How to tell if carbon frame is knackered

[DTD]

A friend had her car rear ended – her bike was on a bike rack the back of the car at the time, it snapped one of the ties and knocked the back wheel out of alignment. The local bike shop is saying the "integrity of the carbon frame may be compromised" – is there a way of telling?

The other's insurance is paying, but they are pleased with the bike (Specialized Ruby) so don't particularly want to replace it, so how do you tell?

 

[Kestevan]

Short answer is you don't.
Unless you're prepared to spend a considerable amount of time and money on xrays etc there's no real way to confirm that the inner structure of the carbon has been affected .
If it was me, I wouldn't risk it, and would be chasing the other parties insurance for a replacement frame.

 

[Yellow Saddle]

"The integrity of the carbon frame may be compromised" is a fancy way of saying "we dont' have a clue how to figure out whether or not it is cracked.

Well, it is easy to figure out. Firstly, carbon doesn't crack in little bits like metal. It is either cracked or not. Cracks will happen not mid-section but at intersections and a quick inspection of the paint will reveal all. Secondly, a cracked carbon frame creaks. Thus, remove all wheels, chains and other semi-loose bits. Now find two strong blokes to manhandle the frame. Bend it this way and that way, pull on the fork, push on the fork etc etc and listen. Then, since it was rear-ended from the side (if that makes sense), put the wheels and chain back on and put the cranks in the 6 'o clock position, stand next to the bike and push hard on the crank with your foot, in an attempt to make the frame flex sideways.

If it passes this test, it is OK to go.

 

[DTD]

Something to be said for steel.

 

[Yellow Saddle]

Something to be said for steel.

Not really. Steel cracks with fatigue and the cracks happen slowly and usually manifest suddenly. In a rear-end, it would have bent and dented.

 

[Salar]

Something to be said for steel.

Agree

 

[gbb]

No amount of unqualified inspection would quell any unease about a frame that's been in an accident. It may for some but it wouldnt me. Inspect to your hearts content but that won't definitively tell you.

Forks ? how do you know the forks are ok ? Cracks between the crown and steerer ?

All very unlikely but ....you're not qualified to say, the LBS isnt, that's why theyve quite rightly said what they did (IMO)

Push the insurance, demand proper inspection. I did with my carbon with a local bus company, talked about liability if it failed in the future...they soon paid up.

 

[Drago]

Someone else's insurance, someone else's problem. They either have the frame inspected and certified by someone qualified at working with structural composites, or they provide a new one. I wouldn't waste a moment's thought on it myself, until the new bike arrived.

 

[migrantwing]

Just get a new/same frame and swap the components over, if they're all OK. If not, just get a full replacement of the bike.

 

[gbb]

Just re-reading the line 'The other's insurance is paying, but they are pleased with the bike (Specialized Ruby) so don't particularly want to replace it, so how do you tell?'

Who doesnt want to replace it, insurance or owners ? Sorry if i've missed the obvious.
If the insurance is paying, there's no problem surely, take the replacement and sleep easy.

 

[DTD]

Sorry, I worded it badly. The person who crashed into the back of my friend's car and damaged the bike will have to pay.
My friend likes her bike and does not particularly want to have to find an identical replacement (it's a couple of seasons ago and is a less common size).
Also I think she's a bit old school (like me, apart from only having steel bikes) and doesn't want to throw things away or do an insurance job if it's not necessary, though the other driver will have to pay for the repairs to her car.

 

[Smokin Joe]

Short answer is you don't.
Unless you're prepared to spend a considerable amount of time and money on xrays etc there's no real way to confirm that the inner structure of the carbon has been affected .
If it was me, I wouldn't risk it, and would be chasing the other parties insurance for a replacement frame.

This stuff about X-Raying carbon frames always crops up. Who the hell offers such a service and has anyone in the world ever had it done? When pros sling their bikes down the road at 40mph the mechanic gives the frame a quick once over and if nothing is obviously amiss they sit them back on and send them off to continue down the mountain. No doubt they get a proper inspection afterwards but it's still only to look for obvious damage.

 

[DTD]

I did read (possibly here?) about someone who's girlfriend worked at British Aerospace and favoured tapping frames with a 50p as a true test of integrity.

 

[Drago]

This stuff about X-Raying carbon frames always crops up. Who the hell offers such a service and has anyone in the world ever had it done? When pros sling their bikes down the road at 40mph the mechanic gives the frame a quick once over and if nothing is obviously amiss they sit them back on and send them off to continue down the mountain. No doubt they get a proper inspection afterwards but it's still only to look for obvious damage.

A work colleague has a good friend who works for Red Bulls F1 team. When his rear wheel collapsed, went skewiff in the frame and damaged a rear triangle he was able to get it x rayed and invisibly repaired. That's a case of who you know, but there are such folk out there.

 

[Svendo]

She could get the insurance payout for the frame, she will still get to keep the old frame. Insurers don't assert their technical ownership of claimed-for bikes. Then she can try to find a replacement or additional frame, get the old one x-rayed, buy a crate of champagne or whatever with the money.