[zsapphire7]

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?

Originally Posted by stressdoc

We really need to get a few cars together for a comparison test. Wonderful that we have several experienced suspension gurus working with the E9x.

[HP Autosport]

Originally Posted by zsapphire7

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?

I think we need a suspension tuner shoot out and hire an independent party for vehicle evaluation.

[zsapphire7]

Originally Posted by HP Autowerks

I think we need a suspension tuner shoot out and hire an independent party for vehicle evaluation.

sounds like lots of fun... !

[jah29]

Originally Posted by Orb

At least someone is looking for the truth. Just to help you get to the bottom of this the motion ratio are:

F: 0.96^2 * spring rate = wheel rate
R: 0.57^2 * spring rate = wheel rate

The rear damper motion ratio is about 0.81

As you seem to know the frequancy is the only thing that matters.

Orb

Question for Orb or Harold:

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

[Jeller]

With all this being said are there any off the shelf units that are correct? or reccomended/closer to the "correct" specs than others?

[eltoshan]

Originally Posted by Jeller

With all this being said are there any off the shelf units that are correct? or reccomended/closer to the "correct" specs than others?

There really isn't a "correct" setup depending on preference and application. Working things out mathematically gives us a starting point for what will produce the most neutral handling. Most of the kits on the market are too over sprung in the front. The best bet is getting properly valved dampers with custom spring rates.

Originally Posted by jah29

Question for Orb or Harold:

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

I think the math is sound, Orb or Harold correct me if I'm wrong.

[JM3]

Originally Posted by eltoshan

I've always liked the few autocross cars I've driven on the street and track valved to 65-70% initial critical damping with a digressive knee at 3 in/sec. Most people I've talked to seem to feel that 65% is really the threshold where the excess motion gets a little too high below that.

I'll address this specifically, and I think you may have also asked what "custom valved GC " means.

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.

Originally Posted by eltoshan

This applet should be useful in the future.

That link needs to be taken with a grain of salt. I have written many letters suggesting he correct some errors, but he hasnt. (I think he is actually in the military now)

Originally Posted by eltoshan

It really is a shame that in order to have a competently set up suspension system you really have to build your own. Considering that none of the major manufactures really do their homework.

The problem is that the biggest companies are all required to sub out. Not really one company can make everything, so KW, HR, GC etc, all have to pay people to manufacture components for them.

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

[JM3]

Originally Posted by jah29

Question for Orb or Harold:

I know you didn't ask me, but I know the answers. Orb or Harold are welcome to chime in with their input obviously.

Originally Posted by jah29

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?

Not exactly. The "expected damping" should actually account for the difference. The damping as dictated by shock location should be expected and anticipated.

Fortunately, most competent tuners do the math on this, as do pretty much all European shock manufacturers.

Originally Posted by jah29

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.

Thats not how I do it. Your math may end up the same, but spring and shocks tuning is very hands on and visual, and imho not as math oriented as experience oriented.

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.

Originally Posted by jah29

The damper should be set for 65% critical damping on a 350lb spring?

All I can say about this is, try typing the phrase "65% critical damping" into google and see what pops up. You will notice a a small number of people repeating people repeating people.

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.

Originally Posted by jah29

thanks,
justin

I hope I have helped

Jay from GC

[stressdoc]

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.

[JM3]

Originally Posted by eltoshan

Ground Control kits are looking pretty good now a days, especially with dyno matched Koni sports!

Originally Posted by eltoshan

Just a couple observations"
If you really want more control, though, I would suggest trying out some Hypercoil springs. At least the older Eibach springs were known to sag over time, and Hypercoil has just as good a selection of rates/ID/lengths.

I'll just say that I personally have always had the best performance from Eibach, so I stick with them. I have looked at other companies very very very closely, and have gone back to Eibach.

Originally Posted by eltoshan

Did you measure the motion ratios of rear?

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.

Originally Posted by eltoshan

I have a feeling that 525/650 will be rather understeery unless the rear has an unusually high motion ratio for a multi-link setup.

It is not particularly understeery at all. The ratio between front wheel rate and rear wheel rate is a very small part of the entire front/rear balance. Bumpstops, camber, sway bars, all have HUGE effects on the balance. To a lesser extent, LSD (or not), ride height, damping all have a lesser effect but are still always there.

Originally Posted by eltoshan

Doing some quick calculations with your corner weights show that 525lb/in springs on the front (struts, assume MR of .99 or so), results in a ~2.3Hz natural frequency, that's quite a harsh ride for street.

The MR in front is lower than that, but I agree with you 525 a bit high for the street. But remember, this is NOT a pure street car, and its not my car either.

Originally Posted by eltoshan

For track you will need some very very sticky tires, or a very very smooth track.

All the tracks around here are smooth enough, but on a race car the rates are MUCH higher still.

Originally Posted by eltoshan

Using a sporty yet more compliant natural frequency of 1.8Hz, the proper spring rate for the front works out to be roughly 287lb/in.

That rate would be too low. That is probably lower than the TRUE spring rate of the car (spring plus bumpstop minus mount) The car will roll on its door handles with that rate. Honest. (GC has already tried low rates on the e9x and it just didnt work)


Jay from GC

[jah29]

Originally Posted by JM3

I know you didn't ask me, but I know the answers. Orb or Harold are welcome to chime in with their input obviously.

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.

Of course you can reply, I just didn't remember your login name or i would have asked you specifically too. I have lots of technical questions, but I need to let what you said sink in for a little bit. Maybe others will be able to jump in on this right away.

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

[Speediance]

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...

Originally Posted by JM3

I'll just say that I personally have always had the best performance from Eibach, so I stick with them. I have looked at other companies very very very closely, and have gone back to Eibach.



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.




It is not particularly understeery at all. The ratio between front wheel rate and rear wheel rate is a very small part of the entire front/rear balance. Bumpstops, camber, sway bars, all have HUGE effects on the balance. To a lesser extent, LSD (or not), ride height, damping all have a lesser effect but are still always there.



The MR in front is lower than that, but I agree with you 525 a bit high for the street. But remember, this is NOT a pure street car, and its not my car either.




All the tracks around here are smooth enough, but on a race car the rates are MUCH higher still.




That rate would be too low. That is probably lower than the TRUE spring rate of the car (spring plus bumpstop minus mount) The car will roll on its door handles with that rate. Honest. (GC has already tried low rates on the e9x and it just didnt work)


Jay from GC

[eltoshan]

Originally Posted by JM3

I'll address this specifically, and I think you may have also asked what "custom valved GC " means.

Hrm, I don't believe I've ever actually posed that question, but it is good to have someone from GC chime in on the other side of things.

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.

[Orb]

Originally Posted by eltoshan

I think the math is sound, Orb or Harold correct me if I'm wrong.

Yikes….where did this equation come from. The link I provided about springs and dampeners do tell you exactly what to do and it 100% correct. Get the force (Newton) at the wheel for assumed dampening coefficient so use 0.60 and 0.20. Now take the next step and plot a graph. The motion ratio for the damper is a must to do for the most basic starting point to tune a damper. Just like the spring motion ratio it is also squared. However, if you tuned a damper like this you are not going to like it much at all. The mathematic for damper calculation are far more complex and if you want to get into it then read the shock absorber handbook. I can’t explain this in simple terms nor do I want to. Keep in mind none of these calculations assume compliance issue and stiffness spikes in the system which are not trivial.

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 ½” 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

[jah29]

Originally Posted by Orb

Yikes….where did this equation come from.

You mention dampening at 65% critical but what about high speed dampening and the knee that the curves join.
Orb

Geeeeeeze. Of course I'm not going to use such a simple equation. I just wanted to make sure I'm heading in the right direction with the multiple motion ratios in the back of this car.

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

[jah29]

Originally Posted by JM3

That rate would be too low. That is probably lower than the TRUE spring rate of the car (spring plus bumpstop minus mount) The car will roll on its door handles with that rate. Honest. (GC has already tried low rates on the e9x and it just didnt work)

Jay from GC

Where can I find out more about the use of bumpstops?

justin

[StartupJunkie]

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

[Speediance]

I forgot to mention, I'm in the Santa Clara/Sunnyvale area for the most part. Seems like quite a few people live in Cupertino.

[Chowbow]

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.

[Speediance]

WOW! Who changed the title of my post? It used to be "Ground Control + M3 Conversion (long & lots of pics)" ??!! Its not bad, just curious...

[JM3]

Originally Posted by Speediance

WOW! Who changed the title of my post? It used to be "Ground Control + M3 Conversion (long & lots of pics)" ??!! Its not bad, just curious...

They might not know that Ground Control is a supporting vendor. I didnt use the company name as a user name

JM3 from GC

[335togo]

How much $$$$ for all this....Fun...I mean work...just curious