a funny thing happened on the way to the hill...

[giverdada]

i only got up the first hill, made the right hander to head over to the next monstrosity for the bulk of my lunchtime workout today, and something just didn't feel right. spongey, as it were, is a terrible way for a cockpit to feel. bearing play in the front hub, for sure, but this was something different. almost like a loose headset.

nope.

wait.

it 'pings' when i wrench the bars. not 'one ping only' either.

got home. wrenched the bars for sure. disassembled. and of course:

a cracked full-carbon steerer tube.

after reading about king headsets and steerer tubes and bladdy blah blah for weeks, i figured that had to be it. i also discovered that my lbs put in a star nut instead of a compression plug!!! woah. anyway, none of these things are anywhere near the crack. the crack is all the way around the tube, about an inch and a half from the top of the head tube. not near or against anything. no scoring from the king headset. no cracks from the star nut. just a wrecked steerer on an otherwise fine fork. off to check for ebay replacements i suppose... the one-inchers are hard to come by. :rolleyes:

[forrestw]

jeebus!

Exactly here *is* the crack wrt head tube, 1.5" above or below the top? -- looking at the photo it looks like below.

How much height in spacers?

The star nut *is* not adjacent to the crack now but was it originally? star nuts can and do migrate.

What make fork? age? history?

This kind of failure is downright scary, the more so absent any apparent cause.

I would love to have this to section and do failure analysis.

[giverdada]

to think i was bombing down hills two days ago on that set-up, upwards of 43mph. man...

the crack is, quite literally, in the middle of nowhere. it's on bare steerer tube that contacts nothing, between the headset cups in the middle of the bike's head tube. nothing there but air. no sign of scoring anywhere, let alone around the crack area. i don't know the make, but my guess is profile. superlight. alloy dropouts. otherwise full carbon. started using from brand new, not used. just gave out. thankfully i noticed while riding along between bomber descents to hill repeats!

[bicycletricycle]

maybe Grant Peterson is right

[Ken Robb]

Serotta sells 1" carbon forks and if this experience has you nervous Rivendell sells all steel in-stock forks. Seeing things like this is taking the fun out of 45mph descents for me. Lucky you are sensitive enough to discover this crack before it hurt you. :beer:

[AngryScientist]

hmm, that is scarey stuff.

if you're looking for a cost effective solution, i just picked up a Winwood 1" fork, carbon blades, alloy steerer. its pretty light and rides very well. price is pretty good at just over 100.

glad you make it out ok and were able to keep the rubber side down.

http://i1003.photobucket.com/albums/af153/aero_dynamic8/DSCN1103.jpg

[mike p]

When something just dosen't feel quite there's usually a reason, most people tend to ignore it.....Good Catch!

Mike

[Louis]

What burns me up about stuff like this is that doubling the thickness of the steerer tube would add so much strength and so little weight.

However, we only have ourselves to blame. If we did not insist on buying the lightest possible stuff then manufacturers would not make silly-light components, especially for safety-critical parts like the fork.

Every time I look at one of my Alpha-Q forks I'm amazed how light it is compared to a steel fork, but then I look at the steerer tube and it scares the h3ll out of me.

I guess all we can say about that part is that at least it failed somewhat gracefully.

Louis

[InspectorGadget]

Even though you need a new fork, which sucks, a steerer tube failure at any speed could have seriously ugly results. :eek:

[giverdada]

I was thinking the same. I rode a little more just to minimize the distance to hike home, but all I could think about was hincapie in that Paris roubaix. So I got off and walked and got yelled at for walking. Jokes. Insult to (almost) injury.

[rice rocket]

That's odd to have the failure in the middle of the tube.

Has anyone ever filled their steerer with structural expanding foam? It's a pretty common technique to add strength and stiffness in composites.

http://www.uscomposites.com/foam.html

[Don49]

the crack is, quite literally, in the middle of nowhere. it's on bare steerer tube that contacts nothing, between the headset cups in the middle of the bike's head tube. nothing there but air. no sign of scoring anywhere, let alone around the crack area.

Just speculating here, but is there any chance that an improperly faced head tube could cause this type of failure? If the top and bottom surfaces of the head tube were not precisely parallel, wouldn't that allow the headset to apply a slight bending force to the steerer? If so, could that stress the steerer tube over time and with road impacts?

I've occasionally thought about this failure on my Ouzo Pro fork with CK headset and Ritchey WCS (carbon safe) stem.

[BumbleBeeDave]

. . . "Sh*t happens" if it weren't for your discovery that the LBS had installed a star nut.

An expander plug simply pushes outward and braces the carbon steerer from the inside against the clamping force from your stem bolts.

But as I understand it a star nut is made to bite into the actual tube AND pull upward on the tube to snug the fork against the frame steerer tube an eliminate play. If your LBS mechanic put that star nut in there it's been biting into the carbon and pulling up on the carbon steerer the whole time you're been riding it.

I think it's a legit possibility the improper installation could have had a lot to do with the failure of the carbon tube even though the actual crack is not where the nut was biting into the inside of the carbon tube. With the tension created when the top bolt is tightened, that nut has been trying to pull your fork up through your steering tube ever since it was installed. Sooner or later something had to give--and it did. Fortunately it gave when you were not descending a hill at 50mph.

I don't claim to be an engineering expert, but I figure there's probably a pretty good reason that you're supposed to install an expander plug instead of a star nut in a carbon steer tube. I think you need to have a serious discussion with the owner of that LBS as to the training of his mechanics. That improper installation could have led to a serious injury for you--or even death.

BBD

[mgd]

what sort of bike is it? is it the original spec for that bike or an (up?)grade fork?

if it's a nice bike and a keeper, maybe a steel fork would be worth it and not prone to such steerer tube failures.

[sg8357]

maybe Grant Peterson is right

You'll never beat Cavendish in the sprint on a GP designed bike. :)

[bicycletricycle]

You'll never beat Cavendish in the sprint on a GP designed bike. :)

this would be a very good point if the thread was called-

a funny thing happened in the sprint against Cavendish...

:) just joking, steel breaks as well, it is all about what is an acceptable risk to you, millions of people have carbon forks, blah blag blah....

[giverdada]

what sort of bike is it? is it the original spec for that bike or an (up?)grade fork?

if it's a nice bike and a keeper, maybe a steel fork would be worth it and not prone to such steerer tube failures.

the bike is a 1990's-ish Ti Serotta, though unclear as to whether it's a legend or not. it has colorado concept tubing, and this was the tubing that cracked last summer and found me all kinds of friends and enemies in and out of the forum. (as a note: the crack was fixed for a nominal fee by Ti guru Matt Chester in 4 days and with a full buff of the frame that made it look like new. no problems with it since.) i don't know the original spec for the frame though i would suspect that it was a threaded headset, suggested by the 1" headtube/headset requirements. i was very fortunate to have the chris king headset in 1", and the full carbon fork was unused when i installed it. after i couldn't get the compression plug to keep the headset tight, i took it to the LBS and the rest is history. it stayed tight until it almost killed me... (and Dave - i agree, and will be heading to the shop later this week for a good discussion about these practices).

currently, i am thinking a good deal about a steel fork. maybe even a threaded assembly, but that would require more sourcing of parts and i've already got a headset and corresponding cockpit ready to go. thanks for all the points, friends.

nick.

[bobswire]

I recently installed a 1" Wound Up with "steel" steerer on my Merlin.
LOve it !
Handling has improved as well as my confidence in descending at speed.

http://i54.tinypic.com/a58gar.jpg

[forrestw]

But as I understand it a star nut is made to bite into the actual tube AND pull upward on the tube to snug the fork against the frame steerer tube an eliminate play. If your LBS mechanic put that star nut in there it's been biting into the carbon and pulling up on the carbon steerer the whole time you're been riding it.

I think it's a legit possibility the improper installation could have had a lot to do with the failure of the carbon tube even though the actual crack is not where the nut was biting into the inside of the carbon tube. With the tension created when the top bolt is tightened, that nut has been trying to pull your fork up through your steering tube ever since it was installed. Sooner or later something had to give--and it did. Fortunately it gave when you were not descending a hill at 50mph.

I don't claim to be an engineering expert, but I figure there's probably a pretty good reason that you're supposed to install an expander plug instead of a star nut in a carbon steer tube. I think you need to have a serious discussion with the owner of that LBS as to the training of his mechanics. That improper installation could have led to a serious injury for you--or even death.

BBD

Whether using star nut or an expander plug, the fitting is used to apply tension through the steerer tube and pre-load to the bearings. However this amount of tension is small and once the stem is clamped to the steerer then that connection is carrying the load. The initial tension (should be) quite small in comparison to tension loads induced in riding.

Looking at the photo it seems unlikely that a crack would have propagated 2" or more from the star nut all the way to the point of failure. Short of sectioning the steerer there's really no way to tell.

[forrestw]

... after i couldn't get the compression plug to keep the headset tight, i took it to the LBS and the rest is history.
As noted above, the plug is (should be) only used to apply pre-load to the bearings, it isn't designed to resist loads from riding.

Headsets loosen up due to bearing wear or due to slippage of mechanical components, if a HS becomes loose in under several hundred miles of riding the latter would be the cause. I.e. you possibly weren't applying sufficient torque to the stem clamp bolts?

[merckx]

does the frame have a headtube badge? if so, did you check to see if the rivits/screws are protruding into the headtube and scoring the steertube? i've seen this happen before.

[mgd]

the bike is a 1990's-ish Ti Serotta, though unclear as to whether it's a legend or not. it has colorado concept tubing, and this was the tubing that cracked last summer and found me all kinds of friends and enemies in and out of the forum. (as a note: the crack was fixed for a nominal fee by Ti guru Matt Chester in 4 days and with a full buff of the frame that made it look like new. no problems with it since.) i don't know the original spec for the frame though i would suspect that it was a threaded headset, suggested by the 1" headtube/headset requirements. i was very fortunate to have the chris king headset in 1", and the full carbon fork was unused when i installed it. after i couldn't get the compression plug to keep the headset tight, i took it to the LBS and the rest is history. it stayed tight until it almost killed me... (and Dave - i agree, and will be heading to the shop later this week for a good discussion about these practices).

currently, i am thinking a good deal about a steel fork. maybe even a threaded assembly, but that would require more sourcing of parts and i've already got a headset and corresponding cockpit ready to go. thanks for all the points, friends.

nick.

works fine.

[drewski]

You'll never beat Cavendish in the sprint on a GP designed bike. :)

This is true, but then again most people on this forum can't get new bike
in the middle of a bike ride either if we suffer a structural integrity failure
on our bike de jour.

[firerescuefin]

http://velonews.competitor.com/2011/07/bikes-and-tech/technical-faq/technical-faq-pro-bike-choices-carbon-fork-fatigue-and-fitting-tools_181993


Dear Lennard,
A buddy of mine and I were recently debating the merits of regularly replacing carbon forks as a preventive measure. My wife has a 2002 Bianchi Veloce. It has a decent steel frame, a 1-inch carbon fork (w/ a steel steerer), and parts that still work great. We met when I sold her the bike back in my shop days; consequently, the bike has some sentimental value. She continues to love riding the bike, too.

But I’m starting to wonder if the relatively generic fork should be replaced. It shows no outward signs of fatigue (chips, cracks, etc.), but the thought of her fork snapping on a descent is starting to keep me up at night and getting my brain spinning about getting a local builder to put together a nice, new steel fork. So, what’s your take? Is an apparently fine 10-year-old carbon fork a peril or am I just making up excuses to buy bike stuff? (If there’s no peril, believe me, I can think of other ways to buy stuff. This is a zero sum game for the bike industry.)
— John


A. Dear John,
I wouldn’t worry about it, as carbon has very good fatigue life if not damaged by an exceptionally high stress or impact. Here is what Bert Hull, an expert on carbon and other frame materials as a former True Temper/AlphaQ engineer, has to say about it:

“Carbon parts should last for a very long time (aka lifetime) if not damaged, unlike aluminum, which has no fatigue limit. Since I sold my Vitus 979 back in 1990, I can’t remember any aluminum road racing forks being sold. I think that is about the time carbon fiber was hitting the market in strong numbers.

By damage, I’m talking about a wreck or any other over-load situation.

I have tested a lot of steel (mostly True Temper brand tubes) and of course carbon (lots of brands) in fatigue tests and also load-to-fail tests. In high fatigue loading, the carbon forks would eventually lose some stiffness (as much as 5 percent) after many thousands of cycles to represent many years of actual riding conditions. So I would not say the forks would last forever at high loading. You don’t hit high loads on most of your rides though … You should get a lifetime of JRA riding (just riding along).

Steel forks did not lose any stiffness in the fatigue tests. They are typically kind of over built so they never got stressed past the endurance limit (about 50 percent of ultimate tensile strength). In load-to-fail tests, the steel forks bend until they crack, or we would stop when the fork had bent more than 10-20 percent (un-useable