The redemption of the E32 sport bar

[Hyper]

An E32/750sport 26mm front bar is installed onto an e31/840.
This was done as an alternative to continuing with the stock 24mm bar, or switching to the 25mm 840 sport (aka low-slung Mtech sport) bar or the 27mm CSi bar.
Fyi, the rear definitely got the 17mm CSi bar, and I was not so interested in dialing out understeer, so the front had to grow.
E32 v 840 sport? The e32 was cheaper ($113 v 160, Apr 2013). If I did it over, I'd probably go 840 sport just to follow the factory design but also to avoid a conflict that's detailed below.

*** Myth Busting ****
A dozen years ago one our current members made a causual observation about the e32 vs e31 bar part numbers in the EPC, suggested a significance, warned that the conclusion was untested.
Later, others built on these remarks and eventually asserted as known fact that you can't put an E32 sport bar on a 92+ e31.
Search long enough, and you can also find it said that the two bars are different widths.
Foolishly I didn't use the search function and installed it anyway.

The original logic went like this: According to the EPC...
* The early e31 and e32 share the same stock part number.
* A larger sport bar was available for the e32 since the early years and the PN remained unchanged thru out the MY's.
* Meanwhile the e31 bar changed at the 92 break, and the early e31 chassis is incompatible with this later e31 bar.

Using just this limited information, one is entitled to assume you can't use the e32 bar on the later e31.

Here is my current reality:
The e32 sport bar, that I just now installed easily, has the shape of the later e31/850 bar and not the shape of the earlier e31.

There are several ways to resolve the logical conflict, all unlikely.
Perhaps (!)...
* The EPC was wrong about shared part numbers, and/or the
* The 750 sport model (but not the base) got the Xframe for all MY's.
* Either style bar will fit perfectly on any MY E32/750.
* The E32 sport bar was redesigned but the PN wasn't rolled.
* The bar I now have is not an e32 sport bar. The dealer screwed up and shipped some other bar that just happens to be 26mm.


*** The Bar Exam ***

Here is the bar survey done by Mwrench. From top to bottom: early e31, '92+ e31/850, e31/840, CSi.


Here I overlay the e31/840 bar on the e32 sport bar. Same width, within a half-inch. The e31/840 bar has a straight middle section, for reasons discussed below.
Otherwise, the e32 bar seems to follow the profile of the '92+ e31/850 and CSi bars.


On the e32 bar the end link is roughly 5/8 inch further out from the pivot center.



*** 840 fitment ***

The E32 bar with associated rubber installs into the existing brackets with no conflict to the X-frame.


The additional arm length did not threaten the lower control arm.


Now we come to the one known compatibility problem, which should not be unique to the E32 bar design.
The V12 bars all have the forward kink in the center section, whereas the 840 stock bar (and I presume the 840 sport bar) is straight.
As the suspension and engine mounts compress, the kink on the E32 bar swings upward and collides with a tab cast into the rear of the V8 engine, projecting down about an inch.


This tab looks like it has no useful function, on at least this M60/62 + 5HP24 combo.
Well...I've got a bar to install, so the tab got taken out. Hopefully someday I don't find out I need that tab to, say, align the torque converter.
What have other ppl done with the CSi bar on the V8?

Without tranny


Bar hits tab


Tab removed. Should be ok thru entire suspension travel.

[Timm]

That's great information Hyper, thanks for taking the time to bust a few myths!

[m6bigdog]

Redemption? Myth Buster? To be determined, however I think not.

You will want to check the control arm and swaybar link clearance with the wheel turned to full stop.

IMHO, the E-32, 26mm front swaybar (p/n: 31352226379) is really better used on the early model E-31.
My personal preference is to only to use the most compatible BMW ”BOLT-ON” upgrades.

Since the E-31, E-32 and E-34 have a lot of common parts the opportunity for bolt-on performance upgrades between models and series is abundant if your search is thorough and all variants such as engine and transmission type are included in your compatibility search. Given the desire, almost any part can be retrofitted if you are willing to hack on some parts for clearance or make an adapter. Also, my experience with BMW parts bins has been without exception flawless and I don’t for a minute believe that there has been any change to the E-32, 750 sport 26mm swaybar. I’m not saying that the warehouse doesn’t mix-up parts since I have experienced that one.

I was the individual that originally posted (on Roadfly) the E-32, 26mm front bar was an option for the early model 850. The logic behind this recommendation is still sound as the E-32 & early model E-31 use a common front 24mm bar (p/n: 31351131620), the E-31 M-Sport front 25mm bar (p/n: 31351136056) for the early 850 is used on the E-32, 750iLS and the 26mm bar has been bolted-on to numerous early model 850's without issue. Also, the E-32, 750 with the Sport suspension has common front end parts with non-sport 750’s and the x-frame was never used on the E-32.

As for using the CSi (late model 850) bar on the 840 which also has an x-frame, that issue was resolved quite some time ago by Mwrench and he used a spacer under the bar to prevent the rubbing you observed. (See attaches photo)
840spacer.jpg
For whatever it is worth and that I can see, the EPC’s reference to an E-31 M-Sport kit (p/n: 33 32 9 059 315) is only for the 850/M70/M73 and 840/M60 with reference to the 25mm swaybar p/n: 31 35 1 090 393 used for the late model 850 with x-frame. However, that I can find the M-Sport kit excludes a reference to the 840/M62 and I am aware of some significant differences between the M60 & M62 engine.

Installing the E32, 26mm bar on a 840/M62 is all yours since you are plowing ground un-furrowed by others that elected to use the Mwrench bar spacer and a 27mm CSi bar.

As for the suspension performance upgrade, the E-32 front 26mm bar with a longer arm has an approximate (calculated) 193-lb/in roll rate, which is an increase of only 21% over the stock 24mm front bar (p/n: 31 35 1 090 392), mainly because of the longer bar arms. Comparatively a late model stock 24mm bar is 160-lbs/in, the M-sport 25mm bar (p/n: 31 35 1 090 393 used with the stock 15.5mm rear bar) will be 185-lbs/in (16%) and the CSi 27mm bar is 253-lbs/in (58%). Given the installation of the CSi rear bar which is 45% stiffer than the stock rear bar you will want to test your cars under/over steer balance to determine if the 26mm bar provides sufficient front roll stiffness at 21% to counter the increased rear suspension roll stiffness by 45%.

[toomanyparts]

Interesting, my CSI bar doesn't rub possibly because the bilsteins make the car sit so high.

[Hyper]

...You will want to check the control arm and swaybar link clearance with the wheel turned to full stop...

Checked it at full lock and its too close to be considered safe. I'll assume you knew this to be true about the early e31 bar.
I will bring both the edge and the hole back 5/8" so that it matches late e31. Easy for me but probably not for others.

I'm finding the 31351090393 bar coming up for the M62 as shown by realoem and bmwfans.
Since its also used on the V12, can I assume that it also has the kink? A picture would be nice.
If it has the kink, then to avoid the tab conflict on the M62, it must be different than the e32 kink.

I'm still left with the unexpected: My 26mm bar, tagged 31352226379, does not match the shape of the early e31 bar.
I guess that's not significant.

[Mike in CT]

A picture.

[Max Lumens]

FWIW, the only significant geometry difference I've found among e31, e32, and e34 front ends is the width of the center section, ie sway bar and center link. e31 is about a half inch wider than e32 which is about a half inch wider than e34. Everything outboard of the frame rails is interchangeable, subject to the limitations you've discovered, thanks. As long as the bushings don't come too close to the bends in the bar, the width shouldn't matter much, as the end links compensate for the minor location difference.

[m6bigdog]

....its too close to be considered safe. I'll assume you knew this to be true about the early e31 bar.
...

I'm finding the 31351090393 bar coming up for the M62 as shown by realoem and bmwfans.
Since its also used on the V12, can I assume that it also has the kink? A picture would be nice.
If it has the kink, then to avoid the tab conflict on the M62, it must be different than the e32 kink.

I'm still left with the unexpected: My 26mm bar, tagged 31352226379, does not match the shape of the early e31 bar.
I guess that's not significant.

You are the first, that I am aware of, that has tried the early bar on a late model chassis however, others have built adjustable swaybars for the E-31 and unfortunately extended the arm length and discovered what you now know; which is, the bar arm cannot be lengthened without causing clearance problems at full wheel lock, I just thought I’d pass that on.

I posted that the “M-Sport kit” is not listed while I was aware the 31351090393 25mm swaybar is.
The EPC is neither a perfect document of the replacement parts for your car let alone the compatible parts for a model/series and it is the cross listings that provided the best confidence. So when I find that only one of the two possible cross listing is valid it may be telling me the part has problems and may not be compatible (like the M-Sport guys tried the kit with the M62 and decided there were issues – however, as you know, the parts are in a parts group listing (image and list of part numbers) for the E-31, year-date, etc, that often spans several model/series (the microfiche had image numbers for each page and the collection of images made up the parts catalog) and if that gets screwed up and it is more often than I care for, you get parts that won’t fit or no parts. Most of the time I find the parts group listing is omitted and you need to find another model/series with the parts group listing to find the part #.

The early and late model bars definitely have a different shapes and I would anticipate the early model bar has more opportunity to interfere since its shape is more exaggerated.
Attached is Mwrench’s profile shot of the 4 bar styles with the CSi bar on the left, 840, late model and then the early bar on the far right. E-31 Swaybars side by side.jpg

[Hyper]

I could tell by your original e32 post from long ago that you are cautious and considered with your assessments.
It was other ppl that extended your conclusions that I had trouble with.

Got it on the EPC kit vs components, and overloaded diagrams.

After Europe I will round out the Mwrench survey by bringing in a 31351090393 25mm e31-sport bar and do a side-by-side with the e32-sport and the e31/840-stock, mount it and check for M62 tab clearance.
I'm detecting from Mike's pics that, while the plan view may be similar, the e31-sport may (?) step down/away from the chassis more than the e32-sport.

By the end of next week I should be able to post my e32 tip mods.

...As for using the CSi (late model 850) bar on the 840 which also has an x-frame, that issue was resolved quite some time ago by Mwrench and he used a spacer under the bar to prevent the rubbing you observed...

I'm a little curious about your choice of word "rubbing", as I found no interference between the x-frame and the e32 bar, and I would call the m62 tab interference a "dead-center collision".
Makes me think that the e32-sport and CSi have a significantly different profile. I suppose I'll have to dig through the RF archives to see what Mwrench was up to.

[Max Lumens]

http://www.mwrench.com/

[Hyper]

Thanks.
I Googled the Mwrench spacer jpeg and got to the RF thread. 10-03-2005, 04:33PM where Mwrench describes the purpose and usage of the spacer with the CSI bar on a '95 840/M60, to avoid "contact with the bellhousing under any loading condition".

Re: my e32 bar fitment, the offending engine tab is located on the upper oil pan (pn 11137513374) which the epc (via realoem/bmwfan) indicates is shared by the M60 & M62.
Since the engine tab was likely present during the Mwrench engineering, but wasn't called out specifically by him, its seems like the my e32 fitment issue is different from his CSi issue.
{edit: On the otherhand, since we know the engineering was done on a '95 it could be it was the 5HP30 rather than the 5HP24, why I'm seeing a different conflict, and that the tab is a remnant of that app.}

I see from the Mwrench site that he was the one trying to do the adjustable bar.

[m6bigdog]

Thanks.
I Googled the Mwrench spacer jpeg and got to the RF thread. 10-03-2005, 04:33PM where Mwrench describes the purpose and usage of the spacer with the CSI bar on a '95 840/M60, to avoid "contact with the bellhousing under any loading condition".

Re: my e32 bar fitment, the offending engine tab...
Since the engine tab was likely present during the Mwrench engineering, but wasn't called out specifically by him, its seems like the my e32 fitment issue is different from his CSi issue.
{edit: On the otherhand, since we know the engineering was done on a '95 it could be it was the 5HP30 rather than the 5HP24, why I'm seeing a different conflict, and that the tab is a remnant of that app.}

I see from the Mwrench site that he was the one trying to do the adjustable bar.

I anticipate the issue you are having is with the shape of the early vs late bar in the mid-section, so what is a rub for others is a dead on collision for you. Also, the 5HP30 was used on all years of the 840-M60/M62

I anticipate you are the first to have installed the early model chassis sway bar on the late model X-frame chassis and therefore you have been confronted with clearance issues (center section and lower control arm) others have not, when the late model X-frame CSi 27mm swaybars are installed with the M60/M62 engine.

No, No! Mwrench had nothing to do with the adjustable bar!!!
Mwrench has exceptional technical knowledge and abilities, is a trusted friend of the E-31 community, at times has worked tirelessly to create technical solutions and most of all resolve/refereed technical issues on posted topics to prevent the whole thing from going down the truth-lost-in-the-noise Rabbit Hole!! The bar issues you see on his site is a small but significant example of his work to support the E-31 community.

For clarification, the individual that developed the adjustable K-Bars for profit, that was a dead on collision (example on Mwrench’s web site) with other suspension members was Greg K. He was/is an Intellectual Property Attorney/Practitioner and part-time seat-of-the-pants chassis tuner/mechanical engineer profiteer.
IMHO, the two occupations were incompatible especially since his knowledge of ground vehicle dynamics engineering and chassis tuning was questionable at best and when confronted he considered his knowledge Intellectual Property backed up with ramblings of seat-of-the-pants track-tested results and proof of concept. Greg K offered E-31 suspension upgrade services in his shop for profit - using the H&R spring set (F&R), Bilstein sport strut inserts/shock and his custom made K-Bar with the Roadfly messageboard as the advertising medium to the E-31 community. The swaybar suspension collisions were resolved with future generations of the K-Bar, however the unresolved dealings with those that put trust in his honesty and effort are well documented on Roadfly. Hence, the relationship between Greg k and E-31 community ended.

[Hyper]

Checked it at full lock and its too close to be considered safe...

This is my final report on the E32 sport bar fitment, and I've changed my assessment.
My initial assessment regarding clearance was with the vehicle on the ground, tire installed.
As you can imagine it's difficult to get an eyeball in there, but looking forward from the rear, it looked marginal and that's what I reported.
Today it was my intent to modify the arm length to bring the arm length back to that of the late e31 bar.
I had already thought about the method options and welding supplies but Step One was to document the "before".

So now that the car is up and the tire off, I can look straight down on the gap and the situation is looking acceptable.
Here is the left side at full extension at full right lock, an highly unlikely condition to begin with, and the clearance is 0.280". Same story, other side.
I don't see that gap closing significantly under braking or acceleration, because at this steering angle the control arm and the end link don't move forward & aft independently.
However with the longer arm, it seems like the suspension geometry would be slightly different from stock design as steering goes towards to full lock. Another topic.





So as far as clearance is concerned, IMO it looks like the bar is good to go, off the shelf without mods.
Since there can be car-to-car variances, especially on repaired cars, check your clearance to your control arm full lock.

I'm taking the tip mod off my ToDo list.
If you do decide to move the end link hole the procedure should be to partially fill using welding rod, and either drill or file.

If you have the V8+5HP24 (from 9/1996), cut back the oil pan tab to definitely avoid any contact with the middle kink.
You may need a different solution with the V8+5HP30, perhaps the Mwrench spacer, but I don't know, haven't seen the situation personally.

[m60power]

Apologies for bumping this thread from the dead...

Does anyone have pictures of the 31351136056 front sway bar mentioned above? This is the E31 M-Sport sway bar for the early 850 up to 4/1992 production date and the E32 750iLS.

I've searched on forums, google, etc. and had no luck finding photos of this bar. I'm trying to figure out the 'routing' of this bar in the center section. I'm ultimately looking for a 25mm or 26mm OE front bar for an e32 740 with getrag 6-speed that won't interfere with other hardware... I've been cross referencing part numbers for e32, e31, and e34 front sway bars (some are still available from BMW, some are now NLA), but ideally looking for a suitable e32 or e31 bar because the e34 front bars seem to be a narrower overall width.

[Hyper]

Apologies for bumping ... 31351136056... E31 M-Sport sway bar...

My quick review of this thread and contributing sources concludes, in agreement with you, that this bar was camera shy.
I'll assume your interest in a e31 specific item is due to overall NLA's.
This scrambling is our future, trying to keep older platforms repaired and updated.

[m60power]

My quick review of this thread and contributing sources concludes, in agreement with you, that this bar was camera shy.
I'll assume your interest in a e31 specific item is due to overall NLA's.
This scrambling is our future, trying to keep older platforms repaired and updated.

Haha, yes; the amount of e32 (and e34) parts that have gone NLA in just the last few years drives me crazy.

Your assumption is accurate, some of the 'usual suspects' for upgrade E32 bars are NLA so I've done some deep dives into the ETK to try and understand all of the potential sway bar options, including e31 and e34 variants that might be a good solution.

It turns out there are quite a lot of different bars depending on model and specific configurations. There are a handful of part numbers I wasn't previously aware of, including specific sway bar part numbers for EDC equipped cars, and even different variants between EDC auto and manual cars (which makes sense based on the hardware clearances with the 5hp30 auto and its oil cooler, for example). I've compiled a list of potential bars so it's a matter of filtering by what's still available from BMW then making a best-guess at fitment on my particular car (based on any info I can find)...

I also switched to the larger under body air guide (p/n 51711969484) when I swapped in the 420g 6-speed, which only fits with some sway bar variants, however I won't use that as a hard constraint for sway bar choice.

Also - thank you for all the pictures and info you provided in this thread; your experimentation on sway bar fitment helped me gain some knowledge on things I hadn't previously thought about.

[m60power]

Hyper, In one of your above posts you mentioned you were going to compare the 26mm E32 bar with the 25mm E31 M-Sport bar, p/n 31351090393:

After Europe I will round out the Mwrench survey by bringing in a 31351090393 25mm e31-sport bar and do a side-by-side with the e32-sport and the e31/840-stock, mount it and check for M62 tab clearance.
I'm detecting from Mike's pics that, while the plan view may be similar, the e31-sport may (?) step down/away from the chassis more than the e32-sport.

By the end of next week I should be able to post my e32 tip mods.

Did you ever end up comparing the 25mm E31 sport sway bar, or checking if that bar would still interfere with the tab at the back of the V8 engine in your car?

Interestingly, that E31 25mm sport bar (31351090393) comes up in the ETK as applicable to post 4/92 m60, m62, and m70 engine E31s, both auto and manual... I wonder if it actually fits on m60/m62 cars because those engines have that tab at the back of the oil pan, and 'Mike in CT' posted photos above showing that this sway bar has a forward kink in the middle:

25mm m-sport bar.JPG

I would expect m60/m62 cars would need a 'straight' center section like the original bar in your 840. My e32 740iL has the m60 engine with that same tab at the back of the oil pan where the engine mates to the getrag transmission. (Note that the clearances in that immediate area were also the same when I had the 5hp30 auto trans in the car). I'm trying to gain as much knowledge as possible on the various sway bar options before I go off and buy 3 or 4 different sway bars just to see what fits...

[Hyper]

Did you ever end up comparing the 25mm E31 sport sway bar...

No, and then had my geek credentials revoked.

...I'm trying to gain as much knowledge as possible on the various sway bar options before I go off and buy 3 or 4 different sway bars just to see what fits...

Often it comes down to this, to cut thru misinformation and wrong assumptions.

[Auraraptor]

I ended up with a CSI 27mm front and Kmac 19mm rear on my 97. Not the cheapest solution but I need to tone that understeer a bit.

[m6bigdog]

My quick review of this thread and contributing sources concludes, in agreement with you, that this bar was camera shy.
I'll assume your interest in a e31 specific item is due to overall NLA's.
This scrambling is our future, trying to keep older platforms repaired and updated.

The Naked truth..E31 Bars on Camera!! Credit to Mwrench http://www.mwrench.com/Whitepapers/
The early E31 and E32 front bars are the same formfactor and P/N in common. https://www.realoem.com/bmw/enUS/par...&q=31351131620
Once the X-frame was added 4/92 the front swaybar arm was shortened, however the early bars have been installed on the X-Frame chassis.
The rear swaybar formfactor was changed in 9/92 when the rear subframe was changed at the front diff mount.
The image of the front swarbar mount with the aluminum spacer is the upgrade to install the CSi bar on an 840 chassis.

FWIW,
Swaybars are the suspension element designed to mainly balance the suspension front and rear roll stiffness (under/oversteer propensity) and increasing the bar stuffiness on the wrong axle can lead to a vehicle that can easily become uncontrollable (stops turning) during aggressive steering maneuvers.
My knowledge of the E31 suspension in stock form as well as most vintage 80-90's BMW's (E24, E28, E32, E34) is they are an understeer bias suspension in stock form and needs a rear swaybar upgrade rather than front.
If the spring rates are upgraded from stock rates the suspension roll stiffness must be evaluated to determine the under/oversteer balance and at which axle the swaybar increase is needed most.

[m60power]

m6bigdog - thank you for those attachments, the mwrench link, and the excellent info! That comparison really helps visualize why the late model x-frame cars have shorter front sway bar arms than the early cars (or E32 bars).

FWIW,
Swaybars are the suspension element designed to mainly balance the suspension front and rear roll stiffness (under/oversteer propensity) and increasing the bar stuffiness on the wrong axle can lead to a vehicle that can easily become uncontrollable (stops turning) during aggressive steering maneuvers.
My knowledge of the E31 suspension in stock form as well as most vintage 80-90's BMW's (E24, E28, E32, E34) is they are an understeer bias suspension in stock form and needs a rear swaybar upgrade rather than front.
If the spring rates are upgraded from stock rates the suspension roll stiffness must be evaluated to determine the under/oversteer balance and at which axle the swaybar increase is needed most.

Yeah I'm with you on this sentiment, and I recently posted some thoughts about the handling balance in a thread on the e32 subforum - My e32 740iL cars and my old e34 540 (in stock form) all 'push' or plow the front end when aggressively thrown into a tight corner, like BMWs typically do at the limit. If you turn in too hard the front understeers; you need to lower the corner entry speed and be heavy on the throttle for initiating oversteer. On one of my 740s I've installed rear H&R sport springs that are ~22% stiffer than the stock rate, a larger E32 M-Technic rear sway bar, and powerflex rear subframe bushings. The entire front suspension of that car is currently unmodified from stock. It handles completely different (in a good way). The cornering balance is actually fantastic and I can aggressively chuck it into a corner and there's no pushing of the front end; the car has a tiny lick of oversteer, and when you roll on the throttle in the corner the rear end predictably steps out in a graceful slide with minimal body lean. I'm also running equal width front and rear tires.

Technically, I'm probably reducing the total potential grip of the chassis (at least in the rear) by stiffening up the rear end compared to the front, but it's definitely much more fun to drive it like that. I've actually now been debating whether or not to install a slightly stiffer sway bar on the front end as well, because that might ruin the currently excellent balance, especially once I have the stiffer H&R front springs installed too. I have a pretty thorough suspension spreadsheet for calculating front and rear wheel rates, ride frequencies, roll stiffness / roll couple, etc... I'll be running those numbers to make sure I don't get too far off from optimum chassis handling.

[m6bigdog]

Technically, ...I have a pretty thorough suspension spreadsheet for calculating front and rear wheel rates, ride frequencies, roll stiffness / roll couple, etc... I'll be running those numbers to make sure I don't get too far off from optimum chassis handling.

Way cool!! My Man...
My vehicle suspension dynamics spreadsheet is over 30 years old (I started with Lotus 123).
I've purchased several suspension engineering software packages over the years however they become obsolete with OS upgrades and staying current is way too expensive.
Also, the more advanced suspension engineering software is way too expensive for a amature.

While I'm not a Mechanical Engineer, have had help from many, I know I have more than several thousand hours of studying and calculating the "Fundamentals of Vehicle Suspension Dynamics".
The big deal is getting the suspension geometry and spring rate numbers correct for an accurate wheel rate; as you know "garbage-in-garbage-out".

IMHO, the most overlooked behaviors of vehicle suspension dynamics is Bounce/Pitch motion. The interaction between the front and rear wheel rates. Why? because it is a complex concept requiring an iterative process to calculate.
While it is impossible to calculate the true dynamics of vehicle suspension in an Excel spreadsheet the static suspension calculations are a huge step in producing a performance upgrade that actually works and sorting through the aftermarket "not-so" performance upgrade products.
Half-Car model would dictate the rear wheel rate must be greater then the front for controlled bump recovery. Also, this is the suspension model BMW uses in their suspension design.
Attached are the results of my Bounce/Pitch Frequency and Motion Center calculations for the E31 suspension with the various spring options.
The spring upgrades that are more vertical and cluster around the graph center are optimal (i.e., Stock, CSi. M-Sport, Dinan, H&R Front with M-Sport Rear).
The spring upgrades that are horizontal with the bounce center value off the graph may have acceptable ride quality but are not as good for cornering stability (H&R, AC Schnitzer, Eibach).
IMHO, this is the definitive calculation for the functional "performance" spring rate upgrade.
Ride quality is good however it is a subjective dynamic; where cornering stability is the true proof of the suspension performance.

[m60power]

Way cool!! My Man...
My vehicle suspension dynamics spreadsheet is over 30 years old (I started with Lotus 123).
I've purchased several suspension engineering software packages over the years however they become obsolete with OS upgrades and staying current is way too expensive.
Also, the more advanced suspension engineering software is way too expensive for a amature.

Oh wow, that's awesome! Suspension calculations before Excel even existed haha!

Yeah I'm by no means a suspension dynamics expert, I just know enough basics to be dangerous. I figured static calculations and front/rear ride frequencies are enough for rough understanding since I'm not totally redesigning the geometry of the e32's suspension. I definitely want to make sure I keep the rear axle ride natural frequency higher than the front axle, but I certainly haven't gotten down into the weeds enough to know what would be the 'optimum' percent difference between front and rear frequencies. Probably depends a lot on what speed range the car is driven at most. The other thing I want to pay attention to is spacing the lower control arm / thrust arm / steering rod knuckle off the bottom of the front strut by an amount close to how much I end up lowering the front end (in an effort to not deviate too much from the intended suspension geometry under compression and rebound when using a lowering spring).

Thank you for those pdf files and data points! Yes, in the E34 / E32 world I have also found it quite interesting how so many people install these aftermarket 'sport' spring kits or coilover kits that seem to almost always have a much much higher spring rate in the front than the rear, which is quite the opposite from how BMW designed the suspension for these vehicles too...

[Fatandre]

Thats interesting.
My car is running the x brace that my mechani added along with the early sway bar. That seams to sound pretty bad to be honest.

[m6bigdog]

Thats interesting.
My car is running the x brace that my mechani added along with the early sway bar. That seams to sound pretty bad to be honest.

Actually not.
Hyper confirms the X-Frame and early E31 swaybar is a compatible setup.
The early swaybar is a common part used on the E31/E32 chassis, as are a few other front end parts.
Also, for grins, the X-Frame is a compatible upgrade for the E32 & E34 chassis. Hence there is more competition for the X-Frame than just an upgrade for the early model E31!!

FWIW,
#1 priority - select F & R spring rates for the desired ride quality, ride height and maintain the Bounce/Pitch correctness.
#2 Priority - select F & R swaybar sizes to correct the roll stiffness for a somewhat neutral steer and the E31 never installed a 26mm bar from the factory, not even with the M-Sport Low-Slung suspension.
Reality - Not bad or good - Just Reality - the E31, 5-link rear suspension includes a passive rear roll steer geometry, reactive to lateral cornering forces and increasing chassis roll-stiffness limits the function of this passive rear roll steer geometry.
The attached document includes an English translation of the German description of the lateral acceleration vector for the E31 5-Link suspension - roll steer diagram.
BMW AG Press release (URL Below) - "BMW Integral Rear Axle" explanation of the E31 5-Link suspension: Anti-Dive, Anti-Squat and passive rear steer. Complements of Wuffer:
https://www.wuffer.ca/_files/ugd/060...b82ae2b437.pdf