[E91 Hoarder]

Planning to occasionally track and autocross the wagon.

Given it is a wagon body, I imagine there is less rigidity in the rear than a coupe or sedan. Thinking what if you add a rear strut brace bar there, would it help?

Has anyone installed a rear strut tower brace in an e91 and noticed any difference at all?

[TGTIW]

I don't see how a traditional rear strut tower brace could add any rigidity, with the rear suspension having an actual "shock" vs a "strut." The upper mounting point experiences no lateral forces due to the shocks movement. All the lateral forces with the rear suspension are contained within the rear sub frame. The shocks and springs only transfer a vertical force, which a "strut bar" would do nothing to counter act.
Now if it was a brace that triangulated the upper mounting points to an opposite lower point, that could stiffen the floor area that the sub frame mounts to.

[E91 Hoarder]

Originally Posted by TGTIW

I don't see how a traditional rear strut tower brace could add any rigidity, with the rear suspension having an actual "shock" vs a "strut." The upper mounting point experiences no lateral forces due to the shocks movement. All the lateral forces with the rear suspension are contained within the rear sub frame. The shocks and springs only transfer a vertical force, which a "strut bar" would do nothing to counter act.
Now if it was a brace that triangulated the upper mounting points to an opposite lower point, that could stiffen the floor area that the sub frame mounts to.

Makes sense. Thanks for the input!

[ptpending]

Originally Posted by E91 Hoarder

Planning to occasionally track and autocross the wagon.

Given it is a wagon body, I imagine there is less rigidity in the rear than a coupe or sedan. Thinking what if you add a rear strut brace bar there, would it help?

Has anyone installed a rear strut tower brace in an e91 and noticed any difference at all?

actually e91 will be more stiffer than coupe and sedan
and if you never saw its under floor, it has a strengthening V brace already

[Tambohamilton]

Originally Posted by ptpending

actually e91 will be more stiffer than coupe and sedan
and if you never saw its under floor, it has a strengthening V brace already

The e91 only has that brace because the chassis isn't as stiff as the e90 or 92. If you look at others, and particularly the e93, there are ways to add more/better bracing under there too.

But regarding the strut brace; it'll make practically no difference as mentioned above.

[ryan stewart]

I would think you'd need a cross, like a cage, impacting the spring mounting points to really do anything.

My poor wagon doesn't rattle but she creaks like an old spanish galleon, def not the stiffest chassis BMW made but none of that shimmy like verts.

[Onizukachan]

Try an e34 touring with double sunroofs and go up an inclined driveway at an angle if you want to see visible body twist. By comparison the e91 is very very rigid… far more so than the e46/3.

[Tambohamilton]

For sure it's really not bad! But it's not as inherently stiff as the e90 or 92. The e93 is another matter...

[ptpending]

e91 is actually stiffer because it has redundant pillars connected to roof, while sedan and coupe have their back only with lower rigid bars
the only what is stiffer is z3 and z4 coupe, where body is smaller and rear door is connected to roof and not lower parts

[Tambohamilton]

The C pillar adds more on the e90 Vs the C+D of the 91. The evidence is in the fact that BMW didn't spec the e91's additional rear chassis brace on the e90 - it's not needed.

I'm sure this is listed in a BMW doc somewhere, but a quick search came up with nothing...

[Onizukachan]

Doesn’t matter anyway.

Now that the body doesn’t twist an inch or more out of alignment from new like on prev Tourings,I think we can all agree at the current age of e91s you get more movement from the subframe/suspension bushings wearing out than the body possibly moving a mm or so under load. .

Other than style/show points, or ‘gram flex, your hard earned dollars are better spent elsewhere. Especially since it is NOT a strut rear suspension, but separate coil amd shock. No lateral loads

[E91 Hoarder]

On the other hand, adding the V-brace bar from the wagon (as pictured above) to sedan or coupe, will that improve E90/E92's stiffness?

[Tambohamilton]

Yes.

Other options are to look at the M3 bracing and apply that. There are all sorts of variations between chassis and M/non-M, some are interchangeable and others less so.

[ptpending]

wow,
didn't knew that e90 m3 also has undebody brace
that means that i completely right that e91 with brace is more stiff than standard e90 and e92