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Carbon forks and danger - question(14 posts)

Carbon forks and danger - questionmuncher
Oct 15, 2001 5:53 AM
Please see the below, posted on my club's forum:-

"Broken forks are one of every cyclist's worst nightmares - usually a hospital job if not "half a day out with the undertaker". A few weeks ago Richard Hallett reported in Cycling Weekly a rash of carbon fibre fork failures which he more or less dismissed as coincidence and he said that he thought the actual failure rate was probably 1/100th of 1%, i.e. 1 in 10,000.

If he was right about that figure, and I doubt whether enough data exists to be confident, it is actually a very high rate which would be unacceptable for a safety critical component in, for example, the aerospace industry. Again if he was right about the 0.0001 failure probability then given that only a few thousand of these forks are in use in the UK, 3 failures in one weekend would give grave cause for concern that something was amiss, the obvious possibility being that the forks concerned had reached the end their (short) but not accurately predictable lifetime or that there are inherent manufacturing problems which may cause a high but undetected defect rate.

Personally I would be unhappy about using either alloy or carbon fibre forks unless their use was confined to smooth roads and tracks. Both materials (and the adhesive joints by which they are joined to other components such as the steerer) are prone to fatigue failure after a finite lifetime which is difficult to predict unless the loads sustained, e.g. potholes hit, are continuously monitored and regular inspection for cracks is carried out as in the aviation industry (for potholes read gusts, high g manoeuvres, heavy landings, etc!).

I know that I am ultra-conservative about equipment whereas racing cyclists by and large are dedicated followers of fashion and carbon fibre forks now seem almost obligatory; it may be that the safety concerns are met by the fact that people dispose of their frames after a few thousand miles use. That however begs the question of what happens or may happen to the subsequent owners!

I would have thought that there is certainly a need for the manufacturers to give advice on what is a sensible maximum mileage for such forks (as a function of the type of use they are put to. Do they do that?

Any comments?"

Anyone out there able to offer any insight? Thanks in advance - M.
re: Carbon forks and danger - questionMcAndrus
Oct 15, 2001 5:59 AM
In the USA's litigious society, if there were a systemic design weakness with carbon forks I believe the lawyers would have sued the manufacturers out of business by now.
Good point, but...muncher
Oct 15, 2001 6:05 AM
For the same reason I would have thought that the forks would have come festooned with stickers re inspecting before every ride, replacing every 18 months or whatever, not storing in oxygenated air etc etc - the "warning these nuts may contain nuts" disclaimer culture. Mine didn't - did anyone else's? Any "experts" able to chip in with info re the life span of carbon, it's behaviour under repeated strain and so on.
Numbers=headachesChicken Little
Oct 15, 2001 6:20 AM
So, Hallet has a 1 in 10,000 figure. You doubt this figure. Any figures concerning steel forks is in doubt. You doubt that enough data exists. A figure of a few thousand forks in the UK is is doubt. The figure for the predictible lifetime of a fork is in doubt. The very predictibility of their lifetime is in doubt. The number of failures in a weekend (which weekend?) is in doubt. The sustained load over a forks lifetime is in doubt.
Maybe manufactures of CF forks haven't come up with a final mileage number because the cyclists are still using the fork. If the fork does break, even if it's after a million miles, doubters will say, "Ahh haa, I knew those weak forks had a finite lifetime!"
Should have said...muncher
Oct 15, 2001 6:43 AM
Not my question I was quoting there - just thought that I might be able to get an answer for the guy here, and having a carbon fork myself, I was interested. Just seemed odd to me that such a piece of safety critical equipment came (in my case) with no "use guidance" at all - in stark contrast to, for example, by bike and motorbike helmets, and indeed the whole manual for my motorbike (check tyres and fluids before each ride etc etc).

My suspicion (as a layman) is that the CF fork is prob less prone to wear than steel/al(as opposed to radical damage) failure as it is more pliant. CF frames seem to manage, from what I hear from Look271 et al. I just don't have any empirical evidence to back that up.
If forks are like framesJesse Smith
Oct 15, 2001 7:00 AM
If you're willing to accept that failure rates of forks would be comparable to failure rates of frames, then this test
http://www.damonrinard.com/EFBe/frame_fatigue_test.htm
suggests that CF forks with their current construction methods would last longer than steel forks.
InterestingSamDC
Oct 15, 2001 8:05 AM
The frames that one would think would fail first (AL, CF) surpassed those that would intuitively last forever (Ti, steel). Just thought that was an interesting study. Those Germans, esh.
InterestingVictorChan
Oct 15, 2001 8:37 AM
The article is kind of old. So, things maybe different now???
InterestingLen J
Oct 15, 2001 8:51 AM
While it is an old study, I wouldn't think that the bikes that performed well would get worse, rather if anything I would expect some of the others to get better.

Len
OLD studyTrent S
Oct 15, 2001 9:19 AM
also commissioned by someone that had a stake in seeing CF come out on top. I'd take it with a grain of salt. Also questions about the load placed on the bikes not representing real world.
OLD studyDavid Feldman
Oct 15, 2001 5:44 PM
What I'd wonder about re that study would be the realism, loacing a frame that's fixed in place instead of free to flex plus having wheels share the load. I have to wonder how valid that whole test was.
take a notecyclopathic
Oct 16, 2001 6:56 AM
they all fail alone welds

crack needs to originate somewhere and such anomalies as different strength/thickness/density (welds), microfractures (machining, drilling) are the good spots.

CAAD3 withstand the test because the way Cdale builds frames (weld, sand, 24hr heat treating), not because Al is superior, but because material is uniformed

Fibers in Trek CF frame stop (or at least slow down) crack development

Lugged steel frames supposed to be very strong, yet DeRosa and Barellia faild.. my guess they messed up head tube lugs trying to save a few gramms
Carbon forks or carbon steerer tubes?Tig
Oct 15, 2001 10:15 AM
I seriously doubt that a quality carbon fork would fail outside of a result of a severe crash. Carbon forks themselves aren't or shouldn't really be in question. A CF fork with a steel or aluminum steerer should be quite safe.

Maybe he was talking about carbon steerer tubes. We've all heard about some failures with them. No, not all steerers are created or installed equally! Many of the failures could have been easily prevented if the installer was competent. In general they are safe for most riders. I'm still wondering if I should go with a CF steerer or not. The forks I like the most all have them. I'm down to 132 pounds, so a well-installed CF fork/steerer shouldn't be a problem for me at all.
Think first, then quote statisticsKerry Irons
Oct 15, 2001 5:59 PM
A failure rate of 1/10,000. What does this mean? One per day per 10,000 forks on the road? One fork in 10K fails some time during its "user life"? One of every 10K forks fails per year? The difference between these three is immense, and yet we have no idea what 1/10K means. This is meaningless without some reference point.