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    Thread: Under or Over?

    1. Member
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      05-24-2019 06:21 PM #1
      Can someone explain to me what an underdamped suspension feels like? As in, if I'm understanding things correctly, shocks/struts are essentially too soft for their springs. (Or is it that the springs are too stiff for their shocks/struts? Or possibly both or either?)

      and

      Can someone explain to me what an overdamped suspension feels like? As in, if I'm understanding things correctly, shocks/struts are essentially too stiff for their springs. (Or is it that the springs are too soft for their shocks/struts? Or possibly both or either?)

      many thanks

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    3. Member
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      05-28-2019 09:57 PM #2
      Any older car that isn't maintained will probably have underdamped suspension. When you hit a bump the vehicle will continue to bounce up and down. People will describe this as washy or bouncy.

      Overdamped suspension is not really that common unless the car is heavily modified. The shocks will be so stiff that when a car hits a bump the shocks won't allow the springs to compress as much as they should. The ride will be overly harsh.


      If you push down on your back bumper (trunk) and compress the suspension the vehicle should jump back to it's original height with very little overshoot and stay there.
      If the car oscillates a few times it's underdamped
      If the car rises slowly it's overdamped.

      This Quora answer explains it okay, with graphs!
      https://www.quora.com/What-are-over-...damped-systems

    4. 05-30-2019 01:43 AM #3
      When the springs are too soft you will get a lot of body roll. With a good suspension set up you can hit speed bumps at high speeds without issue, your car doesn't tilt far to the side when turning, it doesn't lean forward on regular braking or lean back on hard acceleration. Driving highway 65mph+ can be done with just a few fingers on the steering wheel and the car grips like you bought really sticky tires. My two inch suspension lift also changed geometry though so it's even better but with good much much firmer stock height springs or an inch lift in front for best results plus even just some inexpensive Bilstein TC Sport shocks for $150 for all of them it will completely change the driving experience. The more lift to a point you put on the Jetta UNLESS you properly change the control arms or even just lifting the engine up then you can lower it and have good geometry still but anyways the more you lift it to a point the less it will understeer and keep going straight when you turn and the more it will be a better balance with some oversteer possiblity like a rwd car especially if you lightly tap the brakes. My Jetta feels like it would do very good on a race track and also on amateur rally so it's a win win. People think you can do one or the other but that isn't true unless you go semi pro because with different tires rally cars do drive amazing on road as well but people talk before they think on here.

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    6. Member
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      05-30-2019 03:13 PM #4
      IceCruncher,

      I think you went way off topic here The OP specifically asked about how to tell the difference between overdamped or underdamped suspension.
      Body roll, understeer and suspension geometry should probably be left as separate topics.

      Body roll is more a function of spring rate and roll-bar stiffness than shock damping, although stiff shocks can slow down the affect of body roll on quick transitions.
      Saying that you can slam into speed bumps at high speed with a "good" suspension is a bit of a misnomer. My Porsche has great suspension... but bad things would happen if I hit a speed bump at anything faster than a crawl. As you mentioned it's all about compromise!


      YikeGrymon,
      Re-reading your post you basically hit the nail on the head with your understanding of the concept.

    7. 06-01-2019 10:10 PM #5
      You're right there are suspensions that are good that you cannot hit a speed bump with at a high speed lol. I went off topic to talk about springs because it seemed like he was using dampening as a general term for suspension and springs more than actual dampening that the shocks do. I believe he even was talking about springs. But yes technically shocks not springs do most of the dampening and any set of decent bilstein or koni shocks should have you covered without even worrying about it. Body roll on Jetta's and golfs can be fixed with proper firmer springs, no need for anything but stock anti sway/roll bar parts unless you are hitting sharp turns at 65mph +.

      If your Porsche was as high as a stock Jetta in terms of undercarriage and body and with bilstein TC Sports, HD or maybe Special Red wouldn't it have no issue with hitting a speed bump and a good speed? I know people who rally stock height Jetta's and they do great. I think they might be driving smoother dirt roads than I though.

    8. 06-01-2019 10:13 PM #6
      Under dampened shocks doesn't allow you to drive comfortably at high speeds 80mphish usually if it's really bad and you will bottom out easily. Over dampened shocks will have you spinning wheels with high torque modded engine and also, "bounce" or feel like you're riding on bump stops. There simple. 🙂

      like the horrendously awful majority of mk4 low rider slow crowd that buy raceland coil overs.

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      06-14-2019 12:06 AM #7
      Thanks for weighing in, all.

      I phrased my original post the way I did because sometimes things are more easily gotten to if you don't ask directly. Like make it more open-ended I suppose. But: Here's what's going on.

      Tiguan has Eibach Pro-Kit springs and a set of Koni FSD dampers on it. So about 1.25" lower than OEM. So, way back when FSDs were introduced, Koni was all about "FOR USE WITH OE SPRINGS ONLY." Ever. Since then, for nearly any application (as far as I'm aware) they've relaxed that a bit and they say that a minimal drop is okay. It's all to do with having enough shock travel to allow the FSD science to work properly, of course.

      I've had FSDs on three earlier VWs over the last 12 or so years, each with a similar mild drop (H&R "OE Sport" springs on the Y2K GTI, OE Euro springs on the MkIV R32, and Eibach Pro-Kit again on the MkV Jetta). No issues, worked great on each.

      Koni also sold for a while (and still might, I'm just not sure) an FSD + Eibach Pro-Kit set for a lot of cars. The Tiguan was not one for which it was offered. Koni Tech Support told me that that doesn't necessarily mean anything, just that they never paired and tested it for that platform "because the Tiguan is not a particularly popular vehicle." Okay. But I do have the right spring set and the right FSD set for this car. So there's that.

      Most of the time it feels great. Highway speeds are crazy planted and stable. What's weird is that sometimes, at lower or just plain low speeds, the car seems to "heave" over certain things. Not crummy pavement or speed bumps so much. The best example is probably like a random dip in a stretch of asphalt or one of those brick walkways you see that cross a parking area (like there's asphalt, then a strip of concrete then the brick, then another strip of concrete, then the asphalt continues). There's one in particular I'm thinking of where you can see that each feature there is not quite so level with what's before and after it, like the first concrete strip is angled a little side to side, then the brick is more level with the asphalt, etc.

      So the HEAVING is the best way to describe it. Like sometimes I get pitched around a bit inside. It's not like oscillation, where the motion continues (typical of worn shocks) or a pounding that you get with springs that are simply too stiff. It's just one well, heave. Sort of to one side or to one and then the other sometimes, a harsh "rocking" for an instant. But again, not actual oscillating or anything.

      I put this in terms of asking about over/under damping thinking that somebody might hit on the same thing I've described here. But it doesn't really sound like it. Could be (??) that this is the particular platform on which Pro-Kit springs and FSDs just don't play together so nice. And again, it's not all the time. Not even close. Just some pavement upsets what feels great otherwise. But it's certainly annoying and has freaked out a passenger or two.

      So I'm stumped. Once again: Any input appreciated. Sorry this is as much to read as it is. Just trying to be descriptive.
      Last edited by YikeGrymon; 06-14-2019 at 12:12 AM.

    10. Member
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      06-14-2019 01:52 AM #8
      It could be that there is a certain frequency of excitation that your car just doesn't like, and you happen to have found it with that certain walkway that you describe. It could also be a phenomenon with your particular wheelbase and the speed at which you are going.
      Koni FSD's are pretty sophisticated shocks, they have velocity sensitive valving which makes them behave in a non-linear fashion. It's possible that some Koni Sports would behave better over that particular section of the road BUT they will be harsher than the FSD's everywhere else.

      I know we have concrete freeways where I live and if you drive on certain sections of the highway at certain speeds you can get cars to heave violently to the point where your butt is no longer in the chair. Going either faster/slower will get you out of the "sweet spot".

      FWIW soft motor mounts can also make the car have some strange sensations when that 500 lb block of aluminum is jostling around at a different frequency than the rest of the chassis.

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      06-14-2019 01:35 PM #9
      aha

      Thanks, Chaos. You've mentioned some of the very things I've thought of, in fact.

      Certain frequency of excitation, yep. Maybe: just a fluke of the underlying dynamics of a 4Motion Tiguan having been tweaked a little. Like those dynamics + those springs + those dampers = some random oddball characteristics in certain situations (crossing walkways like the one I mentioned, plus the other stuff). I resigned myself a while ago to thinking "That's just the trade-off maybe, in this case."

      Frequency of Excitation might be a good name for a band, also.

      FSDs are indeed pretty sophisticated. No doubt. A very slick idea also. It is not a stretch to refer to it as "semi-active suspension." There's a certain other PQ35 Tiguan owner who clearly knows his stuff and posts up a lot in that Forum; he's said that those springs and Koni Yellaz set on full soft is a great combination. I was sort of itching to make this change, but after thinking about it a while I realized that, as real "performance" dampers (whereas FSDs are not quite the same idea) I would almost assuredly end up with a harsher ride in general, yes. This was confirmed with another Koni Tech Support chat. My suspicion, which the fellow I was speaking with validated, was that Koni Sports on full soft would still be quite a bit firmer than FSDs when FSDs are at their "softest" (in quotes because the whole science and function of FSDs indicates that "soft" and "firm" are not really terms that should be applied there, it's a more fluid kind of thing).

      So if I make a change, damper-wise, to anything... well. I'm not really sure what I'd go with. Could be that the best thing to do is nothing. And just deal. As I've said, it's not like every day I get this sensation. One thing that I've noticed, and wondered about, is how over those stretches of concrete that we all encounter where each successive block of concrete is not perfectly aligned (the way a smooth run of asphalt is) and you get that fore/aft sort of "rocking"... it feels like any other car going over that stuff. It just jostles you around a little. It's the stretches of asphalt that have some undulations (or the random dip, like I said just above) that beget the HEAVE, the side-to-side rocking, whatever I've called it. There are a few spots I encounter during my usual running around like this. In fact, I got curious and took a Volvo XC90 on a little ride over some of that (I work at a Volvo dealership) just to compare. It was a similar experience but not as objectionable. Of course, a late-model XC90 has at least another 1000 lbs to it.

      Engine mounts as a factor I had not thought of, but that's certainly a good point. Could changing up a suspension cause something like that, from motor mounts? I bet it could.

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      06-14-2019 02:10 PM #10
      Quote Originally Posted by Chaoscreature80 View Post
      Any older car that isn't maintained will probably have underdamped suspension. When you hit a bump the vehicle will continue to bounce up and down. People will describe this as washy or bouncy.

      Overdamped suspension is not really that common unless the car is heavily modified. The shocks will be so stiff that when a car hits a bump the shocks won't allow the springs to compress as much as they should. The ride will be overly harsh.


      If you push down on your back bumper (trunk) and compress the suspension the vehicle should jump back to it's original height with very little overshoot and stay there.
      If the car oscillates a few times it's underdamped
      If the car rises slowly it's overdamped.

      This Quora answer explains it okay, with graphs!
      https://www.quora.com/What-are-over-...damped-systems
      Bingo.

      It's not as uncommon to arrive at an over-damped setup however, as Bilstein frequently uses an initial gas pressure that is too high for road use.

      https://www.youtube.com/user/SuspensionTruth - This fellow's channel has a lot of excellent information on the matter.

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      06-16-2019 05:33 PM #11
      Hmm.

      Well, this is why I've gone on the way I have, trying to be all sorts of descriptive. Because -- if I'm understanding things correctly, and it sounds like I am -- what I've got going on doesn't seem to be underdamped or overdamped. Hence my suspicion that I've hit on a slight lowering + FSDs situation that might not work as expected.

      If not a switch to Koni Sports ("Yellaz")... then what? Open to suggestions. Eibach says their Pro-Kit springs are intended to be used with OEM dampers. But VW OEM dampers aren't exactly known to last very long or be particularly great hardware to begin with. These slightly stiffer springs certainly wouldn't help anything in that regard.

    14. 07-22-2019 12:08 PM #12
      Quote Originally Posted by YikeGrymon View Post
      Hmm.

      Well, this is why I've gone on the way I have,my ip birthday wishes tneb trying to be all sorts of descriptive. Because -- if I'm understanding things correctly, and it sounds like I am -- what I've got going on doesn't seem to be underdamped or overdamped. Hence my suspicion that I've hit on a slight lowering + FSDs situation that might not work as expected.

      If not a switch to Koni Sports ("Yellaz")... then what? Open to suggestions. Eibach says their Pro-Kit springs are intended to be used with OEM dampers. But VW OEM dampers aren't exactly known to last very long or be particularly great hardware to begin with. These slightly stiffer springs certainly wouldn't help anything in that regard.
      If you push down on your back bumper (trunk) and compress the suspension the vehicle should jump back to it's original height with very little overshoot and stay there.
      Last edited by mopakarim4300; 07-24-2019 at 05:13 PM.

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      08-05-2019 10:48 PM #13
      Quote Originally Posted by mopakarim4300 View Post
      If you push down on your back bumper (trunk) and compress the suspension the vehicle should jump back to it's original height with very little overshoot and stay there.
      Right. That all checks out the way it's supposed to. Front and rear. Thought that was all pretty clear.

      ah well

    16. 08-26-2019 12:29 PM #14
      Quote Originally Posted by Icecruncher View Post
      You're right there are suspensions that are good that you cannot hit a speed bump with at a high speed lol. I went off topic to talk about springs because it seemed like he was using dampening as a general term for suspension and springs more than actual dampening that the shocks do. I believe he even was talking about springs. But yes technically shocks not springs do most of the dampening and any set of decent bilstein or koni shocks should have you covered without even worrying about it. Body roll on Jetta's and golfs can be fixed with proper firmer springs, no need for anything but stock anti sway/roll bar parts unless you are hitting sharp turns at 65mph +.

      If your Porsche was as high as a stock Jetta in terms of undercarriage and body and with bilstein TC Sports, HD or maybe Special Red wouldn't it have no issue with hitting a speed bump and a good speed? I know people who rally stock height Jetta's and they do great. I think they might be driving smoother dirt roads than my ip birthday wishes tnebI though.
      Can someone explain to me what an overdamped suspension feels like? As in, if I'm understanding things correctly, shocks/struts are essentially too stiff for their springs. (Or is it that the springs are too soft for their shocks/struts? Or possibly both or either?)
      Last edited by mopakarim20; 08-28-2019 at 02:38 PM.

    17. Member
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      09-02-2019 11:41 PM #15
      ^^

      I have no idea what point you might be trying to make.

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