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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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      03-24-2009, 12:35 PM   #45
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its fine... as long as everyone learns something . OP have u been able to do more testing with ur new M swaybars? I wonder if this is the route i should go too...
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      03-25-2009, 10:47 PM   #46
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Quote:
Originally Posted by Mr. 5 View Post
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.
The margin for error is too great doing it this way and I’m sure something is not right with your recent re measure. We also need another formula to do this. It is too painful for me to explain in simple terms. If you get the right info I will calculate the rate with a small margin of error. Then I will show you the math which makes it all clear.

The information you need is on the straight length of the spring. Count the number of coils and mean diameter. On any lengths with changing mean diameters you will need to measure the mean diameter at the being and at the end of on one full coil until you have measure them all.

It would be easer if you marked up and picture to show this so I know you got all the information correct.

Edit: Tip, rig the spring with a string down the center line to measure the raduis....be a bit creative like this to get good measurments. The paint thickness will be about 0.003" x 2 so remove this from the wire diameter and round to the nearest x.x mm

Orb

Last edited by Orb; 03-26-2009 at 01:47 AM.
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      03-25-2009, 11:45 PM   #47
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Quote:
Originally Posted by Orb View Post
The margin for error is too great doing it this way and Iím sure something is not right with your recent re measure. We also need another much bigger formula to do this. It is too painful for me to explain in simple terms. If you get the right info I will calculate the rate with a small margin of error. Then I will show you the math which makes it all clear.

The information we need on any straight length of the spring you count the number of coils and mean diameter. On any lengths with changing mean diameters you will need to measure the mean diameter at the being and at the end of on one full coil until you have measure them all.

It would be easer if you marked up and picture to show this so I know you got all the information correct.

Orb
Will do. Thanks.
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      03-27-2009, 04:27 PM   #48
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"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."
Orb,
Are you saying that switching to lighter weight wheels and non-rft tires with ths zsp would adversely affect handling/ride instead of improving it?
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      03-29-2009, 01:43 AM   #49
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Quote:
Originally Posted by cvc 22349a View Post
"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."
Orb,
Are you saying that switching to lighter weight wheels and non-rft tires with ths zsp would adversely affect handling/ride instead of improving it?
This is not exactly what I was implying. There is just not a lot room for addition stiffness with spring or sway bars. Dump the RFT and the car grip improves but you start noticing how sloppy the stock dampening is. Lighter wheels increase suspension frequency slightly. These changes are tolerable but doubling the spring roll bar stiffness is another story.

Orb
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      04-26-2009, 08:02 PM   #50
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Will the M3 sway bars fit the XI?

Does anyone know if the M3 front and rear sway bars will fit the 335XI?

I'd love to know if they will work on my car.

Thanks.

Gumpy.
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      04-26-2009, 10:02 PM   #51
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Quote:
Originally Posted by gumpy View Post
Does anyone know if the M3 front and rear sway bars will fit the 335XI?

I'd love to know if they will work on my car.

Thanks.

Gumpy.
Just the rear will.
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      04-26-2009, 10:41 PM   #52
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Would the M3 swaybars be much different from the "BMW Performance" kit?

I am guessing the Perfomrance kit would be designed for RFT tyres, so wouldn't be as good with conventional go-flat tyres. True or Flase?
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      04-27-2009, 06:02 AM   #53
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Quote:
Originally Posted by John_01 View Post
Would the M3 swaybars be much different from the "BMW Performance" kit?

I am guessing the Perfomrance kit would be designed for RFT tyres, so wouldn't be as good with conventional go-flat tyres. True or Flase?

The newest BMW Performance Kit only upgrades only the front sway(see attached thread). The M3 sway bars are little different. The rear sway is 20mm.....

http://www.e90post.com/forums/showthread.php?t=230208
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      04-27-2009, 01:51 PM   #54
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Quote:
Originally Posted by mwahlert View Post
i never thought suspension tuning required so much thought.
That's barely anything actually, lol.

I am sure Orb or I could go on for hours about it, but that won't help anyone here. Too bad he isn't local, he would be cool to chat with at meets.

Most of the technicalities were left out, and I am sure he was trying to make it as understandable as possible for everyone else.
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      04-28-2009, 12:38 AM   #55
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Quote:
Originally Posted by Malekreza11 View Post
That's barely anything actually, lol.

I am sure Orb or I could go on for hours about it, but that won't help anyone here. Too bad he isn't local, he would be cool to chat with at meets.

Most of the technicalities were left out, and I am sure he was trying to make it as understandable as possible for everyone else.
LOL, your right…the technicalities were avoided like the plague. I consider what is posted here is page one…the index. I have been waiting for at least one question on spread sheet but not a single taker yet except for Mr. 5. I would have gone to page 2 if some whould have asked.....see my point.

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      04-28-2009, 01:59 AM   #56
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Quote:
Originally Posted by Orb View Post
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.
Orb, Thanks for your post on page 1 of this thread. I probably should have quoted it all because it was such good reading. I can imagine how unpredictable the handling would be with the inside front wheel being lightly loaded. There a couple of areas where I have some quetsions if it ok for me to ask.

From reading your post, one aspect that controls the car's pitch is the balance of resonant frequencies between front and rear. If all else is equal, it seems the front sway bar should not affect pitch because it can not apply any net vertical force to the front of the car. Correct?

You wrote about a potential lack of damping in roll due to the stiffness of the sway bar. I am wondering how the roll damping should be analysed. Doesn't it mean we need to consider the angular momentum of the car as it rolls? Is it reasonable to assume the roll damping was correctly tuned in the factory setup?

When adding a front sway bar, would it be a good idea to add both stiffer front springs and dampers to avoid changing the ratio of resonant frequencies between front and rear?

If front and rear sway bars are used to make a balanced setup, isn't the car likely to be underdamped in roll or overdamped in pitch, or is it less important for a balanced setup?
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