Carbon roof and risk when crash?

[hybris4u]

After have seen a number of pictures of crashed 1Ms a bunch seem to end up on the roof.

Considering this how much would changing the roof to a full carbon affect structural integrity of the car? Read that it should not affect it but would love to hear if there are some experts on the forum regarding this?

[Pig Farmer]

I wouldn't call myself an expert, but I have fabricated many parts for boats, cars and motorcycles with carbon fiber and have a general understanding of it's benefits. When using carbon fiber you first need to understand what type of strength you are looking to achieve... tensile strength? shear strength? compression strength? This will dictate the direction of the fiber orientation, epoxy used, and the possible use of core material such as high density foam or honeycomb materials. The beauty of carbon fiber is that you can design the part to achieve a specific strength profile. In short, you could surely fabricate a roof that is essentially bullet-proof but it boils down to a cost/benefit analysis.

[Pete_vB]

Originally Posted by hybris4u

After have seen a number of pictures of crashed 1Ms a bunch seem to end up on the roof.

Considering this how much would changing the roof to a full carbon affect structural integrity of the car? Read that it should not affect it but would love to hear if there are some experts on the forum regarding this?

Well they got away with crash testing, etc in the M3...

A well done carbon roof such as the M3 style is going to be as stiff or stiffer than the stock metal assuming it's bonded in, so the torsional stiffness of the car, etc will be about the same. However it won't have the impact and intrusion resistance of the metal part- if you rolled the car you'd rather have the metal roof. If you cared you could improve impact resistance be adding a kevlar layer, for example, but I don't know if the factory did that on the M3, and I'd be very surprised if the aftermarket roofs had it.

Overall I'd say equally as safe most of the time, slightly less safe some of the time. Of course I added a carbon roof to my 911, so the difference wasn't enough for me to worry about...

[JohnCena]

Carbon is stronger than aluminum and steal, I wish I knew why they didnt do the carbon roof on the 1M

[mlhj83]

Originally Posted by JohnCena

Carbon is stronger than aluminum and steal, I wish I knew why they didnt do the carbon roof on the 1M

Gram for gram, carbon fibre has a higher tensile strength than steel or aluminium. But as the above poster has said, there are variations of how carbon fibre is manufactured depending on its application. A carbon roof on the 1M would have added significantly to the base price, which is not financially sensible from the perspective of BMW, especially for a low volume car. The 1m could easily cost more than an m3 if it had composite wings, carbon Kevlar bumper bars, carbon roof and aluminium hood like the m3, simply because of the high production cost relative to low production volume.

[eeghie]

Roof sheet, regardless of material, mostly prevents external stuff from entering your personal space. The pillars and linking roof beams (3x) are the key elements safeguarding your the headroom. Carbon can indeed be made stronger than the OEM steel sheet, yet it's non-metalic bonding will become the weakest link (and most likely sheer).

Agree with others on exclusively non-technical arguments for not incorporating this in a semi-limited run.

[hybris4u]

I was thinking of the aftermarket options and how that might affect the car in a crash. RevoZport, Ind and similar carbon roof. Thoughts? Maybe the most sensible option is to just wrap the roof in black high gloss or carbon (if there is any carbon 2*2 wrap weave that would match the BMW Performance carbon?)

[Jean-Marc]

Would also be quite concern about the reliability of the bonding with an aftermarket product.
When BMW marketed the M3 CSL with, for a first time, a carbon fiber roof, they were quite proud about solving this bonding issue.
But I acknowledge that a white or orange 1M with a carbon roof would look quite cool...