[Biginboca]

Originally Posted by Torgus

Nice list How do you have full rear m3 arms? Did BMW make an m3 performance suspension? I only ask as I know I had to specifically get m3 rear ohlins for my build.

I have the 2 aluminum upper M3 Arms, the small ones that look like bones you would give the dog lol.

Then main lower arm the spring perched on is the stamped steel oem one, and then the other lower arms (toe and trailing) are replaced (ECS and Manzo).

I installed the BMW performance Suspension before I did the M3 arms swap and like you noticed the shock is made for the mount on the large stamped steel LCA so I didn’t replace that arm with the aluminum one. I don’t think BMW made an M3 performance suspension the M3 suspension was the performance suspension lol

[Torgus]

Originally Posted by tlow98

There is almost always some gain.

Look at some of the crap UltraRacing makes for cars. They make up braces for no good reason. Just because there is a factory bolt/connection does not mean it needs a brace bar. They make braces for things that don't need to be braced all the time.

Originally Posted by tlow98

Take off all the skins in the trunk and you can see why a rear strut brace is useless.

Curious what you mean by this?

It is a metal hole. The wheel wells are braced by the floor. There is literally an L brace from the factory right at the top of the rear strut tower:







[IMG]https://www.***********.com/images/imported/2012/01/IMG_1306-1.jpg[/IMG]




Where the rear strut brace connects:
https://**********s.com/cusco-rear-s...e92-bm5-526-a/



It just replaces a metal bracket that is already there:



The actual shock mount is more into the wheel well area and the bar would have to be much lower to have an effect. Bracing the rear shock towers probably wouldn't yield a significant benefit since they don't support the weight of the car (the springs do). This is unlike the front of the car.

Whatever you do do not connect your 4 point harness to this bar. It will fail in a crash and you will die.

[Biginboca]

Torgus I assume the stripped coupe pics are your car? The black bracing in your last pic is not present on your car, I believe that’s a sedan only piece, and I believe tlow98 has added that to his e91 by welding it in.

I can see the stock L shaped piece you are talking about circled in your pic below. And then a few of your pics seem to show a cross brace connecting them at the bottom and then a few of your pics do not show it. Like this pic does not seem to show the cross connection?

[Torgus]

Not my car just pictures I found online. I like my interior

No idea why some have that other bottom brace and it seems others do not.

"Another reason a strut bar is useful in the front but not the rear is the front is not triangulated by unibody above the towers, since the hood is not strutural. The rear is a different story entirely, so it flexes much less inherently."

"E92's do not have rear struts, everything rides on the sub-frame. The only forces acting on the shock mount would be a very slight up and down."

A fun read: https://www.m3post.com/forums/showthread.php?t=244529

At least that bar is in the right location. But again there are VERY little forces from the rear dampeners. Vertical not horizontal stress. Unless you convert to a true rear coilover suspension which is $$$ and only needed if you really race the car and it would disqualify you from certain classes. Even then...your car would be caged.

Edit: Don't get me wrong I wish this product did something for the car. It is dirt cheap in comparison to other suspension modifications. I did a TON of research before I settled on my suspension: https://www.e90post.com/forums/showt...5#post25439025 The amount of time I spent researching this stupid rear brace is embarrassing. I just can't see how it does anything useful.

[Biginboca]

Originally Posted by Torgus

Not my car just pictures I found online. I like my interior

No idea why some have that other bottom brace and it seems others do not.

"Another reason a strut bar is useful in the front but not the rear is the front is not triangulated by unibody above the towers, since the hood is not strutural. The rear is a different story entirely, so it flexes much less inherently."

"E92's do not have rear struts, everything rides on the sub-frame. The only forces acting on the shock mount would be a very slight up and down."

A run read: https://www.m3post.com/forums/showthread.php?t=244529

At least that bar is in the right location. But again there are VERY little forces from the rear dampeners. Vertical not horizontal stress. Unless you convert to a true rear coilover suspension which is $$$ and only needed if you really race the car and it would disqualify you from certain classes.

Edit: Don't get me wrong I wish this product did something for the car. It is dirt cheap in comparison to other suspension modifications. I did a TON of research before I settled on my suspension: https://www.e90post.com/forums/showt...5#post25439025 The ammount of time I spent reaching this stupid rear brace is embarrassing. I just can't see how it does anything useful.

I saw that M3 thread you referenced and had read it before I started this thread. I feel those quotes you have referenced are not entirely accurate. Not everything rides on the rear subframe. The springs and shocks anchor directly to the body not the subframe.



So in reality there’s those 2 quotes, and a lot of other info from that thread we both read that I think are not accurate...

Multilink Suspension can definitely benefit from strut brace. See Toyota Supra A90 has one stock and has pretty much identical rear suspension to our cars. I mentioned this before so I know it’s redundant at this point.

Maybe the rear benefits less from a subframe brace but these braces have been shown to be beneficial on many platforms. 350/370z and Supra have them stock. And many track cars have them added even with solid subframe bushing inserts.

Not everything is attached to the subframe. In reality the only parts that would really make stress to the chassis (Springs mostly, plus Dampers somewhat) are not anchored to the subframe at all. They attach to control arm and body only, so it’s definitely feasible they could bypass the subframe and pass stress/flex to the chassis

We still have that video from the IG post. It’s an e46m3, but that car uses a similar set up to ours with control arms anchored to subframe and springs and shocks attached to the body. And it’s showing some chassis flex in the video.

I’m kind of at the point where I’m willing to gamble $200 and see how it feels. Mostly because simply adding the front M3 chassis plate did make a noticeable difference in the turn in and chassis solidity on my car, and I’m liking it so much I want more of it.

I also wonder if it’s possible because you have solid subframe inserts that bracing might do less for you than for me. The subframe is still able to shift slightly on rubber bushings and since the springs and dampers are attached to the control arms which could be shifting with the subframe, they might be actually inducing some lateral loads on my car that they would not on yours with the solid inserts.

[Tambohamilton]

Go for it...discussing it more isn't going to get you anywhere. I hope it gives you what you want, but I bet you a cup of tea at my place that it makes no significant difference when driving. If I could put into words why I think that, I would, but I'm not that good an engineer!

[Torgus]

Boca my reccomendation remains the same for about the same money is for you to upgrade to solid subframe bushings. They add no NVH. I can guarantee they will have more of an effect you can feel over the rear brace, which does not tie the rear struts together but sits higher up.

But it is your money and inexpensive, i hope you feel a difference. Be interesting to hear your feedback.

What is the m3 front chassis plate mod again?

[Biginboca]

Originally Posted by Torgus

What is the m3 front chassis plate mod again?

https://www.e90post.com/forums/showt...579797&page=13

See post 276

[tlow98]

Originally Posted by Phil325i

Interested to know why the sedan is stiffer than the coupe, since the sedan bodyshell has two huge pieces cut out to accommodate the rear doors.

And I suspect the least rigid E9X would be the cabriolet - especially with the roof down!

Sadly, I used to know the definitive answer. If you look up the chassis rigidity figures published by BMW for each series this is what it is. It's some twising measurement newton meter per distance - something.

Here's a quick google that breaks down the E46. This is exactly why the E46M community loves their rear braces. Having a fold down rear brace on that chassis really sucks from a rigidity standpoint. Again, tape up that open-ended cardboard box and BAM, strength!
http://youwheel.com/home/2016/06/20/...ehensive-list/

Also, there's a reason BMW and it's club racers almost always choose the sedan as starting points. Take a look at the turner E90 race cars.

Of course, once you start to get into factory E92 race cars all of that goes out the window since they basically rebuild the car anyway and then aero is more important.

From the factory tho, hard to beat the sedan.

And about those rear "holes" - I would think of them more as bending the steel to make a hole and that makes steel stronger. Long, flat pieces of steel, a la, the side of a car are relatively weak. Bent and conformed steel is very strong on many more axis.

[tlow98]

Originally Posted by Biginboca

Torgus I assume the stripped coupe pics are your car? The black bracing in your last pic is not present on your car, I believe that’s a sedan only piece, and I believe tlow98 has added that to his e91 by welding it in.

I can see the stock L shaped piece you are talking about circled in your pic below. And then a few of your pics seem to show a cross brace connecting them at the bottom and then a few of your pics do not show it. Like this pic does not seem to show the cross connection?

Master tetsuo111 pioneered this M Sedan only piece. He has been my sensei for many moons. I am but a wry grasshopper. One day to be master? Maybe, but many moons of wax-on wax-off yet to come.

Bottom line: Any x-brace in the rear that effectively connects the floor to the shock towers to the rear deck will yield results. The objective here is not to stop the rear shock towers from moving but it is to box in the entire structure so that twisting is greatly reduced.

Another way to think about this: The only other "bulkhead" in a car like this is the firewall and it does a pretty damn great job.

[autoart]

have you seen this: https://www.e90post.com/forums/showp...postcount=4300

[Biginboca]

Originally Posted by autoart

have you seen this: https://www.e90post.com/forums/showp...postcount=4300

My coupe came with a brace like that from the factory

[Phil325i]

Originally Posted by Biginboca

My coupe came with a brace like that from the factory

Mine did too. All European MSport spec coupes have one. Though to be fair, I think the brace bars on the M3 look a heavier gauge alloy...

[The Nightman]

Originally Posted by tlow98

Sadly, I used to know the definitive answer. If you look up the chassis rigidity figures published by BMW for each series this is what it is. It's some twising measurement newton meter per distance - something.

Here's a quick google that breaks down the E46. This is exactly why the E46M community loves their rear braces. Having a fold down rear brace on that chassis really sucks from a rigidity standpoint. Again, tape up that open-ended cardboard box and BAM, strength!
http://youwheel.com/home/2016/06/20/...ehensive-list/

Also, there's a reason BMW and it's club racers almost always choose the sedan as starting points. Take a look at the turner E90 race cars.

Of course, once you start to get into factory E92 race cars all of that goes out the window since they basically rebuild the car anyway and then aero is more important.

From the factory tho, hard to beat the sedan.

And about those rear "holes" - I would think of them more as bending the steel to make a hole and that makes steel stronger. Long, flat pieces of steel, a la, the side of a car are relatively weak. Bent and conformed steel is very strong on many more axis.

The opposite may be true for the E9x. Some publications have stated that the E92 chassis is stiffer than the E90:

"With a combination of steel, aluminum and plastic, the new Coupe body weighs 22 lb. less than the sedan's, yet is 25 percent stiffer."
https://www.roadandtrack.com/new-car...mw-335i-coupe/

"Fortunately, the 335i avoids the perpetual weight gain of modern cars, squeaking in at 22 pounds lighter than its sedan stablemate, despite besting the sedan's chassis stiffness by 25 percent."
https://www.edmunds.com/bmw/3-series...oad-test1.html

"Engine by engine, the Coupe is no lighter than the Sedan, so performance is virtually identical. However, its handling is slightly superior, thanks to a 20% increase of chassis rigidity (due to the loss of rear doors), a 12mm lower ride height and stiffer suspension setting."
https://www.autozine.org/Archive/BMW/old/3er_E90.html

I've also noticed that the E90 lacks various braces that are found on other E9x models. I assume this is due to cost cutting and that the E90 was designed for the lowest common denominator. My E90 did not have the rear subframe braces, front frame rail braces, and rear shock tower braces. The latter two cannot be easily retrofitted as the mounting points are welded on at the factory.

[Torgus]

Most of the track cars seem to be E90s or 135s from everything I have seen. I always thought the extra pillar helped rigidity?

I really don't buy the 25%. That is a huge difference. I would love to know how it was determined.

[The Nightman]

Keeping in mind that suspension works as a whole, I think there is something to gain with a rear brace if the rest of your suspension is sorted. Those that have one have positive feedback, although it could be a placebo, while those that don't have one claim it is useless. They've made a significant difference on other vehicles I've had, but that doesn't transfer to different vehicles. In the end, I think it's cheap enough to experiment with to see for yourself.

These braces mount at the cargo hook locations, which are part of the factory shock tower reinforcement:

BR Racing (E8x only?):

https://www.1addicts.com/forums/showthread.php?t=311813

Ultra Racing:

https://www.facebook.com/ultraracing...3582773695593/

This guy made his own that mounts to the upper shock mount:

https://www.e90post.com/forums/showthread.php?t=255748

[tlow98]

Originally Posted by Torgus

Most of the track cars seem to be E90s or 135s from everything I have seen. I always thought the extra pillar helped rigidity?

I really don't buy the 25%. That is a huge difference. I would love to know how it was determined.

It always seemed crazy to me too, but the difference here is super illustrative:
E46 Sedan w/ folding seats = 13,000 (whatever units)
E46 Sedan w/o folding seats = 18,000 (whatever units)

46% increase in stiffness! Insanity.

Good info freedomfries !

As ever I think we need to compare apples to apples. if it came with fold rear seats or not. Didn't all US Coupes come with folding rear seats? It was an option on the Sedan iirc.

[Tambohamilton]

I'm with tlow on this one; if you want to make a significant difference, you need to do something that mimics closing up the hole where the backs of the rear seats are. Just a bar from wheel arch-wheel arch is going to do so little in comparison.

I seem to remember e61 (?) has a tailgate which is mechanically pulled tight closed, in order to close up the back end of the chassis structure. There are wedge parts which locate against each other as the tailgate is cinched down, and prevent the body from skewing.

Also, food for thought...let's say you do install something, what result are you looking for? What problem are you trying to solve? Stiffer is not always better, and not in all scenarios - just bear in mind rft vs non rft tyres.

[Biginboca]

Gentlemen, I think I found something obvious we all missed...

Does anyone know the part number for these:






It was proposed earlier that these are present on the E90M3 only, but I found another source stating they are present on coupes as well. I have gone through realoem for e90m3 and e92m3 but cannot find these anywhere on a diagram.

What is the purpose of these? I assume it’s a brace. What is it bracing? It appears the strut towers? And it’s only present on the M3 car(s).

Why would bmw install a brace above the rear spring/shock mounts on the M3 and not the normal 3 series. I think we know.

Why would they use these and not a cross bar? Maybe consumers with folding seats don’t want a cross bar blocking the utility, so these are a compromised strut brace of sorts. It looks to me like they are supporting lateral and vertical movements.

I propose a crossbar welded/bolted to a set of these would make a very good strut brace.

[The Nightman]

Torgus mentioned those braces above. I first learned about them from tetsuo111. We were never able to find the part number. I'm not an engineer but I believe the braces are designed to limit vertical deflection. The lower mounting point isn't threaded on the E90 and E91, but I don't know about the E92. Tetsuo had a nut welded in when he retrofitted them: https://www.e90post.com/forums/showt...9#post26289659

Cusco, Ultra Racing and others have braces that mount to the upper location. The Cusco appears to be a superior design as its mounting brackets connect the upper and lower positions like the factory brace:


Feedback is mixed on the already stiff M3:
Cusco: https://www.m3post.com/forums/showth...7#post20888267
Ultra Racing: https://www.m3post.com/forums/showpo...9&postcount=57

I'm not sure how beneficial an upper bar like Ultra Racing's would be without connecting the upper and lower points. It would be interesting to see what both upper and lower braces yield on a non-M E9x though.

While we're at it, check out the rear bracing on an E93:

[The Nightman]

Originally Posted by tlow98

It always seemed crazy to me too, but the difference here is super illustrative:
E46 Sedan w/ folding seats = 13,000 (whatever units)
E46 Sedan w/o folding seats = 18,000 (whatever units)

46% increase in stiffness! Insanity.

Good info freedomfries !

As ever I think we need to compare apples to apples. if it came with fold rear seats or not. Didn't all US Coupes come with folding rear seats? It was an option on the Sedan iirc.

I don't think there are any structural differences between folding and non-folding seats on an E9x. Looking at retrofit guides, there are no modifications to the sheet metal like on E46s

https://www.e90post.com/forums/showthread.php?t=461974

I wish we had official rigidity figures from BMW!

[Buug959]

Thank you gentlemen, this has been a very interesting read. I am not familiar enough with either the e90 or e92 chassis to have an informed opinion about the brace you started discussing but I believe I have a better understanding of both of them now. It will help me decide how to proceed with my own build.