Just how brittle is carbon?

Cyclum

I was knocked off my bike around 6 months ago. I had a few minor injuries, most of which have heeled. I'm just waiting for surgery on my knee.

Now the weather is brightening up I want to try getting back on my bike - to boost my confidence more than anything. The problem is, the insurance company haven't paid a penny, despite there being no query about whose fault it was (she pulled out of a side-street onto an empty road and drove into the side of me. I even have a witness). Anyway, I digress.

So, my bike has been written off. There is quite a bit of damage but the car hit me rather than the bike (she didn't think she should inform her insurers as her car wasn't damaged!), the damage is from be me falling off the bonnet and scrapping the bike on the road. I definitely need to replace the bike at some point but I don't want to do it until I know what, if anything, I'm going to get from her insurance company.

So, do you think I'll be ok to ride it or not? And by ride I mean short 10-15 mile rides rather than the 100+k I was doing before - I'll save that for my shiny new bike.

debeli

This is an odd one. You know that the bicycle is a write-off, but you're not sure whether it's safe to ride.

You can satisfy your curiosity in many ways, but an online cycling forum may not be one of them.

I do not favour carbon fibre on bicycles. I have one or two with cf forks or seat posts, but I prefer steel or alloy for frames.

If you are in doubt, do not ride it. You would not want to be whipping down a steep descent while wondering whether your frame or fork might snap. It would take some of the pleasure out of the experience.

I'm surprised that the money has not been forthcoming. Is there some unsettled issue about the injuries? Six months seems a long time to wait.

But in the meantime, do not ride it until an expert has looked at it - unless you are sure it really is just a scratch or two... and then why is it a write-off?

Steel's the thing. Plastic is for toys.

rafletcher

Impossible to advise you. CF is very strong in the directions it needs to be strong in, and very weak in others. Without seeing the damage who can tell if your bike is ok? It could just be scratched and scraped (and that sounds the most likely) and would be fine to ride, but if there are any dents then that may affect safety - depending on if it's in a highly stressed area of the frame or not.

noodleman

You would be better off posting some pics mate. To be honest though, if it's written off and has in your words 'quite a bit of damage' It sounds like its ready for the skip.

slowbike

Carbon isn't brittle - the resin may be. I had a boat with a carbon mast, put the mainsail up and the mast bent into shape - it was designed like that.

If your bike has been written off then I wouldn't ride it. You don't say which bits are bust - so it may be just the wheels or it may be the frame - without seeing it we can't tell.

This is one of the many reasons for N+1 - a "cheap" runabout would've seen you back on the road PDQ whilst you wait for the insurance co to cough up ...

btw - waiting for the insurance co to cough up - I'd be contemplating a solicitors letter long before now ...

bompington

Debeli wrote:

I do not favour carbon fibre on bicycles... Steel's the thing. Plastic is for toys.

I did buy a plastic bike once, it was indeed a toy (toddlebike).

However, carbon fibre reinforced plastic is a very different thing. And I would rather choose materials based on their physical properties than myths and prejudices, so I'm very happy with my carbon bike. (As long as the sun's shining, of course I wouldn't go out on it when it's raining ;-))

cougie

hassle the insurance company. Threaten them with the cost of taxis for your journeys ? They should pay up fairly quickly.

iron-clover

I wouldn't have said carbon bikes are very brittle- however compared to metals then obviously they will shatter when you massively overload them. Being a composite the failure of the material is much more complicated than with just a single metal, especially as the properties of the carbon fibres and the resin holding them together are quite different.

However, this video shows that carbon frames certainly aren't fragile if made properly:
https://www.youtube.com/watch?v=-lsDXEEUlRE

However, as soon as the carbon tubes are compromised their strength will be reduced dramatically and provides a very weak point for catastrophic failure. It can also be very difficult to determine how badly damaged the material is which is why the general advice is not to ride it if you spot any cracks or suspect it to be damaged.

If in your words you say the frame has been written off, I wouldn't risk it on any rides at all unless it's been thoroughly checked over by a competent person.

You could always sign up to one of the 'no win no fee' companies to see if they can help- they would be able to hassle in insurance company much easier, or if you are a member of CTC or BC get in touch with their legal services.
Good luck!

Smokin Joe

If it was mine and there was no visible damage I'd continue to use it as normal. That's what pro teams do after a crash.

Miles253

Have you had a professional look it over?

ElectronShepherd

Unrelated to the actual structural integrity of the frame, you may want to consider how this would affect your claim. It will be more difficult to make a claim on the basis that the bike is a write off if the insurance company find out you were riding it after the accident.

The insurance company won't do anything of their own volition. They certainly won't come to you and offer reimbursement - you need to chase them.

simon_masterson

Take it to a good bike shop. Do not entrust your safety to the speculation of people on the internet.

Manc33

No you can't because insurance companies send out photographers taking pictures of bikes that have been reported as wrote off in case anyone rides one. I'm joking.

OP no one else was there and you shouldn't take what anyone here says as gospel. Go around the frame tapping it with a penny. I don't know what that does but people do it.

plowmar

You say that the driver didn't advise her insurance company - who did then?. Have you had any admittance of liability ?. Had any communication with them?.

Is your knee being sorted by NHS as seems likely given delay - private apparently a lot quicker. Re bike - as others have said get a written professional opinion and send it - keeping a copy to insurers. Are you insured ? get yours to contact driver's.

Don't let things slow down, keep the pressure on and don't ride bike if at all unsure.

Sorry if this is not very helpful but there does seem to be a few gaps in your tale of woe which just need filling.

Good luck.

t4tomo

Bear in mind they make quite a lot of bits of F1 cars out of CF so it's not that brittle.

First port of call does it look damaged?

sungod

Cyclum wrote:

I was knocked off my bike around 6 months ago. I had a few minor injuries, most of which have heeled. I'm just waiting for surgery on my knee.

Now the weather is brightening up I want to try getting back on my bike - to boost my confidence more than anything. The problem is, the insurance company haven't paid a penny, despite there being no query about whose fault it was (she pulled out of a side-street onto an empty road and drove into the side of me. I even have a witness). Anyway, I digress.

So, my bike has been written off. There is quite a bit of damage but the car hit me rather than the bike (she didn't think she should inform her insurers as her car wasn't damaged!), the damage is from be me falling off the bonnet and scrapping the bike on the road. I definitely need to replace the bike at some point but I don't want to do it until I know what, if anything, I'm going to get from her insurance company.

So, do you think I'll be ok to ride it or not? And by ride I mean short 10-15 mile rides rather than the 100+k I was doing before - I'll save that for my shiny new bike.

as above, you need to push this or nothing will happen

make a full list of all your costs (transport, lost earnings, cancelled holidays/events, clothing, bike etc.) ideally with pictures of damage, send letter requiring payment in full with 14 days, otherwise you will take legal action for your costs plus all additional costs of taking action including your time

do not negotiate down, the cost is the cost

if they pay, go shopping, otherwise go direct to lawyer who specialises, get them to sort it out

needing knee surgery does not sound like "minor injuries", if you've suffered significant injury with any long term impact on your health/fitness/capabilty i'd first get legal advice about claiming damages, you can replace a bike, you can't replace your health

reds99

Having worked with cf composites for 8 years, i think i can dispel some myths regards CF. The first thing carbon is strong but it is also brittle, thats the first thing the manager told me about CF. The brittle part mainly if its hit dropped, smashed into etc. the strength comes from the multi directional laying of the ply, uni directional(1way) will have nowhere near the same strength as multi directional. It is light, thats why it is used on aircraft, F1 cars, not cause of its strength. F1 cars have a fuel limit remember, heavier car = more fuel. Aircraft need to operate as cheap as poss. If CF is so strong why are cars not built from CF.? Lighter car = smaller engine therefore less fuel used. IMO its not used because it wouldnt offer the same protection as ally does, would also suffer stone chip damage so cosmetically wouldnt look as good.
This is all based on my experience of the stuff, and the way it was manufactured. There are other ways of producing which will be inferior to the way i worked with of which i have no knowledge.
We used solvent wipes, detergent AND sealants which have no effect whatsoever on CF.
The only way to tell if the bike is damaged is for a NDT test to be carried out. Personally it sounds ok, any scratch type damage you can use car body filler to repair, but then you need to repray. A lot of complaints on here regards " this hole appeared" etc will be filler used in the prep stage before spraying thats worked loose for a better phrase.
Thanks

plowmar

Is not the reason that cars are not made from CF is that it is more expensive than steel and also whilst it does give protection and strength in specified areas it cannot be as easily/conveniently repaired as steel. Don't forget there are a fair few car makers that use CF in their cars.

And you're surely not suggesting that plane operators are not concerned with safety just fuel savings.

reds99

My point was boeing/airbus need to make aircraft more economical to sell more to customers without compromising safety. Where CF panels are used in aircraft does not compromise safety but it doesnt half reduce the weight of aircraft.

holiver

Others have pointed out the important things about your write off. I just wanted to share this video:

https://www.youtube.com/watch?v=6APhKvaW6ig

norvernrob

reds99 wrote:

Having worked with cf composites for 8 years, i think i can dispel some myths regards CF. The first thing carbon is strong but it is also brittle, thats the first thing the manager told me about CF. The brittle part mainly if its hit dropped, smashed into etc. the strength comes from the multi directional laying of the ply, uni directional(1way) will have nowhere near the same strength as multi directional. It is light, thats why it is used on aircraft, F1 cars, not cause of its strength. F1 cars have a fuel limit remember, heavier car = more fuel. Aircraft need to operate as cheap as poss. If CF is so strong why are cars not built from CF.? Lighter car = smaller engine therefore less fuel used. IMO its not used because it wouldnt offer the same protection as ally does, would also suffer stone chip damage so cosmetically wouldnt look as good.
This is all based on my experience of the stuff, and the way it was manufactured. There are other ways of producing which will be inferior to the way i worked with of which i have no knowledge.
We used solvent wipes, detergent AND sealants which have no effect whatsoever on CF.
The only way to tell if the bike is damaged is for a NDT test to be carried out. Personally it sounds ok, any scratch type damage you can use car body filler to repair, but then you need to repray. A lot of complaints on here regards " this hole appeared" etc will be filler used in the prep stage before spraying thats worked loose for a better phrase.
Thanks

So are you saying the carbon composite monocoque survival cell in an F1 car is only made of carbon because its light, not because of its strength, and that alumium would give more protection?

ElectronShepherd

reds99 wrote:

If CF is so strong why are cars not built from CF.? Lighter car = smaller engine therefore less fuel used.

True up to a point, but for e.g. cruising at 70mph on a motorway, weight is almost irrelevant, since you aren't accelerating - it's drag that's the main impact on fuel economy.

reds99 wrote:

If CF is so strong why are cars not built from CF.? IMO its not used because it wouldnt offer the same protection as ally does

I think the protection offered is much worse. Metal deforms when hit, and absorbs energy. This is the basis of crumple zones at the front and rear, and why even small crashes look really bad. The bits outside the passenger cell are designed to be weaker, so in a crash, they deform, soaking up the energy and hence protecting the occupants from some of the impact's severity. I'm not a materials expert, but I think it's much more difficult to get carbon fibre to exhibit those characteristics.

There's also costs to consider. For a buyer of a McLaren P1, which does use a lot of carbon fibre, cost is not a concern for them. Cars like that fall into the "if you have to ask the price, you can't afford it" category. For a base model Ford Fiesta, cost is *really* important, and the manufacturer can't afford to use carbon fibre, since at the bottom end of the market for new cars even an extra £500 on the manufacturing cost is a huge amount of money.

frisbee

The survival shell in a formula 1 car needs to withstand certain impacts, a carbon fibre survival shell will be lighter than an aluminium or steel survival cell. The strength of all 3 shells will be the same (assuming no other design criteria or constraints).

The actual impact absorbing material isn't carbon fibre, it'll most likely be an aluminium honeycomb structure.

ben@31

When I came off my (aluminium) mountain bike earlier today, as I was flying through the air over the bars I was thinking about this thread.

They make mtb frames from carbon, so...

1). The owners of carbon mtb frames must be that good, they never crash.
2). They must have money / team sponsor to write off carbon frames after a bad spill.
or
3). Carbon mtb frames can't be that bad.

Edit. I've Just seen the SantaCruz video. Was an eye opener, but were the tests true to real life scenarios?

pippi_langsamer-2

t4tomo wrote:

Bear in mind they make quite a lot of bits of F1 cars out of CF so it's not that brittle.

First port of call does it look damaged?

Have you seen what happens to a cf suspension strut assembly on an F1 car when they take a lateral impact?

Bozman

Looking at some of the posts and scare stories on here, I'd guess that there's a large skip full of carbon frames after every race day in the pro world. Bunch of ar5e.

MountainMonster

I wonder how many years it will be before the carbon is accepted finally as a good material, and people give up with the mthys that it is going to break if a fly flies into it sideways.

reds99

In my post i havent suggested carbon isnt a useful material, i suggested its usefullness is because it is light in comparison to aluminium/steel. Thats why people buy bikes as it is easier to ride than a 15 kg steel frame.
The video which i briefly watched on an iphone, shown a carbon frame against an ally frame. The carbon frame had a solid carbon top tube, it looked to me anyway a full diameter of carbon, that snapped at 2000lbs of pressure. To me it was interesting to know it snapped in that place. The ally frame is hollow, im assuming it was hollow. I cant remember but did that start buckling at 1400lbs. Would a solid frame buckle at that point, beit a damn sight heavier?
Some of the cheaper carbon frames will not be pure carbon top tube, probably have a honeycomb structure with the carbon layed around it. This gives it bulk, whilst retaining strength but in the cure process can create voids, which means at a guess a12 mth warranty is offered as against a lifetime warranty, that is just an example as i dont think there gonna scrap a costly panel off so easy.
I have never been involved in cf bike frame so have no knowledge of their process, but i have in the past been involved in high spec cf panels and have a good understanding of the processes.

bompington

reds99 wrote:

I have never been involved in cf bike frame so have no knowledge of their process

This bit, at least, makes sense...

noodleman

Some of the cheaper carbon frames will not be pure carbon top tube, probably have a honeycomb structure with the carbon layed around it. This gives it bulk, whilst retaining strength but in the cure process can create voids.

Not so sure about this statement. Sounds like the sort of scaremonger stories that used to circulate a few years back.

Cyclum

Thanks all. That's really helpful.

To fill in a few gaps...

I reported it to the police who took the witness details and went round to speak to her. She admitted liability - that's never been in question.

The driver thought that should be it (she didn't like that the police were involved) and didn't think that it should be reported to her insurance company. I had to nudge her and it got a bit nasty (her). At that point I instructed a solicitor so I could keep out of it. I'm not a member of BC or any other helpful membership (I've learnt the hard way) so I found a solicitor that specialised in cycle accidents... Or so I thought.

They've been pretty rubbish and from what I can gather I'n not actually getting legal advice, simply someone who passes messages between me and the insurance company.

An example - I spent hours photographing my damaged bike, clothing etc, providing receipts for it all... And sent it all to my solicitor. A couple of weeks later I had a message from my 'case handler' to say that they had lost any evidence of purchase and so we're offering an insultingly low figure on the basis that they were calculating it on the assumption that it was a few years old and subject to wear and tear (most was actually only a couple of weeks old). My case handler asked if I was prepared to accept that. I then had to go back and suggest that the receipts were resent to the insurance company. And so it goes on...

I understand that the injury part is treated separately so I should get something for the bike before sorting my knee out. In theory.

And to think I went with them because in my first conversation they talked bikes and told me that "they make it their priority to get you back on the road..." which is actually quite a big deal for me as I don't drive so that is my transport - I don't really have an alternative.