Update on frame failure

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

Quoted message said:

If anybody has any ideas about where I might get a simple
made-to-measure frame in raw aluminum for cheap (sub-US$1,000), do
tell.

Chalo Colina

Ask Cannondale. They make tandems so they should have some tubes that might
be strong enough for your needs. They do make custom frames but they don't
advertise.

Bruce

"Bruce Frech" <bfrech@no_spam_verizon.net> wrote in message
news:jd0ld.3795$Bj2.2763@trndny01...
|
| "Chalo" <[email hidden]> wrote in message
| news:[email hidden]...
|
| > If anybody has any ideas about where I might get a simple
| > made-to-measure frame in raw aluminum for cheap (sub-US$1,000), do
| > tell.
| >
| > Chalo Colina
|
| Ask Cannondale. They make tandems so they should have some tubes that
might
| be strong enough for your needs. They do make custom frames but they
don't
| advertise.

Basketballer Shaquille O'Neal has a massive mountain bike mad by
Cannondale to handle his physique. I imagine Shaq isn't far from 175kg
himself.
I saw a picture of the bike one time in a bike magazine. The story goes
Cannondale made 3 frames before they ended up with one the big guy
couldn't break. This would suggest Cannondale could manage to make a
bike that would hold up to the OP.
John Rees

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

Quoted message said:

I reported a few weeks ago that I had buckled the frame of my bike
while braking and had broken my arms in the process. At that time I
said I'd be furnishing more details after I reached some agreement
with the manufacturer about a replacement.

Like they have done a couple of times before for me, Cannondale
replaced my frame under warranty. They took the bent frame back for
testing, which they did not do with the earlier failures (one a
fatigue crack and the other a flawed weld).

One week after breaking my arms, I went back to making machined
components for the private space venture where I work. Two weeks
after that, I stopped wearing my wrist brace, and now about 5 1/2
weeks out I am almost back to normal. I have only taken one
noteworthy bicycle ride since my accident, an evening spent chugging
around town on my cargo sidecar with my club, Dead Baby Bikes.

My buddy Pardo has photos and a summary of the failure at his website:

http://pardo.net/bike/pic/fail-001/FAIL-017.html

I have been advised in earnest by the Cannondale dealer that I should
use the original steel unicrown fork, with a rim brake, when I resume
the use of this bike. I reckon that it doesn't matter what sort of
brake I use, only how strong it is-- it must provide less braking
force that what I was able to get with the brake I was using. Right?

Furthermore, I don't see how the suspension fork could have played a
role in the failure. It's got a steel steerer which should be no more
flexible than the original fork's. When I'm hard on the brakes it
packs down almost to the stops, so it's no longer than a rigid fork in
those conditions.

I think I'll put the rigid fork and canti brakes back on, but not use
this bike as my cross-town commuter after all. For that I guess I'll
be putting together a rugged bike with disc brake mounts, dual crown
forks, and clearance for fat tires.

Now that I reflect on that description, I'll probably just commute on
my Bohemian-- and try not to gash up the paint too badly, or get it
heisted:

http://www.uploadimages.net/images/154121bohmside.JPG

If anybody has any ideas about where I might get a simple
made-to-measure frame in raw aluminum for cheap (sub-US$1,000), do
tell.

Chalo Colina

Hmmm....something doesn't look quite right here, to my untrained eye.

On the website with pictures, it states:

"In hard braking he reports it felt like the wheel jammed. The bike flipped
and the rider broke both arms. In looking at the damage he suspects the
frame buckled, allowing the front tire to move back and jam on the frame."

I don't claim to be an expert in this, but I don't see how the front tire
could have been able to move back and "jam on the frame" without causing
significant damage to the head tube and/or forks. But, the pictures on the
website don't show any damage in that area. The "ding" in the frame could
have been caused by the crash due to impact with the ground or other objects
(aluminum frames get dinged pretty easily, and a crash with a 385 lb rider
could certainly cause damage like that).

Given your weight, and the suspension forks, and the fact that you were
intentionally conducting a "hard braking test" with newly mounted disk
brakes, it seems possible that the forks took a sudden downward dive to the
bottom of their travel, sending your weight forward and over the bars (it's
a fairly common "over the bars" scenario in mountain biking accidents).

Again, I'm no expert, but the description of the scenario, and the pictures
on that website don't show "frame failure" that's obvious to me.

GG

GaryG said:

Hmmm....something doesn't look quite right here, to my untrained eye.

On the website with pictures, it states:

"In hard braking he reports it felt like the wheel jammed. The bike flipped
and the rider broke both arms. In looking at the damage he suspects the
frame buckled, allowing the front tire to move back and jam on the frame."

I don't claim to be an expert in this, but I don't see how the front tire
could have been able to move back and "jam on the frame" without causing
significant damage to the head tube and/or forks. But, the pictures on the
website don't show any damage in that area. The "ding" in the frame could
have been caused by the crash due to impact with the ground or other objects
(aluminum frames get dinged pretty easily, and a crash with a 385 lb rider
could certainly cause damage like that).

Given your weight, and the suspension forks, and the fact that you were
intentionally conducting a "hard braking test" with newly mounted disk
brakes, it seems possible that the forks took a sudden downward dive to the
bottom of their travel, sending your weight forward and over the bars (it's
a fairly common "over the bars" scenario in mountain biking accidents).

Again, I'm no expert, but the description of the scenario, and the pictures
on that website don't show "frame failure" that's obvious to me.

GG

Can the front wheel even contact the frame under full suspension
compression? This should be easy to test. Also, if it did contact the
frame, there would likely be a tire mark, but that doesn't show in the
photos.

It seems to me he did an endo by locking the front wheel, and the frame
buckling slightly was a another consequence. The "jamming" feel was the
fork bottoming with locked wheel.

Wayne

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

Quoted message said:

GaryG said:

Hmmm....something doesn't look quite right here, to my untrained eye.

On the website with pictures, it states:

"In hard braking he reports it felt like the wheel jammed. The bike

flipped

Quoted message said:

Quoted message said:

and the rider broke both arms. In looking at the damage he suspects the
frame buckled, allowing the front tire to move back and jam on the

frame."

Quoted message said:

Quoted message said:

I don't claim to be an expert in this, but I don't see how the front

tire

Quoted message said:

Quoted message said:

could have been able to move back and "jam on the frame" without causing
significant damage to the head tube and/or forks. But, the pictures on

the

Quoted message said:

Quoted message said:

website don't show any damage in that area. The "ding" in the frame

could

Quoted message said:

Quoted message said:

have been caused by the crash due to impact with the ground or other

objects

Quoted message said:

Quoted message said:

(aluminum frames get dinged pretty easily, and a crash with a 385 lb

rider

Quoted message said:

Quoted message said:

could certainly cause damage like that).

Given your weight, and the suspension forks, and the fact that you were
intentionally conducting a "hard braking test" with newly mounted disk
brakes, it seems possible that the forks took a sudden downward dive to

the

Quoted message said:

Quoted message said:

bottom of their travel, sending your weight forward and over the bars

(it's

Quoted message said:

Quoted message said:

a fairly common "over the bars" scenario in mountain biking accidents).

Again, I'm no expert, but the description of the scenario, and the

pictures

Quoted message said:

Quoted message said:

on that website don't show "frame failure" that's obvious to me.

GG

Can the front wheel even contact the frame under full suspension
compression? This should be easy to test. Also, if it did contact the
frame, there would likely be a tire mark, but that doesn't show in the
photos.

Good point. With that large frame, there's clearly a lot of distance
between the front wheel and the down tube. Any force strong enough to push
the front wheel back into the down tube would have resulted in a broken head
tube and/or fork.

Quoted message said:

It seems to me he did an endo by locking the front wheel, and the frame
buckling slightly was a another consequence. The "jamming" feel was the
fork bottoming with locked wheel.

That sounds more likely than "frame failure", especially given the facts
that it was an intentional "hard braking test", with newly installed disk
brakes, and a very heavy, very tall rider.

GG

Quoted message said:

Wayne

GaryG said:

That sounds more likely than "frame failure", especially given the facts
that it was an intentional "hard braking test", with newly installed disk
brakes, and a very heavy, very tall rider.

I was thinking, "but I'm 175lb and I treat frames with extreme
disrespect" then I realised it was *kg*. Maybe Chalo needs a frame with
twin top tubes?

Chalo Colina said:

I reported a few weeks ago that I had buckled the frame of my bike
while braking and had broken my arms in the process. At that time I
said I'd be furnishing more details after I reached some agreement
with the manufacturer about a replacement.

Quoted message said:

Like they have done a couple of times before for me, Cannondale
replaced my frame under warranty. They took the bent frame back for
testing, which they did not do with the earlier failures (one a
fatigue crack and the other a flawed weld).

Quoted message said:

One week after breaking my arms, I went back to making machined
components for the private space venture where I work. Two weeks
after that, I stopped wearing my wrist brace, and now about 5 1/2
weeks out I am almost back to normal. I have only taken one
noteworthy bicycle ride since my accident, an evening spent chugging
around town on my cargo sidecar with my club, Dead Baby Bikes.

Quoted message said:

My buddy Pardo has photos and a summary of the failure at his
website:

Quoted message said:

http://pardo.net/bike/pic/fail-001/FAIL-017.html

As I look at this picture it strikes me as not a compression failure
from loading or braking. From what I can see this is a ding in the
tube caused by a foreign object. A tube wrinkled by compression has a
different contour and does not have a single indentation as this one
does. That this is a dent in the tube is also apparent from there
being no bend in the tube, which would have to have occurred at the
same time, it supposedly being a compression failure. That is the
nature of buckling of columns.

This does not make sense. This ding probably occurred on loading the
bicycle in or on a car.

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I
should use the original steel unicrown fork, with a rim brake, when
I resume the use of this bike. I reckon that it doesn't matter what
sort of brake I use, only how strong it is-- it must provide less
braking force that what I was able to get with the brake I was
using. Right?

I find this another proof that such bicycle companies have no people
with experience in failure analysis or crash experience. I don't
believe the analysis is correct.

Quoted message said:

Furthermore, I don't see how the suspension fork could have played a
role in the failure. It's got a steel steerer which should be no
more flexible than the original fork's. When I'm hard on the brakes
it packs down almost to the stops, so it's no longer than a rigid
fork in those conditions.

It didn't!

Quoted message said:

I think I'll put the rigid fork and canti brakes back on, but not
use this bike as my cross-town commuter after all. For that I guess
I'll be putting together a rugged bike with disc brake mounts, dual
crown forks, and clearance for fat tires.

Quoted message said:

Now that I reflect on that description, I'll probably just commute
on my Bohemian-- and try not to gash up the paint too badly, or get
it heisted:

Quoted message said:

http://www.uploadimages.net/images/154121bohmside.JPG

Nice looking bicycle!

Jobst Brandt
[email hidden]

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

Quoted message said:

As I look at this picture it strikes me as not a compression failure
from loading or braking. From what I can see this is a ding in the
tube caused by a foreign object. A tube wrinkled by compression has a
different contour and does not have a single indentation as this one
does. That this is a dent in the tube is also apparent from there
being no bend in the tube, which would have to have occurred at the
same time, it supposedly being a compression failure. That is the
nature of buckling of columns.

This does not make sense. This ding probably occurred on loading the
bicycle in or on a car.

The failure looks somewhat like combined loading which resulted in local
buckling. I see how the down tube might be in compression but not how it
might be in bending. It looks like a fixed-fixed column with support
rotation or an eccentrically loaded column. Maybe the head tube rotated
slightly with the fork. I don't think the tire could have contacted the down
tube but could an object get caught between the down tube and the tire?

I loaded the photo into AutoCad and checked the stroke of the fork and the
tire shouldn't hit the tube. A straight line along the top of the down tube
indicates that it is bent.

Quoted message said:

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I
should use the original steel unicrown fork, with a rim brake, when
I resume the use of this bike. I reckon that it doesn't matter what
sort of brake I use, only how strong it is-- it must provide less
braking force that what I was able to get with the brake I was
using. Right?

I find this another proof that such bicycle companies have no people
with experience in failure analysis or crash experience. I don't
believe the analysis is correct.

I agree. A brake cannot have too much braking force. It might be too grabby
for good control but can't be too strong.

Quoted message said:

Quoted message said:

Furthermore, I don't see how the suspension fork could have played a
role in the failure. It's got a steel steerer which should be no
more flexible than the original fork's. When I'm hard on the brakes
it packs down almost to the stops, so it's no longer than a rigid
fork in those conditions.

It didn't!

I agree. The fork isn't the problem.

Quoted message said:

http://www.uploadimages.net/images/154121bohmside.JPG

Nice looking bicycle!

Jobst Brandt
[email hidden][/QUOTE]

A Rohloff hub in a 48 spoke wheel? Rohloff tells me they only do 32 spoke drilling. This must be a custom job.
Dan Burkhart

[email hidden] (Chalo) wrote in message news:<[email hidden]>...
<SNIP>

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I should
use the original steel unicrown fork, with a rim brake, when I resume
the use of this bike. I reckon that it doesn't matter what sort of
brake I use, only how strong it is-- it must provide less braking
force that what I was able to get with the brake I was using. Right?

Furthermore, I don't see how the suspension fork could have played a
role in the failure. It's got a steel steerer which should be no more
flexible than the original fork's. When I'm hard on the brakes it
packs down almost to the stops, so it's no longer than a rigid fork in
those conditions.

First, let me add my wish that your recovery continues
to be rapid and uneventful. The heart you show in your
effort is an inspiration to me. Thank-you.

The pictures and one comment from the linked page caught my eye:
"The suspension fork was almost certainly compressed to the
bottom stop during braking -- the rider can compress it
of the way while standing next to the bike simply by pressing
down firmly on the handlebars. Thus, the forks were not an
unusally long lever. "

1. If the fork can be so easily compressed staticly, it is
likely that during "the event" that the stop was hit and
considerable impulse transferred through the stop. The
energy in the relative motion of everything above the spring
vs below is transferred rapidly by the stop.

2. During this impulse, a greater front tire force will be
generated, which tends to avert the skidding which could
have limited braking force to about 1G.

I don't think I can estimate very well what limit the tire
would provide the braking force in this condition, but it
seems that the suspension stop increase in braking force
should easily eclipse the reduced lever of a compressed
fork (4 inch reduction down to 16? or so from axle to lower
headset bearing).

3. Braking force with fork and headset lengths determine the
headset bearing forces... frame loads.

Before you try this again (bad, less than a joke) I'd suggest
stiffer springs/higher spring rate/more air. The fork would
probably also need more damping than stock to avoid your hitting
the stop hard. Components scaled stiff/enough damping for you
may not be common.

Of course, a rigid fork avoids the dynamics issue. Cannondale
is not necessarily off the mark regarding the fork advice.

I think you know that rim brakes eliminate transmitting braking
torque through hub, spokes etc. I think they're just advising
in the direction of greater structural margin in these components.
Of course, a disk is less likely to buckle your wheel...

Best wishes, Ed.

Quoted message said:

Chalo Colina said:

http://pardo.net/bike/pic/fail-001/FAIL-017.html

As I look at this picture it strikes me as not a compression failure
from loading or braking. From what I can see this is a ding in the
tube caused by a foreign object. A tube wrinkled by compression has a
different contour and does not have a single indentation as this one
does. That this is a dent in the tube is also apparent from there
being no bend in the tube, which would have to have occurred at the
same time, it supposedly being a compression failure. That is the
nature of buckling of columns.

[snip]

Dear Jobst,

I think that you're mistaken--when I look at the frame, it
looks slightly bent to the naked eye:

http://pardo.net/bike/pic/fail-001/img-0.500-img_1242.jpg

And when I snap a straight line across the tube in the
enlarged picture, the "dented" tube is clearly bent. I
tried, but couldn't tell if the top or seat tubes were
distorted. The line of the rear brake cable sorta-kinda
makes it look as if the top tube is slightly bowed.

Here's the free line tool that I used:

http://www.markus-bader.de/MB-Ruler

The "dent" is in about the same place as much worse dent in
the picture in the other thread about this trashed mountain
bike:

http://snipurl.com/akxe

The "dents" in the same places and the similar bending of
the tube suggest the same mode (buckling) and point of
failure, with one example being much worse than the other. I
expect that enough force on the front fork will bend the
frame in at about the same place every time.

On the other hand, I see no scuff marks on the paint of the
tube, much less a hideous black skid mark, so I'm dubious
that the front tire touched the frame, much less jammed
against the buckled frame tube. It seems unlikely that a
spinning rubber tire could hit a painted surface hard enough
to stop a bicycle and rider without leaving a mark.

Carl Fogel

Dan said:

The failure looks somewhat like combined loading which resulted in local
buckling. I see how the down tube might be in compression but not how it
might be in bending.

It's not perpendicular to the force being applied at the
head tube.

I think the guys at Cannondale are right. At least halfway.

The longer lever arm from the extended fork means the
torque around the lug between the head tube and the down
tube would be quite a bit higher than normal.

Even if compressing the suspension would return it
to normal specs, the force is being fully applied from
the beginning of braking.

If Chalo's description of the lengths is correct, the
standard fork would have a 4:1 lever arm, and this one
starts at almost 5:1.

The half the Cannondale guys got wrong is that the sort
of brake being used shouldn't have made any difference;
the torque from the fork at the head tube is determined
by the force at the ground and the distance from there to
the bottom of the head tube.

Quoted message said:

Quoted message said:

Quoted message said:

role in the failure. It's got a steel steerer which should be no
more flexible than the original fork's. When I'm hard on the brakes
it packs down almost to the stops, so it's no longer than a rigid
fork in those conditions.

It didn't!

I agree. The fork isn't the problem.

It is. It's too long until it bottoms out. The frame
apparently was never designed for such a fork and rider.

I'd say if you want to avoid this failure in the future
with this bike, Chalo, weld a tube from the seat lug to
the lug between the head tube and the downtube, making
the frame all triangles.

Oh, and I think Cannondale, while right, halfway, is also
at least partly at fault, because any decent engineer will
build a 100% safety buffer into a project, not something
less than 20% as was done here.

--Blair
"Let's make the next one out
of marzipan!"

Quoted message said:

Chalo Colina said:

I reported a few weeks ago that I had buckled the frame of my bike
while braking and had broken my arms in the process. At that time I
said I'd be furnishing more details after I reached some agreement
with the manufacturer about a replacement.

Quoted message said:

Like they have done a couple of times before for me, Cannondale
replaced my frame under warranty. They took the bent frame back for
testing, which they did not do with the earlier failures (one a
fatigue crack and the other a flawed weld).

Quoted message said:

One week after breaking my arms, I went back to making machined
components for the private space venture where I work. Two weeks
after that, I stopped wearing my wrist brace, and now about 5 1/2
weeks out I am almost back to normal. I have only taken one
noteworthy bicycle ride since my accident, an evening spent chugging
around town on my cargo sidecar with my club, Dead Baby Bikes.

Quoted message said:

My buddy Pardo has photos and a summary of the failure at his
website:

Quoted message said:

http://pardo.net/bike/pic/fail-001/FAIL-017.html

As I look at this picture it strikes me as not a compression failure
from loading or braking. From what I can see this is a ding in the
tube caused by a foreign object. A tube wrinkled by compression has a
different contour and does not have a single indentation as this one
does. That this is a dent in the tube is also apparent from there
being no bend in the tube, which would have to have occurred at the
same time, it supposedly being a compression failure. That is the
nature of buckling of columns.

this not a column, it's a thin wall tube. it's buckling. you can
replicate that kind of failure feature easliy with a beer can.

Quoted message said:

This does not make sense. This ding probably occurred on loading the
bicycle in or on a car.

a minor ding could indeed be an initiator, but buckling is the cause -
the whole tube is bent.

Quoted message said:

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I
should use the original steel unicrown fork, with a rim brake, when
I resume the use of this bike. I reckon that it doesn't matter what
sort of brake I use, only how strong it is-- it must provide less
braking force that what I was able to get with the brake I was
using. Right?

I find this another proof that such bicycle companies have no people
with experience in failure analysis or crash experience. I don't
believe the analysis is correct.

that sir is a _preposterous_ statement. taking the word of a dealer and
using it to condemn a manufacturer's r&d dept is both ignorant and
avaricious.

Quoted message said:

Quoted message said:

Furthermore, I don't see how the suspension fork could have played a
role in the failure. It's got a steel steerer which should be no
more flexible than the original fork's. When I'm hard on the brakes
it packs down almost to the stops, so it's no longer than a rigid
fork in those conditions.

It didn't!

Quoted message said:

I think I'll put the rigid fork and canti brakes back on, but not
use this bike as my cross-town commuter after all. For that I guess
I'll be putting together a rugged bike with disc brake mounts, dual
crown forks, and clearance for fat tires.

Quoted message said:

Now that I reflect on that description, I'll probably just commute
on my Bohemian-- and try not to gash up the paint too badly, or get
it heisted:

Quoted message said:

http://www.uploadimages.net/images/154121bohmside.JPG

Nice looking bicycle!

Jobst Brandt
[email hidden]

Ed Cory said:

[email hidden] (Chalo) wrote in message news:<[email hidden]>...
<SNIP>

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I should
use the original steel unicrown fork, with a rim brake, when I resume
the use of this bike. I reckon that it doesn't matter what sort of
brake I use, only how strong it is-- it must provide less braking
force that what I was able to get with the brake I was using. Right?

Furthermore, I don't see how the suspension fork could have played a
role in the failure. It's got a steel steerer which should be no more
flexible than the original fork's. When I'm hard on the brakes it
packs down almost to the stops, so it's no longer than a rigid fork in
those conditions.

First, let me add my wish that your recovery continues
to be rapid and uneventful. The heart you show in your
effort is an inspiration to me. Thank-you.

The pictures and one comment from the linked page caught my eye:
"The suspension fork was almost certainly compressed to the
bottom stop during braking -- the rider can compress it
of the way while standing next to the bike simply by pressing
down firmly on the handlebars. Thus, the forks were not an
unusally long lever. "

1. If the fork can be so easily compressed staticly, it is
likely that during "the event" that the stop was hit and
considerable impulse transferred through the stop. The
energy in the relative motion of everything above the spring
vs below is transferred rapidly by the stop.

2. During this impulse, a greater front tire force will be
generated, which tends to avert the skidding which could
have limited braking force to about 1G.

I don't think I can estimate very well what limit the tire
would provide the braking force in this condition, but it
seems that the suspension stop increase in braking force
should easily eclipse the reduced lever of a compressed
fork (4 inch reduction down to 16? or so from axle to lower
headset bearing).

3. Braking force with fork and headset lengths determine the
headset bearing forces... frame loads.

Before you try this again (bad, less than a joke) I'd suggest
stiffer springs/higher spring rate/more air. The fork would
probably also need more damping than stock to avoid your hitting
the stop hard. Components scaled stiff/enough damping for you
may not be common.

Of course, a rigid fork avoids the dynamics issue. Cannondale
is not necessarily off the mark regarding the fork advice.

I think you know that rim brakes eliminate transmitting braking
torque through hub, spokes etc. I think they're just advising
in the direction of greater structural margin in these components.
Of course, a disk is less likely to buckle your wheel...

Best wishes, Ed.

nice analysis.

GaryG' garyg@shasta_SPAMBEGONE_software.com said:

On the website with pictures, it states:

"In hard braking he reports it felt like the wheel jammed. The bike flipped
and the rider broke both arms. In looking at the damage he suspects the
frame buckled, allowing the front tire to move back and jam on the frame."

I don't claim to be an expert in this, but I don't see how the front tire
could have been able to move back and "jam on the frame" without causing
significant damage to the head tube and/or forks.

I can't see how it would have happened either-- but the bike went
"crack" and the front wheel suddenly just stopped, like it had seized
up. I am open to other hypotheses as to why that occurred.

Quoted message said:

But, the pictures on the
website don't show any damage in that area. The "ding" in the frame could
have been caused by the crash due to impact with the ground or other objects
(aluminum frames get dinged pretty easily, and a crash with a 385 lb rider
could certainly cause damage like that).

On close examination, I was also unable to find a tire mark, paint
scuff, or any other marking at the site of the crease in the downtube.

The bike didn't hit anything except me, after I had hit the ground .
It came to rest with my legs all tangled up in it, and it took me
probably half a minute to extract myself.

Quoted message said:

Given your weight, and the suspension forks, and the fact that you were
intentionally conducting a "hard braking test" with newly mounted disk
brakes, it seems possible that the forks took a sudden downward dive to the
bottom of their travel, sending your weight forward and over the bars (it's
a fairly common "over the bars" scenario in mountain biking accidents).

I've bottomed out a lot of suspension forks,and none of them make the
"crack" sound that preceded me getting tossed. These forks, Marzocchi
MX Comp 29", I never managed to bottom out at all, despite their
insufficient spring rate.

I was trying to wear in the new pads, plus see if the improved braking
would make anything bend from the added force, so I was stopping from
30-35mph on a steep downhill. I didn't make a sudden jerk at the
brakes, so there was no sudden plunge to the bottom of the fork's
travel. I had been hard on the brakes for about a full second before
the "crack", so the fork had already sunk as low as it was going to
go.

Chalo Colina

Quoted message said:

Quoted message said:

http://pardo.net/bike/pic/fail-001/FAIL-017.html

As I look at this picture it strikes me as not a compression failure
from loading or braking. From what I can see this is a ding in the
tube caused by a foreign object. A tube wrinkled by compression has a
different contour and does not have a single indentation as this one
does.

Just before the bike stopped and pitched me off, there was a "crack"
sound. I am fairly certain that the sound came from the downtube as
it buckled, since it was clearly not the "clunk" that forks make when
the bottom out or the "ping" that frames make when they are struck
with a hard object.

There was not so much as a scratch on the paint at the site of the
crease. The tube was arched upwards. Before I crashed, the frame was
in flawless condition as far as I knew.

During the crash, the bike's handlebars hit the ground, but the rest
of it hit only me. If I had not been on clean open pavement, I would
have wondered whether something kicked up and jammed between tire and
downtube, but there was nothing present that could have done that.

Quoted message said:

That this is a dent in the tube is also apparent from there
being no bend in the tube,

The upward bend in the downtube was quite apparent in just looking at
the bike, though it's relatively subtle in the furnished profile view.
If you use a straightedge, I think you'll see the vertical
displacement of the upper side of the tube is on the order of 1/2".
The downtube itself was originally conical, tapering from about 1.6"
to about 2.25" in diameter.

Chalo Colina

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

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I should
use the original steel unicrown fork, with a rim brake, when I resume
the use of this bike.

How about forget the use of this bike and move to a frame that is less
likely to break, i.e. a steel frame.

In article <[email hidden]>,

(Chalo) said:

http://www.uploadimages.net/images/154121bohmside.JPG

If anybody has any ideas about where I might get a simple
made-to-measure frame in raw aluminum for cheap (sub-US$1,000), do
tell.

Chalo Colina

Is there a particular reason for choosing Al as the material of choice?
I mean, for that price there's a certain Ti builder who might do the
deed, and I think he does custom work too...

http://www.habcycles.com/mtb.html

--
Ryan Cousineau, [email hidden] http://www.wiredcola.com
Verus de parvis; verus de magnis.

Steven M. Scharf said:

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

Quoted message said:

I have been advised in earnest by the Cannondale dealer that I should
use the original steel unicrown fork, with a rim brake, when I resume
the use of this bike.

How about forget the use of this bike and move to a frame that is less
likely to break, i.e. a steel frame.

I wouldn't conclude that just based on the type of material. My
last steel frame ended up looking quite similar to Chalo's after
what felt like a rather mild impact with a medium-size dog.
I picked myself up, set the bike against a fence and was just
about to tell the apologetic dog owner that everything was ok
when I noticed the bent tubes (on mine the top tube also had
a clear bend). The fork and front wheel were unharmed.

Although in my case it took the combination of hard braking
together with the dog impact to bend the frame, my feeling
was that most of the force was due to the braking. And the
load on my bike was less than half that on Chalo's.

I'm still curious about what caused Chalo's front wheel to
lock up. The absence of any tire scuff marks on the downtube
seems pretty conclusive in ruling out th possibility that
the tire hit the tube while still turning. Any possibility
that something jammed in the disk calipers? I could see
a sudden wheel lockup having a similar effect on the frame as
my dog impact, especially given the higher load on the bike.