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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Thu, Sep-27-2018, 04:43:30 PM   #51
10speed
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Shaikh,

In regards to sway bar elbow length, are you measuring bend center as the center of the heel on the elbow 90?

(Also running a GC bar front, It's 32mm diameter, just need to measure the wall thickness.)
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Old Fri, Sep-28-2018, 03:07:00 AM   #52
ShaikhA
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

10Speed - for arm length, these sway bar stiffness & FRC calculations are using the perpendicular projection, dim A in the image below:



In contrast (and for convenience) just now I jacked up the front and measured along the arm of my current GC front Race bar, getting an arm length of ~251mm. This is to the center of the clamp. Granted, that's likely 5-7mm longer than dim A would be. The end link/sway bar clamp is right against and outside of the the nub on the bottom of the GC Race bar. This is the 'indexed soft' bar setting.

So that can be a consistent reference position for us: either softer than or stiffer than the nub. A position on the inside of the nub - the 'indexed hard' position - would end up with an arm length of ~214mm which would be mighty stiff, ~23% jump in roll stiffness on a racing setup.

I need to update a few values in the second section of the E46M3 spreadsheet and at that time will include the new measurements for Christina's current 'Track' setup.

If you want to provide a pair of reference points, we can include your 'current' sway settings & spring rates and then 'after', with Flat Ride. I can make all the edits once you've had some time to test and refine your setup then report back!

By the way, I'm not sure if we've met at Packwood NT (been about 6 years since I've been there) but I love you guys in the NW Region! Best after-event parties ever! BBQ & Karaoke
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Last edited by ShaikhA; Fri, Sep-28-2018 at 03:23:18 AM.
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Old Fri, Sep-28-2018, 02:54:49 PM   #53
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

All good stuff! I will be sure to paint the FSB before I begin changing things up.

--Peter
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Old Fri, Sep-28-2018, 04:28:49 PM   #54
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

I took some measurements last night and my GC bar has a 32mm diameter and 4mm wall thickness. The full length of the arm measurement measured along the arm is approximately 350mm.

Is it possible there are differences between the e46 m3 bar and the non-m3 bar?

Also, I didn't realize that running the endlink clamps on the forward side of the nub was considered the hard setting. Mine is set butted up to the aft side of the nub.

6 years ago was about when I first started campaigning my M3. Packwood is a great location for autocross, isn't it? Oh, and the parties are pretty good too.
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Old Mon, Oct-01-2018, 03:33:24 AM   #55
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

So we just missed each other at Packwood events. Yes, it's a phenomenal site! Huge, with some interesting surface changes to be aware of.

If I said the outer was stiffer (previous page), I spoke incorrectly. The shorter arm length increases bar stiffness by decreasing leverage from the wheel to deflect the bar. So yes, a shorter arm position is stiffer.

The E46 M3 H&R front bar I have here indicates E46 M3 but would fit my 330i. The arm length on the H&R is ~310mm at the outer (softest) hole position and about 270mm at the inner (stiffest) hole position. That's fairly in-line with what you measured. Edge did have to weld in a new bracket when my ~300k mile OE sway bar bracket began to crack (when I was using the Eibach 28mm front bar, BTW!). They could have moved the bar mounting position could shorten up the starting bar length, but the length is within a reasonable range around a stiffer aftermarket bar position.

If you could post a photo from below the car, I can do the same in a day or so and we can compare any chassis differences.

So, if you did soften front springs from 1000 to 500, you may want to bump the front bar to the other side of the nub...

NOTE: Also make sure that with the bar fully disconnected on both ends, you have fairly low friction as you articulate the bar. I've found (which others before me pointed out including Andy Hollis) that sway bar bushing bind is a major cause of cracked / failed sway bar bushing brackets and body work. If someone is running a beefy GC bar, a reinforcement would be a good upgrade to consider. Of course, regular greasing is important, too, plus zeroing out any preload in the sway bar end links. That's sometimes overlooked but contributes to inside wheel lift under braking (flat-spotting, etc.).
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Last edited by ShaikhA; Mon, Oct-01-2018 at 06:36:03 PM.
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Old Mon, Oct-01-2018, 06:55:13 PM   #56
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

I follow you totally on the mechanics of how the sway bar works. I just didn't realize it was part of GC's design for the bar to clamps to be used forward of the nub. I thought that was considered the limit of adjustment. Anyway, good stuff. I'll probably set the clamps on the forward end of the nubs and give it a go.

I'll see if I can get in the garage tonight to get those photos and report back.

2018 setup: (e46 M3, 2860lbs)
800lb/in front and 1000lb/in rear
GC 32mm / 4mm wall / clamps set butted to aft end of nubs (will get measurements)
No bar rear
MCS 2WNR dampers
Approximate ride heights measured center of wheel to fender:
13.5" front
12.5" rear

The new race setup will be running 500lb/in front springs, changed from 800lb/in. Already swapped the springs and reset the alignment to the previous settings.
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Old Mon, Oct-01-2018, 07:06:21 PM   #57
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

10speed - interested in feedback as have a similar set up


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Old Mon, Oct-01-2018, 08:37:05 PM   #58
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

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FCM Elite Ride Harmony suspension spreadsheet for: E46 M3, Shock dyno testing / driving feedback: E46 M3 (with Eric_SMG)

Take our short Ride Harmony survey and earn a credit on FCM Elite Bilstein damper services


Last edited by ShaikhA; Mon, Oct-01-2018 at 08:44:41 PM.
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Old Mon, Oct-01-2018, 09:31:29 PM   #59
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

If I understand this correctly, in monotube dampers like MCS, there is a fixed gas pressure. The level of force required to move the damper shaft will equal the force the gas pressure is providing. In regard to damper models where compression is adjustable, do compression adjustments relate to the gas pressure in any way? When adding compression, do our adjustments simply add to the force required to move the damper shaft?
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Old Tue, Oct-02-2018, 07:11:47 PM   #60
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by 10speed View Post
If I understand this correctly, in monotube dampers like MCS, there is a fixed gas pressure. The level of force required to move the damper shaft will equal the force the gas pressure is providing.
Every standard pressurized damper has an initial gas pressure, yes. The number of nitrogen molecules is fixed, but as the shaft goes into the damper body, the nitrogen chamber volume goes down, which causes the gas pressure to rise. This is Boyle's Law. The amount of gas pressure increase (and resulting measured gas force on the shaft) is generally small, but does depend on how small the nitrogen chamber is and how large the shaft diameter is. On an MCS with 22mm shaft that gas pressure and gas force increase could be quite large. So it's a little dangerous to say 'it's fixed' but I know what you mean. You aren't actively changing the gas pressure of the damper once it's been filled.

Internal to the damper body, the gas pressure has its own force profile and behavior which is independent of the forces generated by the compression valving. Changes to the compression setting (through tightening or loosening the restrictions of the damper adjustment) control the flow rate of hydraulic oil through oil-immersed piston.

In terms of what you feel or can measure at the shock shaft, the nitrogen gas pressure exerted on the shaft's rod area becomes a force pushing the shaft outward. (Rod) Force = (Gas Fill) Pressure * (Shaft) Area. This is also why having a large shaft, which is good for some things like displacing more fluid volume through the piston valves, can have a downside if the gas pressure is too high. This is because now you have a large amount of rod force due to that charge pressure. It's a Catch-22 and illustrates the need to find an optimal shaft diameter and gas fill pressure.

Quote:
In regard to damper models where compression is adjustable, do compression adjustments relate to the gas pressure in any way? When adding compression, do our adjustments simply add to the force required to move the damper shaft?
No, they are independent aspects of the damper design, but in the 'real-world' there is a cumulative effect of gas pressure with compression damping related to how hard it is to push the shaft into the damper body. The presence of any gas fill pressure give a higher effective compression force: total effective compression force = rod force resulting from the gas pressure + force generated by the resistance of compression valving to the hydraulic oil.

The gas pressure decreases the effectiveness of the rebound damping in the same way, because the rebound is trying to keep the shaft/piston assembly of the damper from extending and the gas pressure is trying to extend the shaft/piston assembly.

As I pointed out in another thread but have added the images here, the effect of the gas force, in simple (but not totally accurate) terms is to 'shift the curve upward' toward higher compression forces and lower rebound forces. You 'feel' stiffer compression and softer rebound. If the surfaces were truly glass-smooth, you would notice the 'gas spring' effect of the gas pressure less, but such surfaces don't really exist - not at the microscopic level at least! So along with the 'upward shift' of the dyno curves, there is a FREQUENCY-DEPENDENT effect which can't be detected unless you're using a device that can cycle the damper at small displacement and higher velocities. So the true effect of the gas pressure is only partially visible in standard testing and it's often 'subtracted out' based on certain erroneous assumptions ('if it's much less than your main spring rate, you can subtract it out,' blah blah blah).

=== From this post - EricSMG's custom FCM Elite Bilstein / shock dyno thread ===

Shock dyno graphs illustrating the effect of nitrogen gas pressure. Why isn't gas pressure more talked-about??

Since Eric and I have previously shared shock dynos in this thread, I wanted to add a few more here. Although they're not specific to the E46 M3, the concept (especially the level of nitrogen charge pressure) applies to our BMWs and relates to observations people have made about ride quality and handling behaviors.

I've come to realize how critically important it is to measure and understand the effect of nitrogen gas pressure on a damper's real-world behavior. In this post I'll be more brief and link to two graphs showing damper force vs. velocity with a short discussion. In a subsequent post, I'll go into more detail about why we need nitrogen pressure inside the damper, and what happens if it's too high. In short, you need high-enough nitrogen pressure inside your damper to prevent any dissolved air from 'boiling' and 'foaming' (which reduces the damper's effectiveness) but also you need low-enough nitrogen pressure so you don't 'lock' the damper and prevent the damper from opening!

The graphs below were provided to me by a customer using Bilstein PSS10 on his F80 328 M Sport. He had someone near him perform dyno tests and he asked me to analyze the results and make suggestions on what damper settings and spring rates to use, etc. The first graph has the gas force subtracted, as is the common practice. The second includes the effect of the ~80 lb gas force, which raises the compression force and reduces the rebound force. This is an across-the-board change in the damper's real-world behavior. I've kept the scales the same for both graph so it's apple to apples comparison.



Same damper setting as above, but now gas force NOT subtracted (actual real-world behavior):



High nitrogen pressure and the resulting high gas force has an IMMEDIATE and CONTINUOUS impact on how the suspension tracks the ground. The gas force causes jerk, which is a sudden change in the acceleration of the vehicle. Jerk reduces grip as well as ride quality (grip and ride quality are really synonymous).

Keep in mind that gas pressure of 40 lb or more on our front strut suspensions will feel very stiff because of the high ~1:1 motion ratio of forces from the strut conducted to the wheel (and vice versa).



===

I believe this is one reason why Bilstein eventually designed a check valve in their newer digressive pistons, to help build up MORE rebound low speed force to counteract the 'outward pushing' effect of the gas pressure which reduces low speed rebound and can make a car feel more vague / less controlled in transitional maneuvers.

So you would ideally run the lowest possible gas pressure (where there is no or very little hysteresis and definitely no cavitation) then use your damper settings to properly control the spring you've selected to give you Flat Ride! In which case, you'd need LESS damping than a setup that has pitch.

A final take-away to all this is that the introduction of any gas pressure to a damper makes it an even more non-linear device. Gas pressure creates 'jerk' which suspension engineers say they try to avoid. That vertical offset (ramping STRAIGHT UP from zero force to 80 lb!) that I indicate above produces a sudden and high initial spring rate that is like a high-frequency spring. It's less noticeable at lower speeds and larger road disturbances (although definitely there) but you'll feel it as the speeds go up and the road disturbances get smaller.
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FCM Elite Ride Harmony suspension spreadsheet for: E46 M3, Shock dyno testing / driving feedback: E46 M3 (with Eric_SMG)

Take our short Ride Harmony survey and earn a credit on FCM Elite Bilstein damper services


Last edited by ShaikhA; Tue, Oct-02-2018 at 07:26:37 PM.
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Discussing FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffness) in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)