The “shock dyno” is a Roehrig 10VS damper dynamometer. For those who want to know more, this is their web site: http://www.roehrigengineering.com As a quick quote from there, for those who do not want to waste time in browsing: The 10VS is commonly used in a research and development facility, portable damper development support trailer, or a race team’s shop. The 10VS is fully computer controlled using the SHOCK™ Test Control and Damper Analysis software. The standard 10VS features six English or Metric strokes up to 4 inches (100mm). It has a force capacity to +/- 3,500 lbs. and velocities up to +/- 38 ips (0.9 m/sec). Higher velocities are available as an option. The 10VS is the system of choice by many of the world’s leading automotive companies and OEM damper manufacturers for their vehicle ride and handling activities…..

Here is how it looks like. The computer is not shown, but it is a simple PC with appropriate software and that is it:

The “accelerometer” is a Low-G type from Vernier. For those who want to know more, their site is: http://www.vernier.com It is a one-axis accelerometer, as we are interested (at the moment) at only vertical accelerations. It is incredibly sensitive for our case, with possibility to record up to 500 samples per second! It will measure accelerations in the range of -5G (-49 m/s2) to +5G (+49 m/s2), which really exceeds what we need. It comes with a software and USB cable, so it is quiet user friendly and extremely easy to use by anyone with no requirement to read much from the manual. It is very small, basically fits nicely in your hand, and very light, so it could be mounted almost anywhere in the car. Here is how it looks like:

The first round dampers to go on the dyno are:

1. Stock OE (Boge-Sachs – p/n xxxxxxxxx ) with about 10.000 miles on it.
2. Koni Sport (Yellow – p/n xxxxxxxx) with about 15.000 miles on it.(tested at full soft and full stiff!)
3. Bilstein TC Sport (p/n xxxxxxxxx) with about 1.000 miles on it.

Later on, probably next week, will dyno the remaining: Bilstein HD, Bilstein Sport, Bilstein TC normal, Boge TurboGas and two other stock OE dampers, one is from 2002 car with 90.000 miles and another is pretty freash, but from 2003 model, so it is Monroe. Then there is a plan to try to rebuild one or two of these, and see how do they behave before/after, in an attempt to understand how all this work and how can (if possible) we have the cake and try to taste it too I was thinking to put all this stuff together first and then post it, but then realized that the data is quiet a lot and probably would be much better if we split it somehow and feed this thread as we go…..

So, here we go with the first round of graphs, the Force vs. Displacement. Basically what was done is mount the damper, set the height so the damper will work around the physical range it works when on the car. Then the machine starts compressing-decompressing the damper (converting rotation to linear motion, imagine crank, rod and piston) at certain not very high speed. There is an infrared sensor that is pointed towards the middle of the body of the damper, so on the screen we see the temperature of the damper itself, at specific point that could be arranged. This is done so all dampers do get to the same exact temperature and then the separate cycles start, so to ensure some sort of consistency. It is very interesting to see how incredibly fast dampers heat and how much that heat affects the results, but on this one we will stop later. Then the dyno performs 2 in/sec movements several times, records the data as a graph, then moves to 4 in/sec, then to 6 and the last one is 30 in/sec. that is the fastest it can go. Here we have the graphs for the three dampers:

Then there are several more graphs, that represent Force vs. Velocity and several other ways of comparing them, but that would be too much of pictures for the moment. I will eventually upload them as links, just for the more interested to check all the possible plots that dyno provides. This is just the first round. Later on we will separate each speed and make plots where all three dampers could be seen on the same page, so this way to easily compare the curves. We will see later how there is quiet a substantial difference from what the dyno tells us and what the real life road tells us for each damper. That is where the accelerometer comes to play and shows clearly the difference in ride comfort for each unit. I will edit this topic later on and add the part numbers for the above dampers.

More later.

Great graphs (any chance you can shrink them a bit?)

Just a couple observations from those graphcs.
TC's appear to have good rebound control, making them suitable for a conversative lowering spring. They appear to ride a bit more firm than stock, all in all a nice upgrade.

I"m interested to learn the differnce in the highest speed piston movement between KONI soft and stiff. These should be identical, as the adjusting mechanism only touched the foot valve, not the piston valve, which controls compression.

Definitely looking forward to updates!

get some of the blingier coilovers on there!

Welcome back! Nice to see the graphs online...

Quick question:

What are the "speeds" indicated on the graphs? Are they the actual stroke speeds of the shocks, or do they indicate the tangential velocity of the test rig's "crankshaft"?

The reason I ask is that if the "speed" is the crankshaft speed, the shock will only have a comparable stroke speed at "0.0" displacement, and it'll actually be slower as it approaches the ends of its travel (in this case, the stroke velocity will be a sinusoid). That would explain the rounded shape of many of the curves, wherein the greatest forces occur at zero displacement (where velocity on the test rig is highest).

Here's another way to phrase the question: when you watched the measurements, did you notice whether the test rig ran at a constant rotational speed (rpm of the crankshaft) in each run? And did each run produce a single one of the coloured lines in the output graph? If so, each line is the crankpin speed, and the stroke speed is changing as described above. (If not, then I've a lot of head scratching to do in interpreting these graphs!)

Thanks for the great work, Peter!

- C (W)

P.S. -- at some point, could you please test a rear Koni at the 1/4 turn (90 degree) setting? I'd be curious to see what makes that setting a good comfort point. Thanks again!

Slapt he accelerometers on the shock on the dyno.
That way its easier to compare the "real world" versus the dyno.

My "guess" is tahat you need TWO accelerometers per shock
- one on the fixed portion
- one on the moving portion

For the dyno, the fixed on will stay fixed - ont eh moving one it also allos you to filter out hte road effects (aka the car physically moving up/down)

Yes, the speeds (from 2 in/sec to 30 in/sec) are the tangential speed of the crankshaft, so as you said, the full speed is around the "0,0" displacement. So, in a way, the dyno results do not quiet represent the real life situation as the speed they are tested kind of gradually ramps up and allow more of an ideal scenario for the damper to give its best. In real life, the potholes behave differently, and here is why the dyno results could be quiet misleading. I guess an expert can draw very stable conclusions even from looking those charts, but I am not such and therefore we went for the use of the accelerometer, as to prove the differences between the dyno results and real life. BTW, the idea of that accelerometer came from you and we all owe you one for that! It will simply transform the way we look at suspension from now on. We will be able to finally compare different setups in a more scientific way instead of the usual “this is more comfy than that” type we used till now.

Quote, originally posted by Ceilidh »

P.S. -- at some point, could you please test a rear Koni at the 1/4 turn (90 degree) setting? I'd be curious to see what makes that setting a good comfort point. Thanks again!

That is in the plans, but it may happen only at the very end. I am actually very interested in taking that damper apart and see what is going on inside and watch the dyno guy rebuilding it, so perhaps we can grasp little bit more from the whole concept. If it is not terribly complicated, we can build a quick virtual model and come out with few animations, as to visualize how this whole thing works inside.

Quote, originally posted by MikekiM »

….Just a couple observations from those graphcs. TC's appear to have good rebound control, making them suitable for a conversative lowering spring. They appear to ride a bit more firm than stock, all in all a nice upgrade.

We will find out later on that the TC look good “on paper” (from the dyno, as you observed) but it is quiet far from being the advertised 10 or 20% “stiffer” than stock. I will try to get there today…

Quote, originally posted by MikekiM »

…. I"m interested to learn the differnce in the highest speed piston movement between KONI soft and stiff. These should be identical, as the adjusting mechanism only touched the foot valve, not the piston valve, which controls compression.

In fact, the compression is “almost” indentical at all speeds we tested. I am saying “almost” because there is a very slight difference between the lines, but that could very much be the result of slightly different “zeroing” the damper between the two runs. They are so close that it is absolutely safe to say they are identical. So, the Koni advertising that Koni Sport acts only on rebound and the compression is always the same is correct.

Quote, originally posted by ewongkaizen »

....Slap the accelerometers on the shock on the dyno. That way its easier to compare the "real world" versus the dyno.....

I do not fully understand how would that help? The damper on the dyno is moved up and down by the crank, so the accelerations (vertical, on the damper) are related to the circular motion of the crank. That thing is so smooth, that is we were to put the accelerometer on there, I guess we would get a very nice sinusoidal line….. I just do not understand how to use later this smooth line in comparison to what the real street accelerations are? Perhaps I did not fully understand your thought, please explain more.

Sorry everyone for the big pictures (they were bigger), but they looked pretty small on my screen. I do understand people with laptops suffer with big pictures, but at the same time people with very high resolution monitors may have trouble reading well the pictures…. Hope the current resolution works well for both worlds.

Also, are you going to be testing both with and without the rubber shock buffers? The Bilsteins have the built-in buffers so it may not be a fair comparison with the other dampers. I know the buffers affect compression a great deal, but I wonder about rebound as well? The energy stored up in the compressed buffer must exert some force on rebound...

Great job btw!! Those graphs are excellent!

Very interesting asymmetry, Peter, particularly on the compression side. Can you confirm that the plot trace goes in the clockwise direction (i.e., that the upper left quadrant shows the shock contracting from full droop, and that a negative (-) displacement on the horizontal axis corresponds to extension from baseline)?

If you can confirm the above, then we at last have possible empirical proof of the "slow-action" twin-tube characteristic that's supposed to be one reason why the Koni's are so much less punishing on sharp impacts. (That is, the asymmetry shows that when a wheel first hits a bump, the shock forces build up only gradually.) If the Bilstein HD's turn out to have a much steeper ramp in the upper left quadrant (i.e., if it looks like the Koni upper right quadrant), then that would complete the proof.

Very interesting, Peter -- keep 'em coming!

- C

Phat, the dyno is designed in a way that only rear dampers could be tested. Well, actually I am sure some sort of adaptors could be manufactured and perhaps manage to grab even a front damper, but I am really not that interested in the fronts now. It cost 25$ each time the machine goes on and I rather invest in something else than dynoing fronts as well...... so this leaves us with the rears, where I am not sure internal buffers are involved. If you intend the bump stops we have in the rear, they do not come into play anyway, as the dyno has full stroke of 2" and it never goes all the way up or down. Our rear dampers have full stroke of 9", so it is up to us to decide where to position the damper. We actually took some measurements and found out that the damper works (when on the car) at around 5,5" to 6" from fully compressed, so that is where we fix the damper for the dyno. This way if (just in case) it is not so linear, then we have closer to our daily driving scenario.

Quote, originally posted by Ceilidh »

.....Can you confirm that the plot trace goes in the clockwise direction (i.e., that the upper left quadrant shows the shock contracting from full droop, and that a negative (-) displacement on the horizontal axis corresponds to extension from baseline)?

Yes, it goes clockwise. Basically at 9 o’clock of the graphs the dampers is fully extended (+1”), then at 12 o’clock it is half way compressed (highest speed here too) than at 3 o’clock is fully compressed (-1”). At 6 o’clock is again half way, but in rebound (again, highest speed here)…and the circle is closed.

1. Tire pressure difference of 8 PSI makes huge difference in comfort (40 PSI vs 32 PSI).

2. Our roads are quiet crappy! Consider that accelerations of 0,3 are the comfort limit (numbers taken from some books on suspension), from 0,3 to 0,6 is the “yellow” zone, and beyond 0,6 is where the discomfort starts. So, you all can see what kind of discomfort is just to go up and down the street.

Hi Peter,

I've just noticed that your biggest rebound spikes go beyond -9 m/s^2 -- considering that gravitational acceleration "g" is only -9.8 m/s^2, that means you're close to airborne! Definitely some really bad roads out there; no wonder ride comfort is an issue.

Thanks very much for pointing out the ride comfort degradation from high tire pressures!

- C

Here is where basically the things get very interesting. As you all can see, the dyno showed how the TC Sport are (as also advertised) pretty close to stock, if we look at the compression. The rebound is quiet more than stock thought. But from the graphs is pretty clear that the TC is not any near the advertised 10 or 20% stiffer than stock, because even if it “ideally” is (reading the dyno it could be decided that it is 10-20% stiffer), it definitely it is not according the vertical accelerations in the car. Basically, what I am trying to say here is: They may have dynoed those two dampers (OE and TC) and from the graphs (specially looking at the compression, which they say is more important fro comfort!) it is easy to come out with the conclusion that the TC is 10-20% stiffer than OE, but apparently 10-20% difference on the dyno curve is not really 10-20% difference in real life. Or perhaps it all lies in somewhere else? I have to yet do the accelerometer on OE rear dampers on the Jetta (as it has 15” tires) and then we will see how these two compare to the OE, but for the moment it is pretty clear that a Koni set to 12% rebound in the rear is significantly more comfortable on the same car, same conditions than a TC Sport.

The question here is WHY? Is the rebound the cause of the discomfort (which rebound the TC has much stronger than the Koni at that particular 12%) Or is it something else?

While doing the dynos, I was also talking to the dyno owner (his name is Phil, locals may know him as a big and famous motorbike nut) about these results and how the real life accelerations do not quiet match with what we can see from the dyno. Now, he had not seen the accelerometer’s graphs, neither he knew these dampers well as his world is bikes and not cars, but while looking at the dynos, he managed to describe to me exactly how these dampers would perform in real life and his description fully coincided with my butt feelings, so I would like to rephrase now what he said, what could possibly makes the TC such a harsh damper, even if the absolute values of the curves do show it as a nice mild upgrade. So, here is what he tried to explain to me:

Let’s take a look at the upper left part of the 18 in/sec graph, sort of zoom-in and analyze those three lines from the three dampers. Here it is again in detail:

If we look carefully at the TC line, is starts ramping up as fast and steep as the Koni line. At certain point thought, very close to the start of compression, it bends quiet fast towards the right and “flattens” pretty fast, as to join the OE line where the max speed is (extreme right on the picture). So, according the Phil, this is precisely the reason the TC do ride bad, because the valving inside is kind of very inconsistent. Basically, what he was trying to tell me is that the valve holds pretty well the initial pressure, but once it opens, it lets the fluid go too fast, so there is very quick drop in pressure, at which point the damper does no longer perform in a smooth way, which is apparently what it takes for good comfort…..

I have to go now, but we will dig more into this later.

All I can say is THANKS ... GREAT JOB MAN... this is amazing, it will totally show why some shocks behave they way they do! Specially your real life accelerometer results are PRICELESS... as we all know Dynoing is only half of the story and probably best for marketing.

I do NOT believe any of the tuners out there dared to do similar tests (at least I am not aware of) and no one would be brave enough to publish findings... You may wanna send a resume to Car&Driver... they probably can use someone like you

Looking forward to the rest of the results.

Hello Everyone,

Peter and I have been emailing back and forth a bit about the shock absorber tests, and he's asked me to post one of the emails. I'm afraid I don't have time to edit it and fix it up for Vortex use, but with the context Peter's given in his last post, it should be understandable. The only thing to note are that (1) Peter's sent me pages of a shock absorber text he found in London, which did much to illuminate what appears to be going on, and (2) before the appearance of his textbook, we had two possible explanations for the TC's poor performance, one of which (inertial overshoot) no longer seems to be an issue.

Anyway, here's the message, verbatim:

Hi Peter,

I just wanted to let you know that the articles were excellent! Very informative, and they've got me thinking....

1) Remember when I said there were two ways of interpreting Phil's comments, that either he was referring to the steady state characteristics of the shock valving, or else to some time delays and overshoots arising from inertial forces in the valves? Well, the articles sort of imply that it's the former, and not the latter (I've gone back and reread the email where you described Phil's comments -- they really are consistent with both interpretations). Especially now that I've had a relook at the TC force-displacement graphs (I had to delete the old ones because of email problems, so it's nice to see them again on the forum!) -- the fact that Phil's referring to "steepness" of the initial bump curve, and the fact that that steepness is evident even on the lowest velocity curve, does seem to suggest it's not an inertial problem (the valves opening more than they should because of inertial overshoot, and perhaps fluttering in a dynamic instability), but rather one of the quasi-steady state response to rising shock pressure.

2) If that's the case, we're back to square one on why the TCs look so similar to the Konis on a single bump, but are so much worse on a prolonged bad road. Two possibilities here come to mind: one is that the single bump you used was somehow different from the "normal" bumps on your bad road; the other is that on the bad road, you're starting to get cavitation effects (which can happen more readily on a cheap shock with less carefully machined valving -- basically if there are any notches, pits, bumps, casting flash, hard transitions, etc on the valve surfaces, those sites will initiate cavitation more readily than will a smoothly machined & polished surface).

3) Then again, maybe the issue is the size of your single bump vs. the size of the rough road imperfections: as I sort of recall, the maximum bumps (on your acceleration graphs) are not that dissimilar between TC and Koni, but the TC had a much busier and rougher "noise" between big peaks. That would mean that on the big hits, both shocks felt more or less similar (consistent with your single bump experiment), but on the smaller stuff, the Konis road smoothly whilst the TCs jittered and bumped almost continuously. That sort of behaviour would make sense, given the curves:

Because the "shin" (the initial steep part of the shock curve) is longer (as well as shallower) on the Koni than on the TC, then (on the smaller bumps) the Koni is working on the linear part of the curve (meaning that the valves aren't blowing off pressure in a big way, so that force is roughly proportional to velocity), whereas the TC is initially hitting its near-vertical force curve, but is then transitioning on and off its very nonlinear "knee". Hence the Koni will be feeling less harsh.

4) As to the importance of the "knee" in the curves -- Peter, those articles were eye-opening!!! I should have thought of it before, but the articles gave me one of those "Ah ha -- of course!!" moments when you realize something that you should have realized much earlier:

A) Up to now, I've only thought of ride comfort in terms of acceleration: the greater the acceleration, the greater the force on my body, and the greater the discomfort. That still holds -- but as we saw earlier, such a perspective doesn't explain why something like the TC is less comfortable than the Koni (after all, the TCs apply less ultimate force than the Konis, so they'll accelerate the car (and our bodies) less, so shouldn't they be more comfortable?).

B) But what I forgot to consider was the rate of change of acceleration -- what the articles you sent describe as "jerk" or "abruptness". If something applies a force to my body, I don't necessarily like it -- but I quickly get used to it. It's like being on one of those amusement park rides that spin a big (30 ft) platter and press you against the outer wall -- there's a lot of force, but because it's continuous, it's really not that bad; you can accommodate it without too much discomfort. But if the acceleration itself changes abruptly, that gets your attention pretty quickly!

Hmmm. How should I describe this?.... Ok, imagine you're a passenger in a car, dozing a bit as you're traveling down the highway, and suddenly the driver slams on the brakes. The initial "impact" of the brakes is the worst part -- you slam against the seatbelt harness, your head rocks forward, and suddenly you're wide awake. But after the initial "slam", you're not uncomfortable -- just concerned. The uncomfortable part was the initial moment of brake application. The thing is, a car doesn't decelerate more rapidly with initial application than it does afterwards, so if all we're doing is measuring force and acceleration, we'd say "What's the problem? The peak acceleration never exceeds X g's....").

Conversely though, if you're travelling down the same highway at the same speed, and the driver (perhaps a trained race driver) smoothly rolls onto the brakes instead of slamming onto them, the initial "slam" is much, much more comfortable. Assuming that the driver rolls onto the brakes hard, the peak acceleration is the same as before (in the slamming case), but the rate at which the acceleration rises is lower, and hence much more comfortable.

Thus in addition to peak acceleration, we need to look at the rate of change of acceleration (a/t). Because the TCs have such a sharp knee at low velocities, even smallish bumps will transition from the high force (and thus high acceleration, given F=ma) part of the curve to the low force (low acceleration) segments, and hence the rate of change of acceleration -- the jerkiness -- will be continually high. In contrast, the Konis might have greater ultimate accelerations, but those accelerations are approached gradually, and hence the jerkiness is much less.

C) So here's a question: does the software that came with the accelerometer permit you to take the first derivative of the acceleration curves? If so, that'd be a quanititative measure of the jerkiness, and it'd be an interesting thing to plot along with everything else.

Anyway, Peter, a very interesting issue -- thanks again for diving into the London bookshops and for digging up all this info. I'm learning a lot, and this is cool stuff(!). Let me know what you think of the above, and also let me know how much of this discussion you want to see posted on the forum; I'm happy to keep it within email, but I'd also be happy to discuss these things publicly.

Cheers!
- Ceilidh

END OF EMAIL

Postscript: in a subsequent email, Peter brought up an interesting point. As bad as it may feel if a driver suddenly slams on the brakes (instead of rolling progressively onto them), it feels even worse if he "stabs" the brakes and immediately lets go. That's sort of what the TCs do, with their steep initial rise and sudden flattening....

If all the above doesn't make sense, we'll try to circle back and explain it again. In any case, at some point Peter will show some force vs. velocity curves, which are also instructive. Cheers, folks!

- C

I must admit that I havne had the time to delve deeply into the work you have done. So maybe Im way off base here.

I was thinking that an accelerometer in the car when driving ont he road would only verify (and quantify) the "butt dyno" - i.e. how smooth the car's ride was inside the car

But what is the supensional actually doing?

Consider a bump

Was the car going up and the supension going up too (aka think of a solid suspension)?
Or did the suspension "mush" until it compressed fully and THEN the car went up?

So to cancel these out one would need an accelerometer on both the "wheel" (i.e. the spindle) and on the car (i.e. the strut top)
Then one could "subtract"the two graphs to get the work that the supension was ACTUALLY doing - not how the car was acting....

I take this cue from the BOSE suspension stuff and thinking about the issue of "noise" and perhaps that what Bose wanted to do was to filter "noise" out of the equation... and thus I borrowed the concept of balanced lines and how those filter out noise on the system.

Also based on the other comment about the "knees" and you comment of the sinusioid and stuff about how how human hearing works - the body is VERY sensitive detector; be "noise" bothers us and "music" does not - why is that? Why does "clipping" and "distortion" bother us more than "smooth" tones?

My theory is that we can detect the dX/dT and that we "anticipate" the curve and when it changes rapidly (think of what a clipped signal looks like in the second derivitive) we are temporarily addled - and thus under discomfort.

So the reason for two acceleramoters ont eh dyno was to get that base signal to compare to the cars signal.
- what feels smooth ont he road?
- what does that look like on the acceleramoter in the car
- what does that look like on the acceleramoter onthe wheel?
- what is the suspension actually doing?
- what are the "knee" points and where are those on the dyno?

To make it easier to compare apples to apples - measure the same thing on the dyno with accelerations (this also allows you to remove bushing squish from the equation...)

Hmm - I think we also need to know the pistion "position" as well as its instantaneous acceleration....

Alex, there is nothing to be brave about this and nothing daring. Everyone can go and purchase a simple accelerometer (that thing is sold for schools for experiments for the kids!! LOL)) and stick it in their car and drive around with a laptop, so other people think he is some sort of secret agent. The only other thing needed is a converter, so you do not need the batteries for the laptop as they can’t last the length of the tests. Come on, let’s do not make this look like more than what it is. Magazines have much better equipment and much more money and time to invest in this, but I guess they are not interested, even if it would be nice if they do decide to give some similar data to all their tests, so people, when shopping for cars, especially luxo cars, could not only see what is the noise level 9that they do publish in db) but can see how comfortable the suspension is compare to another car on the same pre-established path…… Several European magazines had been doing this for years and that is where all this started. I was asking in another thread what kind of device those folks would have been using and Winston came out with the accelerometer and the rest is all above here….

Sorry for the confusion - I was kinda few steps ahead of what yer doing now - which BTW is a GREAT service to the VW world and to the automotive tuning world in general....

One thing your graps DO demonstrate clearly - is what YOUR butt dyno confirms to be a "smooth" ride - something which in the past has been quite difficult to quantify - esp when the flame wars start about whose suspension is "better".

SRS has the right approach for the track - whatever reduces the lap times is GOOD.

But for the street - where are the comprimises. Now we have something to comapre.

What we really need is an 8 channel data logger (hmm maybe 5 channels is enuff - as the 4 in the car should be roughly the same - except for chassis twist - wow what we need - even MORE variables to deal with )

Quote, originally posted by pyce »

the misunderstanding we are having at this point is that to you maybe a shock duno is something that simulates random vertical movements, and in fact there are dynos like that, those big platforms that the car manufacturers have, where you bolt the whole car on it and massacre the suspension for hours and hours…..

Ah - a 4 post analizer... the better ones even have a moving road under the car and the entire thing fits in the wind tunnel.... but we are not Ferrari F1 with oodles of $$$$ to spend...

Ya might want to scan the last few years of Racecar Engineering _ I think there was an artilce on
- how to read a shock dyno
- what it can and cant tell you
- the basics of hte "knee" tot he curve and stuff like that....

Possibly a Carrol Smith book has this stuff too?

It's not that your tests were fancy or technologically advanced, but it's daring to go against norm and what is believed to be the truth. No one really knew about the actual way different shocks perform, or the way lowering the springs effect the roll center scientifically, or some other tests that you have dared to do (like mating a soft rear spring with stiff front spring)...

What's daring is to take "tuners" or "testers" or "manufacturer" claims with a grain of salt and go as far as proving them wrong and calling their BS or even teaching them a lesson in suspension design

My hats off to you for your efforts (along with Winston) and vortex suspension forum is much more informative and has much more objective info since you tried to enhance your ride comfort with Bilstein shocks!

Cheers

Modified by alexb75 at 8:11 PM 10-25-2004

Discusses the drawback so the "crank" type damper testing rig.
Points out the advances of the "hydrulic" damper testing rig.
Points out issues of Hysteresis (non linear response), how a mechanical damper test rig cant see this and an hydrulic one can.

Raises an isseu as the crank type tester really looks at the "velocity sensitive" nature of a damper. This presumes that we dont use "position sensitve" dampers (whihc as far as I know no one is doing in a coil over package due to overall complexity issues in packaging).

The author works in a hydrulic damper testing consultancy - your ouwn interpetations are warranted.

He does point out that good computer modelling hasnt been done yet.

One item of interest is the comment:
"Consider a simple corner model of a car - a body and hub mass seperated by and ideal spring and damper, witht he hub further attached to the ground via a tire spring. THe damoer us trying to dampen the motion of the body and the hub. THe higher frequency oscillations will always be damped more than the lower frequency body motion, hust the opposite of what you want 0 a well damped body and a loosely damped hub."

Would you enlighten us up some? Thanks.

I dont have the article in the office with me tonite...

The article was rather short and and thus lacking in details...

First - whats Hysterisis
http://www.lassp.cornell.edu/s....html

BTW - Hysterisis may also have some reation to the Koni/TC issue that Ceilidh raises a few posts back

Off the top of my head (will edit later) the author (who btw was a cunsultant for the "better" type of test rigs and thus may have some hidden bias) claims that the crank type of test rigs will show a "linear" response where the hydrulic rigs will show an response curve that has a "response" envelope.

Pyce - IM me with an email or snail mail so I can get the article over to you.

The main point of the article (that damper response is the opposite of what we really want) was most enlightening - that we want "hard" at low piston velocities and "soft" at high velocities - to a point...

The problem is that hydrulic damper valves are SOFT at low velocities (aka roll on a car) and HARD at high velocities (hitting a kerb)...

What we really want is HARD in roll and SOFT on the bumps.

There is some way to do this with hydrulic lines that go between the left and right sides of the car as well as front and back (pitch issues). There was another Racecar Engineering article where one of the Rally Teams used a rather simple setup with valves and pistions (as the piston moved off center it opened up holes that passed the fluid into the reserviours of hte other shocks...)... This addressed ptich and roll issues seperately from the individual wheel dampening issues....

Of couse - active suspension can solve this too....

--- morr notes from the article

What we really want is "freqency related" damping.Right now there is no workable way to do this (EWong: unless thats what Bose does?).

Ohlins that possibly stands out as tking the most sc ientific approach...

The best intuitive design must go to Kees de Kock at Koni...
(note: Koni uses shim packs not needle valves for adjustability)

Dampers have historicaly been tested on a mechnaical damper dyno.
These have an electric motor with a simple mechanism to produce axial sinusoidal motion in the same way a cranksahft links pistons.
To test a damper they run at a fixed speed for a few cycles, the maximum force and velocity measured ( in bump and rebound). The speed is then regularly increased and the force and velocity measurements are repeated giving a graph in Figure 1 (sloped curve on froce x velocity graph, )

The results, precise points on a force agains velocoty graph can hidea multitude of damper (and eve dyno) abnormailties.
However a single cycle test with a refined hydrulic dyno, measuring force and velocity continiously gives a corrected insight into the damper. The same damper is tested on a hydrulic dyno produced Figure 2 (similar graph as Fig 1, but the line gets "fat" (aka has variance of force) in a certian mid range of velocities in this case in the neg force values where the velocity is neg)

(close)
.... there has been little attempt to understand what dampers are tying to do and how it might be best achieved.

EWong: so maybe Pyce et are are breaking new groud in attempting to UNDERSTAND?

Modified by ewongkaizen at 5:15 PM 10-28-2004

Active suspension is so cool. Have you guys seen that Bose thing?

Your suspsension could double as sub woofers, so you don't have to upgrade your crappy Monsoon system lol!

1. Dynoed an OE damper from Golf TDI and one from Jetta TDI, so we have same engine, same trim, same rims/tires, just basically one is a Golf and the other one is Jetta. We know from the color codes from the springs, that both cars use different springs, even if we do not know yet exactly how different they are. Well, tonight it came out (the outcome of the dyno will be posted tomorrow) that the dampers on the Jetta are quiet different than the dampers on the Golf. Meaning, the Golf has significantly softer compression and rebound! So, we knew they have different part numbers, but we did not know by how much (if any) they differ. Now we found out the difference is there and it is quiet substantial if we look at the graphs. At this point it will be very interesting to see what are the GTI dampers or perhaps dampers from Jetta Wagon........ More on this tomorrow when the graphs come out....

2. The Bilstein TC Sport were tested side by side with the Bilstein TC Standard. If you all remember, various sources talk about the Standard being 10% stiffer than OE and the Sport being 20% stiffer than OE...... Comes out (according to the graphs!) that the Standard actually have even higher compression (not by little!) than the Sports, but significantly smaller rebound. I guess we have ot test them with the accelerometer, but I really do not see how the Standard is going to be more comfortable than the Sport with a graph like this........

More tomorrow...

I usaully don't even look in here because most of the time its just opinions with no technical data.

I've been designing, testing and building shocks and struts for 4 years now (military and very large applications), and have access to all kinds of equipment, but haven't ever had the time to post anything like this as far as relatign to VW's or even cars for that matter.

Good work guys, you have now inspired me to do some testing when I get the chance.

If you have any questions, please ask.

If we have any questions? This whole thread is a giant question of how to really tune these things! I am glad someone with such experience like you decided to stop by and I hope that you can give some light here, so we first understand in more detail how these things work, so this way we can identify where the problems are and why damper "A" behaves the way it does and what makes damper "B" a better one, etc.... My personal plan is to open one of the OE dampers and see actually how exactly it is done. We all know the principle behind, but I want to compare technical solutions between the various dampers, so we have an idea what works better and what not. As had been said, people generally do not realize how much the damper gives to the whole suspension assembly, but if more than one damper is tried on the otherwise same car, then the difference could be noticed and then the user realizes that dampers are very important and a lot could be done with them..... Anyway, tell us more about you, share some knowledge, please. One thing I would like to know for sure is whether we are on the right path here and how seriously we should take those mechanical dyno results? Also, what do you think about "Ceilidh's" comments and Phil's comments about the TC Sport's curve in compression? I assume you read all the stuff above and if you have not, I would be glad if you can spend some time to do so. Thanks....

But at least the 30 in/sec speed was done on one page, so it can be compared (below) so we get an approximate idea of how different they are. At this point I guess that for Golf owners the real “about 10% upgrade” would be actually to get Jetta dampers….. Perhaps the used Jetta dampers on the Classified just went up some! LOL So, here we have it:

Will try to post later the TC “Standard” graphs…

; )

and this begs the question... WHY?

Why would VW engineers get one damper for Golf and another one for Jetta? Is it because of weight?

Are we sure that the Jetta shock doesn't come with some Golf?! Does it depend on the year? Has it been just a supplier change? Was it just luck... it really could be!

I recently changed my CAT/DP and I realized the new one looked different than the old one... so I had to dig in deep (with little help from the dealer) to find out what's the difference. I found that the VWs made in Brazil (mine) had different CAT/DP than the ones made in Germany as they were supplied by different companies. But, the German one was a better (or preferred CAT) and for replacement you can only get the German version!

So, would something like this hold true for shocks as well? We all know that same cars and tranny's have had different colored springs, so I guess that OEM shocks could be the same as well?! Couldn't they?

Modified by alexb75 at 1:56 PM 10-28-2004

Lots to think about.