cracked kestrel fork

[Jim Beam]

skuke wrote:
> On Thu, 05 Feb 2004 08:41:18 GMT, jim beam wrote:
>
>
>>looked at your pics too. yuk.
>
>
> I hope you mean "yuck" as in "that's very nasty" and not "yuk" as in laughing ("yuk yuk yuk"). No
> desire to be the spelling police, but in this context, laughing at someone's crash from a fork
> failure doesn't sit well with me.

relax - it's spelling.

thanks for posting the pics.

jb

 

[Mike Jacoubowsk]

> good question! like i say, i'd buy american if i had a choice, but what is there? avid? american
> company, made in taiwan. ritchey? same. fsa? same. so that leaves italian or japanese.

Chris King & Phil Wood both remain very much American. Nearly all (if not all, I'm not sure)
Bontrager rims are made in the US. And, as you mentioned, there are still many American-made frames.

But what is your definition of American? Is a GM car American if 40% of its components come from
somewhere else?

--Mike-- Chain Reaction Bicycles http://www.ChainReactionBicycles.com

"jim beam" <[email protected]> wrote in message news:[email protected]...
> good question! like i say, i'd buy american if i had a choice, but what is there? avid? american
> company, made in taiwan. ritchey? same. fsa? same. so that leaves italian or japanese.
>
> i /do/ have a *beautiful* american frame though.
>
> jb
>
> Steve Knight wrote:
> >>well, given the choice, i buy american made. call me a flag waving pervert, but i prefer to keep
> >>jobs at home. and yes, i'm prepared to pay more for that. sorry.
> >
> >
> > what components do you ride with then??

 

[Mike Jacoubowsk]

> Ok, I posted some at: http://www.geocities.com/skuke89/fork.html Sorry for the formatting. I just
> "threw" it together.

For what its worth, companies that take carbon fiber seriously can examine pieces like those in
your photos and fairly easily tell the direction of impact or failure based on how the fibers are
torn. I've been walked through this over the phone with engineers at TREK when it was necessary to
try and figure out "what really happened." I'm afraid I can't tell you what to look for (not
because I don't what to, but because I don't get to do it very often and I don't remember, and it's
a lot easier when you're talking to an engineer that has seen photos you sent and knows exactly how
to guide you).

I would hope that Kestrel would have people similarly experienced in such matters and help you get
to the bottom of things. Please do keep in mind that most JRAs (I was "Just Riding Along...") have a
bit of help. One of our staff came into the shop with some pretty nasty facial injuries due to a
"failed" fork on his CycloCross bike. This was a pretty hefty steel fork that had folded forward
about two-thirds of the way up the blades, pitching him into the ground. He was quite positive that
the fork had simply failed, for no good reason.

Very close inspection of the front wheel revealed some nicks in a couple of spokes. But what caused
them? People pick up small branches from time to time, but those usually bend spokes slightly, but
don't typically nick them.

So I headed out to the scene of the crime, and discovered what caused it. PG&E (the local utility
company) had been doing some work in the area, and had carelessly let some hefty braided wire pieces
(apparently used to carry current from one side of the pole to the other, or maybe for grounding
purposes... don't know for sure, but you can look up there and see them) on the ground in several
places on the road. Even found the one that did the job on my employee's wheel. I don't recall if he
was able to recover damages from PG&E or not...

--Mike-- Chain Reaction Bicycles http://www.ChainReactionBicycles.com

"skuke" <[email protected]> wrote in message news:[email protected]...
> On Thu, 05 Feb 2004 11:26:44 +0800, Kenny Lee wrote:
>
> > Can you post some pictures of this failed fork?
> >
> > Kenny Lee
>
>
> Ok, I posted some at: http://www.geocities.com/skuke89/fork.html Sorry for the formatting. I just
> "threw" it together.
>
> I took the photo quite a while ago because I was gonna bring the fork to Kestral since I don't
> live too far. I wanted the pics since I figured I'd never get the fork back. Anyhow, never got
> around to dropping it off so maybe I'll reshoot the pics with a tape measure in the shot for
> reference.
>
> You actually can assemble the broken pieces and everything lines up quite nicely. There is no
> definite "impact" area like you might expect to see from a stick or animal. Also, we don't suspect
> an animal because there
was
> no blood or fur. It's also hard to determine if one blade failed first and that cause an overload
> of the second blade.
>
> Lots of questions that I'd like answers to since I have an identical era fork on my 1995
> CarbonFrames. Hence my ( lackadaisical) desire to bring
it
> to Kestral.
>
>
> --
> Skuke Reverse the domain name to send email

 

[Skuke]

On 5 Feb 2004 18:03:47 -0800, Carl Fogel wrote:

> Dear Jim and Skuke,
>
> Yuck--unpleasant-looking:
>
> http://www.geocities.com/skuke89/fork.html
>
> I assume that one fork leg failed and the sudden increase in stress broke the other one in half
> almost instantly.
>
> What I'm wondering is which fork leg broke first.
>
> My guess is that the less ragged fork leg fractured first. It would be held in place until it
> cracked completely through.
>
> Once the first fork leg was effectively broken, the other fork took the whole load, bent, and
> broke violently, peeling off those long fiber strips just like a broken tree branch trailing
> bark strips.
>
> Any strips not cracked completely through on the first fork leg would snap off short and clean,
> like perforated tractor strips on computer paper.
>
> At least, that's my theory. Does one fork leg really look like a neater break with shorter strips,
> while the other looks more ragged, with longer strips?
>
> Carl Fogel

Yes, the left fork has the "strips" of CF. The right blade is a "cleaner" break. But it's not really
that simple to segregate into those two neat groups. The right blade is just a little cleaner and
the left blade is just a little more ragged.

In the first photo, there is a long strip torn away to the drop out. It is about 1/8" wide. I did
that. There was a strip and I pulled it because I was curious as to how strongly one strip was
attached the next. I wanted an understanding of the epoxy holding everything together.

I just went to the garage and pulled another strip. The amount of pulling force is very little. An
analogy might be similar to tearing 6-7 sheet of paper at once! It almost feels as if the only thing
holding it together is the paint! Also, I just now tried to squeeze and bend it by hand. No
surprise, I didn't feel any flexing. I banged the broken end on the cement floor trying to chip a
piece, nothing.

What's kinda interesting is the outer surface (just under the paint) has only linear fibers. They
run down the length of blade as you can see by the tear I did in the first photo. Then there are
several layer of diagonal fibers. They are not woven, but layered. Diagonal left layer, then
diagonal right layer repeated a bunch of times. The inside surface is "sheet like" and has no
directional fibers as near as I can tell. The broken edges of the innermost layer is just torn like
plastic. Some small fibers, but no distinct fiber directions like the rest.

Gee, I'm motivated to drive over to Kestral again!

--
Skuke Reverse the domain name to send email

 

[A Muzi]

jim beam wrote:
> so, replaced the kestrel with a reynolds ouzo comp.
-snip- riding no hands, i can hardly keep
> a straight line! [yes, the headset is adjusted ok.] haven't taken it on a shimmy test yet, but do
> not expect good results. so, it looks like i'll be abandoning this carbon fork experiment. it
> seems to be great for you lighter folks, but it's no game for a clydesdale to play. steel fork
> goes back on.

Could be one other factor. Is your Ouzo the proper rake and clearance ? Most fork makers offer
a variety.
--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

 

[Kenny Lee]

jim beam wrote:
> so, replaced the kestrel with a reynolds ouzo comp. again, metal [aluminum] steerer tube. slightly
> different constuction in that this has an alloy crown with both the blades bonded to it, not the
> one-piece constuction for both blades like the kestrel. the steerer on the reynolds is also
> interesting because it has an extreme wall thickness taper - the walls appear as thick as the
> center hole near the crown. very strong looking.
>
> this time, did the squeeze test on the renolds before going to the trouble of fitting. no cracking
> noises - seemed stiff. great!
>
> put in on the bike, take it for a spin around the block. no mechanical problems, great stiffness
> in the plane of the frame, that lovely carbon ride, but oh, what a lateral noodle! riding no
> hands, i can hardly keep a straight line! [yes, the headset is adjusted ok.] haven't taken it on a
> shimmy test yet, but do not expect good results.
>
> so, it looks like i'll be abandoning this carbon fork experiment. it seems to be great for you
> lighter folks, but it's no game for a clydesdale to play. steel fork goes back on.
>
>
>
> very disappointed.
>
>
> jb.
>
Make sure the cables aren't affecting the steering. They can influence no-hands riding.

Kenny Lee

 

[Jim Beam]

same cables, same position as with the steel fork.

Kenny Lee wrote:
> jim beam wrote:
>
>> so, replaced the kestrel with a reynolds ouzo comp. again, metal [aluminum] steerer tube.
>> slightly different constuction in that this has an alloy crown with both the blades bonded to it,
>> not the one-piece constuction for both blades like the kestrel. the steerer on the reynolds is
>> also interesting because it has an extreme wall thickness taper - the walls appear as thick as
>> the center hole near the crown. very strong looking.
>>
>> this time, did the squeeze test on the renolds before going to the trouble of fitting. no
>> cracking noises - seemed stiff. great!
>>
>> put in on the bike, take it for a spin around the block. no mechanical problems, great stiffness
>> in the plane of the frame, that lovely carbon ride, but oh, what a lateral noodle! riding no
>> hands, i can hardly keep a straight line! [yes, the headset is adjusted ok.] haven't taken it on
>> a shimmy test yet, but do not expect good results.
>>
>> so, it looks like i'll be abandoning this carbon fork experiment. it seems to be great for you
>> lighter folks, but it's no game for a clydesdale to play. steel fork goes back on.
>>
>>
>>
>> very disappointed.
>>
>>
>> jb.
>>
> Make sure the cables aren't affecting the steering. They can influence no-hands riding.
>
> Kenny Lee

 

[Jim Beam]

same clearance. rake is 43mm vs 45mm on the steel. i can see that making a small difference, but
this is radical. the bike /really/ won't hold a line - just flops around all over the place.
straight line with hands on the bars, it's great, but imo, that's not good enough!

the kestrel was great in this respect - no problem whatsoever hands off.

A Muzi wrote:
> jim beam wrote:
>
>> so, replaced the kestrel with a reynolds ouzo comp.
>
> -snip- riding no hands, i can hardly keep
>
>> a straight line! [yes, the headset is adjusted ok.] haven't taken it on a shimmy test yet, but do
>> not expect good results. so, it looks like i'll be abandoning this carbon fork experiment. it
>> seems to be great for you lighter folks, but it's no game for a clydesdale to play. steel fork
>> goes back on.
>
>
>
> Could be one other factor. Is your Ouzo the proper rake and clearance ? Most fork makers offer a
> variety.

 

[Carl Fogel]

jim beam <[email protected]> wrote in message news:<[email protected]>...
> same clearance. rake is 43mm vs 45mm on the steel. i can see that making a small difference, but
> this is radical. the bike /really/ won't hold a line - just flops around all over the place.
> straight line with hands on the bars, it's great, but imo, that's not good enough!
>
> the kestrel was great in this respect - no problem whatsoever hands off.
>
> A Muzi wrote:
> > jim beam wrote:
> >
> >> so, replaced the kestrel with a reynolds ouzo comp.
> >
> > -snip- riding no hands, i can hardly keep
> >
> >> a straight line! [yes, the headset is adjusted ok.] haven't taken it on a shimmy test yet, but
> >> do not expect good results. so, it looks like i'll be abandoning this carbon fork experiment.
> >> it seems to be great for you lighter folks, but it's no game for a clydesdale to play. steel
> >> fork goes back on.
> >
> >
> >
> > Could be one other factor. Is your Ouzo the proper rake and clearance ? Most fork makers offer a
> > variety.

Dear Jim,

What little I know involves motorcycles that lack the side-to-side pedalling forces that complicate
bicycling no-hands, but sometimes even small fork geometry changes make surprising differences.

In any case, you might find this link interesting:

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

It starts out normally, but as you can see by scrolling down and looking at the pictures, it just
gets weirder and weirder.

Carl Fogel

 

[Jim Beam]

tried all that. everything's fitted right and it's straight as an arrow except under lateral load.
if you hold the handlebar and press your knee sideways against the head tube, you can see this thing
bend like a palm tree in a storm.

when trying to ride no hands, it'll start to veer very slightly off to one side like normal, then
the noodle effect kicks in and it starts flopping right over & you need to grab the bar again -
quickly. happens the same either side.

it's a shame because, in all other respects, this is a beautifully made fork.

David L. Johnson wrote:
> On Fri, 06 Feb 2004 06:08:05 +0000, jim beam wrote:
>
>
>>put in on the bike, take it for a spin around the block. no mechanical problems, great stiffness
>>in the plane of the frame, that lovely carbon ride, but oh, what a lateral noodle! riding no
>>hands, i can hardly keep a straight line! [yes, the headset is adjusted ok.]
>
>
> No-hands problems tend to be alignment, not headset difficulties. Make sure the wheel is on
> straight, and try again. That is, to me, an advantage of carbon forks; they are more likely to be
> properly aligned than a steel fork --- but, if they are off, there is nothing to be done but
> replacement.

 

[Jim Beam]

good article! i'll read it properly when i get home next week - travelling right now.

Carl Fogel wrote:
> jim beam <[email protected]> wrote in message news:<[email protected]>...
>
>>same clearance. rake is 43mm vs 45mm on the steel. i can see that making a small difference, but
>>this is radical. the bike /really/ won't hold a line - just flops around all over the place.
>>straight line with hands on the bars, it's great, but imo, that's not good enough!
>>
>>the kestrel was great in this respect - no problem whatsoever hands off.
>>
>>A Muzi wrote:
>>
>>>jim beam wrote:
>>>
>>>
>>>>so, replaced the kestrel with a reynolds ouzo comp.
>>>
>>>-snip- riding no hands, i can hardly keep
>>>
>>>
>>>>a straight line! [yes, the headset is adjusted ok.] haven't taken it on a shimmy test yet, but
>>>>do not expect good results. so, it looks like i'll be abandoning this carbon fork experiment. it
>>>>seems to be great for you lighter folks, but it's no game for a clydesdale to play. steel fork
>>>>goes back on.
>>>
>>>
>>>
>>>Could be one other factor. Is your Ouzo the proper rake and clearance ? Most fork makers offer a
>>>variety.
>
>
> Dear Jim,
>
> What little I know involves motorcycles that lack the side-to-side pedalling forces that
> complicate bicycling no-hands, but sometimes even small fork geometry changes make surprising
> differences.
>
> In any case, you might find this link interesting:
>
> http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm
>
> It starts out normally, but as you can see by scrolling down and looking at the pictures, it just
> gets weirder and weirder.
>
> Carl Fogel

 

[Jim Beam]

Mike Jacoubowsky wrote: <snip>
>
> Chris King & Phil Wood both remain very much American.

true! can't speak about phil wood, but my experience with chris king hubs is not great. many aspects
of their quality are awesome, but i /really/ don't like the fact that they use an aluminum alloy
freehub body - it just gets mangled by single sprockets. for the money ck charges on those things,
it should be titanium or something that can handle the load. shimano use steel or ti only, and for
good reason. think phil wood is stainless, so no problem there.

the second thing i don't like about ck rear hubs is that their flange spacing exacerbates the
tension differential between drive & non-drive sides. dura-ace has 21.1mm drive & 36.9mm non-drive,
which gives the non-drive spokes a tension of 57.5% that of the drive side. ck hubs have flange
spacings of 18.5mm & 38.5mm resulting in non-drive spoke tension of only 48.4% that of the drive
side. it's not a huge difference, but if shimano can minimize this problem, why not king? surely a
shimano flange spacing can't be proprietary, and certainly not if they've already licensed shimano
spline specs.

lastly, king seals d-r-a-g. like riding through treacle. yes, break-in period, etc. but again, no
one else seems to have this problem, why king?

so, i think i need to qualify my statement. i'll buy american, and pay more, if it's the
best product.

 

[Dianne_1234]

On Sat, 07 Feb 2004 07:46:58 GMT, jim beam <[email protected]> wrote:

>tried all that. everything's fitted right and it's straight as an arrow except under lateral load.
>if you hold the handlebar and press your knee sideways against the head tube, you can see this
>thing bend like a palm tree in a storm.
>
>when trying to ride no hands, it'll start to veer very slightly off to one side like normal, then
>the noodle effect kicks in and it starts flopping right over & you need to grab the bar again -
>quickly. happens the same either side.
>
>it's a shame because, in all other respects, this is a beautifully made fork.
>
>David L. Johnson wrote:
>> On Fri, 06 Feb 2004 06:08:05 +0000, jim beam wrote:
>>
>>
>>>put in on the bike, take it for a spin around the block. no mechanical problems, great stiffness
>>>in the plane of the frame, that lovely carbon ride, but oh, what a lateral noodle! riding no
>>>hands, i can hardly keep a straight line! [yes, the headset is adjusted ok.]
>>
>>
>> No-hands problems tend to be alignment, not headset difficulties. Make sure the wheel is on
>> straight, and try again. That is, to me, an advantage of carbon forks; they are more likely to be
>> properly aligned than a steel fork --- but, if they are off, there is nothing to be done but
>> replacement.
>>

Can you measure the torque (static and dynamic) of the fork turning in the headset?

I've had similar problems with even mildly sticky head bearings.

 

[Jim Beam]

dianne_1234 wrote: <snip>
> Can you measure the torque (static and dynamic) of the fork turning in the headset?
>
> I've had similar problems with even mildly sticky head bearings.

haven't measured anything, no, but i have plenty of experience setting up head sets over the years,
and i've never had this problem before. the bearings are as good as they get. the cables are by far
the biggest turning resistance, and they're also set up pretty well. certainly no different to the
steel fork & the kestrel fork which both rode just fine.

jb

 

[Jeff Wills]

jim beam <[email protected]> wrote in message news:<[email protected]>...
> dianne_1234 wrote: <snip>
> > Can you measure the torque (static and dynamic) of the fork turning in the headset?
> >
> > I've had similar problems with even mildly sticky head bearings.
>
> haven't measured anything, no, but i have plenty of experience setting up head sets over the
> years, and i've never had this problem before. the bearings are as good as they get. the cables
> are by far the biggest turning resistance, and they're also set up pretty well. certainly no
> different to the steel fork & the kestrel fork which both rode just fine.
>
> jb

I've had similar symptoms crop up with slightly *loose* headsets. Is it a cartridge bearing headset?
I wonder if a cartridge has developed some play in its cup- the adjustment would *feel* right, but
there'd still be some play in the fork under pressure.

It's freakin' weird, though- that much floppiness in any fork sounds outrageous.

Jeff