Busted Carbon

[willhub]

I pulled the carbon steerer in two on the kaffenback a couple of months back when climbing a steep hill. Luckily I wasn't dropping off holme moss at 40mph......

How did that happen?

 

[beanzontoast]

I pulled the carbon steerer in two on the kaffenback a couple of months back when climbing a steep hill. Luckily I wasn't dropping off holme moss at 40mph......

Echoing Willhub, this is what intrigues me - are all the failures the result of impacts? Are there some that just 'happen' unexpectedly?

Kirstie: tapping a 50p along to test for faults hidden within the carbon - that's really interesting, and also a bit scary. And another reason why that material doesn't appeal to me! Is it easier to spot metal fatigue than 'carbon fatigue'?

 

[buggi]

my magnesium frame sheered at the seat post just from wear and tear so i think most materials have their breaking point. that's interesting to know kirstie.

 

[Mr Pig]

The thing is that on a steel frame the wear and failure pattern are very predictable, it's easy to have confidence in steel. Carbon I would never be totally sure about.

 

[fossyant]

I pulled the carbon steerer in two on the kaffenback a couple of months back when climbing a steep hill. Luckily I wasn't dropping off holme moss at 40mph......

 

[Bigtwin]

I just don't get forks with carbon steerers. The difference in weight between them and ones with alloy is, effectively, nothing. About an energy bar in your back pocket perhaps. And yet the failure rate of alloy steerers is about zero.

 

[dellzeqq]

The alu/carbon compound steerer/forks arrangement used to be the most susceptible to failure.

All these photographs prove nothing. I've rear-ended a bus, ran in to the back of a van, and been hit by a bus. The all-carbon frame and forks just shook it all off. It did develop a small crack, but that happened after running over ridged ice at high speed, bouncing up and down by about six inches. I didn't give a thought to going for any other material to replace it.

 

[Gerry Attrick]

And the failure rate of carbon steerers is.......?

There are millions of carbon framed bikes out there being ridden in all conditions daily. do you really think that if the material was as fragile as some posters would have it, that the dramatic dailies would not be full of reports of gory injuries caused by such nasties?

Granted, when it fails, carbon fails big style, but no more than other materials. Let's face it, if a bike is hit by a truck, then whatever material it is made of, it will go bang.

 

[Bigtwin]

And the failure rate of carbon steerers is.......?

No idea but there's one in the link, and I know a couple of guys in the club have snapped/mashed them. But I bet it's more than Al, just through people cranking them up too hard, but lots have a weight limit - or did when I built my last bike - likewise seat posts. Which must tell you something. Especially in the day of compact frames where people have a bunch of spaces on top of the head tube - or put another way, a lot of carbon sticking up taking a lot of torsional force.

Point being, they have no advantage in terms of ride quality etc, whereas fork blades do.

 

[dellzeqq]

Point being, they have no advantage in terms of ride quality etc, whereas fork blades do.

You stick to what you know, then. Me, I'll have a ride that feels as if my butler has gone out and ironed out the bumps....

 

[Bigtwin]

You stick to what you know, then. Me, I'll have a ride that feels as if my butler has gone out and ironed out the bumps....

If you think you can feel the difference between a carbon steerer and an Al one on the same blades, you crack on.

 

[Tim Bennet.]

No idea, but I bet it's more than Al

I bet you're wrong. The most tricky joint is carbon to aluminium. Just witness all those early carbon frames that used alu lugs to join carbon tubes.

It makes no sense to try and join an alu steerer to carbon fork legs at the point of maximum flexure. Just a cheap bodge to avoid making a mold for the steerer tube. (that is for monocoque forks, not those other cheapskate forks that bond the carbon fork legs to a carbon steerer tube).

All this pig ignorance about carbon fibre has become the modern replacement for all those sad old people who kept repeating the urban myth that Reynolds 853 was stiffer than 531.

 

[dellzeqq]

It makes no sense to try and join an alu steerer to carbon fork legs at the point of maximum flexure. Just a cheap bodge to avoid making a mold for the steerer tube. (that is for monocoque forks, not those other cheapskate forks that bond the carbon fork legs to a carbon steerer tube).

That's how I've always understood it.

 

[Bigtwin]

I bet you're wrong. The most tricky joint is carbon to aluminium. Just witness all those early carbon frames that used alu lugs to join carbon tubes.

It makes no sense to try and join an alu steerer to carbon fork legs at the point of maximum flexure. Just a cheap bodge to avoid making a mold for the steerer tube. (that is for monocoque forks, not those other cheapskate forks that bond the carbon fork legs to a carbon steerer tube).

I'm not sure it's the joint that fails - a scan through google results seems to show that it's the actual steerer tube that fails, rather than the steerer/crown join area, typically in the stack area. Of course, that's a somewhat random selection of evidence. I did see some research on fork failure a while back, which I'm trying to find again.

But you're right - mine are not bonded there, but the steerer projects down into the forks - precisely as I didn't want forks with a bond as you describe which seems to me to be asking for it.

I wonder how many people have any idea what they are riding fork construction-wise?

Which reminds me - I bet that carbon steerer George Hincapie snaped clean off in the Paris-Roubais wasn't a cheapie one. Or was it Alloy? either way, it was the tube that snapped, rather than the fork/tube join was it not?

 

[dellzeqq]

Steel frames used to go on the Paris-Roubaix. I've written off a 531C steel frame hitting a taxi at a very modest speed. The C40/bus impact was much, much bigger...and the frame and forks were undamaged. Ears rang for a couple of days after...