[ornicar]

Originally Posted by Simbl

That small green section is in bending so may not do much. Without a sheet to create shear strength you will not get much benefit in terms of feel. The green bar linking rear mounts looks great.

If you had to stick with this design I would put a sheet on 3mm aluminum on the entire triangle. But with several caveats…

As mentioned about what you will feel- The single point at the front of the subframe where the bars connect will allow the front corners to pivot around the centre allowing twist particularly effect the tension strut mounts. That’s your biggest loss.

The second biggest loss is that the reinforcement needs to be as close to its input as possible (control arms). The front of your brace does not pickup on all control arm points- this is specifically mentioned in the article you posted earlier. Local reinforcement is best for effects on handling.

What will make the front feel tight and solid is less twisting and less racking.

The key to the M3 belly pan is shear strength to reduce twisting and racking, pickups up on all mounts and suspension points. Closer you can get to that the better.

Remember the chassis on the M3 is the same except for some external body panels, subframe, strut brace, belly pan and rear subframe brace. The rest of the body parts are shared across equivalent e9x. There’s not much in the recipe in terms of chassis stiffening.

Thanks for your feedback. Much appreciate.

The small bar function is to connect the x2 main bars, in order to have an assembly. By the way i am agree that a sheet Aluminium plate will do the same but in a better way. I wil try to fit one on all the triangle with some structural rivets ( BÖLLHOFF HUCK )

I will fit the 1/2 M3 belly pan for sure when i will fin a used one. I don't want to buy a new one to cut it in 2 parts...


This front subframe is really light. It is amazing.

[The Nightman]

I've posted some relevant information from BMW technical training here:

https://zpost.com/forums/showpost.ph...&postcount=761

[Simbl]

Originally Posted by The Nightman

I've posted some relevant information from BMW technical training here:

https://zpost.com/forums/showpost.ph...&postcount=761

I’ve been reading through BMW factory training and product information documents for the E9x platform and the 4th Gen M3, mainly out of interest, to see what BMW actually say about front-end or front subframe stiffening on the E9x M3.

In 05_M Chassis and Suspension (pages 15–18), BMW describe the M3 front axle carrier as an aluminium, high-pressure-formed part designed for optimum strength and torsional rigidity. They explain stiffness in terms of carrier design, material choice, and how loads are introduced. The same section also shows the revised strut clamp geometry used on the M3. There’s no mention of thicker front body panels.

In the 4th Generation M3 Chassis Dynamics document, BMW talk about improved precision and reduced compliance through geometry and load-path optimisation. This is more about overall design philosophy and doesn’t mention changes to front floor panel thickness or body shell metal.

In the E90 Chassis document (around page 10), BMW explain that the double-pivot front axle uses a frame that provides significant stiffening of the front end. This applies to the E9x platform generally and helps explain BMW’s approach to stiffness via subframes and frames rather than changes to the body-in-white.

In BMW Suspension Systems (pages 14–16), BMW describe bolted “thrust zone” or reinforcement panels that increase transverse rigidity at the front of the car. This is the same principle used for underbody braces and belly pans, again focusing on bolt-on structures rather than thicker shell panels.

In M Complete Vehicles (page 25), BMW mention thickness differences on some bolt-on reinforcement panels on M cars, but there’s no reference to thicker front floor panels, wheel wells, or different body pressings on the E9x M3.

Overall, the documents describe front-end stiffness on the E9x M3 as coming from the front axle carrier, clamp geometry, bolt-on reinforcement panels, and reduced compliance at interfaces, rather than from thicker or stronger front body shell metal.

[ornicar]

Originally Posted by ornicar

Ok, so it is maybe the good timing to finalize one idea.

Attached a sketch of a bracket that would replace the e88 frame fixing points.

What do you think about this design? Criticals are welcome!

I could had some holes in order to fit the horizontal bar of the upside down "A" in order to triangulate the structure.

The Oil cooler 335is / 1M bracket is not so far to do the job !

51647154546

51647975360

swap Left with the right; but the water cooler would not fit....

So maybe cutting the bottom tab and then welding the correct side bottom.


Then i would only need a "simple" bracket to connect the front V bar.

[Simbl]

Originally Posted by ornicar

The Oil cooler 335is / 1M bracket is not so far to do the job !

51647154546

51647975360

swap Left with the right; but the water cooler would not fit....

So maybe cutting the bottom tab and then welding the correct side bottom.


Then i would only need a "simple" bracket to connect the front V bar.

Have you checked if it’s a weld on part from BMW that can just weld on. Might be easier and cheaper!

[ornicar]

Originally Posted by Simbl

Have you checked if it’s a weld on part from BMW that can just weld on. Might be easier and cheaper!

Yes it is possible to buy it individually. You are correct it is a better choice.

It is too much job to do these brackets, and to fit it!

The diffcult point for me is find anyone that can weld it and do it well. Not so easy in my place. But again You are really correct it is a better choice.

[whyzee125]

I am interested in the stiffening plate mod for my 335i sedan. Will I still need to cut half off if I don’t have EPS?

[Simbl]

Originally Posted by whyzee125

I am interested in the stiffening plate mod for my 335i sedan. Will I still need to cut half off if I don’t have EPS?

I don’t think so the rear subframe holes don’t line up. There is some post on this forum or baby bmw forum with what in the rear looks like it might be possible..

The eps issue is with front half. On e92 the is an additional brace that obstructs the m3 belly ban.

[Simbl]

Originally Posted by ornicar

Yes it is possible to buy it individually. You are correct it is a better choice.

It is too much job to do these brackets, and to fit it!

The diffcult point for me is find anyone that can weld it and do it well. Not so easy in my place. But again You are really correct it is a better choice.

Rivets and proper panel bond will be as strong.

[ornicar]

Originally Posted by Simbl

Rivets and proper panel bond will be as strong.

This is another idea! thanks.

What kind of bond and rivets woul you suggest if you know?

I thought about the bellly pan, can't we use the M F** version?

It have an EPS so it could being a better base --> Less cut needed?

[The Nightman]

Originally Posted by Simbl

Rivets and proper panel bond will be as strong.

I'm almost certain the mounting pieces are bonded to the frame rather than welded.

But I wouldn't stress about those braces and focus on the subframe first. Even the M3 doesn't have those frame rail braces:

[ornicar]

Originally Posted by The Nightman

I'm almost certain the mounting pieces are bonded to the frame rather than welded.

But I wouldn't stress about those braces and focus on the subframe first. Even the M3 doesn't have those frame rail braces:

See the attached photo. They seems to being electrical welded.

there is not enough surface for bonding IMO. But maybe with some rivets + bonding could be a good tradeoff.


I don't stress but i would really like to do something close of as the New M ( Fxx Gxx) bracing .

[ornicar]

These brackets are solid!

[ornicar]

First dry fit of the M FXX Belly pan.

it is Not plug & play.

No interferences with the EPS but there is really not a lot of clearance!


Maybe a spacer of 1 or 2 mm will be needed in the front.

I wil use a cutting belly pan (Front part only) .

[Phil325i]

Woah that is tight on the EPS! I might just stick with my two bars...

[ornicar]

Originally Posted by Phil325i

Woah that is tight on the EPS! I might just stick with my two bars...

Yes it is tight! But it is not so bad. The photo is misleading due to the "slope" of the belly pan. With some spacers it should be ok. I will try to weld 2mm or 3mm aluminium washers to the belly pan.

Contact is ponctual and only in periphery of the embossment.

[Simbl]

Originally Posted by Phil325i

Woah that is tight on the EPS! I might just stick with my two bars...

That’s f series pan. Honestly the bars do nothing in comparison to the e9x m3 pan. I have a minimum on 10mm clearance everywhere.

[Simbl]

Originally Posted by ornicar

Yes it is tight! But it is not so bad. The photo is misleading due to the "slope" of the belly pan. With some spacers it should be ok. I will try to weld 2mm or 3mm aluminium washers to the belly pan.

Contact is ponctual and only in periphery of the embossment.

Your going to this amount of effort it would be easier and cheaper to buy a sheet of aluminum and fabricate your own panel. Easily done with some cardboard. The only reason I didn’t was because I got the belly pan so cheap.

The welds on those brackets are fairly small a ss rivet in it’s place should work. The panel bond is belt and braces and helps with shear strength.

[ornicar]

Originally Posted by Simbl

Your going to this amount of effort it would be easier and cheaper to buy a sheet of aluminum and fabricate your own panel. Easily done with some cardboard. The only reason I didn’t was because I got the belly pan so cheap.

The welds on those brackets are fairly small a ss rivet in it’s place should work. The panel bond is belt and braces and helps with shear strength.

I didn't pay the F BP too much also

IMO the x2 main positives point of the F BP Vs E BP are less cut (no cut) so i hope a better efficiency; It is widther in the front (less trapezoidal) so the x2 front external fixings points are really close to the front control arm.

By the way you are correct, it is a lot of job for an unknown/incertain result. It is winter project!

I have a plan to fit monoball in the FLCA & with this BP i hope that it will also limit / avoid excessive NVH.



About the brackets, thanks for your advice. If i can Rivet instead of welding i would prefer! Much easy, and i can do it myself.

I didn't well understand, do you think that is better to bond + rivets? or only rivets? If so do you know what bond reference could do the job?

[The Nightman]

Originally Posted by ornicar

I have a plan to fit monoball in the FLCA & with this BP i hope that it will also limit / avoid excessive NVH.

How are your roads? If they are in decent condition and smooth, the NVH from monoball tension struts shouldn't be too bad. I ran them briefly and while the performance gain was significant, you feel every pebble on the road. It was too much for a city driven daily and I ended up going back to M3 tension struts.

[ornicar]

Originally Posted by The Nightman

How are your roads? If they are in decent condition and smooth, the NVH from monoball tension struts shouldn't be too bad. I ran them briefly and while the performance gain was significant, you feel every pebble on the road. It was too much for a city driven daily and I ended up going back to M3 tension struts.

Thanks for your feedback!

Roads around me are not really smooth, so i will maybe make this monoball plan in standby.

I have cut the BP in half today.

[Simbl]

Originally Posted by ornicar

Thanks for your feedback!

Roads around me are not really smooth, so i will maybe make this monoball plan in standby.

I have cut the BP in half today.

As a bit of a half way house between m3 arms and monoballs. Powerflex make an offset caster bush. This allows for additional caster that would give subjectively better steering feel, more self centering, straight line stability and the most important part more dynamic camber about an extra -0.25 when cornering. Something people don’t realize about the m3 is that the additional caster and some camber is build into the m3 hub geometry not just the control arms. This gets closer to m3 geometry.

The only reason I have not gone with them myself is the roads are awful in the UK at the moment m. The M3 Arms are just about bearable.