[aremmell]

I apologize, as I know this has probably been hashed and rehashed on this forum, but I'm looking to replace the OEM strut brace on my G82 M4.

I like this one, and it's great for the price. Anyone have experience with this brand/particular part and have any feedback on their impressions?

Is the Turner better? Is there another brand I haven't heard of yet that's better?

TIA!

[tom @ eas]

Originally Posted by aremmell

I apologize, as I know this has probably been hashed and rehashed on this forum, but I'm looking to replace the OEM strut brace on my G82 M4.

I like this one, and it's great for the price. Anyone have experience with this brand/particular part and have any feedback on their impressions?

Is the Turner better? Is there another brand I haven't heard of yet that's better?

TIA!

Looking it it from a hinged vs fixed - the Turner Strut Tower Brace would be the better choice of the two. A hinged strut tower brace would be going a step backwards.

[M3SQRD]

Originally Posted by tom @ eas

Looking it it from a hinged vs fixed - the Turner Strut Tower Brace would be the better choice of the two. A hinged strut tower brace would be going a step backwards.

A strut tower brace is used to limit the lateral out-if-plane movement of one strut tower relative to the other. A design that uses monoballs at each mounting location will still limit the relative lateral motion of a strut tower just as effectively as a design that uses fixed interface mounting points at each mounting location - think of it as the one highly loaded strut towers is pulling inward on the other lightly laterally loaded tower. Primarily, it’s tension-compression loading between the towers. Most people think its job is to increase torsional stiffness but that’s incorrect.

[tom @ eas]

Originally Posted by M3SQRD

A strut tower brace is used to limit the lateral out-if-plane movement of one strut tower relative to the other. A design that uses monoballs at each mounting location will still limit the relative lateral motion of a strut tower just as effectively as a design that uses fixed interface mounting points at each mounting location - think of it as the one highly loaded strut towers is pulling inward on the other lightly laterally loaded tower. Primarily, it’s tension-compression loading between the towers. Most people think its job is to increase torsional stiffness but that’s incorrect.

Probably most are doing it for cosmetic reasons, since a majority of these will never see the track. There's numerous debates on the internet discussing this in detail, but a hinged bar introduces flex at the hinges.

Fixed strut bar is preferable. It's the route the BMW engineers went.

[M3SQRD]

Originally Posted by tom @ eas

Probably most are doing it for cosmetic reasons, since a majority of these will never see the track. There's numerous debates on the internet discussing this in detail, but a hinged bar introduces flex at the hinges.

Fixed strut bar is preferable. It's the route the BMW engineers went.

I have over 40 years of aerospace structural engineering and design experience. Most fixed (6DOF) designs do not have the local stiffness required in the rotational DOFs to achieve a fixed design interface and, therefore, although they may appear to be a fixed design, they actually perform as a pinned (3DOF) design when it comes to effective stiffness.

[thompsac25]

[aremmell]

Originally Posted by M3SQRD

I have over 40 years of aerospace structural engineering and design experience. Most fixed (6DOF) designs do not have the local stiffness required in the rotational DOFs to achieve a fixed design interface and, therefore, although they may appear to be a fixed design, they actually perform as a pinned (3DOF) design when it comes to effective stiffness.

DOF = direction of force? Left, right, back, foward, up, down?

[moonluv810]

Someone posted a pic of CSL-style brace made of carbon. I recall someone saying it’s a prototype and not in production yet.

I think that would be a great OEM+ option, assuming it doesn’t cost your left testicle.

[M3SQRD]

Originally Posted by aremmell

DOF = direction of force? Left, right, back, foward, up, down?

DOF = degree of freedom.

Three orthogonal forces/displacements acting along the x, y and z axes, and three orthogonal moments/rotations acting about the x, y and z axes.

Practically, it is difficult to provide supporting structure that is stiff enough in rotational DOF to support moment continuity. So even though a design may appear to be supporting structure in all six DOF, there isn’t sufficient local stiffness to support some or all of the local rotations and, therefore, what appears to be a six DOF, “clamped” design, actually only supports three translational DOF, “pinned” design. In reality, the actual design is between a “clamped” and “pinned” design, usually closer to a “pinned” design.

[Needsdecaf]

Originally Posted by M3SQRD

DOF = degree of freedom.

Three orthogonal forces/displacements acting along the x, y and z axes, and three orthogonal moments/rotations acting about the x, y and z axes.

Practically, it is difficult to provide supporting structure that is stiff enough in rotational DOF to support moment continuity. So even though a design may appear to be supporting structure in all six DOF, there isn’t sufficient local stiffness to support some or all of the local rotations and, therefore, what appears to be a six DOF, “clamped” design, actually only supports three translational DOF, “pinned” design. In reality, the actual design is between a “clamped” and “pinned” design, usually closer to a “pinned” design.

Thank you for reminding me of why I chose not to use all those statics and structural engineering classes.

[M3SQRD]

Originally Posted by Needsdecaf

Thank you for reminding me of why I chose not to use all those statics and structural engineering classes.

Anytime

[aremmell]

Originally Posted by moonluv810

Someone posted a pic of CSL-style brace made of carbon. I recall someone saying it’s a prototype and not in production yet.

I think that would be a great OEM+ option, assuming it doesn’t cost your left testicle.

Dinan also makes a brace (which is pretty much BMW OEM+), and so does Turner. Both super reputable brands, but I'm not a big fan of the logos on them. I think they would look better plain, and it may prevent me from buying one . Nice price on the Dinan (hope it's not from China).

[aremmell]

Originally Posted by M3SQRD

DOF = degree of freedom.

Three orthogonal forces/displacements acting along the x, y and z axes, and three orthogonal moments/rotations acting about the x, y and z axes.

Practically, it is difficult to provide supporting structure that is stiff enough in rotational DOF to support moment continuity. So even though a design may appear to be supporting structure in all six DOF, there isn’t sufficient local stiffness to support some or all of the local rotations and, therefore, what appears to be a six DOF, “clamped” design, actually only supports three translational DOF, “pinned” design. In reality, the actual design is between a “clamped” and “pinned” design, usually closer to a “pinned” design.

So, in non-aerospace engineer speak, you're saying it doesn't matter if you get one designed like the Kies or a traditional style one like Turner or Dinan, because both design types have the same capability of limiting relative lateral movement of the strut towers and that is their only practical purpose?

[M3SQRD]

Originally Posted by aremmell

So, in non-aerospace engineer speak, you're saying it doesn't matter if you get one designed like the Kies or a traditional style one like Turner or Dinan, because both design types have the same capability of limiting relative lateral movement of the strut towers and that is their only practical purpose?

For limiting the strut towers from moving laterally relative to each other it’s the in-plane stiffness that’s the primary stiffness and any rotational/bending stiffness is secondary. For example, the CSL design has moment continuity at the front (single fastener attachment to the chassis) and strut mount locations; however, its primary stiffeness comes from triangulation of the three legs (work in tension-compression). The sections are quite thin so the bending stiffness provides little additional overall stiffness.

[somer]

Originally Posted by M3SQRD

For limiting the strut towers from moving laterally relative to each other it’s the in-plane stiffness that’s the primary stiffness and any rotational/bending stiffness is secondary. For example, the CSL design has moment continuity at the front (single fastener attachment to the chassis) and strut mount locations; however, its primary stiffeness comes from triangulation of the three legs (work in tension-compression). The sections are quite thin so the bending stiffness provides little additional overall stiffness.

So of all the options available I assume the CSL brace would be the best? Any opinions on the Karbonius carbon version of the CSL brace?

[M3SQRD]

Originally Posted by somer

So of all the options available I assume the CSL brace would be the best? Any opinions on the Karbonius carbon version of the CSL brace?

The CSL has a nice single attachment fitting at the two strut tower interfaces. The Dinan CF strut brace has poor design details at the strut tower interfaces which makes their design unnecessarily complex, and has more compliance due to local torsion and bending of the rear strut tower mounting point as well as torsion and out-of-plane bending of their forward cross bean near the front strut tower mounting point. The Karbonius has straightforward load path and mounting interfaces. Kies strut tower also has straightforward load path and machined fittings at each chassis interface with simple monoball connections of each CF tube. I’d really like to get the dimensions and local thickness (assuming they’re all open tube sections) of the three cross members in each design; however, for a CF design, I’d go with the Karbonius design because its CF rectangular cross sectional design goes well with the design details of CF engine cover designs as well as its simple one-piece bonded construction. If I wanted max stiffness then I’d go with the CSL or Karbonius designs because of its two additional engine bay mounting locations.

Edit: how many different companies make strut tower braces for the G8x?!?! Turner Motorsports also offers a CF strut tower. Any other strut towers out there? It would be great if these companies would provide measurements of main cross sections and CF wall thickness (and CF material used which will never happen) so quantitative assessments of the performance of each design can be assessed. However, most people are adding them based on looks rather than actual function/performancd - just look at the people drooling over the Dinan design.

Order based on stiffness:
Karbonius
OEM CSL
Turner/Kies
Dinan

Aesthetics:
Karbonius
Dinan
OEM CSL
Kies
Turner