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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > M3 Sways, Front and Rear!!



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      03-21-2009, 09:09 PM   #23
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Originally Posted by mwahlert View Post
i think i am just going to stuff the street comforts in - your right - i'm not sure i will even be happy at that point.....so before i spend an additional 1200 bucks on roll bars, etc, etc i should make sure i'm close to happy w/ the feel of the car.

i change cars very very quickly....i am 24 and this bmw is my 14th car....i have had 5 in the past 2 years alone.

i love this car and the power plant but always have the urge to try something else (135, or m3). maybe used m3 will be available soon with DCT and i can upgrade. there are always used c6 vettes and 09 cts-v's should be available used soon too.
At the end of the day it your call so if you guess wrong it’s fixable either way. I did warn you about the street comfort may be to stiff. The only way to know is to try them. The 135 would suck as it worse that the e9x…..M3 seems to fit your needs for ride quality at least and it will do a very good job at it more than most cars. Vettes…ah bone jarring comes to mind.

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      03-21-2009, 11:50 PM   #24
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Originally Posted by stressdoc View Post
I think Orb made an excellent suggestion: test drive a M3 with EDC. Alternatively, you could get the Bilstein EDC for your 335, which are fine for the street. Street comforts should be OK too.

The 335 suspension is engineered for high speed luxury touring on rfts. Some of us go to a lot of time, trouble & $ modding to emulate what the M3 does stock.
You just recommend stuff that will make things a lot worse this guy and I doubt you know why. BTW, the references to clueless in my previous post are for people like you. In fact I put you in top 3. It will not be the first time you blurted out nonsense and then people buy stuff. I later get a PM to help fix it. At what point will you realize you don’t have even the slightest clue about suspension tuning. Most of your comments are speculation based on your own made up thoughts. Some of this stuff is just out there…I mean wacko theories from hell that can not be supported in this universe! Be careful what you say because your costing people their hard earned money and that pisses me off.

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Last edited by Orb; 03-22-2009 at 01:37 AM.
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      03-22-2009, 09:46 AM   #25
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Originally Posted by Orb View Post
At the end of the day it your call so if you guess wrong it’s fixable either way. I did warn you about the street comfort may be to stiff. The only way to know is to try them. The 135 would suck as it worse that the e9x…..M3 seems to fit your needs for ride quality at least and it will do a very good job at it more than most cars. Vettes…ah bone jarring comes to mind.

Orb
i knew going into it that the springs were stiffer but also understood that the compression dampening was softer from what you told me. i have my fingers crossed that it will be what i'm after. i figured that suspension travel was probably just as important as anything else - and i have a very limited amount of travel as it is right now so raising the car a solid 1" + would be very helpful.

the v1's were only borderline too stiff - had i kept them in for a while longer i probably would have just gotten used to them - but my gripe was the limited suspension travel. so hopefully the street comforts will be a good compromise.
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      03-22-2009, 03:09 PM   #26
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The initial reason why I was concerned about the bigger rear sway was because of leftcoastman's issue.
He added only the rear H&R sway and it was a huge difference that caused snap oversteer for him. This issue transfered over to myself (and I believe others) that sway bars are a bad thing.
On top of that, it was even worse for me when we all started talking about front and rear biasing. It made sense to me since I could see the reason for leftcoastman's issues.
I really do want to go bigger in the rear, but I haven't made up my mind with what to do.
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      03-22-2009, 03:24 PM   #27
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Orb, I would have thought that you had learned more from Harold by now.
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      03-22-2009, 04:09 PM   #28
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Originally Posted by Orb View Post
I not sure you will be totally happy with the end results with out taking care of the fundamental bushing problems with this car. As soon as you change the tires, damper, springs and sway bars you going to change how the car behaves as a system. The stock bushings are no doubt finally tuned for the stock suspension and tires. Change one of these variables and it will upset the balance and the tuned frequency of the suspension as system which is expected. In this case, the added stiffness for either stiffer springs or roll bars will add substantial deflection to the bushing which translates into harshness, less traction and more roll. Isolation system like these are very difficult to tune and when they are this soft and you go out of range you actually make things a lot worse and this is indeed the case. I have already made the mistake of trying to tune the suspension with this problem and was futile…it can’t be done. The stiffer you go the worse the problem is and you will hit a resonance frequency with many setups. The offending isolators are the rear sub frame bushing and the tension strut. Replace these items and you have the ability to create a firmer compliant suspension which will exceed the OEM ride quality on non RFT.

Snap over steer is caused by large load transfers at high rate. You are actually more likely to get in trouble with a car that has more understeer as the actually amount of load transfer is more and at a higher rate and it very difficult to recover. Snap over steer is a tuning condition not an inherent flaw in balanced setup. A balanced car allows control of under steer and over steer conditions safely especially give the weight balance of this car. The whole subject is pointless with traction control on or partly disabled. You be amazed how difficult it is to over steer this car under any conditions. In a wet parking lot I tired very hard to over steer the car will traction control partly disabled. It wasn’t until I went full bore into a corner at 60 MPH lift the throttle and then turned the wheel almost to full lock before I could get the ass end to swing out and it was still easily recoverable. I was unsuccessful in losing control of this car after 20 attempts. This was with my H&R bar setup. This is yet another made up problem that doesn’t exists and it is nonsense statement that is never supported!

The whole subject of inside wheel spin is yet another unsupported statement by the truly clueless!!! We have a very high powered car for open differential so traction will always be an issue under acceleration with out a LSD. We have to look at how traction is generated which is by friction and forces on the tire. The friction is the nature of the tire compound while the forces are generated by the weight of the car, load transfer and external forces like acceleration. If we look at this stock car load transfer under a 0.9 G load will see the car has about 450 lbs on force on inside wheel. The same car will M3 roll bars will have about 350 lbs of force on the inside wheel. Give the low forces on the inside wheel we are not gaining much for traction and there not much point looking this as ratio either. The real thing you want to measure against is an LSD. A LSD driven car has 1700 lbs on the out side wheel combined with the inside wheel weight of 350 lbs under no acceleration. When it comes to traction it is in the order of magnitudes difference between the two systems. What does this all mean to open differential. It means you with the stock suspension you put down at extra 35 ft-lbs of torque when compared to M3 roll bar setup….you never put any real power down compared to LSD so you will have accept that you will be a cripple on the track no matter what. On the street not much of an issue in the real world and most will never notice. If we add acceleration to this scenario we naturally increase forces to outside wheel; hence, more traction…not so on the inside wheel so yet another loss for open diff’s.

There are ways to deal with inside wheel spin with open diff but you better be prepared for the nose dive of comprises and ride quality will be as bad as you can get it with no hope of improvement. I really don’t even like discussing this hack but anyone can get this to work with out any for thought. If you put a big enough front bar (28 mm solid or bigger) you will change the way load is transfer which is favourable to help reduce initial understeer (it will still understeer no matter what) and increase the force on the inside wheel. To really get this to work properly you should remove the rear roll bar…yes remove. Most think this will improve understeer and traction because of favourable camber profile but it is not the case it to do with how load is transferred. Your roll is dictated by the sum of reactions from the spring and roll bars as system not discreetly. Rest assured most of the load will be now on 3 wheels not 4 and the inside front wheel will become air born. It will make the car far less stable and you will be susceptible to snap oversteer and massive understeer. The car will never take set in corner so thinking it will is pipe dream but this is okay for autocross. Massive understeer will happen on any bumpy corner but can be compensated with the right dampening but will result in a massive loss in pitch control. Will we need to dig into dampening and roll bars for on a side bar on more negatives of this setup coming next.

One of the key setup parameters of car is selecting the spring rate. Spring rate are selected based on desired natural suspension frequencies. Almost all BMW are set with a natural frequencies 10-15% higher in the rear than the front since it allow for a flat ride. The reason this is so is when you hit bump the front and rear suspension return to static position at the same time. The effect of this setup is that it gives you comfortable ride. Pitch is very important in balancing the car but for most it is the key in giving you great ride quality and you know when it not right because human find it very uncomfortable more than anything else. On a more performance setup we can change the natural frequencies to equal front and rear up to 10% higher in the front. KW would be an exception at they will typically set the front frequencies 10-15% higher than the rear. We can do this on performance setup since with can compensate with dampening to achieve the same flat ride qualities. Spring rates are selected with purpose and for a desired result. For example, I select my frequencies at 4% higher on the front than the rear. My setup gaols was specific, as I wanted the front and rear of the car to take set in corner at the same time with minimal damping influence.

The sway bars have a massive influence on how the car handles in single bump and roll. Many think that coil spring rate have major effect on roll but it not the case unless we are talking about true race cars. The sway bars on average add 3X the stiffness over springs. The effect that sway bars have on the suspension is in single bump and roll. In single bump the stiffness of the sway bar plus the spring is you spring rate. In roll the stiffness of the sway bar x 2 plus the spring rate is your spring rate. For example, a front spring rate is 285 lb/in and the roll bar is rated at 300 lb/in I single wheel bump. The overall rate will be 585 lb/in as the spring rate. In roll, it would be 300 lb/in x 2 plus the front spring at 285 lb/in. The overall spring rate would be 885 lb/in. If we consider the basing of sway bar stiffness front and rear that can change the frequency of the suspension and this will effect pitch and thus ride quality as I already mentioned. We can compensate with dampening but it will affect our pitch control just the same. In the end, we our compromising pitch control vs in roll and single wheel bump. The more unbalanced your car the more you will comprise ride quality and handling.

Sidebar: Back to the big front bar with no rear bar

Now we know something about pitch and sway bar stiffness we understand some of the compromises. If we take the example of 285 lb/in front spring with a big front roll bar rated at 500 lb/in we are going to have a overall spring rate of 1300 lb/in. We are going to have to compensate for this with less compression dampening and a lot more rebound dampening. Guess what….you can not do it. When you drive the car straight it will always be over dampened and in roll in will be under dampened. The car will never take set because of lack of rebound dampening in roll. Okay, throw pitch control in to this equation….we have none what so ever as we had to compromise our dampening to control the car in roll and that was never meet. Think about what 1300 lb/in spring rate will do for traction over bumps. Go with this setup and you can expect very bad ride quality for this magical 3 wheel wonder.

If you want a fun good ride quality car go for a balanced setup. The trade off of small amount of loss of power to the ground out weighs all the compromises for any other setup and is why I will always recommend it.

I would go with the KW street comfort with the M3 roll bars, sub frame bushing and tension struts. Change the rear damping to 1-2 clicks stiffer and possible the front dampening one click softer to correct pitch control.

Orb

LoL I barely understood any of this until the last paragraph. So Orb, in similar fashion as to the way you articulated it on the last paragraph.

What would you recommend for me? I don't care much about the ride being stiffer, so should I then go with the same setup as your mentioned m3 rolls bars, bushings, tension struts, but instead KW V2 or maybe even FK Silverline X with the same settings 1-2 clicks stiffer on the rear and front one click softer? I'm planning for a minimal drop if that helps, so would Street Comforts still be the best solution? Thanks.
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      03-22-2009, 05:20 PM   #29
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Quote:
Originally Posted by mwahlert View Post
i knew going into it that the springs were stiffer but also understood that the compression dampening was softer from what you told me. i have my fingers crossed that it will be what i'm after. i figured that suspension travel was probably just as important as anything else - and i have a very limited amount of travel as it is right now so raising the car a solid 1" + would be very helpful.

the v1's were only borderline too stiff - had i kept them in for a while longer i probably would have just gotten used to them - but my gripe was the limited suspension travel. so hopefully the street comforts will be a good compromise.
I have to give credit for a 3rd setup. Hopefully it has the potential to meet your goals.

Quote:
Originally Posted by Mr. 5 View Post
The initial reason why I was concerned about the bigger rear sway was because of leftcoastman's issue.
He added only the rear H&R sway and it was a huge difference that caused snap oversteer for him. This issue transfered over to myself (and I believe others) that sway bars are a bad thing.
On top of that, it was even worse for me when we all started talking about front and rear biasing. It made sense to me since I could see the reason for leftcoastman's issues.
I really do want to go bigger in the rear, but I haven't made up my mind with what to do.
I do not think anyone cares what you do with your car. I’m sure the vendors will the happy to keep selling you what ever you want for your experiments. You made a bunch of assumption but you have no info to support it either way. You have not even made the slightest effort to educate yourself. I gave you the opportunity to review this analytically but your where foolish enough to delete the file…your loss and everyone else’s. My professional career is based on understanding this stuff. It was not too difficult for me to take this to full blown analysis in MSC Adams simulation package…it has been done for along time now.

I would not give any race car driver any technical credibility as they tend to be have the worst understanding of physics. It was only last year I got my racing license and part of the course was about vehicle dynamics. This well renowned instructor of 25 year made up his own course notes. He also made laws of physics while doing so which was just weird. Many of his idea were okay but he did not understand the basics nor could he link the concepts together. I can tell you it was an embarrassing moment for this guy during the intermission but I took the time to help him straighten it out.

The only thing I know for sure you’re still at ground zero.


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Originally Posted by stressdoc View Post
Orb, I would have thought that you had learned more from Harold by now.
Doc, you’re back to the wacko comments again! What do you think I learned from Harold…really? Your friggen delusional with your of way thinking. At least attempt to educate your self before sending other on a wild goose chase. Maybe just bitch slap yourself or something.

Last edited by Orb; 03-22-2009 at 07:23 PM.
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      03-22-2009, 05:27 PM   #30
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Orb can you answer my question above? Thanks.
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      03-22-2009, 05:57 PM   #31
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Quote:
Originally Posted by GAaaAR View Post
LoL I barely understood any of this until the last paragraph. So Orb, in similar fashion as to the way you articulated it on the last paragraph.

What would you recommend for me? I don't care much about the ride being stiffer, so should I then go with the same setup as your mentioned m3 rolls bars, bushings, tension struts, but instead KW V2 or maybe even FK Silverline X with the same settings 1-2 clicks stiffer on the rear and front one click softer? I'm planning for a minimal drop if that helps, so would Street Comforts still be the best solution? Thanks.
The previous paragraphs lead to the last paragraph so if you got the last paragraph then good enough. Suspension tuning is endless compromises. You need to decide on what you can live with and what the consequences are for are for taking another path. The biggest mistake is making the wrong or just bad assumption form the get go and most do including myself at times.

The street comfort would be a good choice with hardware you selected. The spring that come with the kit are closer to liner and the rear spring is stiffer than the v2 or v3. It would be better to make new thread for tuning options for KW’s but v3 are my first choice with changing the springs to the rate you like while optimizing balance.

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      03-22-2009, 06:51 PM   #32
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Quote:
Originally Posted by Orb View Post
I have to give credit for a 3rd setup. Hopefully it has the potential to meet you goals.



I do not think anyone cares what you do with your car. I’m sure the vendors will the happy to keep selling you what ever you want for your experiments. You made a bunch of assumption but you have no info to support it either way. You have not even made the slightest effort to educate yourself. I gave you the opportunity to review this analytically but your where foolish enough to delete the file…your loss and everyone else’s. My professional career is based on understanding this stuff. It was not too difficult for me to take this to full blown analysis in MSC Adams simulation package…it has been done for along time now.
I don't remember this, so tell me where it is and I'll resurect it.
You have to understand that we don't have the same education and experiences as yourself. I'm sorry that you feel like I'm not any more educated.
BTW, there are a bunch of people that care about what others do to their cars. This is what the forum is about and that is to share experiences.
Edit...
Is this it? I deleted the irrelevant info and also highlighted in bold so we don't get any messages with why the txt version doesn't work.


Quote:
Originally Posted by Orb
A roll bar is a torsional spring that redirect load differently than the main springs. Forget diameter just look at spring rate of roll bar. Why did BMW change the rear bar for M-sport? It is simple the Euro car is lower by several mm and this offset the roll. You should be able to rationalize what 24 lbs of weigh movement in the car would do and what effect it will have. You don’t need the theatrics with the rest of what you said.

The extra M3 parts are not going to change load transfer on 335i. The M3 and 335i share common suspension geometry and we know this as fact now! If you put on M3 roll bar on, which do fit front and rear, you will get close to the same balance as a M3 but biased a bit more towards under steer. It is the closest you get to neutral steer car with BMW suspension systems.

Attached is a load transfer worksheet for BMW 335i. The worksheet is based on many authors (50 years of automotive engineering and know how) but in particular William & Douglas Milliken who are the authors of Race Car Vehicle Dynamics. I selected this as a reference as it is a will know university academic book and recognised by SAE. There should be no nonsense about this so do a bit of homework. Like any calculations the worksheet was verified against testing and statically measured data and with 2-3% or actual even with out perfect data sets. That is 3 points of reference but I am not going to explain this or go into in any details.

What you need to understand before using the worksheet:

1. Suspension frequency: your front and rear suspension have a natural frequency and this is what we care about not spring rate. A typical BMW with have a frequency 10-15% high the rear than the front for flat ride which is perfect for soft sprung car with lighter dampening. As we move to performance setup will see equal suspension frequencies front and rear up to 10 higher in the front than the rear. KW will be the expectation with front frequencies about 15% higher than the rear so they typical use very soft rear spring with their setups.
2. Spring selection: Your spring selection is based on suspension frequencies and you select a range based son spring stiffness and application. If you running a 285 -336 lb/in front spring then you want your suspension frequencies to be close to equal so you can control pitch with lighter damping. If you running 400 lb/in front spring then equal suspension frequencies front and rear up to 3-10% higher in the front than the rear is better.
3. Motion ratio: The 335i motion for the front is 0.96^2 and rear is 0.563^2. The motion ration is squared because we have force and displacement component; hence, lb/in. The motion ratio in the rear is very high for this car. To put it in perspective a 1000 lb/in spring is only about 315 lb/in at the wheel and this is what you feel not the coil spring. High motion ratio like this are very difficult to deal with and all coulomb friction must be eliminated when possible in the joints. Also, the spring must be free to rate on it preaches as even a small amount of binding result in huge spikes in spring rate (use only Swift spring with thrust sheets).
4. Roll bars: This is what balances the car but will have to do some small adjust in spring rates since it not likely will get the perfect bar. We change spring rate based on suspension frequency and application.
5. Roll: You goal is to keep the car under 2 degrees but it okay to have more. You are fighting a car with limited front camber control so it important to make compromises. Do everything you can t run the least amount of front camber within reason. You don’t want to run more than -2 degrees front camber and this goal is obtainable.
6. Tire calculator: One should use this to get sense of changes in load transfer with stiffer spring because it starts to make a big difference. This part of the worksheet is variable and doesn’t take in account for the tire friction curve. However, the effect of load transfer and more predominant and this is useful in making your discussions. Yes, staggered tire setup will induce more oversteer and yet another folk lore dies.
7. The magic number (coined by another respected race car engineer Claude Rouelle) is on the last page in the worksheet and tells you when the car is balanced with a reasonable amount of under steer. You will find this reference on page 605 of Race Car Vehicle Dynamics but its called Total Load Transfer Distribution or TTLTD.
8. You can still make a mess of things with this worksheet so look closely at the loads on each wheel.
9. Damper calculator: It not 100% complete as I did this with MathCAD because excel can’t do it so it is wrong. Damper only matter for the last 10% of tuning so if the previous 90% is not working right then this will not matter. Damping setup is far more subjective than the rest but it can easily be calculated as references stated in John Dixon “Shock absorber handbook”.

What you should only change in the worksheet:

1. Front and rear spring rates
2. Front rear roll bar diameter. If there is no inside diameter leave it blank
3. Weight percentage: 51% for a manual and 52% for an auto
4. G load. It set to 1 G by default

Okay this is enough to keep you busy for a while. I haven’t told you near enough but the point is to get you and other to start digging for the facts. If you do enough research you will quickly find this is not magic or even subjective.

The file attachment is with a txt extension so rename this Excel file to BMW-335i-e92-Full-Calc.xls. You may need to enable this option is windows to see the file extension.

Orb
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      03-22-2009, 09:26 PM   #33
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Quote:
Originally Posted by Mr. 5 View Post
I don't remember this, so tell me where it is and I'll resurect it.
You have to understand that we don't have the same education and experiences as yourself. I'm sorry that you feel like I'm not any more educated.
BTW, there are a bunch of people that care about what others do to their cars. This is what the forum is about and that is to share experiences.
Edit...
Is this it? I deleted the irrelevant info and also highlighted in bold so we don't get any messages with why the txt version doesn't work.
You have to enable view file extensions in windows so it can be renamed. By default you can not view or rename a file extension in windows. It works for me and I’m sure you will figure it out.

You have the skill to do this so do try. This is mathematics and some very basic physic which you already have the training for. You are going to explain to other how to use it when you learn everything.

The roll center needs to be corrected which you will figure out how measure on your own….very easy for math for someone like yourself. The accuracy of the data is within 2% at the moment.

I already gone a couple step beyond this so it not to useful to me anymore. It is all you need to tune a suspension and its in great detail for that purpose. This is what real race team’s use with a real Mechanical Engineer and this is also taught to suspension designers.

The light will go on in few days if you try.

Orb

Last edited by Orb; 11-25-2011 at 01:09 PM.
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      03-22-2009, 10:14 PM   #34
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Quote:
Originally Posted by Orb
A roll bar is a torsional spring that redirect load differently than the main springs. Forget diameter just look at spring rate of roll bar. Why did BMW change the rear bar for M-sport? It is simple the Euro car is lower by several mm and this offset the roll. You should be able to rationalize what 24 lbs of weigh movement in the car would do and what effect it will have. You don’t need the theatrics with the rest of what you said.

The extra M3 parts are not going to change load transfer on 335i. The M3 and 335i share common suspension geometry and we know this as fact now! If you put on M3 roll bar on, which do fit front and rear, you will get close to the same balance as a M3 but biased a bit more towards under steer. It is the closest you get to neutral steer car with BMW suspension systems.
Very good info! I've never read this before.
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      03-22-2009, 11:46 PM   #35
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Quote:
Originally Posted by Orb View Post
You have to enable view file extensions in windows so it can be renamed. By default you can not view or rename a file extension in windows. It works for me and I’m sure you will figure it out.

You have the skill to do this so do try. This is mathematics and some very basic physic which you already have the training for. You are going to explain to other how to use it when you learn everything.

The roll center needs to be corrected which you will figure out how measure on your own….very easy for math for someone like yourself. The accuracy of the data is within 2% at the moment.

I already gone a couple step beyond this so it not to useful to me anymore. It is all you need to tune a suspension and its in great detail for that purpose. This is what real race team’s use with a real Mechanical Engineer and this is also taught to suspension designers.

The light will go on in few days if you try.

Orb
Yah, that's a pretty cool spread sheet.
Based on my calculations, my spring rates (the BMW Performance Springs) are 195 lb/in in the front and 505 lb/in in the rear.
I wish I knew for sure, but I think the calculations are close.
So, by adding both M3 bars will give my car a front WT bias of 5.85%

Stock is 15.6%
Stock with 14mm bar is 14.39%
My car now is 14.7%
Interesting.
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      03-22-2009, 11:53 PM   #36
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Wow, that's a serious spreadsheet. I'd love to learn how to manipulate this into creating a well balanced car for myself.
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      03-23-2009, 12:15 AM   #37
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Quote:
Originally Posted by Mr. 5 View Post
Yah, that's a pretty cool spread sheet.
Based on my calculations, my spring rates (the BMW Performance Springs) are 195 lb/in in the front and 505 lb/in in the rear.
I wish I knew for sure, but I think the calculations are close.
So, by adding both M3 bars will give my car a front WT bias of 5.85%

Stock is 15.6%
Stock with 14mm bar is 14.39%
My car now is 14.7%

Interesting.
Your spring numbers are wrong.....why! Did you include the spring seat and how it affect rate because you have to with open end springs. It is more than 1 full dead coil for the rear. I not sure how you did the front but the same rules apply. Do the front at 1/2 coil at a time in series to calculate. If you are more than 1 mm off then it is no good for the outside diameter. The coil diameter is to power of 4 so you got to remove the paint thickness for the calculation and it a big deal as you know. I say you are out by +/- 35% but could have gotten lucky.

I would suggest you spend some time understanding the math behind this so it makes scene to yourself. You got the end answer so now got back to the beginning. For example, do you know why the motion ratio is squared. The devil is in the details.

FWIW, the spread sheet is not enough. You still have to use good judgement so understanding the basic is the key to success. You can still make a mess of things.

Now what will blow your mind is that staggered setup will induce oversteer which is the opposite what others say. It is a big deal with stiffer racing spring setups.

Like I said before the rear 14 mm bar does nothing so goto the roll bar cacluator to see why. It is a spring with a rate and only deflect 3"

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      03-23-2009, 12:27 AM   #38
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Quote:
Originally Posted by Orb View Post
Your spring numbers are wrong.....why! Did you include the spring seat and how it affect rate because you have to with open end springs. It is more than 1 full dead coil for the rear. I not sure how you did the front but the same rules apply. Do the front at 1/2 coil at a time in series to calculate. If you are more than 1 mm then it is no good for the outside diameter. The coil diameter is to power of 4 so you got to remove the paint thickness for the calculation and it a big deal as you know. I say you are out by +/- 35%.

I would suggest you spend some time understanding the math behind this so it makes scene to yourself. You got the end answer so now got back to the beginning. For example, do you know why the motion ratio is squared. The devil is in the details.

FWIW, the spread there is not enough. You still have to use good judgement so understanding the basic which is the key to success.

Now what will blow your mind is that staggered setup will induce oversteer which is the opposite what others say. It is a big deal with stiffer racing spring setups.

Like I said before the rear 14 mm bar does nothing so goto the roll bar cacluator to see why. It is a spring with a rate and only deflect 3"

Orb
Maybe you can help with the calculations then.
I assumed that the material made up of the performance springs were the same as the ZSP springs.
This was my thread on my measurements here.
http://www.e90post.com/forums/showpo...76&postcount=1
I also assumed that the paint thickness for the ZSP springs were the same as the performance springs.
This was what I used to calculate the springs:
http://www.engineersedge.com/calcula...ring_k_pop.htm

If you already know the spring rates for the T3 and T4 springs then please let us know.
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      03-23-2009, 09:37 AM   #39
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Quote:
Originally Posted by Mr. 5 View Post
Maybe you can help with the calculations then.
I assumed that the material made up of the performance springs were the same as the ZSP springs.
This was my thread on my measurements here.
http://www.e90post.com/forums/showpo...76&postcount=1
I also assumed that the paint thickness for the ZSP springs were the same as the performance springs.
This was what I used to calculate the springs:
http://www.engineersedge.com/calcula...ring_k_pop.htm

If you already know the spring rates for the T3 and T4 springs then please let us know.
Please tell me you did not use the defaults for G on the calculator. The correct number for G= 11.6 x 10^6 for spring steel.

You need good measuring tools which I have access to. You are better off arranging a spring rate test in your local area. While you’re at do a shock dyno. Make sure you include the rubber spring seats as they must be used .

I already knew you had the wrong rate a while ago...I don't expect you to pick on the fine details which make a significant difference.

You can make the assumption that BMW will want to maintain flat ride quality and we know that suspension frequency ratio. You have a tool to make some sense of this so start learning… and your first stop of the day:

http://www.optimumg.com/OptimumGWebS.../TechTips.html (read them all)

Orb

Last edited by Orb; 03-23-2009 at 12:41 PM.
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      03-23-2009, 03:03 PM   #40
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Quote:
Originally Posted by Orb View Post
Please tell me you did not use the defaults for G on the calculator. The correct number for G= 11.6 x 10^6 for spring steel.

You need good measuring tools which I have access to. You are better off arranging a spring rate test in your local area. While you’re at do a shock dyno. Make sure you include the rubber spring seats as they must be used .

I already knew you had the wrong rate a while ago...I don't expect you to pick on the fine details which make a significant difference.

You can make the assumption that BMW will want to maintain flat ride quality and we know that suspension frequency ratio. You have a tool to make some sense of this so start learning… and your first stop of the day:

http://www.optimumg.com/OptimumGWebS.../TechTips.html (read them all)

Orb
No no no.
I put in all of the variables of the ZSP springs and solved for G. That was the only thing that I didn't know so I solved for that.

I had the following:

Given:
460 lb/in

Measured:
d = .556
n = 7 (total - 2)
D = 3.871

So, I got the G to be aproximately 15.6 x 10^6
I then used the same G to solve for the force for the performance springs given the measurements that I came up with.
I kept everything the same because the coils were the same. I assumed that the G is the same.
I changed the d to .581 and D to 3.978 and got my 505 lb/in.

I did the same for the front spring:

Given:
145 lb/in

Measured:
d = .476
n = 3 (total - 2)
D = 5.702

So, I got the G to be aproximately 12.5 x 10^6

I then used the same G to solve for the force for the performance springs given the measurements that I came up with.

I assumed that the G is the same.
I changed the n to 2.25 since there was 3/4 less of a coil.
I changed the d to .506 and D to 6.172 and got my 195 lb/in.

I know that the best way was to get them actually tested but I reallky didn't know where.
I figured that I would do my best with the info that I had to come up with a close aproximation.


I'll read what you gave but it would be nice to know the spring rates with these new springs.
I can tell by feel that the fronts are stiffer but the rears are hardly noticeable.
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      03-23-2009, 11:07 PM   #41
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Orb,

If i purchase KW Street Comforts, do you think its better to purchase the m3 sways after or the bushing and & tension rods before the sways? And should i opt out on the sway bars, would KW Street Comforts, rear bushings and tension rods perform well and have good ride quality?
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      03-24-2009, 09:41 AM   #42
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Quote:
Originally Posted by Mr. 5 View Post
No no no.
I put in all of the variables of the ZSP springs and solved for G. That was the only thing that I didn't know so I solved for that.

I had the following:

Given:
460 lb/in

Measured:
d = .556
n = 7 (total - 2)
D = 3.871

So, I got the G to be aproximately 15.6 x 10^6
I then used the same G to solve for the force for the performance springs given the measurements that I came up with.
I kept everything the same because the coils were the same. I assumed that the G is the same.
I changed the d to .581 and D to 3.978 and got my 505 lb/in.

I did the same for the front spring:

Given:
145 lb/in

Measured:
d = .476
n = 3 (total - 2)
D = 5.702

So, I got the G to be aproximately 12.5 x 10^6

I then used the same G to solve for the force for the performance springs given the measurements that I came up with.

I assumed that the G is the same.
I changed the n to 2.25 since there was 3/4 less of a coil.
I changed the d to .506 and D to 6.172 and got my 195 lb/in.

I know that the best way was to get them actually tested but I reallky didn't know where.
I figured that I would do my best with the info that I had to come up with a close aproximation.


I'll read what you gave but it would be nice to know the spring rates with these new springs.
I can tell by feel that the fronts are stiffer but the rears are hardly noticeable.
I see what you did but it is not very accurate and subject to a lot of error. The springs are conical and barrel shape so you have to measure one coil at a time and then add them in series. Just in case you did not know the “D mean” is measured from the center of wire not the outside diameter. The diameter is to power of 3 some even small change makes a difference so you cannot be guessing or simplifying. No need to solve for G as it’s a given and it did not work out close enough. Remove 1.75 active coils in the rear (close enough). I’m not sure about the front but it is not going to be -2 coils.

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      03-24-2009, 11:49 AM   #43
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Orb, you may have a wealth of information about suspension and setups, but talking down to everyone in your "informational" posts and attacking other members only makes you look like a massive dick. I hope that someone can repay the favor at some point.
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      03-24-2009, 12:34 PM   #44
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Quote:
Originally Posted by Orb View Post
I see what you did but it is not very accurate and subject to a lot of error. The springs are conical and barrel shape so you have to measure one coil at a time and then add them in series. Just in case you did not know the “D mean” is measured from the center of wire not the outside diameter. The diameter is to power of 3 some even small change makes a difference so you cannot be guessing or simplifying. No need to solve for G as it’s a given and it did not work out close enough. Remove 1.75 active coils in the rear (close enough). I’m not sure about the front but it is not going to be -2 coils.

Orb
I'll redo the measurements unless I am able to find a place close to me that has a spring dyno. And, you're correct. I measured from the outside to the outside for my D, so all I have to do is take the thickness of one coil away for it to be more acurate.
Again, I know that this is not the most acurate way to get the spring rates but I wanted to get a pretty good estimation and I actually think that I was close.

I recalculated the rear spring with the more correct D and changed the coils to 1 less coil and the G went to 11.2 x 10^6 which is closer than before. The spring rate only changed to 510 lb/in.

The Front had about the same G of 11.2^6 and the spring rate went to 185 in/lb.

These seem more proportional to the ZSP springs.
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