Anyone make a Rear Shock Tower Bar for the e90/e92m3??

[mastek]

Tried the usual suspects but came up empty handed.

It always helps to brace the chassis anywhere you can -- no matter how strong they claim this body is ..over the last design

[Mr. Wata]

Originally Posted by mastek

It always helps to brace the chassis anywhere you can

No, it doesn't.

A rear strut tower brace will just be dead weight on this chassis, as there is no load introduced on that plane.

[mastek]

Originally Posted by Mr. Wata

No, it doesn't.

A rear strut tower brace will just be dead weight on this chassis, as there is no load introduced on that plane.

no twist load at the rear shock towers on a front engine/rear wheel drive car??

[Mr. Wata]

Originally Posted by mastek

no twist load at the rear shock towers on a front engine/rear wheel drive car??

What is this "twist load" that you speak of? The strut towers do not take any lateral load on the rear of a E9x chassis.

The engine placement and drive wheels are not nearly as relevant as the suspension design. I'm sorry to rain on your parade if you merely wanted a strut bar for bling, if so, please carry on. But as far as function goes, you don't need it.

[swamp2]

ACS makes one. I got in a huge argument with them about all sorts of points, how it is manufactured, the design flaws, etc. Follow the fun here.

[1MOREMOD]

swamp i just read that other thread for almost an hour. pretty funny stuff. i always wonder about the products we are sold. thanks for your input.

[mastek]

Originally Posted by Mr. Wata

What is this "twist load" that you speak of? The strut towers do not take any lateral load on the rear of a E9x chassis.

The engine placement and drive wheels are not nearly as relevant as the suspension design. I'm sorry to rain on your parade if you merely wanted a strut bar for bling, if so, please carry on. But as far as function goes, you don't need it.

The "twist load" i speak of ... is the torsional flex an empty area of a car's chassis, like that of the rear trunk pass-through, under the rear parcel shelf/deck will experience under a 1G+ load powering out of a turn.

This is why the race versions of the e90/e92 chassis receive extensive weld-in roll cage configurations in that area - to stiffen and prevent any chassis flex under extreme loads.

Try to be less of a dikc in your replies - and help some of us that are obviously not as smart as you understand this.
Better yet, hopefully someone with less attitude can chime in.

[mastek]

Originally Posted by swamp2

ACS makes one. I got in a huge argument with them about all sorts of points, how it is manufactured, the design flaws, etc. Follow the fun here.

So ive read through 109 posts of that thread and walked away with this:

- according to the 'box-design' of the rear-trunk pass through area - it is not necessary to brace the two shock towers, as that area and the rear upper parcel/shelf deck already reinforce the said area .... (Please correct if im wrong)

- i noticed the brackets are bolted into sheet metal ...and not a structural, load-bearing support. That would seem to be the 2nd biggest problem in THAT particular design.

- the single bolt through the bar - lying on the bracket bridge acts as a pivot point ... but does allow the two shock towers to move horizontally in-unison.
I understand the 'pivot point' on this design to be useless in preventing vertical motion -- but doesn't that apply to ANY rear shock tower design -- even a solid one -- any rear shock tower design that does not feature a third mounting point (triangle) would be victim to this ... one-piece ..or 3-piece.
So is the point of a rear shock tower bar to unite the 2 towers in horizontal motion ... keeping the upper part of the rear suspension solid ... while the lower portion of the rear suspension acts independently Left to Right?? ...rather then preventing vertical motion as only a triangle-design or race car cages provide??

- im a driver - not an engineer ... but ive had to deal with engineers at the factory and paddock all my life ....and the differnence between a race engineer with humility and without can make or break a teams success to build a better performing race car.
its easy to say - the parts of your brains that were reserved for people skills have been flooded with CFD data and other various ME tidbits ....so take it easy on us laymen, drivers, rest-of-society, etc ...were not retarded ...just need help understanding this stuff.

[swamp2]

I think you understand things pretty well.

Let me add a couple comments since you seem interested in more details.

Originally Posted by mastek

- according to the 'box-design' of the rear-trunk pass through area - it is not necessary to brace the two shock towers, as that area and the rear upper parcel/shelf deck already reinforce the said area .... (Please correct if im wrong)

Nothing is ever wrong with some more strength and stiffness it is just that in this particular design it might be like trying to stiffen a steel beam with a popsicle stick.

Originally Posted by mastek

- the single bolt through the bar - lying on the bracket bridge acts as a pivot point ... but does allow the two shock towers to move horizontally in-unison.
I understand the 'pivot point' on this design to be useless in preventing vertical motion -- but doesn't that apply to ANY rear shock tower design -- even a solid one -- any rear shock tower design that does not feature a third mounting point (triangle) would be victim to this ... one-piece ..or 3-piece.
So is the point of a rear shock tower bar to unite the 2 towers in horizontal motion ... keeping the upper part of the rear suspension solid ... while the lower portion of the rear suspension acts independently Left to Right?? ...rather then preventing vertical motion as only a triangle-design or race car cages provide??

The faulty pivot design allows more of a out of unison motion of the rear towers - the natural response to a torsion or twisting on the rear of the unibody. A solid design (of some sort) is much better at resisting this type of motion

Originally Posted by mastek

- im a driver - not an engineer ... but ive had to deal with engineers at the factory and paddock all my life ....and the differnence between a race engineer with humility and without can make or break a teams success to build a better performing race car.
its easy to say - the parts of your brains that were reserved for people skills have been flooded with CFD data and other various ME tidbits ....so take it easy on us laymen, drivers, rest-of-society, etc ...were not retarded ...just need help understanding this stuff.

There are actually a lot of engineers and scientists who really know their stuff, can talk about it and can even explain it to non technical folks. Not all engineers are like Milton from Office Space...

Cheers

[JCtx]

Hey OP, the better question is this: Are you such a good driver that you NEED extra bracing? Do you feel the effects of flexing while driving, or were just wondering if they're needed? Two different things.

As an engineer myself (NOT an automotive one though ), I would never say our car doesn't need bracing. The reality is probably close to this: The M3 does not need bracing for maybe the 95th percentile of owners driving STOCK CARS (remember bean counters rarely let engineers get away with what they want). And even if it's the 100th percentile, the key word is STOCK CAR. Once you even switch to stickier tires, introducing higher cornering loads, it's a different ball game IMO. And the more you mod the car (power, brakes, suspension, etc), the more likely you're going to introduce unwanted flex. The key is knowing WHEN the extra weight and expense of extra bracing actually improves your lap times. Good luck with that . Few drivers have the 'developmental' skills to know that, and that's why you have race teams.

I feel we have 2 issues here: one is the car, and the other the driver. I can drive a race car and wouldn't stress it even remotely close to its limits. We know a race M3 needs the bracing, so the first question is how modded is your car from stock (1) to race (10)? Then how good of a driver you really are, from no racing experience (1) to a world champion (10)? In racing, you don't want anything you don't really need IMO. Interesting discussion, and very valid subject as well . Good luck.

[jah29]

The springs and the dampers connect to the chassis in different points. You can easily access the damper mounts in the trunk of the car, and it would be very easy to create a "strut" bar between these two points. Unfortunately it is more important to have a brace between the two mount points for the springs.
This is less easy to do, because the mount point is not visible in side the trunk. You'd probably have to locate the area above the springs and weld something in.

Even before you start bracing things the flexy-est point in the rear suspension would be where the subframe mounts. You will notice a big stiffness improvement if you replace these four bushings with firmer, or even solid mounts(ride will be horrible). The 335/135 guys have been upgrading their subframe bushings with the M3 ones with a huge improvement in handling stability. Follow their lead and go even further. I think turner and/or bimmerworld sells the parts.

[swamp2]

^ A fine point. This only reinforces my prior comments and those of others. The system (suspension, body, braces, mounts, etc) as a big system of springs. It makes no sense to swap out the stiff parts if the flexy parts are left untouched. Further evidence agains this mod from my perspective.