than digressive curves. Yes, it is true, i am generalizing, and i think thats very appropriate for what people are looking for here.

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OC .What the dyno shows is how a damper operates at a given force.

SS. No it shows what forces the damper generates at given velocity's.
yes, i was wrong their. Nice correction.


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OC. Bump (compression) is on the bottom half of the graph and rebound (expansion) is on the top. Of these, rebound is more important for good control. Because of this, most 1 way adjustable shocks only affect the rebound side.

SS. Bump is actually represented(by most manufactuers default such as SPA, Roehrig) on the top half...and just to be sure look at the force #s positive = compression, negative= rebound. so the adjustments depicted are actually in compression.
Well, no, not at all. This is kinda a funny thing, you would think that the negative numbers would be bump; because that makes sense for compression right? I questioned that too when i first saw the negative numbers on the bottom. This link can kind of explain it. Paragraphs 4 and 5.
http://e30m3performance.com/tech_art...shock_dyno.htm
I guess the reason is because positive/negative force is arbitrary. Someone did explains this to me, and their was something about double negatives on the bump side and what Black91 said. But I think it just might be something like tradition. There is some exceptions, but virtually all dynos you will see will have rebound on top.

Heres an easy way to see if the bump is on the top or bottom: the bump side has less damping force than rebound... Yes, i know their is exceptions to this too, but i don't think people here run dirt circle track or high downforce vehicles or other applications where its used.

Every dyno graph on that page i linked to has rebound on top and bump on the bottom. Of course, like you pointed out, their is exceptions.

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OC. First thing that we note is that the adjustments only change the rebound side and have virtually no effect on the bump side.

SS. again, no this is compression.
Explained above.

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OC. Digressive is what you want. This is why: Digressive gives you lots of control and a firm ride on smooth roads. This is good because thats where you want it. This allows you to have good handling by having the shocks very firm when you want it to be; but its also great when the road becomes rough because as the force increases, the shock gets softer. So its the best of both worlds!

SS. a digressive comp. curve will tend do as you describe...however with the buddy clubs...you can clearly see you are increasing the hs portion of the curve nearly the same if not more than the LS...not going to give you the "best of both worlds"...not to mention not very digressive
it wont 'tend', it will DO as i describe. I guess your talking about the top of the graph as the compression side for this, which we know is actually the rebound side for reasons explained above. Anyway, you do point out that this is not a very digressive shock. The reason for the progressive curve when the shock is on the soft settings is the way the adjust **** works, i explained that in the original post.

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OC. we can really see how crappy the KYB AGX shock really is when we look at the dyno:

SS. Um, actually this is a very nice range of adjustment to have....since you can increase LS compression with out increasing the hs portion..making for a more digressive compression curve thus giving you the ability to increase platform stiffness with increasing harshness.
???? look at that graph! there is very little change between adjustments! there is some change between settings 1 and 2, but 2, 3 and 4 are all about the same! Look at some of the other shocks on the page, they have much more defined changes between clicks!
Why would you want increasing harshness?

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if you would like to learn more on damper valving and dyno interpretation check out

roehrigengineering.com
Better yet, get a book. There is some good information on the net, but it seems to be scattered about.

I can recommend a book by Allan Staniforth called "Competition Car Suspension: Design, Construction, Tuning"

Theres some other books by people like Herb Adams, but those books provide a real quick overview.

Then their books on the real dynamics and engineering behind this stuff. The target audience with those are engineers.
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Old 01-18-08, 07:07 PM   #19
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black91. You'd be wrong on that one, whether it's positive or negative is basically arbitrary as it depends on the sign convention used and from what point of view we're talking about (shock vs dyno). The compression will almost always be the lower value, in this case on the bottom, and they're specifically rebound adjusters. In all cases that I'm aware of for off the shelf shocks, if there's one adjustment only it'll be rebound. Sometimes it's rebound and compression at the same time, but I'm not aware of any that are only compression, as that'd be stupid.

SS. nope. walk into any race race paddock or most OEM test facilities , the only dyno's you will see are Roehrig's,SPA's and dynamics...all of which have a load cell mounted to the cross bar and read positive forces when the shock is compressed and plot this curve in the top/positive region of the graph no mater what graph you are reading(force vs displacement, avg. force vs. absolute velocity, force vs velocity etc.) this is also true in both cvp and pvp. as well as scotch yoke, Hydraulic and even EMA actuated units. Like I said I do not recognize the software in the links But again there is no reason for the forces to be reversed unless for some reason this brand of dyno's has decided to alienate itself form the rest of world.

OC. but virtually all dynos you will see will have rebound on top.

SS. How can you make a statement like this??? how many dyno's have you used? what manufacturer's?? Sorry to burst your bubble but you are wrong. how can I make a statement like that...well I build build shocks for a living and just yesterday ran a roehrig bench top for 15hrs.

OC ???? look at that graph! there is very little change between adjustments! there is some change between settings 1 and 2, but 2, 3 and 4 are all about the same! Look at some of the other shocks on the page, they have much more defined changes between clicks!
Why would you want increasing harshness?

SS. woops forgot the out part they will give you good platform firmness adjustment withOUT increasing harshness. the Graph in in meters/sec and it is a CVP trace at .350 meter/sec which is like 13 inches/sec so first of all the resolution of this graph at the velocity at which this change is most affective is crap being both an avg force vs velocity and it being such a fast cvp. but it appears that most of the change occurs at a relatively low speed which is what most people would want and is what you will feel the most as far as the cars. attitude to changes. So yes there is very little change in HS portion of the trace But a ton of change in the LS this is due to them having a very nicely tuned bleed adjustment.

OC. Better yet, get a book. There is some good information on the net, but it seems to be scattered about.

I can recommend a book by Allan Staniforth called "Competition Car Suspension: Design, Construction, Tuning"

Theres some other books by people like Herb Adams, but those books provide a real quick overview.

SS. HMMM I kinda thought that linking you to Roehrigs site where you can download a manual and demo version of the worlds most popular and recognized shock Dyno for free would have been quit helpfull for you?? I also figured that if you didn't want to take my word for it maybe you would listen to the guys who build the dyno's.
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Old 01-18-08, 10:01 PM   #20
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Originally Posted by sereneseven View Post
SS. nope. walk into any race race paddock or most OEM test facilities , the only dyno's you will see are Roehrig's,SPA's and dynamics...all of which have a load cell mounted to the cross bar and read positive forces when the shock is compressed and plot this curve in the top/positive region of the graph no mater what graph you are reading(force vs displacement, avg. force vs. absolute velocity, force vs velocity etc.) this is also true in both cvp and pvp. as well as scotch yoke, Hydraulic and even EMA actuated units. Like I said I do not recognize the software in the links But again there is no reason for the forces to be reversed unless for some reason this brand of dyno's has decided to alienate itself form the rest of world.
Then explain why ALL of the graphs on that page show rebound on top as a positive number. It really doesn't matter what the dyno outputs, it can get flipped, the signs changed and all that by the software before the customer sees it. The dynos from KONI themselves show rebound on top as a positive number. Or can you explain why Koni Yellows adjust only rebound according to their own graphs when that's not the case at all.

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Originally Posted by sereneseven View Post
OC. but virtually all dynos you will see will have rebound on top.

SS. How can you make a statement like this??? how many dyno's have you used? what manufacturer's?? Sorry to burst your bubble but you are wrong. how can I make a statement like that...well I build build shocks for a living and just yesterday ran a roehrig bench top for 15hrs.
See above.

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Originally Posted by sereneseven View Post
SS. woops forgot the out part they will give you good platform firmness adjustment withOUT increasing harshness. the Graph in in meters/sec and it is a CVP trace at .350 meter/sec which is like 13 inches/sec so first of all the resolution of this graph at the velocity at which this change is most affective is crap being both an avg force vs velocity and it being such a fast cvp. but it appears that most of the change occurs at a relatively low speed which is what most people would want and is what you will feel the most as far as the cars. attitude to changes. So yes there is very little change in HS portion of the trace But a ton of change in the LS this is due to them having a very nicely tuned bleed adjustment.
I'd agree, the KYB's seem decent to me, maybe not as much adjustment range as the Konis, but not exactly terrible.
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Old 01-18-08, 10:31 PM   #21
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Black91. Then explain why ALL of the graphs on that page show rebound on top as a positive number. It really doesn't matter what the dyno outputs, it can get flipped, the signs changed and all that by the software before the customer sees it. The dynos from KONI themselves show rebound on top as a positive number. Or can you explain why Koni Yellows adjust only rebound according to their own graphs when that's not the case at all.

SS. Well after looking again apparently for some silly reason Koni does show rebound on top however this is not the norm and should not be represented as being so.
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Old 01-19-08, 12:26 AM   #22
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Anyway, the fact is there's no one all encompasing standard. Compression can be shown as positive or negative, on top or on the bottom, it just depends on how you want to display it. I've seen examples of it like you describe, then there's all those other examples on the Honda-Tech forum there that are different.

To everyone: Don't just blindly think that it's only one way, have a look and think about it for yourself and you'll figure it out.
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Old 01-20-08, 04:49 PM   #23
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Good post gents.
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Old 01-20-08, 05:37 PM   #24
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Originally Posted by sereneseven View Post
Black91. Then explain why ALL of the graphs on that page show rebound on top as a positive number. It really doesn't matter what the dyno outputs, it can get flipped, the signs changed and all that by the software before the customer sees it. The dynos from KONI themselves show rebound on top as a positive number. Or can you explain why Koni Yellows adjust only rebound according to their own graphs when that's not the case at all.

SS. Well after looking again apparently for some silly reason Koni does show rebound on top however this is not the norm and should not be represented as being so.
You've seen lots of crosstalk on the Koni Rebound adjusters?
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Well, when you say it like that, it sounds much more balanced. D-cups are easily worth paying thousands in interest.
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Old 01-20-08, 05:49 PM   #25
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I just realised that I said the wrong thing there. I meant to say adjusted only compression. The Konis actually adjust only rebound with very little cross talk.
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Old 01-20-08, 05:49 PM
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