Carbon forks and crashes

Ngalbrai

After some advice, crashed into a car door the other day. Bike seems undamaged but checked it into LBS just in case, worried about carbon fork (Specialized Sirrus Elite hybrid). They ummed and ahed about given this is my second crash whether to replace the fork, they couldnt see any damage.

So, my question is:
1) Am I now rightly paranoid about my fork?
2) Should i replace it?
3) Thinking of going with steel (kona p2) as more robust alternative for a commuter bike - thoughts?

Would really appreciate some opinions as I am frankly rather worried about taking the same shoulder shrugging attitude as LBS guy, doing a high speed face plant on the Pacific Highway and then promptly being run over doesnt really fit into my immediate plans...

JWSurrey

The problem with carbon is that I'm lead to believe you are more likely to suffer sudden and "catastrophic" i.e total failure without warning or any sign of a bend, due to the ductility of the material, especially when fatigued.

The chances are that it's alright, but then again, if you've lost confidence in it, and don't fancy a sudden spill on to the road as you sink a pothole at 30mph, then perhaps changing it for either a new carbon or a steel fork is a better option.

Question is, were your impacts of much greater force than the average pothole dipping experience?

The question was discussed on the forum some months ago, and the cost of a fork vs. medical bills or having it X-rayed / cross polarisation tested outweigh the cost of a new fork.

I'd look on it as a fortunate opportunity to go out and spend dosh on one of those new improved wave forks by someone like Deda.

Gotta dash.

P.S: What about the frame?!

Bugly

JWSurrey wrote:

The problem with carbon is that I'm lead to believe you are more likely to suffer sudden and "catastrophic" i.e total failure without warning or any sign of a bend, due to the ductility of the material, especially when fatigued.
!

MMM Carbon fibre is not ductile its the lack of ductility that causes the failure with fatigue

redddraggon

Bugly wrote:

JWSurrey wrote:

The problem with carbon is that I'm lead to believe you are more likely to suffer sudden and "catastrophic" i.e total failure without warning or any sign of a bend, due to the ductility of the material, especially when fatigued.
!

MMM Carbon fibre is not ductile its the lack of ductility that causes the failure with fatigue

CFRP doesn't suffer from fatigue either (although perhaps that can be disputed, but it probably doesn't happen in a fork).

OP - I suggest taking the fork off the frame yourself, and if there's any visible damage to err on the side of caution and not use the fork and get a new one.

simbil1

Has the fork been removed and the steerer examined? The force of the impact may have stressed the area just above the crown where it is supported by the headset.
The other areas to look at would be where the CFRP bonds to something else - the drop outs and the crown.
The CFRP itself shouldn't be a problem if you cannot see any sign of damage, softening or delamination. But for peace of mind, might be worth a change anyway.

"After some advice, crashed into a car door the other day. "

I bet you won't be taking that advice again

(Sorry, someone had to, I take it you weren't injured)

Bugly

:oops: True the CF is insetsitive to fatigue however the polymer matrix which it strenghtens is not so insensitive.

Tell you what If there was any frame damage I dont think that I would be too keen to ride on the forks :shock:

Monty Dog

A careful visual inspection undertaken regularly should be OK, particularly if there is no visible signs of damage. It's highly unlikely that a fork fails suddenly and catastrophically - you would anticipate some sort of indication through cracking of paint / lacquer, creaking whilst riding - particularly out of the saddle. From my own experience - I hit a bank of sand riding my Colnago in the Surrey Hills a number of years ago - it stopped me dead and I executed a perfect roll whilst attached to the bike - the fork taking the brunt of impact. I'm still using the same forks years later and they've been ridden and raced since then with no probelms including a couple of Paris-Roubaix sportives.

cougie

Did someone open their car door on you or was it a sideways hit ?

If its an insurance job, then I'd take no risks and get it replaced.

If it were my own money, then I'd have to think about it a bit more ?

synchronicity

I agree with Reddraggon, simbil1 & monty dog.

I'd remove it and check it over carefully for any superficial damage.

Yeah I sware the term "catastrophic failure" was invented by the bike industry in the mid to late nineties... when I used to test composites in the lab, it was very clear when they were past the ultimate strength. They make all sorts of popping & cracking noises. And you can visually see the failure mode. Broken fibres, etc. Techincally it has failed but isn't completely broken.

I can't explain it well here, but there are multiple plateaus where the strength rises and falls off again, but each peak/trough smaller than the last. I couldn't find any stress-strain graphs on google to show you...

Brittle metals like cast iron are far worse to predict the breaking point...

pjm-84

Having broken a set of carbon forks you will hear an almighty "crack". (Those uphill sprints - :roll: ). I whipped the front wheel off after the ride and you could see the cracks going around each fork legs.

heffordvtr

i imagine the carbon in the forks is designed to withstand impacts like that. it like fishing rods and carbon wheels

my fishing rods can withstand some awesome power when bent on a cast but will disintigrate if twisted and crack if troden on. same with carbon whels, they are very good going round but will fold in half when pressure is put on it sideways.(like the t-mobile rider in last years tour with the dog)

id make a visual inspection of the fork. you should be able to se if theres anything wrong with it.

Ngalbrai

Thanks for all the suggestions, given the lack of certainty and that if it breaks on the roads I use i will be killed i am going to replace it with an alloy fork for durability and predicatability. Its worth the money in my view not to be feeling apprehensive about it (which i definately would!).

I am guessing that since its not a particulary high end fork that there will be negligable weight difference with say a kona p2?

Mikey1280

The kona p2 for mountain bikes appears to be around 1kg, not sure if the road version has a smaller mass. The cheapest carbon forks tend to be around 5-600g so you could be almost doubling the mass.