How safe will the 4C be compared to other modern cars? - Alfa Romeo Forum
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(Post Link) post #1 of 26 Old 17-05-13 Thread Starter
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How safe will the 4C be compared to other modern cars?

With such light weight, and the lack of side airbags that other modern cars normally gets, how safe will the 4C be in the event of a collision when compared to it's competitors, like the Cayman?

Anyone care to speculate?
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Does it have an NCAP rating?
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It wont get Ncap rated, volume too low. You will get a good indication from USA, whether it goes in fully compliant or on exemptions
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I think it's probably at least as safe as a Cayman. The carbon fibre tub should be much stronger and safer than a standard chassis
 
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Originally Posted by deppi0 View Post
I think it's probably at least as safe as a Cayman. The carbon fibre tub should be much stronger and safer than a standard chassis
Why are carbon fibre tubs stronger?
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Forget its lightness for a moment. It's a much, much stronger material than steel or aluminium. If you've seen the nose cone of a formula 1 car in a head on impact it's resistance is almost beyond scientific belief. The very nature of the material, that you can add layers in areas where extra strength is needed and lay the weave in opposite directions makes it very, very versatile, if not a tad expensive to buy and produce.

Last edited by Stabilo; 17-05-13 at 20:21.
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Originally Posted by Stabilo View Post
Forget its lightness for a moment. It's a much, much stronger material than steel or aluminium. If you've seen the nose cone of a formula 1 car in a head on impact it's resistance is almost beyond scientific belief. The very nature of the material, that you can add layers in areas where extra strength is needed and lay the weave in opposite directions makes it very, very versatile, if not a tad expensive to buy and produce.
Indeed. Pagani have done something like 15 crash tests on their Zondas, but have never needed to change the tub. The tub is still the chassis 001, which is crazy. Tells you how strong they are.
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Indeed. Pagani have done something like 15 crash tests on their Zondas, but have never needed to change the tub. The tub is still the chassis 001, which is crazy. Tells you how strong they are.
Thanks for the info, that's good to know. However, would the lack of side airbags be a concern to anyone?
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Rigid isn't good in a crash though
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That's why the front & rear structures will incorporate crash structures, they'll dissipate the energy away from the tub.

On the subject of carbon tubs, the first McLaren F1 was apparently driven away after its crash test the chassis was that strong.
 
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Carbon -depending on how it's laid - has the propensity to soak up shock. Look to bicycle forks and frame construction for examples.
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If it's laid in Italy, it'll be interlaced with Spaghetti....lol
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Ok ,it's true in the days of John Barnard as Ferrari F1 chief engineer the carbon fibre work was done in Guildford , but they've probably improved since then!
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Originally Posted by Squadrone Rosso View Post
Rigid isn't good in a crash though
Rigid is good for the saftey cell. The 4C's front and rear crumple zones are aluminium subframes. Also, carbon fibre is very good at absorbing vibration and impacts which is why it's used in high-end road and mountain bike frames and forks.

However, I believe that its main weakness is that it doesn't really show signs when it's about to fail unlike say an alloy chassis that would show cracks. I think an x-ray has to be used, but I'm not 100% on this.

Last edited by Stabilo; 18-05-13 at 20:58.
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It is about absorbing the energy of the collision (into shattering the plastic bodywork and deforming aluminium frames at front and rear), while holding the passengers so they do not strike any surfaces, and preventing any hard or sharp things intruding into the passenger compartment.

Did you see the episode of Richard Hammond's Wonders of Nature where he through a light bulb from the edge of space down onto a rocky mountain? The bulb was held tight in a rigid tube, surrounded by soft beads, inside another rigid tube. The outer cracked, the inner shifted, but the contents were intact when they found them, days later...

That is how cars are designed. Stiff outer, soft layers, hard and tight inners.

The factor they are all trying to manage is the 'deceleration', by spreading the impact over a few more milliseconds, the forces on the occupants are reduced massively. You can have a bit of fun plugging numbers into this model: Car Crash Example

Then their is the lightness issue: if you are in a lighter car, you have less energy to deal with (if you hit a solid object), or are more likely to rebound (if struck). That helps spread the energy dissipation over time as well.

Which leaves us with the immense strength of carbon fibre shells.

The simple comparison between carbon fiber, steel and aluminum can be understood using common forms of the high-strength versions of these materials.

Compare the mechanical properties, the modulus of elasticity (stiffness) and the tensile strength (strength under tension) of these three materials:

1. Carbon fiber T700S from Toray, a standard modulus high-strength fiber, in an epoxy 250 F-cure composite
2. Alloy steel AISI 5130, a low hardenability alloy steel with moderate strength and good toughness
3. Aluminum alloy 7075-T6, a standard aerospace aluminum alloy

Modulus of Elasticity Tensile Strength Density
MPa MPa g/cm^3
CF 120 2500 1.5
Steel 205 1275 7.9
Alu 71 570 2.8

So, CF, even at its current development stage, hugely outperforms aluminium and steel and is lighter, but is possibly *too* stiff for some designed to collapse structures.

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Originally Posted by davidjwbailey View Post
It is about absorbing the energy of the collision (into shattering the plastic bodywork and deforming aluminium frames at front and rear), while holding the passengers so they do not strike any surfaces, and preventing any hard or sharp things intruding into the passenger compartment.

Did you see the episode of Richard Hammond's Wonders of Nature where he through a light bulb from the edge of space down onto a rocky mountain? The bulb was held tight in a rigid tube, surrounded by soft beads, inside another rigid tube. The outer cracked, the inner shifted, but the contents were intact when they found them, days later...

That is how cars are designed. Stiff outer, soft layers, hard and tight inners.

The factor they are all trying to manage is the 'deceleration', by spreading the impact over a few more milliseconds, the forces on the occupants are reduced massively. You can have a bit of fun plugging numbers into this model: Car Crash Example

Then their is the lightness issue: if you are in a lighter car, you have less energy to deal with (if you hit a solid object), or are more likely to rebound (if struck). That helps spread the energy dissipation over time as well.

Which leaves us with the immense strength of carbon fibre shells.

The simple comparison between carbon fiber, steel and aluminum can be understood using common forms of the high-strength versions of these materials.

Compare the mechanical properties, the modulus of elasticity (stiffness) and the tensile strength (strength under tension) of these three materials:

1. Carbon fiber T700S from Toray, a standard modulus high-strength fiber, in an epoxy 250 F-cure composite
2. Alloy steel AISI 5130, a low hardenability alloy steel with moderate strength and good toughness
3. Aluminum alloy 7075-T6, a standard aerospace aluminum alloy

Modulus of Elasticity Tensile Strength Density
MPa MPa g/cm^3
CF 120 2500 1.5
Steel 205 1275 7.9
Alu 71 570 2.8

So, CF, even at its current development stage, hugely outperforms aluminium and steel and is lighter, but is possibly *too* stiff for some designed to collapse structures.
Thanks for the explanation. Very good info.
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I have a 3mm's thick piece of carbon fibre as an adjuster for my alternator , since the steel one cracked --- not on my road car though. It's slotted for the adjustment clamp and the holes each end are clamped using penny washers and so far it's not been a problem.
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There is a myth that carbon fibre is fragile and prone to cracking and splitting.

Anecdotes that this is not so come from my road and mountain bikes are both carbon. I'm 210lbs, so they take a major beating when used. The only parts that have failed were aluminium. My record player tone arm is carbon fibre. My walking poles (ultradistance & mountain walker) are carbon fibre). My pocket knife (leatherman skeletool) has carbon fibre parts. I trust carbon fibre.
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Quote:
Originally Posted by davidjwbailey View Post
There is a myth that carbon fibre is fragile and prone to cracking and splitting.

Anecdotes that this is not so come from my road and mountain bikes are both carbon. I'm 210lbs, so they take a major beating when used. The only parts that have failed were aluminium. My record player tone arm is carbon fibre. My walking poles (ultradistance & mountain walker) are carbon fibre). My pocket knife (leatherman skeletool) has carbon fibre parts. I trust carbon fibre.
David ..Is it a Well Tempered tone arm/Turntable? Woops, only cars to talk about here!

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Good for it's weight, but in a head on with an Audi Q7.. ..not so good
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Good for it's weight, but in a head on with an Audi Q7.. ..not so good
Few cars are as the Audi weighs nearly 2.5 tonnes
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Good for it's weight, but in a head on with an Audi Q7.. ..not so good
There are always cost/benefits to light-weight cars. I would rather be in a car that is better able to avoid that "head on." What if a Hummer hit the Q7-we could go on and on.
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the likelihood is that the Q& ('lard shed on wheels') will either flip on its roof under heavy braking or snap off the road and hit a solid object. The sad truth for the roadtards who buy SUV's because they are "safer" is that they are not: they are MORE likely to have accidents, MORE likely to kill the occupants, MORE likely to kill pedestrians, and MORE likely to kill other drivers. They take about 50% longer to stop, so, when their massive bulk causes them to slide off a wet bend, they hit walls, houses and trees far harder than the 4C ever will.

And, given the agility of a 4C, it should be quite easy to avoid the shed driving roadtards
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Quote:
Originally Posted by alstoy View Post
There are always cost/benefits to light-weight cars. I would rather be in a car that is better able to avoid that "head on." What if a Hummer hit the Q7-we could go on and on.
The most common Hummer was not well rated for crash performance/ occupant protection as it was Chevrolet Blazer-based , but it would certainly have some momentum against any other car.
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and we cut back to the 4C discussion...........
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