CF Roof Crash Test

[HALOTHANE]

Does anyone have factual information regarding the structural integrity of our CF roofs in a rollover and/or crush impact? The recent surge in posted vehicular accidents prompts the question: Lowered center of gravity, but at what price?

[LateBraking]

I think you should just get a moon roof and not worry about it too much.

Also, expense aside, carbon fiber can be a very lightweight but very, very strong material. It's used in exceeding quantities in many fields nowadays, not just a car's roof, but Formula 1 (think crashes and survival), safety devices themselves (HANS devices and even whole helmets structured in carbon fiber), vehicle monocoque shells, aerospace and flight, even medical uses. Also remember that the car does clear the required safety testing in most if not all nations in the world, which means, of course, Germany's and Americas. I would think that the material strength on a 70,000 dollar car is going to be higher than, say that of a Scion trashCan's....and those clear mandated safety requirements.

I think life is too short to worry about your roof. in a roll-over crash that is never going to happen unless you turn off traction control in the rain or with bald tires, or go racing in the canyons or go on a "Mexico run". Knock on wood, but roll over crashes don't just happen when you're at cruising speed minding your own business on freeways, or happen when you're driving 45 in stop and go traffic in cities. So, unless you're a serious offender of society's imposed safety limits, I'd be more worried about your plastic fenders and front bumper.

Oh, also, FYI, old E46 M3's (2002 era) front bumper supports were made out of carbon fiber. They were replaced with non-CF ones in subsequent years due to cost reduction, but if the front bumper support of a car is made out of it, and many more front end collisions happen than roll-overs, then yeah, I wouldn't worry.

Fun story, a friend told me that shady body shops used to take the CF front bumper support of older cars off and sell them, then replace them with the cheaper OEM ones, when these cars would go to cheap body shops after being involved in a collision and the front bumper support was okay.

[mlhj83]

Originally Posted by HALOTHANE

Does anyone have factual information regarding the structural integrity of our CF roofs in a rollover and/or crush impact? The recent surge in posted vehicular accidents prompts the question: Lowered center of gravity, but at what price?

Don't think BMW has ever released structural info regarding the CF roof apart from weight. However, a little logical assumptions can be made. First off, the CF roof isn't a significant part of the roof's structural integrity in terms of support upon blunt impact, neither is a steel roof - it's the underlying cross beams, roof rails, A, B and C pillars. What the roof will do however is protect against intrusion of external matter, and this regard, the CF roof should do better than the steel roof, as the CF roof is thicker, stiffer and the fibre itself will be better at resisting punctures than a steel roof - CF has higher shear strength than sheet steel.

Also, another interesting feature of the M3, the front and rear bumper carriers of the E9X M3 is made out of carbon kevlar, which evolved from the E46.

[Legion5]

This seems like quite a sensationalist and delusional issue to bring up.

For the record the 3 series doesn't have problems in crashes. They are the 3rd least likely in their class to result in injury from hitting a telephone poll at highway speeds. With the only damage being injury to lower left leg, ankle and heel, not severe injury but just injury meaning broken bones. That's very good considering the competiton's results and the fact that you're slamming into a telephone poll at highway speeds. To potentially limp away with broken bones in your lower leg and no other injuries to other sections of the body according to the test from a crash that would kill people other cars isn't bad at all.

Regarding the carbon roof and crashes. The roof is in no way shape or form a crash structure. The regular metal roof is sheet metal so thin that you could easily bend it with your bare hands if you removed the roof pannel. You can even bend the roof with your bare hands while it's on the car and it will pop back into shape. The roof has as much to do with the crash worthiness of the car as the floormats.

Despite the fact that the roof material does not matter at all in a crash if anything the carbon roof is substantially stronger than the regular roof. The roof is made of either DX 54 or 56 low strength steel and is 0.5 mm thick.



The carbon roof (correct me if I'm wrong) is made of 3 layers of 3k 1x1 carbon and 1 layer of plastic with a polymer binder.

If we disregard the plastic layer, and just concentrate on the carbon fiber matrix and look up the material strengths of a standard 3 layer carbon matrix material vs the specific type of 0.5mm low strength steel BMW uses in the roof we find that the carbon roof would actually absorb at least 43 times as much enegry as the steel roof before deforming and similar amounts of energy before being pierced. Again this very rough estimate is on the low side not the high side.

So:

Q: What's the price in terms of crash worthiness of the carbon roof?

A. There is none. Quite the opposite. It's about 50 times stronger.

So really you should be asking yourself if it's worth having a flimsy extremely dangerous and life threatening steel roof over a carbon roof that's 50 times stronger.

[m3an]

Originally Posted by LateBraking

I think you should just get a moon roof and not worry about it too much.

Also, expense aside, carbon fiber can be a very lightweight but very, very strong material. It's used in exceeding quantities in many fields nowadays, not just a car's roof, but Formula 1 (think crashes and survival), safety devices themselves (HANS devices and even whole helmets structured in carbon fiber), vehicle monocoque shells, aerospace and flight, even medical uses. Also remember that the car does clear the required safety testing in most if not all nations in the world, which means, of course, Germany's and Americas. I would think that the material strength on a 70,000 dollar car is going to be higher than, say that of a Scion trashCan's....and those clear mandated safety requirements.

I think life is too short to worry about your roof. in a roll-over crash that is never going to happen unless you turn off traction control in the rain or with bald tires, or go racing in the canyons or go on a "Mexico run". Knock on wood, but roll over crashes don't just happen when you're at cruising speed minding your own business on freeways, or happen when you're driving 45 in stop and go traffic in cities. So, unless you're a serious offender of society's imposed safety limits, I'd be more worried about your plastic fenders and front bumper.

Oh, also, FYI, old E46 M3's (2002 era) front bumper supports were made out of carbon fiber. They were replaced with non-CF ones in subsequent years due to cost reduction, but if the front bumper support of a car is made out of it, and many more front end collisions happen than roll-overs, then yeah, I wouldn't worry.

Fun story, a friend told me that shady body shops used to take the CF front bumper support of older cars off and sell them, then replace them with the cheaper OEM ones, when these cars would go to cheap body shops after being involved in a collision and the front bumper support was okay.

early ones are aluminum and they switched in 03 I believe to CF (really kevlar I think) reinforcements.

[LateBraking]

Originally Posted by talontid

early ones are aluminum and they switched in 03 I believe to CF (really kevlar I think) reinforcements.

Oh, is it the other way around? Maybe I didn't hear right when I heard the story. lol

[m3an]

yeah other way around; but it goes to show that it is a strong/lightweight component

[Space Ghost]

FWTW I've seen a few E92 M3's on their roofs with nothing but minimal damage to their roof. Also, I had a tree limb fall on my CF roof with no damage not even a scratch that couldn't be buffed out.

[kosmo69]

Originally Posted by mlhj83

Don't think BMW has ever released structural info regarding the CF roof apart from weight. However, a little logical assumptions can be made. First off, the CF roof isn't a significant part of the roof's structural integrity in terms of support upon blunt impact, neither is a steel roof - it's the underlying cross beams, roof rails, A, B and C pillars. What the roof will do however is protect against intrusion of external matter, and this regard, the CF roof should do better than the steel roof, as the CF roof is thicker, stiffer and the fibre itself will be better at resisting punctures than a steel roof - CF has higher shear strength than sheet steel.

Also, another interesting feature of the M3, the front and rear bumper carriers of the E9X M3 is made out of carbon kevlar, which evolved from the E46.

this.
Separately why wasnt a CF roof available on the Sedan, Cost?

[Porschefile]

It is not structural, it is simply a cover for the pillars etc.

CF is way stronger than aluminum.

Don't worry about it, but also try not to roll your car.

[HALOTHANE]

Originally Posted by Space Ghost

FWTW I've seen a few E92 M3's on their roofs with nothing but minimal damage to their roof. Also, I had a tree limb fall on my CF roof with no damage not even a scratch that couldn't be buffed out.

Nothing quite like a real world test!

[tibra1]

CF Roof..Its the only way to fly///

[mdosu]

It's not a roof issue here when you're in a rollover. It's frame strength that you care about. The frame is what structurly holds the occupant section of the car in place. That's why you can do CF roof retrofits with no major impact on safety. The key thing is, the roof just has to be strong enough to prevent easy punctures.

[weaksauce]

What a weird thing to worry about...

[klammer]

The fear mongering continues, why not just stay inside. You want to know what the most dangerous thing in the world is???? Being ALIVE