Question on developing split in carbon steerer tube

Kovie said:

Last year I purchased a Forte Axis Pro Carbon road fork
from Performance Bike as part of a combo that also
included a Cane Creek S2 headset, a Forte Pro stem, and
carbon spacers. I used it to build up a new Ti road bike.
I actually had a local bike shop press the headset and cut
and install the fork, as I didn't have the tools or
expertise to do this myself. I gave them the instructions
that came with these components, including the recommended
torque settings. The fork, I have to add, has a carbon
steerer tube as well.

So far I've ridden over 700 miles on this bike and it's
been just great. Recently, however, I noticed that a
slight amount of play had developed in the headset, so I
released the stem- steerer tube bolts and plug bolt in
order to remove the stem. When I did this, I noticed that
the carbon steerer tube had developed a split or fracture
along the top inch or so, at precisely the same place
where the metal shim was split. As I have no reason to
believe that the bike shop overtorqued the stem bolts, it
appears that there's some sort of defect in the carbon
steerer tube, and I'm hesitant to put any more miles on
the bike for fear of a catastrophic failure.

Is this common, and what could have caused this? Am I
correct in assuming that it's unwise to ride this fork,
and that it needs to be replaced right away?

Yes, it is common and Yes, it would be prudent to retire
that fork.

--
Andrew Muzi www.yellowjersey.org Open every day since 1
April, 1971

Kovie-<< Is this common, and what could have caused this? Am
I correct in assuming that it's unwise to ride this fork,
and that it needs to be replaced right away? >><BR><BR>

Not common, don't ride it.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St.
Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote convenzionali
costruite eccezionalmente bene"

On 25 Jun 2004 12:41:06 GMT, [email hidden] (Qui si parla

Campagnolo ) said:

Kovie-<< Is this common, and what could have caused this?
Am I correct in assuming that it's unwise to ride this
fork, and that it needs to be replaced right away?

Quoted message said:

Quoted message said:

<BR><BR>

Not common, don't ride it.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St.
Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote convenzionali
costruite eccezionalmente bene"

Dear Andrew and Peter,

So the crack seems to be either common or uncommon?

Hamlet: Ay, madam, it is common.

Queen: If it be, Why seems it so particular with thee?

Hamlet: Seems, madam? nay it is, I know not "seems." 'Tis
not alone my nastily split metal shim, good mother, Nor
customary cracked carbon steerer tube of solemn black. 'Tis
that wicked [censored] Claudius, who hath hired Sinful slaveys
who doth over-torque all that they touch, More often in
Madison than in Boulder.

Queen: Madison? Boulder? O, my son runs mad, And babbles stone-
mad of unknown places!

Hamlet: I say we will have no moe carbon steerers. A horse!
A horse! My kingdom for a horse!

Bill S.

I like the way you slipped some Richard III in there at the
end. But didn't you mean bike instead of horse? ;-)

--
Kovie [email hidden]

<[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

On 25 Jun 2004 12:41:06 GMT, [email hidden] (Qui si

parla Campagnolo ) said:

Kovie-<< Is this common, and what could have caused this?
Am I correct in assuming that it's unwise to ride this
fork, and that it needs to be replaced

right

Quoted message said:

Quoted message said:

away? >><BR><BR>

Not common, don't ride it.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St.
Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote
convenzionali costruite eccezionalmente bene"

Dear Andrew and Peter,

So the crack seems to be either common or uncommon?

Hamlet: Ay, madam, it is common.

Queen: If it be, Why seems it so particular with thee?

Hamlet: Seems, madam? nay it is, I know not "seems." 'Tis
not alone my nastily split metal shim, good mother, Nor
customary cracked carbon steerer tube of solemn black.
'Tis that wicked [censored] Claudius, who hath hired Sinful
slaveys who doth over-torque all that they touch, More
often in Madison than in Boulder.

Queen: Madison? Boulder? O, my son runs mad, And babbles
stone-mad of unknown places!

Hamlet: I say we will have no moe carbon steerers. A
horse! A horse! My kingdom for a horse!

Bill S.

So does this sound like it's due to overtorqueing, to using
a split shim, or to a defect in the carbon steerer?

--
Kovie [email hidden]

"Qui si parla Campagnolo " <[email hidden]> wrote in
message "]news:[email hidden]...

Quoted message said:

Kovie-<< Is this common, and what could have caused this?
Am I correct in assuming that it's unwise to ride this
fork, and that it needs to be replaced right away?

Quoted message said:

Quoted message said:

<BR><BR>

Not common, don't ride it.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St.
Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote convenzionali
costruite eccezionalmente bene"

The split might have been from improper installation or improper trimming. Either way, its not a good sign.

Carbon steerer tubes with minimal bias filaments are stiff in bending and tension but lack significant hoop strength, or more precisely, compressive modulus. When initially tightened, the stem clamp's pressure "grabbed" the surface of the tube with enough "grip" to prevent sliding and additional torque on the bolts caused the gap to close, concentrating the stress on the clamp split.

This is avoided with a bias cut as on Ritchey stems and others.

Its possible to use a True Temper Alpha Q style insert in lieu of the star nut to restore strength to the steerer and prevent further damage. Since the limited bias fibers in the steerer have been compromised, I would not recommend repair if the split extends below the insert. Be sure to sand the ID of the steerer tube for the full length of the insert and coat both surfaces with slow expoy. Tape the insert/steerer tube well to prevent epoxy leaking when you invert the stem to allow bubbles to escape before the epoxy cures.

The compromised strength is in torsion. It would be prudent to limit spacers to 5mm below the stem. likewise, discontinue use if the torsional stiffness changes.

Kovie said:

I like the way you slipped some Richard III in there at the
end. But didn't you mean bike instead of horse? ;-)

Dear Kovie,

Well, no . . .

When the wind is southerly, I know a hawk from a handsaw And
roared but for a horse to replace a bike

What's in a name? That which we call a bike By any other
word would smell as sweet, Were it but greased before
installation.

Blow, winds, and crack your carbon steerers!

Hopalong Cassidy

Quoted message said:

Quoted message said:

Kovie-<< Is this common, and what could have caused

this? Am I correct in

Quoted message said:

Quoted message said:

assuming that it's unwise to ride this fork, and that it
needs to be replaced right away? >><BR><BR>

Quoted message said:

On 25 Jun 2004 12:41:06 GMT, [email hidden] (Qui si

parla Campagnolo ) said:

Not common, don't ride it.

Quoted message said:

Dear Andrew and Peter, So the crack seems to be either
common or uncommon?

-snip-

Semantics. My reply: When you do that, this is the result.
Do not ride it. Peter's reply: Not everyone wrecks their
forks. Do not ride it.

I think we are in agreement, actually.
--
Andrew Muzi www.yellowjersey.org Open every day since 1
April, 1971

Thanks to all for your comments and tips. I took the fork
back to Performance today and they were nice enough to
install a replacement fork under warranty. The mechanic said
that this could have been caused by the shim's split being
aligned with the stem's split. When I got the stem I
actually inserted the shim with the split opposite the
stem's split, which seemed intuitive to me, but the shop
that cut and installed the fork reversed it so that they
aligned. I figured that this was how it was supposed to work
so I didn't question them. It also occured to me that torque
readings don't necessary apply to carbon. Is that the case?

--
Kovie [email hidden]