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BMW 3-Series (E90 E92) Forum
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335i suspension overhaul via M3 suspension + Ground Control (long & lots of pics)
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12-18-2009, 12:39 PM | #67 |
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yea seriously... i think somewhere in norcal ? orionredwing i know is running kwv3 on swift springs setup by hpauto, and OP is probably nearby too. Could easily test and compare em except for the fact that... theres too many variables with tires/wheels and the other fact that its too dangerous to bring our cars out to the limits on the streets. At least we could test comfort of the ride maybe?
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12-18-2009, 01:17 PM | #68 | |
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12-18-2009, 01:23 PM | #69 |
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12-18-2009, 03:54 PM | #70 | |
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Just to be clear, don't the dampers need to be valved differently than expected since they have a different motion ratio from the springs? If I were tell a shock builder that I want a damper built for 700lb rear springs, I need to determine the effective spring rate at the damper, right? 700lbs * (.57^2 / .81^2) = 347lbs. The damper should be set for 65% critical damping on a 350lb spring? thanks, justin |
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12-18-2009, 04:51 PM | #72 | ||
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12-18-2009, 05:39 PM | #73 | |||
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It means that Ground Control tells Koni what to build, and then Koni figures out how to build it. After the first shocks and struts are tested, they go into production with a special part number (SPGC) printed on the damper. The advantage of going into full scale production, with a production based company like Koni, is the the service and warranty are "Consumer style" rather than boutique or race style. The SPGC Koni dampers have a lifetime warranty, that is simply not possible with smaller boutique type companies. Ground Control also builds one at a time race shocks in house, so we know how hard it is to truly offer a lifetime warranty. Thats one of the main reasons to enlist the manufacturing capabilities of a huge international company rather than doing it ourselves. Oh tech details, degressive actually starts about 2 inches per second which I prefer, and rebound is linear, but very adjustable. We just can't use degressive rebound on anything for the street, it doesn't "feel right" although it can be faster on the track sometimes. Critical damping calculations are not used as much in designing shocks as they are talked about by consumers. I am sorry to say that, but it's just that other criteria can overshadow even the most well intentioned math, and very often the best end result is NOT the one you thought you would start with. Don't flame me for saying that^ but it is really true once you really start getting your hands dirty and are taking a product from idea to end user. The math is very often wrong. Maybe not wrong in calculation, but wrong in preconceived assumptions and semi arbitrary goals. So I'm just saying that if the shock is great and the math is wrong, then you need to shy away from the math. Quote:
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It is the chef combining the ingredients of the "soup" where the differences in approach and opinion can serve to make something that people are very happy with. Some people like different soups than others, so that's why the chefs have to always be learning, but everybody will never like just one soup recipe. Jay from GC Last edited by JM3; 12-18-2009 at 06:20 PM.. |
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12-18-2009, 05:53 PM | #74 | |||
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I know you didn't ask me, but I know the answers. Orb or Harold are welcome to chime in with their input obviously. Quote:
Fortunately, most competent tuners do the math on this, as do pretty much all European shock manufacturers. Quote:
Its easier for me to keep the values and their relationships to each other intuitive by thinking from the wheel rate inward rather than from the spring rate outward. How I approach such situations is first confirm that whatever the customer said is true. And then I actually back the customer requested spring rate out to the wheel rate, and then work the damping at the wheel rate. Then work the wheel rate forward into the motion ratio of the shock. Quote:
So I would change your phrase from "The damper should be set for 65% critical damping" to "The damper should be evaluated at 65% critical damping". And then try other values! This is actually not that fine of a point. All you have to do is follow any 3 series down the freeway, and see the rear bobbing up and down (compared to the front) to realize that being fixated on a number (like 65) may not translate into a successful ride/handling compromise. I hope I have helped Jay from GC Last edited by JM3; 12-18-2009 at 07:05 PM.. |
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12-18-2009, 06:03 PM | #75 |
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Great discussion!
It would be awesome to get Speediance together with some of the other modded suspensions and do a few runs through some twisties.
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12-18-2009, 06:19 PM | #76 | ||||||
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Yes GC has many many times. I honestly still don't know why BMW did it this way on the e9x. I have almost the exact same number as HP for the rear. BTW, the 2 door M3, 4 door M3 and 335 all have different front MR. Quote:
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Jay from GC Last edited by JM3; 12-18-2009 at 06:46 PM.. |
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12-18-2009, 08:25 PM | #77 | |
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I agree on my poor phrasing. What I meant was to have the middle adjustment of the shocks targeted at 65% of the initial spring rates I choose. I don't quite understand what you're getting at about the 3-series bobbing on the highway. I've certainly seen and felt it. I thought the rear was just way underdamped for comfort. How does this relate to the 65% number we been discussing? Also, I read your website description to mean that the konis would be custom valved to match the chosen spring rates. Is that incorrect? Or do you just sell one damper valving and we adjust the knobs to match the spring rates we choose? Thanks for your help. I'm trying to get as much knowledge as I can so I don't spend as much time on the phone with whomever, when I place an order. justin |
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12-18-2009, 08:35 PM | #78 | |
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Thanks Jay for clarifying all the confusion going around here.
Once again, I am glad I came to you. Something from awhile back comes to mind. The first thing you learn in track school: no amount of reading about racing is a substitute for a single lap around the track! People looking for "good" suspension should first learn to trust their judgment and experience. Or else nothing will be "good" to you... To all that are local, I would be more than happy to give you a ride in my car, go on twisties or whatever... As for bringing independent third-party people; Its none of their business. You can tell I dont like consultants either... Quote:
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12-18-2009, 11:03 PM | #79 | |
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Of course what Dennis Grant says should be taken with a grain of salt, considering it is only the voice of one man. His work have done wonders to my DSM, as well as many other autocrossers in my region. I am actually very interested in seeing the mistakes he made in his math, so that we can benefit from not making the same mistake. And if it is possible, can you also share the measurements you made for motion ratio with us? On the note about real world experience vs theory, while I believe that there is no better mod than seat-time, I am also a firm believer that a neutral handling car will always be the fastest, given all else equal. |
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12-19-2009, 02:54 PM | #80 | |
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You mention dampening at 65% critical but what about high speed dampening and the knee that the curves join. Without more in depth analysis of the dynamic of the whole car we are left guessing but that is okay. We need two data sets to do this so we can use hand calculation with model tuning as complete system, data accusation/measuring and experience/know how. If I had unlimited resources I be using something like this along with other tools: http://www.chassissim.com/index.php There are a few things we can do to get really reasonable accuracy of the suspension frequency as a system by doing a bounce test. All you have to do is remove the dampers and disconnect the sway bar. Push up down on the back of the car with good amount of force and count the number of cycle for a given time period. Now lower the cars via the spring adjusters ˝” and repeat the test. Do this few more times. What we have now is a reasonable plot of the frequency of the suspension through its arc. If we are smart about this we now can see some changes in spring motion ratio as well but more data can be had. There is some error to this approach due spring binding which is a big deal in practice but not so much in this test. It is very important to have a good quality spring and like swift spring and it should be tested prior to the bounce test as it key data point. This is good enough short of 7 post shaker. Orb Last edited by Orb; 12-19-2009 at 09:13 PM.. |
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12-19-2009, 10:58 PM | #81 | |
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Yes I do want a knee in the compression graph. Though, I'm unclear about the need for and use of a knee in the rebound graph. I haven't found that chapter in a book yet... justin |
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12-19-2009, 11:08 PM | #82 | |
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12-20-2009, 12:11 AM | #83 |
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I'm in the Cupertino area ... I've got most of the HP's goodies (minus the bushings) and running the Koni FSD.
If the Cupertino, Sunnyvale folks want to get together during the holiday slowdown, we can find some nice empty corporate parking lots to trade rides and get our own opinions. Junk
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12-20-2009, 04:20 AM | #85 |
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I'm in the East Bay and work in the Palo Alto area and have a basic PSS10 setup for comparison. However I will be out of town for a while during xmas though so it wouldn't be until next year when I can meet up.
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12-21-2009, 12:51 PM | #87 | |
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