Head tube ovalization: myth or fact
Larry Leveen
--
Larry Leveen
Velorution! The Bicycle "Freeware" Infopage
http://www.olywa.net/leveen/
David T. Blake
>Can head tubes be ovalized through normal bike use? What causes it?
I sent two such frames back to Bridgestone.
Both were always kept in good working order and never had
outstanding singular incidents. Both were ridden without
suspension on very rocky trails with high regularity.
The bottom press of the headset would no longer fit -
it would simply fall out.
--
Dave Blake
dbl...@phy.ucsf.edu
Brevetatto
good working order. Ovalization is caused by a fore-aft force on the frame,
acting through the lever of the fork, on the headtube.
There have been some VERY light steel frames that seemed prone to this in
normal use. Although in all honesty, it is difficult to know how "normal" the
use was. (see references to "JRA".)
The two usual causes are a significantly loose headset which has been
ignored for a long time. The repeated fore-aft motion of the fork will express
itself as impacts at the headtube, which will ovalize in the planeof the frame.
The second usual cause is a head-on crash at a good speed. This acts in the
same fashion as the loose hdst, but the one-time force is much higher.
One classic case that I saw was an early cannondale super-v, which had been
ridden head-on into a tree in Capitol forest. The headshock was bent, the
headtube was ovalized, and the rider had 2-odd stitches in one ear. The early
V's were not what you would call light, yet the ovalization was rather
dramatic.
Hope I was helpful
Eamon Stanley
tku...@diabloresearch.com
This was a manufacturing error Dave. Normal use will not ovalize head tubes.
This is generally done by overheating and warping the heat tube during
construction.
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David T. Blake
tku...@diabloresearch.com writes:
>dbl...@phy.ucsf.edu (David T. Blake) wrote:
>> lev...@olywa.net (Larry Leveen) writes:
>>
>> >Can head tubes be ovalized through normal bike use? What causes it?
>>
>> I sent two such frames back to Bridgestone.
>>
>> Both were always kept in good working order and never had
>> outstanding singular incidents. Both were ridden without
>> suspension on very rocky trails with high regularity.
>>
>> The bottom press of the headset would no longer fit -
>> it would simply fall out.
>
>This was a manufacturing error Dave. Normal use will not ovalize head tubes.
>This is generally done by overheating and warping the heat tube during
>construction.
The head tubes both fit when I received the frame, and
pressing the bottom headset into the frame was not
unusual in either case.
The first frame took almost a year before the bottom headset
cup no longer fit. The second took about 6 months. At that point
I switched to a different brand.
I don't doubt that there were manufacturing problems with
the head tube construction. But the end result was clearly
ovalization.
As to whether it was normal use - well, each frame took about
3-5000 miles of training for expert MTB racing.
--
Dave Blake
dbl...@phy.ucsf.edu
ma...@abtcorp.com
my (former) capacity as a shop manager, i personally saw several mtb's with
ovalized head tubes. these head tubes were originally round (we built some of
the bikes), were ridden for a couple years, and then were no longer round. all
of them were light steel frames with 1" headsets. a couple had suspension
forks, but a couple did not. while there may have been some overheating or
other error that led to reduced strength in the head tube area, these were not
bikes that were somehow delivered with oval head tubes.
coincidentally enough, at least half of such bikes that i saw were
bridgestones (of course we were a big bridgestone dealer at the time). -mark
weaver
In article <75dqh1$vff$1...@nnrp1.dejanews.com>,
tku...@diabloresearch.com wrote:
> In article <k07lvq7...@dylan.ucsf.edu>,
> dbl...@phy.ucsf.edu (David T. Blake) wrote:
> > lev...@olywa.net (Larry Leveen) writes:
> >
> > >Can head tubes be ovalized through normal bike use? What causes it?
> >
> > I sent two such frames back to Bridgestone.
> >
> > Both were always kept in good working order and never had
> > outstanding singular incidents. Both were ridden without
> > suspension on very rocky trails with high regularity.
> >
> > The bottom press of the headset would no longer fit -
> > it would simply fall out.
>
> This was a manufacturing error Dave. Normal use will not ovalize head tubes.
> This is generally done by overheating and warping the heat tube during
> construction.
>
Joshua_Putnam
>tku...@diabloresearch.com writes:
>>dbl...@phy.ucsf.edu (David T. Blake) wrote:
>>> lev...@olywa.net (Larry Leveen) writes:
>>> >Can head tubes be ovalized through normal bike use? What causes it?
>>> I sent two such frames back to Bridgestone.
>>>
>>> Both were always kept in good working order and never had
>>> outstanding singular incidents. Both were ridden without
>>> suspension on very rocky trails with high regularity.
>>This was a manufacturing error Dave. Normal use will not ovalize head tubes.
>>This is generally done by overheating and warping the heat tube during
>>construction.
>I don't doubt that there were manufacturing problems with
>the head tube construction. But the end result was clearly
>ovalization.
>As to whether it was normal use - well, each frame took about
>3-5000 miles of training for expert MTB racing.
"Normal use" varies a lot depending on the style of bike.
I've seen quite a few BMX bikes with ovalized head tubes and
even buckled downtubes from "normal use" in the context of a BMX
street course. BMXers break a lot of stuff in "normal" BMX use,
but they understand that their riding style breaks stuff, so
they generally don't flood shops with "just riding along"
warranty claims. ("I took a perfectly normal three foot dropoff,
and all of a sudden my bars were bent. I don't know how it could
have happened!")
I've seen some cheap mountain bikes with headtube damage from
hard use -- was it "normal use"? Well, if you read the manuals
on a cheap mountain bike, you'll probably find that even riding
slowly on singletrack violates the warranty definition of "normal
use," despite the mountain bike styling.
--
Jo...@WolfeNet.com is Joshua Putnam / P.O. Box 13220 / Burton, WA 98013
"My other bike is a car."
http://www.wolfenet.com/~josh/
G.T.
ma...@abtcorp.com wrote in message <75e3h9$809$1...@nnrp1.dejanews.com>...
>tom, i reiterate my earlier questions. what the hell are you talking about?
in
>my (former) capacity as a shop manager, i personally saw several mtb's with
>ovalized head tubes. these head tubes were originally round (we built some
of
>the bikes), were ridden for a couple years, and then were no longer round.
all
>of them were light steel frames with 1" headsets. a couple had suspension
>forks, but a couple did not. while there may have been some overheating or
>other error that led to reduced strength in the head tube area, these were
not
>bikes that were somehow delivered with oval head tubes.
>
>coincidentally enough, at least half of such bikes that i saw were
>bridgestones (of course we were a big bridgestone dealer at the
time). -mark
yeah, it happened to my 2nd mb-1 from about '89. headset was never loose
and after about a year you could pull the top cup right out.
greg
tku...@diabloresearch.com
ma...@abtcorp.com wrote:
> tom, i reiterate my earlier questions. what the hell are you talking about? in
> my (former) capacity as a shop manager, i personally saw several mtb's with
> ovalized head tubes. these head tubes were originally round (we built some of
> the bikes), were ridden for a couple years, and then were no longer round. all
> of them were light steel frames with 1" headsets. a couple had suspension
> forks, but a couple did not. while there may have been some overheating or
> other error that led to reduced strength in the head tube area, these were not
> bikes that were somehow delivered with oval head tubes.
What mechanism do you propose for round tubes being ovalized? Do you
think that the head tube itself is so weak that it can sustain a force
above it's yield strength despite the fact that the steering tube will
bend first?
Do you suscribe to the idea that AFTER you braze a doubling via the lug
onto the head tube it will grow weaker? And then what of the headset
which does a really nice job of spreading the forces from the fork
throughout the entire steering head?
Obviously there needs to be some sort of theory as to how this ovalizing
can occur. The problem is that all of the associated mechanism is weaker
than the head tube. And there can be no wear if the headset is properly
installed.
I cannot answer as to why a couple of Bridgestones had ovalized head
tubes unless they came that way.
So, you always pull the races off of an assembled bike and test the
fit of the headset? Am I mistaken or do they not make a headset that
is installed in most production bikes that has a smaller OD on the
headtube races so that you can install them in a STANDARD sized head
tube without machining? Very little normal warping/"ovalization" needs
be there for these races to come loose after delivery.
Scribe2b
so that the headset cup would just fall out--- when it was new the cup fit
perfectly, and the frame itself was beautifully brazed. this may have resulted
from a number of mild crashes, but the fork remained true and unflawed.
jere cunningham
G.T.
>I cannot answer as to why a couple of Bridgestones had ovalized head
>tubes unless they came that way.
>
>So, you always pull the races off of an assembled bike and test the
>fit of the headset? Am I mistaken or do they not make a headset that
>is installed in most production bikes that has a smaller OD on the
>headtube races so that you can install them in a STANDARD sized head
>tube without machining? Very little normal warping/"ovalization" needs
>be there for these races to come loose after delivery.
in my case i received my second mb-1 as just a warranty, frame replacement.
i installed a shimano 600 headset and everything seemed fine to me. after a
year, it was no longer fine.
greg thomas
Jobst Brandt
> Can head tubes be ovalized through normal bike use? What causes it?
It cannot happen from riding. If a head tube is oval, it became that
way from manufacture or faulty installation. If someone tried to
cover up such a flaw with Loctite, this can come loose with time and
not reveal that such a method was used when the head bearing starts
moving.
Forces from riding that might cause this will always bend down and top
tubes first. If the head tube is attached to a massive bulkhead
instead of a conventional bicycle frame, than all sorts of things can
be different. There are frame builders that do not recognize that the
top and downtube are elastically bending elements of the frame. That
is why they have larger diameters than conventional rear triangles.
Is your question about conventional bicycles or an aluminum one with
some huge practically inelastic box frame or triangulation.
Jobst Brandt <jbr...@hpl.hp.com>
G.T.
Jobst Brandt wrote in message <75emsi$9af$1...@hplms2.hpl.hp.com>...
that's strange. by the time i received a new bridgestone mb-1 frame in 1989
i had successfully installed 5 or 6 headsets with absolutely no problems. i
seemed to have properly installed a shimano 600 headset on the bridgestone
and by a year later the upper cup would just fall out of the frame. the
headset was never loose, i never ran directly into anything, nor can i think
of anything else but normal riding that would have caused this. the only
thing that i haven't done is install a new headset to see if it was the
headset that was damaged, not the headtube. i still have the frame sitting
in my garage. i'd really like to know what caused this.
also, i'd really like to know why mr brandt and others here have such
unwavering faith in theory and aritificial tests that can't possibly cover
all the variables of a real environment. why do you all discount things
that have clearly happened to people and aren't just simple myth and lore?
greg thomas
gr...@nadel.com
Mark Chandler
would become out-of-round (or whatever the correct
term is).
But hey, only a minor glitch when you've got thumbshifters
and a low q-factor, right?
**************************************************
Mark Chandler Concord, CA m...@hooked.net
* http://www.bikecolorado.com/articles/index.cfm *
*********** http://www.hooked.net/~mpc ***********
Jobst Brandt
>> It cannot happen from riding. If a head tube is oval, it became
>> that way from manufacture or faulty installation. If someone tried
>> to cover up such a flaw with Loctite, this can come loose with time
>> and not reveal that such a method was used when the head bearing
>> starts moving.
>> Forces from riding that might cause this will always bend down and
>> top tubes first. If the head tube is attached to a massive
>> bulkhead instead of a conventional bicycle frame, than all sorts of
>> things can be different. There are frame builders that do not
>> recognize that the top and downtube are elastically bending
>> elements of the frame. That is why they have larger diameters than
>> conventional rear triangles.
>> Is your question about conventional bicycles or an aluminum one
>> with some huge practically inelastic box frame or triangulation.
> That's strange. By the time I received a new Bridgestone MB-1 frame
> in 1989 I had successfully installed 5 or 6 headsets with absolutely
> no problems. I seemed to have properly installed a Shimano 600
> headset on the Bridgestone and by a year later the upper cup would
> just fall out of the frame. The headset was never loose, I never
> ran directly into anything, nor can I think of anything else but
> normal riding that would have caused this. The only thing that I
> haven't done is install a new headset to see if it was the headset
> that was damaged, not the headtube. I still have the frame sitting
> in my garage. I'd really like to know what caused this.
The upper bearing receives about half the radial load the bottom
bearing does, so if the bottom one is not loose, then the upper one
had something else happen to it, but it wasn't from riding. The
reason I say that with such certainty is that I have seen many frames
damaged by impact that bent forks steer tubes and completely wrinkled
the frame. None of these had any damage to the bearing sockets unless
the fork crown was bent to an angle to the head tube.
> Also, I'd really like to know why Mr Brandt and others here have
> such unwavering faith in theory and artificial tests that can't
> possibly cover all the variables of a real environment. Why do you
> all discount things that have clearly happened to people and aren't
> just simple myth and lore?
To what artificial tests are you referring? I state these things for
the same reason I wrote the bicycle wheel before which time everyone
was sure that loading a bicycle wheel increased tension in the upper
spokes of a wheel and that spokes broke because the rider rode over a
bump. None of that was correct. Similarly, the cause of dimpled head
bearings was not understood until I wrote the article about head
bearing failure that is now in the FAQ. There is a lot of urban
legend and mis-attribution of cause and effect in bicycling... and
many other technical subjects.
Jobst Brandt <jbr...@hpl.hp.com>
Tom Kunich
>
> Jobst Brandt wrote in message <75emsi$9af$1...@hplms2.hpl.hp.com>...
> >Larry Leveen writes:
> >
> >> Can head tubes be ovalized through normal bike use? What causes it?
> >
> >way from manufacture or faulty installation. If someone tried to
> >cover up such a flaw with Loctite, this can come loose with time and
> >not reveal that such a method was used when the head bearing starts
> >moving.
> >
> >Forces from riding that might cause this will always bend down and
> >top tubes first. If the head tube is attached to a massive bulkhead
> >instead of a conventional bicycle frame, than all sorts of things can
> >be different. There are frame builders that do not recognize that the
> >top and downtube are elastically bending elements of the frame. That
> >is why they have larger diameters than conventional rear triangles.
> >
> >Is your question about conventional bicycles or an aluminum one with
> >some huge practically inelastic box frame or triangulation.
>
> problems. i seemed to have properly installed a shimano 600 headset
> on the bridgestone and by a year later the upper cup would just fall
> out of the frame. the headset was never loose, i never ran directly
> into anything, nor can i think of anything else but normal riding that
> would have caused this. the only thing that i haven't done is install
> like to know what caused this.
The frame had a warped head tube from the manufacturer. When the
head tube was reamed it was done with a ream with some wear on it.
A part of the diameter of the head tube was slightly undersized and
because of the out-of-round another part of it was loose. When you
pressed in the headset races they felt tight because they were tight
over a percentage of their circumference. As you rode the bike the
headset could rock slightly and wear both the headset race and the
headtube. This only happens with a fairly badly warped head tube.
> also, i'd really like to know why mr brandt and others here have such
> unwavering faith in theory and aritificial tests that can't possibly
> cover all the variables of a real environment. why do you all
> discount things that have clearly happened to people and aren't just
> simple myth and lore?
The interesting thing about physics is that it supplies a set of
rules that work everywhere in the universe. I find I don't need
to suppose that steel, with forces at a fraction of the yeild strength
of the material applied, will move around simply by looking at
the strength of the material in a handbook of materials.
Jon Isaacs
ovalized? Do you
>think that the head tube itself is so weak that it >can sustain a force
>above it's yield strength despite the fact that the >steering tube will
>bend first?
I once owned a Trek Mountain bike in which the headtube where the lower headset
bearing rode had been pounded out. I believe that the mechanism for this is
that the bearing itself is harder than head tube in this region and the
constant pounding of off road use had deformed the steel in the head tube.
Since most of the pounding occurs is the for-aft direction, this is direction
of ovalization. Head tubes can be pounded oval. I imagine that the problem
initated with a loose head set which allowed the pounding. Notice with this
mechanism, that just as the handle of hammer does not need to be as hard as
what is being hit, neither does the steerer tube, only the head of the hammer
needs to be harder (higher yield strength also.)
Please note Tom:
>Do you think that the head tube itself is so weak that it can sustain a force
above it's yield strength
Yes, ductile materials such as most metals, as I am sure you know, certainly
have strength well beyond their yield. That is their advantage, plasticity,
large strains to failure, all those things, work hardening. I would be
surprised to see a Carbon Fiber bike with a ovalized head tube because the
strain to failure is small and CF does not work harden. Thus I would expect to
see a crack head tube.
Jon Isaacs
Mark Bulgier
wrong in this case.
Bridgestone lugged-steel mountainbikes used a construction method that left
the headtube and lug in an extremely weak condition. They did indeed
ovalize from "normal" hard off-road riding rather often.
The headtubes were copper brazed to the head lugs only, as a subassembly,
and then later brass brazed to the top and downtubes. Copper brazing
happens at a much higher temperature than brass brazing, and takes place in
an atmosphere-controlled oven (sorry I don't know what the atmosphere is,
but it isn't air). The cooling rate was so slow that the subassemblies
were completely annealed; that is, as weak as steel can be.
I am a framebuilder with over 20 years experience, and I know that's not
enough credential by itself to convince Jobst, but I hope you'll believe
that by now I can tell if a headtube is seriously oval or not. Quite often
Bridgestones went out with a proper headset fit (verified because the
headset was installed in our shop, as with warranty replacements) and came
back later with clearance on the order of a millimeter in the fore-aft
direction. Not a subtle change or one that could be missed or attributed
to other causes. The metal stretched. The fork steerer managed to apply a
force to the headtube that exceeded the yield strength of the headtube/lug
assembly. Shocking and amazing as it may be that the headtube and lug
could be that weak, I saw it with my own eyes.
Mark Bulgier
Troy A. Courtney
head tube can and does become ovalized if too much heat is applied while the
frame is being built. It is hard to imaging the forces being applied that
would cause the headtube to ovalize through normal use.
There are a couple other things to consider that have to do with the
prepping of the frame (facing and such).
If the head tube is cut to fit the headset more than once the fit will tend
to get sloppy.
When facing the headtube a sharp lip that protrudes inward is left behind.
If this is not removed (de-burr) it has a profound effect on the headset
race. Initially the headset will feel tight but because of the reduced
contact surface area it becomes loose over time.
Regards,
Troy A. Courtney
Courtney Custom Cycles
Geneva, IL
(630) 232-8720
tr...@cccycles.com
Mark W. wrote...
ma...@abtcorp.com wrote in message <75e3h9$809$1...@nnrp1.dejanews.com>...
>tom, i reiterate my earlier questions. what the hell are you talking about?
in
>my (former) capacity as a shop manager, i personally saw several mtb's with
>ovalized head tubes. these head tubes were originally round (we built some
of
>the bikes), were ridden for a couple years, and then were no longer round.
all
>of them were light steel frames with 1" headsets. a couple had suspension
>forks, but a couple did not. while there may have been some overheating or
>other error that led to reduced strength in the head tube area, these were
not
>bikes that were somehow delivered with oval head tubes.
>
>coincidentally enough, at least half of such bikes that i saw were
>bridgestones (of course we were a big bridgestone dealer at the
time). -mark
>weaver
>
>
>
>
>In article <75dqh1$vff$1...@nnrp1.dejanews.com>,
> tku...@diabloresearch.com wrote:
>> In article <k07lvq7...@dylan.ucsf.edu>,
>> dbl...@phy.ucsf.edu (David T. Blake) wrote:
>> > lev...@olywa.net (Larry Leveen) writes:
>> >
>> > >Can head tubes be ovalized through normal bike use? What causes it?
>> >
>> > I sent two such frames back to Bridgestone.
>> >
>> > Both were always kept in good working order and never had
>> > outstanding singular incidents. Both were ridden without
>> > suspension on very rocky trails with high regularity.
>> >
>> > The bottom press of the headset would no longer fit -
>> > it would simply fall out.
>>
>> This was a manufacturing error Dave. Normal use will not ovalize head
tubes.
>> This is generally done by overheating and warping the heat tube during
>> construction.
>>
Tom Kunich
>
> > T. Kunich wrote: What mechanism do you >propose for round tubes
> > being ovalized? Do you think that the head tube itself is so weak
> > that it can sustain a force above it's yield strength despite the
> > fact that the steering tube will bend first?
(Wow, guess I was really tired when I wrote that. What a hard
to understand sentence.)
> I once owned a Trek Mountain bike in which the headtube where the
> lower headset bearing rode had been pounded out. I believe that the
> mechanism for this is that the bearing itself is harder than head
> tube in this region and the constant pounding of off road use had
> deformed the steel in the head tube.
I'll have to think about that Jon -- here's the reason -- the frame
should actually flex away far before there is sufficient force on the
headset to cause such an ovalization. Also the tires, rims, spokes
and forks absorb so much shock that it is very difficult to believe
that enough shock can be transmitted to the head tube to cause any
such shape changes.
A loose outer race might cause problems but that implies that the
ovalization was already there.
> Please note Tom:
> >Do you think that the head tube itself is so weak that it can sustain
> >a force above it's yield strength
Yeah, yeah, you don't have to hit me over the head with it. I don't
understand what I was trying to say either.
> Yes, ductile materials such as most metals, as I am sure you know,
> certainly have strength well beyond their yield. That is their
> advantage, plasticity, large strains to failure, all those things,
> work hardening. I would be surprised to see a Carbon Fiber bike with
> a ovalized head tube because the strain to failure is small and CF
> does not work harden. Thus I would expect to see a crack head tube.
Thge yield point of steel is so high compared to the forces applied
in this particular set of circumstances that "ovalization" is another
of those urban myths that bicycling seems to have in such plenty.
In fact, ovalization from warping is very common. All you have to
do is ream out some frames and you'll spot right off that most frames
have some distortion and some frames have a lot of distortion. When
you first install a headset it seems to go in correctly but after
some time the headset race container which is generally aluminum will
fit itself to the distortion and will generally start to loosen. In
some cases it will get loose enough to practically fall out when
you pull the fork off.
Tom Kunich
>
> Shocking and amazing as it may be that the headtube and lug
> could be that weak, I saw it with my own eyes.
Mark, the problem I have with this is that the headset is a solid
block of steel to all intents and purposes and so maintains
it's roundness. This all goes to say that a head tube is very
well braced. While the rest of the frame absorbs the worst part
of the shocks.
Jon Isaacs
>When
>you first install a headset it seems to go in correctly but after
>some time the headset race container which is generally aluminum will
>fit itself to the distortion and will generally start to loosen. In
>some cases it will get loose enough to practically fall out when
>you pull the fork off.
></PRE></HTML>
I actually don't know what happened to the head tube on the Trek in question.
All I know is that it looked liked someone hit it with a hammer many times, the
bottom of the tube was flared and the head set was very loose.
Jon Isaacs
Bob Brown
posting a responce to this one.
tku...@diabloresearch.com wrote in message
<75ee79$h6n$1...@nnrp1.dejanews.com>...
>In article <75e3h9$809$1...@nnrp1.dejanews.com>,
> ma...@abtcorp.com wrote:
>> tom, i reiterate my earlier questions. what the hell are you talking
about? in
>> my (former) capacity as a shop manager, i personally saw several mtb's
with
>> ovalized head tubes. these head tubes were originally round (we built
some of
>> the bikes), were ridden for a couple years, and then were no longer
round. all
>> of them were light steel frames with 1" headsets. a couple had suspension
>> forks, but a couple did not. while there may have been some overheating
or
>> other error that led to reduced strength in the head tube area, these
were not
>> bikes that were somehow delivered with oval head tubes.
>
>What mechanism do you propose for round tubes being ovalized? Do you
>think that the head tube itself is so weak that it can sustain a force
>above it's yield strength despite the fact that the steering tube will
>bend first?
>
>Do you suscribe to the idea that AFTER you braze a doubling via the lug
>onto the head tube it will grow weaker? And then what of the headset
>which does a really nice job of spreading the forces from the fork
>throughout the entire steering head?
>
Absolutely. If you read Mark Bulgier's (sorry if I mis-spelled it Mark)
post, you would know that the Bridgestone frames had that particular lug
copper brazed to the headtube before joining to the downtube. Copper
brazing is a rather hightemperature process, the headtube alone is a very
small heatsink. Therefore, it was heated enough to significantly alter the
heat treatement of the tube, then allowed to slow cool to room temp. this
anneals the steel bringing it to a weakened condition. The headtube is now
MUCH weaker than when we started.
Also, the area where the lug contacts the headtube is heated the most. If
this bridgestone is like the one sitting in my basement, the lug encircles
the entire bottom of the headtube. The headset cup is
pressed into the bottom of the headtube. Now you have a load carrying
member attached directly to the weakest portion of the headtube. Weak
enough that yes, forces transmitted from the fork
are probably enough to plastically deform this specific area.
The weakening was a function of the high temperature used on a small amount
of metal. How's that for a theory? it only applies to a frame that was
heated in this manner though.
Bob Brown
>Obviously there needs to be some sort of theory as to how this ovalizing
>can occur. The problem is that all of the associated mechanism is weaker
>than the head tube. And there can be no wear if the headset is properly
>installed.
>
>I cannot answer as to why a couple of Bridgestones had ovalized head
>tubes unless they came that way.
>
>So, you always pull the races off of an assembled bike and test the
>fit of the headset? Am I mistaken or do they not make a headset that
>is installed in most production bikes that has a smaller OD on the
>headtube races so that you can install them in a STANDARD sized head
>tube without machining? Very little normal warping/"ovalization" needs
>be there for these races to come loose after delivery.
>
>-----------== Posted via Deja News, The Discussion Network ==----------
>http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Opinions expressed herein are my own and may not represent those of my employer.
tku...@diabloresearch.com
rpb...@mmm.com (Bob Brown) wrote:
> I've been reading all these and chuckling. I just can't resist
> posting a responce to this one.
>
> of metal. How's that for a theory? it only applies to a frame that was
> heated in this manner though.
Sounds good Bob. Unfortunately the problem is that Chrome-moly steel doesn't
derive it's strength from heat treatment but rather from it's structure.
Which the heat didn't change.
Also I find it interesting to hear all this about Bridgestones. I lived
in San Leandro at the time they were in business and rode with about
50 different riders with Bridgestones and I still have two or three of
them around the house (uh... an XO-1 and a 550 can't think of any others
right off hand). I also frequented a couple of shops in the area
that specialized in Bridgestones and had a lot of work done by the local
framebuilder who did 'factory' repairs in the area. I still ride with quite
a few riders that ride them and I even ride with the guy who bought my
old MB-2 which was (and IS) ridden very hard and since 1989 when I bought
it new.
Not once before this have I heard these stories about Bridgestone and
ovalized head tubes. What other factors contributed to their demise
that we will learn about now that they are safely in the past where
people who really know about them are dispersed to the winds?
Bob Brown
tku...@diabloresearch.com wrote in message
<75meat$pqb$1...@nnrp1.dejanews.com>...
>In article <75lv25$1io$1...@magnum.mmm.com>,
> rpb...@mmm.com (Bob Brown) wrote:
>> I've been reading all these and chuckling. I just can't resist
>> posting a responce to this one.
>>
>> The weakening was a function of the high temperature used on a small
amount
>> of metal. How's that for a theory? it only applies to a frame that was
>> heated in this manner though.
>
>Sounds good Bob. Unfortunately the problem is that Chrome-moly steel
doesn't
>derive it's strength from heat treatment but rather from it's structure.
>Which the heat didn't change.
Not to beat a dead horse here, but that's just not true. Chrome-moly
does change it's material properties from heat treatment. The particular
tubing used in the Bridestone bike may not have been heat treated, but that
does not mean it will not anneal. What is the difference between Reynolds
525 and 725? the 725 is a heat treated tube of the same material as 525
resulting in increases UTS. It really doesn't matter much what steel you
are using, you will get a HAZ when welding or high temp brazing. The HAZ
has a changed microstructure causing the falloff in UTS in this region. If
you don't believe me, check your ASTM handbook for strengths of heat-treated
vs. non-heat treated 4130 steels.
Bob Brown
Mark Bulgier
Tom Kunich wrote:
> [...] bicycle steels are generally not heat treated.
They quite often are these days, including the top of the line Bridgestones
we were talking about, which are made of Tange Prestige,
a quenched and tempered 4130.
Bike tubing that isn't heat treated is delivered in a heat treat state
known as "normalized", which is substantially stronger than the same steel
annealed. The copper brazed Bridgestone head tubes were totally annealed.
>
> The heat affected zone still has as much strength as any other
> head tube in general use. Remember that the thickness is the
> same for all of these tubes. They are all reamed for the headset
> diameter.
Even normalized bike steel also has some degree of extra strength due
to the cold-rolling process. The grain growth and re-crystallization that
occurred in these head tubes during the subsequent copper brazing process
left them as soft as steel can be.
If you could have seen one of these ovalized, you would agree there was
plastic deformation that occurred from riding. The degree of ovalization
was way more than can occur from the framebuilding process, for one thing.
As I said, there was 1mm or more of clearance fore-aft of the headset cup.
Also the direction they were ovalized (longer fore-aft) is opposite to the
ovalization that occurs during brazing. I've brazed hundreds (maybe a
thousand?) lugged frames and they always ovalize to wider, not longer, and
even in the extreme don't come close to the degree I saw in some of the
lugged Bridgestones.
The reason not all lugged Bridgestones ovalized is that their spec called
for the copper-brazed head subassemblies to be heat-treated after copper
brazing. Some missed this step. This is according to Bridgestone of
America.
Mark Bulgier
Tom Kunich
>
> Not to beat a dead horse here, but that's just not true. Chrome-moly
> does change it's material properties from heat treatment. The
> particular tubing used in the Bridestone bike may not have been heat
> treated, but that does not mean it will not anneal. What is the
> difference between Reynolds 525 and 725? the 725 is a heat treated
> tube of the same material as 525 resulting in increases UTS. It
> really doesn't matter much what steel you are using, you will get a
> HAZ when welding or high temp brazing. The HAZ has a changed
> microstructure causing the falloff in UTS in this region. If
> you don't believe me, check your ASTM handbook for strengths of
> heat-treated vs. non-heat treated 4130 steels.
Not arguing with you about the general properties of chrome-moly
steel Bob, but bicycle steels are generally not heat treated.
(I'm sure that you meant that the yield strength is affected
when you say the ultimate strength is affected)
Bob Brown
Tom Kunich wrote in message <367E8462...@home.com>...
>Bob Brown wrote:
>>
>> Not to beat a dead horse here, but that's just not true. Chrome-moly
>> does change it's material properties from heat treatment. The
>> particular tubing used in the Bridestone bike may not have been heat
>> treated, but that does not mean it will not anneal. What is the
>> difference between Reynolds 525 and 725? the 725 is a heat treated
>> tube of the same material as 525 resulting in increases UTS. It
>> really doesn't matter much what steel you are using, you will get a
>> HAZ when welding or high temp brazing. The HAZ has a changed
>> microstructure causing the falloff in UTS in this region. If
>> you don't believe me, check your ASTM handbook for strengths of
>> heat-treated vs. non-heat treated 4130 steels.
>
>Not arguing with you about the general properties of chrome-moly
>steel Bob, but bicycle steels are generally not heat treated.
>(I'm sure that you meant that the yield strength is affected
>when you say the ultimate strength is affected)
>
heat treated. Most notable Reynolds 853, 725, 753, and Tange
Prestige (as Mark Bulgier noted the last material is what the
Bridestones in question were built from). And I do mean UTS.
I will note that the Yield strength also changes proportionatly.
Also, this is what you wrote originally:
>Sounds good Bob. Unfortunately the problem is that Chrome-moly >steel
doesn't derive it's strength from heat treatment but rather from >it's
structure. Which the heat didn't change.
That statement does not say "most bikes are not made from
heat treated chromoly steel" It says that chromoly steels in general do not
change with heat treatment. I was talking about chromoly in general as you
originally seemed to, but nonetheless many bike tubesets come from the
manufacturer in a heat treated state.
>The heat affected zone still has as much strength as any other
>head tube in general use. Remember that the thickness is the
>same for all of these tubes. They are all reamed for the headset
>diameter.
This is also not true. The HAZ does not have the strength that the tube had
before brazing (or welding). The heating process has changed the
microstructure of the steel and weakened it. As Mark Bulgier has said, most
of that strength could be reclaimed through proper post weld heat treatment,
but the headtubes in question mistakenly missed this step. hence the steel
was fuly annealled and in a very weakened state.
I hope I'm not offending you here, but I'm just trying to show you why this
happened. if you still don't believe me about this, I suggest you
look into some metallurgy classes, It's pretty interesting stuff. Also
if you want to see more about heat treated steels in bicycle frames, take a
look at Reynolds page www.reynoldsusa.com
Naomi and Eric
>
> Bob Brown wrote:
> >
> > Not to beat a dead horse here, but that's just not true. Chrome-moly
> > does change it's material properties from heat treatment. The
> > particular tubing used in the Bridestone bike may not have been heat
> > treated, but that does not mean it will not anneal. What is the
> > difference between Reynolds 525 and 725? the 725 is a heat treated
> > tube of the same material as 525 resulting in increases UTS. It
> > really doesn't matter much what steel you are using, you will get a
> > HAZ when welding or high temp brazing. The HAZ has a changed
> > microstructure causing the falloff in UTS in this region. If
> > you don't believe me, check your ASTM handbook for strengths of
> > heat-treated vs. non-heat treated 4130 steels.
>
> Not arguing with you about the general properties of chrome-moly
> steel Bob, but bicycle steels are generally not heat treated.
> (I'm sure that you meant that the yield strength is affected
> when you say the ultimate strength is affected)
There are lots of bikes that utilize heat-treated steels. Tange
Prestige (and thus Ibis and up-to-this-year Ritchey), several of
the Reynolds offerings (such as 753 and 725 being HT versions of
531 and 525, respectively), Dedacciai's Zero tubesets (which
are HT versions of the 18MCDV6 alloy, which is used in non-HT
form for the heavier Zero-Uno tubesets), True Temper's OX3, RCX and
OXRCX, and Columbus' new Thermacrom are all heat treated. In
fact, many (most?) of the high-performance steels owe at least
some of their properties to the control of heating/cooling during
manufacture and/or assembly.
>
> The heat affected zone still has as much strength as any other
> head tube in general use. Remember that the thickness is the
> same for all of these tubes. They are all reamed for the headset
> diameter.
Not to nitpick, but what do you mean exactly by "...the thickness
is the same for all these tubes." ? Do you mean that all headtubes
for bikes that use, say, 1" steerers are the same thickness? They
are not, of course - many, if not most, TIG-welded MTB's use head
tubes that have a wall thickness of 1.2-1.5mm, while almost
all bikes which use lugs for the headtube joints must use head
tube with 0.8-1.0mm walls. The non-lugged headtubes have a larger
external diameter, often 32.5-32.9mm or so instead of 31.7mm (1.25").
(Most people get away with the thinner-walled ones on lighweight
road bikes which are TIG-welded as well, though.)
Finally, if you were to make two test joints to break - one with
a TIG-weld, and one with a big, sloppy, overheated brass fillet
(make sure that you heat the tubes up 'till they're nice and red,
and cool em' down slowly) - then break them, you would generally
see that the TIG welded one will flex somewhat then break at the
edge of the HAZ. The overheated tubes will generall bend and
crumple and twist, not break, until strained considerably, and the
force needed is noticeably less than that needed to break the TIG
joint.
(Note that I'm not saying that you should fillet-braze as described
above, but that would be closer to what happened to the MTB head
tubes in question. A _proper_ fillet-brazed joint is VERY strong.)
Finally, if a tube is NOT heat-treated in some manner after
the forming operations (something such as normalization), then it
has cold-worked or work-hardened properties that will be lost
through re-crystallization when abused in the manner of the
head tube in question. This is why, as someone noted, Bridgestone
had spec'd a heat treatment cycle after the copper-brazing
operation.
I don't really have any idea about what's going on with the
Bridgestone bikes, having never seen one with the malady described.
These are just my observations in general.
Eric
ma...@abtcorp.com
take away his voluminous knowledge?
that's right, you get the post below. others have cited numerous instances to
support the claim that most steel tubes used for good bicycles are
heat-treated. tom is (unexplainedly) not refuting these claims, just denying
them.
since when are all head tubes the same thickness? what planet are you from,
tom, where outside diameter of all tubes is the same, and only 1 wall
thickness is allowed by law? it must be a strange place. on the other hand,
it makes for plenty entertaining reading.
so to what do you attribude all the ovalized head tubes that people (including
me) have seen with their own eyes and touched with their own hands? mass
hysteria? self-hypnotism?
i think most of the people who've followed this ng for a while already know
that your posts are mostly to be read for entertainment value only, to see how
wrong you are today (i confess that when i see "tkunich" i usually read it for
a good laugh, even if i have no interest in the topic). but what about less
experienced readers? they might actually think you have the vaguest idea what
the hell you're talking about.
-mark weaver
In article <367E8462...@home.com>,
Tom Kunich <elizab...@home.com> wrote:
> Not arguing with you about the general properties of chrome-moly
> steel Bob, but bicycle steels are generally not heat treated.
> (I'm sure that you meant that the yield strength is affected
> when you say the ultimate strength is affected)
>
> The heat affected zone still has as much strength as any other
> head tube in general use. Remember that the thickness is the
> same for all of these tubes. They are all reamed for the headset
> diameter.
>
-----------== Posted via Deja News, The Discussion Network ==----------
Jobst Brandt
the like. Head bearings have had aluminum housings for many years now
and are pressed in with a light press fit. If anything were to yield
from operating loads, it would be the aluminum, steel in all its forms
being harder or having a higher yield strength than aluminum. If you
doubt this, just show me a scratch made with a piece of aluminum in a
piece of steel.
What you are most likely seeing are oversized bores that had paint in
them and that subsequently loosened when the paint wore off. A head
bearing cup pressed into a steel head tube cannot be pushed off axis
without a force great enough to damage the fork. In any event, the
aluminum shell of the head bearing will fail first.
Jobst Brandt <jbr...@hpl.hp.com>
Mark Bulgier
Jobst Brandt wrote:
>
> What we are seeing here are oversized bores that had paint in them and
> that subsequently loosened when the paint wore off. A head bearing
> cup pressed into a steel head tube cannot be pushed off axis without a
> force great enough to break the fork.
And yet it happened. Your theory is faulty. The extra clearance was a
millimeter or more. The paint on the OUTSIDE of the frame cracked and fell
off, but the paint that had been on the inside was still there. The
MANUFACTURER said the head tube had stretched in use due to incorrect heat
treatment. And bumblebees do fly.
Mark Bulgier
Joshua_Putnam
>Bob Brown wrote:
>> Not to beat a dead horse here, but that's just not true. Chrome-moly
>> does change it's material properties from heat treatment. The
>> particular tubing used in the Bridestone bike may not have been heat
>> treated, but that does not mean it will not anneal.
>Not arguing with you about the general properties of chrome-moly
>steel Bob, but bicycle steels are generally not heat treated.
I know that was true back when 531 ruled the roost, but a lot of
the better steel bikes on the market are made with heat treated
steels these days, from Tange Prestige and Ultimate to Reynolds
653, 708, 731, 753, etc, and so on.
Even for tubes that aren't heat treated, overheating will
eliminate the strength added by cold working, e.g. drawing and
butting the tubing.
>The heat affected zone still has as much strength as any other
>head tube in general use.
Not necessarily so. Even plain old normalized CrMo aircraft
tubing loses some strength when heated enough for copper brazing.
I don't know what filler B-stone used on these joints, but many
copper brazing alloys have a liquidus over 1800 F.
>Remember that the thickness is the
>same for all of these tubes. They are all reamed for the headset
>diameter.
Well, besides the obvious problem that there's more than one
standard head cup diameter (JIS vs. English/italian), the
outside diameter can also differ. A 33mm diameter head tube
reamed to 29.8mm for 30.0mm cups has 1.6mm remaining wall
thickness; a 31.75mm (standard 1-3/8") tube reamed to 30.0mm for
30.2mm cups has 0.875mm remaining wall thickness. If you
restrict yourself to lugged frames with standard lugs the
varation is smaller, of course.
But then, on a lugged frame, you need to look at the
reinforcement provided by the lug surrounding the tube, which
can range from a thin mild steel stamped lug to a thick, cast,
CrMo lug. And some fillet brazed frames have been made with
thin head tubes and reinforcing sleeves brazed to the outside.
So it's really unrealistic to say they're all identical.
--
Jo...@WolfeNet.com is Joshua Putnam / P.O. Box 13220 / Burton, WA 98013
"My other bike is a car."
http://www.wolfenet.com/~josh/
tku...@diabloresearch.com
nao...@uhs.umass.edu wrote:
> Tom Kunich wrote:
> >
> > Bob Brown wrote:
> > >
> > > Not to beat a dead horse here, but that's just not true. Chrome-moly
> > > does change it's material properties from heat treatment. The
> > > particular tubing used in the Bridestone bike may not have been heat
> > > difference between Reynolds 525 and 725? the 725 is a heat treated
> > > tube of the same material as 525 resulting in increases UTS. It
> > > really doesn't matter much what steel you are using, you will get a
> > > HAZ when welding or high temp brazing. The HAZ has a changed
> > > microstructure causing the falloff in UTS in this region. If
> > > you don't believe me, check your ASTM handbook for strengths of
> > > heat-treated vs. non-heat treated 4130 steels.
> >
> > steel Bob, but bicycle steels are generally not heat treated.
> > when you say the ultimate strength is affected)
>
> Prestige (and thus Ibis and up-to-this-year Ritchey), several of
> the Reynolds offerings (such as 753 and 725 being HT versions of
> 531 and 525, respectively), Dedacciai's Zero tubesets (which
> are HT versions of the 18MCDV6 alloy, which is used in non-HT
> form for the heavier Zero-Uno tubesets), True Temper's OX3, RCX and
> OXRCX, and Columbus' new Thermacrom are all heat treated. In
> fact, many (most?) of the high-performance steels owe at least
> some of their properties to the control of heating/cooling during
> manufacture and/or assembly.
Maybe I'm not making myself clear enough. MOST HIGHER CLASS BICYCLES
ARE MADE WITH CHROME MOLY TUBES THAT ARE NOT HEAT TREATED. Modern
high quality bikes have been made from heat treated alloys in order
to lighten the tube sets marginally for MARKETING REASONS and not
for mechanical reasons.
How many "ovalized" 531 head tubes have you seen? Please raise your hand
if you think that the head tubes for a Tange Prestige tube set have been
heat treated. Why are all of the old Peugeots and Gitanes that were
constructed essentially out of low grade steel still tight in the headsets?
Why with all of these overheating problems and the weakeness of head tubes
so well known we should have people by the thousands lining up to tell
us that they 531 frames failed miserably to maintain a round tube in
the front despite the fact that all of the shock is absorbed mostly in
the fork flexure.
I've just rebuilt another Peugeot UO-8. Darned if I could see the slightest
bit of distortion in the head tubes. And these bikes were built as cheaply
and as rapidly as possible. But obviously these Frenchmen knew something
that Bridgestone Japan couldn't figure out. Obviously those Japanese
don't understand technology.
> > The heat affected zone still has as much strength as any other
> > head tube in general use. Remember that the thickness is the
> > same for all of these tubes. They are all reamed for the headset
> > diameter.
>
> Not to nitpick, but what do you mean exactly by "...the thickness
> is the same for all these tubes." ? Do you mean that all headtubes
> for bikes that use, say, 1" steerers are the same thickness?
I would like to see some real information about the specifications of
head tubes. Chances are that there are no differences in any of the
lugged head tubes beyond pure material differences. And that is
highly unlikely to be significant.
> I don't really have any idea about what's going on with the
> Bridgestone bikes, having never seen one with the malady described.
Until this argument started I'd never even heard of such a thing.
ma...@abtcorp.com
i will damage the bat but not dent the hood? obviously this is wrong. equally
obviously (since i have seen ovalized head tubes, easily visible to the naked
eye, with apparently undamaged forks), your conclusions are wrong. no one
mentioned a scratched headtube, but rather a bent one. and i don't see how
you can possibly claim with such certainty that all forks are weaker than all
headtubes. honestly, your post is so implausible that it almost sounds like
tom kunich is posting from your computer.
at any rate, just about all bridgestones (and certainly the reasonably priced
ones) came with steel headsets. steel headsets are easy (and cheap) to buy,
and seem to hold up great. i even have one on my rb1 (head tube still round
so far). -mark weaver
In article <75oj3n$s4j$3...@hplms2.hpl.hp.com>,
jbr...@hpl.hp.com (Jobst Brandt) wrote:
> Forget about heat affected zone, work hardening, heat treatment and
> the like. Head bearings have had aluminum housings for many years now
> and are pressed in with a light press fit. If anything were to yield
> from operating loads, it would be the aluminum, steel in all its forms
> being harder or having a higher yield strength than aluminum. If you
> doubt this, just show me a scratch made with a piece of aluminum in a
> piece of steel.
>
> What you are most likely seeing are oversized bores that had paint in
> them and that subsequently loosened when the paint wore off. A head
> bearing cup pressed into a steel head tube cannot be pushed off axis
> without a force great enough to damage the fork. In any event, the
> aluminum shell of the head bearing will fail first.
>
> Jobst Brandt <jbr...@hpl.hp.com>
>
>
-----------== Posted via Deja News, The Discussion Network ==----------
Bob Brown
ma...@abtcorp.com wrote in message <75oo5t$mgr$1...@nnrp1.dejanews.com>...
>i think most of the people who've followed this ng for a while already know
>that your posts are mostly to be read for entertainment value only, to see
how
>wrong you are today (i confess that when i see "tkunich" i usually read it
for
>a good laugh, even if i have no interest in the topic). but what about less
>experienced readers? they might actually think you have the vaguest idea
what
>the hell you're talking about.
>-mark weaver
>
Mark great post, I do really start laughing at each responce I see
from Tom to my rebuttles. You'd think I would have convinced him, oh well.
Good entertainment Can we add one more quote to your ridiculous list:
Tom Kunich wrote:
>Maybe I'm not making myself clear enough. MOST HIGHER CLASS >BICYCLES ARE
MADE WITH CHROME MOLY TUBES THAT ARE >NOT HEAT TREATED.
>How many "ovalized" 531 head tubes have you seen? Please raise >your hand
if you think that the head tubes for a Tange Prestige tube >set have been
heat treated. Why are all of the old Peugeots and >Gitanes that were
constructed essentially out of low grade steel still >tight in the headsets?
>Why with all of these overheating problems and the weakeness of >head tubes
so well known we should have people by the thousands >lining up to tell us
that they 531 frames failed miserably to maintain a >round tube in the front
despite the fact that all of the shock is >absorbed mostly in the fork
flexure.
Gee I even directly told Tom that 531 was not-heat treated and does not fall
into the class under discussion. And I'll raise my hand for the Tange
Prestige tube being heat treated.
Bob
Jobst Brandt
>> Forget about heat affected zone, work hardening, heat treatment and
>> the like. Head bearings have had aluminum housings for many years
>> now and are pressed in with a light press fit. If anything were to
>> yield from operating loads, it would be the aluminum, steel in all
>> its forms being harder or having a higher yield strength than
>> aluminum. If you doubt this, just show me a scratch made with a
>> piece of aluminum in a piece of steel.
> Extrapolating from this, if I hit my car hood with an aluminum
> baseball bat, I will damage the bat but not dent the hood? obviously
> this is wrong.
There is no parallel there. I only mention this so that you can
assure yourself that steel is stronger than aluminum, not "paper-
rock-scissors" form factor has anything to do with it. Your aluminum
baseball bat will dent aluminum sheet metal as well as steel.
> Equally obviously (since I have seen ovalized head tubes, easily
> visible to the naked eye, with apparently undamaged forks), your
> conclusions are wrong. No one mentioned a scratched headtube, but
> rather a bent one.
Hardness tests are done by indentation, tensile tests by stretching
standard samples. Don't get hung up on scratches, it only shows
which metal is harder.
> And I don't see how you can possibly claim with such certainty that
> all forks are weaker than all headtubes. Honestly, your post is so
> implausible that it almost sounds like tom Kunich is posting from
> your computer.
Just ride bike a bit and visit competent repair shops.
>> What you are most likely seeing are oversized bores that had paint
>> in them and that subsequently loosened when the paint wore off. A
>> head bearing cup pressed into a steel head tube cannot be pushed
>> off axis without a force great enough to damage the fork. In any
>> event, the aluminum shell of the head bearing will fail first.
> At any rate, just about all Bridgestones (and certainly the
> reasonably priced ones) came with steel headsets. Steel headsets
> are easy (and cheap) to buy, and seem to hold up great. I even have
> one on my RB1 (head tube still round so far).
So what. I pointed out that many of the bikes that see the hardest
service are equipped with aluminum head bearing shells and that these
are far weaker than the head tube and its fittings.
Jobst Brandt <jbr...@hpl.hp.com>
John Taglia
>
> extrapolating from this, if i hit my car hood with an aluminum baseball bat,
> i will damage the bat but not dent the hood? obviously this is wrong. equally
> obviously (since i have seen ovalized head tubes, easily visible to the naked
> eye, with apparently undamaged forks), your conclusions are wrong. no one
> mentioned a scratched headtube, but rather a bent one. and i don't see how
> you can possibly claim with such certainty that all forks are weaker than all
> tom kunich is posting from your computer.
>
> at any rate, just about all bridgestones (and certainly the reasonably priced
> ones) came with steel headsets. steel headsets are easy (and cheap) to buy,
> and seem to hold up great. i even have one on my rb1 (head tube still round
> so far). -mark weaver
>
A friend of mine who was a Bridgestone rep also mention the ovalization
occurring. However, he offered no scientific explanation of why.
Sorry.
--
John Taglia
jtagli...@uic.edu
remove the nospam stuff to reply
The walls are built stone by stone,
The fields divided one by one
Joshua_Putnam
>Please raise your hand
>if you think that the head tubes for a Tange Prestige tube set have been
>heat treated.
Yup. Have the technical specs right here, as a matter of fact,
in my Tange frame tubing catalog. Prestige head tubes are heat
treated.
>Why are all of the old Peugeots and Gitanes that were
>constructed essentially out of low grade steel still tight in the headsets?
Because they aren't mountain bikes, and their top and down tubes
buckle long before you'd damage the head tube. Compared to
traditional road bikes, mountain bikes (like the Bridgestones
under discussion) tend to have larger down tubes, thicker top
tube walls, shorter head tubes, thicker steerer walls below the
stem quill portion, and oversized fork blades.
>Why with all of these overheating problems and the weakeness of head tubes
>so well known we should have people by the thousands lining up to tell
>us that they 531 frames failed miserably to maintain a round tube in
>the front despite the fact that all of the shock is absorbed mostly in
>the fork flexure.
Only if they had their 531 frames incompetently constructed, and
used those big EB730 Jack Taylor-pattern blades with the HB131
steerer in place of the HB102 normally used with 531 C road
sets. (Copper brazing temperatures are well beyond the range
allowed for brazing 531, and overheated 531 is in fact far more
failure prone than properly assembled 531. If you want to use
higher temperature machine brazing, Reynolds says you have to
stick with 525 tubes, which are non-heat-treated CrMo.
Oversized blades and thick steerer tubes flex less under load,
transmitting more shock to the head tube you overcooked.)
Joshua_Putnam
>Mark Weaver writes:
>> At any rate, just about all Bridgestones (and certainly the
>> reasonably priced ones) came with steel headsets. Steel headsets
>> are easy (and cheap) to buy, and seem to hold up great. I even have
>> one on my RB1 (head tube still round so far).
>So what. I pointed out that many of the bikes that see the hardest
>service are equipped with aluminum head bearing shells and that these
>are far weaker than the head tube and its fittings.
That's true -- I've seen many more damaged headset cup shells on
mountain bikes than damaged head tubes. This is less common now
than on the rigid bikes just before the front-suspension era,
when the fashion trend was for massively oversized fork blades
and beefy as hell steerers stuck into the same old 1" headsets.
Remember those super-rigid mountain forks that used blades as
big around as suspension fork sliders, and had such long
external butts on the steerers that some fork crown race cutters
wouldn't work on them? I saw people do damage to their frames
in crashes that I thought should have just bent the fork if the
fork had been reasonably matched to the frame -- a fork is a lot
cheaper to replace than a frame, after all. But fashion is
fashion, and making a durable bike often takes third place
behind fashion and price.
Tecnociclo
>head tubes.
From the Columbus catalog:
Head tubes
Nemo 31.7/0.8 and 31.7/1.0
Genius 31.7/1.0 and all below Genius use 31.7/1.0 headtubes according to spec.
From the Dedaccai catalog:
Head tubes
18MCDV6 31.7/1.0
Material spec is all 24CrMo4, 900 N/mm 13% Elongation.
The Nemo 0.8 tube HAS to use reinforcing rings ( which are brazed on ) for the
headset races if the frame is tig welded.
Marco.
tku...@diabloresearch.com
tecno...@aol.com (Tecnociclo) wrote:
> >I would like to see some real information about the specifications of
> >head tubes.
>
> From the Columbus catalog:
>
> Head tubes
> Nemo 31.7/0.8 and 31.7/1.0
> Genius 31.7/1.0
> and all below Genius use 31.7/1.0 headtubes according to spec.
>
> headset races if the frame is tig welded.
These are the Tig tubes and the brazing tubes.
> From the Dedaccai catalog:
>
> Head tubes
> 18MCDV6 31.7/1.0
>
> Material spec is all 24CrMo4, 900 N/mm 13% Elongation.
The elongation probably infers the heat treatment of the tube. Is this
a heat treated tube or not? More importantly, did Dedaccia even bother
to make the differentiation? After all, it isn't very important.
Old french bikes are very common in this area. As are newer Bridgestones.
I've seen lots and lots of older bikes and not a one of them has had
any head tube ovalization that could be credited to road forces. The very
idea seem preposterous to me. I've talked to a couple of dealers about
Bridgestone head tubes and they don't know what the heck I'm talking about.
So if there were some Bridgestones with such head tubes they must have
been pretty rare.
I'm still trying to find out how you could 'hammer' the head tube when
almost all of the forces that go into the fork are absorbed by flexure of
the tire, rim, spokes, fork blades and frame triangle.
I have seen some pretty messed up bikes that were involved in accidents
that had perfectly good head tubes. If you could ovalize a head tube why
wouldn't they also bend in accidents instead of the frame triangle bending?
ma...@abtcorp.com
jbr...@hpl.hp.com (Jobst Brandt) wrote:
>>>If anything were to
> >> yield from operating loads, it would be the aluminum, steel in all
> >> its forms being harder or having a higher yield strength than
> >> aluminum. If you doubt this, just show me a scratch made with a
> >> piece of aluminum in a piece of steel.
jobst also wrote this:
> Hardness tests are done by indentation, tensile tests by stretching
> standard samples. Don't get hung up on scratches, it only shows
> which metal is harder.
and this too!
> >> What you are most likely seeing are oversized bores that had paint
> >> in them and that subsequently loosened when the paint wore off. A
> >> head bearing cup pressed into a steel head tube cannot be pushed
> >> off axis without a force great enough to damage the fork. In any
> >> event, the aluminum shell of the head bearing will fail first.
and also this!!
> So what. I pointed out that many of the bikes that see the hardest
> service are equipped with aluminum head bearing shells and that these
> are far weaker than the head tube and its fittings.
>
> Jobst Brandt <jbr...@hpl.hp.com>
i don't know if he's backpedaling now, or just talking out his ass. usually
what jobst writes is very clear, and i very clearly got the idea that he was
scoffing at the possibility of a head tube becoming ovalized. now i'm not sure
what he's talking about. a discussion was under way about a very limited (but
non-zero) quantity of ovalized headtubes (mostly on bridgestones) that have
been seen by readers of this newsgroup. what this has to do with aluminum
scratching (which jobst brought up to bolster his argument, then scoffed at a
few hours later), i can't imagine.
-mark weaver
(i may not know everything, but at least i'm not a dork)
Naomi and Eric
>
> In article <19981223092344...@ng27.aol.com>,
> tecno...@aol.com (Tecnociclo) wrote:
> > From the Dedaccai catalog:
> >
> > Head tubes
> > 18MCDV6 31.7/1.0
> >
> > Material spec is all 24CrMo4, 900 N/mm 13% Elongation.
>
> The elongation probably infers the heat treatment of the tube. Is this
> a heat treated tube or not? More importantly, did Dedaccia even bother
> to make the differentiation? After all, it isn't very important.
The Dedacciai head tube is not heat treated; it is also not 25CrMo4,
as it is made with 18MCDV6, which has specs of 1250 N/mm2 with 12%
elongation. The rest of the Ded Zero set is 18MCDV6HT, which bumps
the strength to 1400N/mm2 (claimed), including the steerer. Finally,
the claim that I in particular was responding to was that "no quality
bicycles use heat treated tubing", not "no quality bicycles use heat
treated head tubes".
Also, for MTB's, the head tube used with the Dedacciai tubing is
generally the 32.5mm tube, not the 31.7mm one, when TIG-welded. Some
people do get away with the lighter one, but it usually isn't the
recommended setup, and it depends on the person the bike is intended
for. (The 32.5mm tube has 1.3mm walls.) If you are lugging the
head tube, then it would likely be fine, espcially with something like
HJ's head tube lugs for MTB's.
As for the Columbus head tube dimensions, they are correct for the
road bike versions, but the recommended MTB sizes for various
tubesets are as follows:
Genius OR 1.25mm or 1.0mm (builder choice)
Metax OR 1.2mm
Focus OR 1.25mm
Max OR 1.5mm
Cyber OR 1.1mm
Thron OR 1.0mm ("standard", 1" steerer, non-OS tubing)
1.6mm ("OS" version, 1.125 steerer)
Note that these are for MTB sets, and that they are generally
for 1.125" steerers. Note that also, as I said in my earlier
post, that you can only get away with the thicker walls (and
thus the larger OD) if you are NOT using lugs. I don't know
of many places that sell lugs for a 32.5mm head tube, for
instance.
arrrggghhh,
Eric
Bob Brown
technical discussions go too far, so I'll jump back in here and add a few
more comments.
Before I begin, Mark Weaver, I love your posts, great entertainment.
tku...@diabloresearch.com wrote in message
<75r74v$o1c$1...@nnrp1.dejanews.com>...
>In article <19981223092344...@ng27.aol.com>,
> tecno...@aol.com (Tecnociclo) wrote:
>> >I would like to see some real information about the specifications of
>> >head tubes.
>>
>> From the Columbus catalog:
>>
>> Head tubes
>> Nemo 31.7/0.8 and 31.7/1.0
>> Genius 31.7/1.0
>> and all below Genius use 31.7/1.0 headtubes according to spec.
>>
>> The Nemo 0.8 tube HAS to use reinforcing rings (which are brazed on) for
the
>> headset races if the frame is tig welded.
>
>These are the Tig tubes and the brazing tubes.
>
>> From the Dedaccai catalog:
>>
>> Head tubes
>> 18MCDV6 31.7/1.0
>>
>> Material spec is all 24CrMo4, 900 N/mm 13% Elongation.
>
>The elongation probably infers the heat treatment of the tube. Is this
>a heat treated tube or not? More importantly, did Dedaccia even bother
>to make the differentiation? After all, it isn't very important.
>
Golly, I though we were talking about Bridestone frames that had Tange
Prestige head tubes, and the area of debate was the heat treatment of such
tubes. As I have said, Tom, you're wrong! The heat treatment does matter.
Why do you keep saying it doesn't, or that tubes that are heat treated
aren't? I've already given enough reasons for anyone to see why heat
treatment is important in welded or brazed metal structures. I see no
reason to reiterate.
>Old french bikes are very common in this area. As are newer Bridgestones.
>I've seen lots and lots of older bikes and not a one of them has had
>any head tube ovalization that could be credited to road forces. The very
>idea seem preposterous to me. I've talked to a couple of dealers about
>Bridgestone head tubes and they don't know what the heck I'm talking about.
>So if there were some Bridgestones with such head tubes they must have
>been pretty rare.
>
It' been said all along that it was limited to a few frames that had a
mistake in the manufacturing processs. The are rare, but did happen.
Manufacturing process mistakes do happen. That's all this was.
>I'm still trying to find out how you could 'hammer' the head tube when
>almost all of the forces that go into the fork are absorbed by flexure of
>the tire, rim, spokes, fork blades and frame triangle.
>
Tom, how do forces from the front wheel get transmitted to the frame?
Through the headtube of course, that's the only place it can happen. Any
reaction force from the fork acting on the frame acts on the headtube in
some form. Specifically, through the ends of the headtube, where the headset
bearings are attached.
>I have seen some pretty messed up bikes that were involved in accidents
>that had perfectly good head tubes. If you could ovalize a head tube why
>wouldn't they also bend in accidents instead of the frame triangle bending?
>
Alright here there is also a good explaination. First, these frames
you saw probably did not have the manufactuing flaw that the bridgestones in
question did. I can make this assumption with certainty due to the fact
that you have never seen an ovalized headtube, and you have seen these
frames that were in accidents. These frames you talk about proably did not
have weakened headtubes from manufacturing.
(OK, this part is long, and requires a knowledge of statics)
Second, The headtube can be modeled as a simple beam of circular cross
section that is fixed at two points and cantilevered on both ends slightly.
That is, the downtube and top-tube are the two fixed points, the
ends of the headtube where the headset cups are pressed are the cantilevered
ends. For the headtube to bend in this model, it would require a force
acting to create a bending moment about one of the fixed points. Lets say
the fork takes an impact directed straight into the front of the bike. This
will create a force in that same direction acting on the headtube at the
lower headset bearing. it will also create a reaction force in the opposite
direction acting at the top headset bearing.
(at this point if you're still with me, I urge you to draw a free body
diagram) Take a look how the forces are acting, two parallel forces acting
in oposite directions separated by a perpendicualr distance. That defines a
couple if the forces are of the same magnitude.
For the sake of arguement I will say the forces are about the same
magnitude, therefore the resultant force is zero. The two forces do create
two moments about the two fixed points though. The problem is that the
moments act in the same direction(right hand rule). In order for them to be
significant enough to bend the short section of tubing, they would have to
act in the opposite directions. (OK, that part may sound confusing, since
people tend to define direction differently, but it makes sense if you draw
the diagram) Also, the distance from the fixed point to where the forces
act is very small, maybe a cm or two. The force would have to be huge to
generate a moment large enough to bend the headtube.
You see to bend the tube, you need a large moment, which is directly
proportional to the length of the cantilevered member (short in a headtube).
To ovalize the bottom of the headtube, just a force applied at this loaction
if required, and the force must be larger that the yield strength of the
weakened steel.
Now the forces are also trasmited to the down and top tubes. for the
purpose of this model, I will discuss the downtube, and say it is now a
cantilever memeber fixed about the BB. It has a large force applied to the
headtube end. due to it's long length, it has a large bending moment and
thus requires less force to bend than the headtube.
Alright, that's enough statics for one day. Again, if you don't understand
this and think you should be able to, draw the diagrams and do the math. It
will make more sense.
One more thing, Tom Kunich, what is diablo research other than your domain
name? Do you work for a research company? If so, I'd think you could do
more research before you keep making these posts.
Bob Brown
Jon Isaacs
There seem to be two schools, those they say they have seen ovalized head tubes
and those that say it cannot happen.
Interesting.
Analytical solutions to engineering problems are based on estimations and are
subject to verification by experiments and field testing. If the experiments
or field tests show that the analytical solution is incorrect then the analysis
is shown to be either based on faulty assumptions or in error. In either case
new analysis is needed.
Someone once said that there were two types of papers given at scientific
meetings. First type are theoretical papers, these no one in the room believes
them but the author. The second type are experimental papers, these everyone
in the room believes them except the author.
In this case I believe that the head tubes in question did ovalize. Time for
some new analysis.
As a side note, I would like to comment on the idea of aluminum with a lower
yield stress causing deformation in steel, which may have a higher hardness and
yield stress. Note that the loading of the headtube is dynamic. One of
experiments I do on a regular basis involves impact of a Modulan 651 (50% dense
polyurathane foam) sabot with some 17-4 ph steel at somewhere between 400
meters/second and 1000 meters/second. The impact of the 6000 psi yield modulan
causes plastic deformation in the 180,000 psi 17-4 ph. Oh well....
Just a few comments from someone who works doing experiments to prove or
disprove the work of someone who does theory.
Jon Isaacs
Larry Leveen
Brandt) wrote:
> Larry Leveen writes:
>
> > Can head tubes be ovalized through normal bike use? What causes it?
> Is your question about conventional bicycles or an aluminum one with
> some huge practically inelastic box frame or triangulation.
I can only recall it happening to steel frames.
--
Larry Leveen
Velorution! The Bicycle "Freeware" Infopage
http://www.olywa.net/leveen/
Tecnociclo
>as it is made with 18MCDV6, which has specs of 1250 N/mm2 with 12%
>elongation. The rest of the Ded Zero set is 18MCDV6HT, which bumps
>the strength to 1400N/mm2 (claimed), including the steerer.
I thought we were reffering to road frames so I only posted those dimensions.
Deda do not use 18MCDV6 for the head tube but 25CrMo4. Columbus use the same
material, they do not make Nivacrom or Thermacrom headtubes as they say there
is not point to to so. The material does not need to be stronger as it cannot
be any thinner ( which would be the point of using a stronger material ).
As I said in my earlier post, all the information is taken directly from the
companies catalogs. Are you saying they don't know what they use for material ?
The 18MCDV6 only refers to the model tubing ( Zero HT ) which has different
material components depending on the tube ( like Nivacrom. There are no
Nivacrom steerers and only one set of fork blades-which are for use with a
crown only, but the tubeset is referred to as a Nivacrom "set" - ELOS, Genius,
Nemo, Cyber.. ).
Marco.
tku...@diabloresearch.com
joni...@aol.com (Jon Isaacs) wrote:
> I have been following this thread for a while, even making a comment or two.
>
> There seem to be two schools, those they say they have seen ovalized head
> tubes and those that say it cannot happen.
I think that you misunderstand the argument Jon. I don't dispute that
these others have seen ovalized head tubes. I question their theories
on how the tube GOT that way. It is my belief that someone putting
together 100-400 bicycles a year isn't going to pay strict attention
to the fit of pieces that are already installed. Bridgestones were
shipped virtually fully assembled and needed only minor work to put
them on the showroom floor.
I have seen ovalizations on several frames (not particularly serious)
but they were all new. I've never seen any ovalization in head tubes
on bikes that were reamed. Even though some of them have had tens of
thousands miles and were old bikes with head tubes made out of mild
steel. And stresses in the tubes caused by overheating can take months
or even years to normalize. This 'ovalization' may grow worse without
any regard to the stresses the tube sees in operation.
> Analytical solutions to engineering problems are based on estimations and are
> subject to verification by experiments and field testing. If the experiments
> or field tests show that the analytical solution is incorrect then the
> analysis is shown to be either based on faulty assumptions or in error. In
> either case new analysis is needed.
You have to have valid and reliable experimental data to work with. In the
bicycle world we get myths and rumors. We have people telling us that
they saw ovalization but we really don't have a history of those observations.
We do have knowledge of HARD engineering data that tells us that the
forces being exerted on these head tubes is considerably below the value
necessary to cause deformation.
Again, how do you explain ovalization when all of the forces applied to
the head tube are mediated by the tire, tube, rim, spoke, fork and frame
triangle and spread very evenly about the headtube ID with the headset.
> Someone once said that there were two types of papers given at scientific
> meetings. First type are theoretical papers, these no one in the room
> believes them but the author. The second type are experimental papers,
> these everyone in the room believes them except the author.
Trite. But you are missing the point that it is the theories of those
who claim this ovalization from use that are at question and not the
explanations of those of us who are simply quoting standard engineering
practice.
> In this case I believe that the head tubes in question did ovalize. Time for
> some new analysis.
The real question is WHEN did it ovalize, not whether or not it ovalized.
I don't question for a minute the observations of those people posting
such things. Only the interpretations of those observations.
A number of years ago I got into a big argument with a nationally famous
motorcycle racer who was repeating some absolute garbage that had been
printed in Cycle World by none other than that old fool Gordon Jennings
about the strength of steel tubing. Jennings stated that it didn't matter
whether you used mild steel or chrome moly in a frame because they had
essentially identical ultimate strengths. National Number One repeated
this same thing on the premises of Champion Racing Frames where I was
an impromptu consultant. It took me a long time to convince this guy
that Jennings didn't have a clue, that the yield strength was the important
factor and that that changed significantly from material to material and
for specific heat treatments of that material. Once I got the engineering
information into that guy's head (and he was quite a brilliant engineer
himself) he went on to design and build many good frames himself though
his frame business was never successful.
It is possible for people to have all of the data necessary but lack
just the small bit of information that would give them confidence in
the physics. I think that that is the case here.
> As a side note, I would like to comment on the idea of aluminum with a lower
> yield stress causing deformation in steel, which may have a higher hardness
> and yield stress. Note that the loading of the headtube is dynamic. One of
> experiments I do on a regular basis involves impact of a Modulan 651 (50%
> dense polyurathane foam) sabot with some 17-4 ph steel at somewhere between
> 400 meters/second and 1000 meters/second. The impact of the 6000 psi yield
> modulan causes plastic deformation in the 180,000 psi 17-4 ph. Oh well....
Err, you are comparing shooting a slug at something at some 900-2000 mph,
with all of the inertial loadings, to the loadings of a rider riding
down the street on a bicycle? Take that slug and hit it with a lead hammer
and see how long it takes you to deform the slug.
> Just a few comments from someone who works doing experiments to prove or
> disprove the work of someone who does theory.
Just a few comments from someone that has been in research since 1967.
Starting as a technician and working my way up to senior engineer. So
I've seen my days of engineers and scientists that were full of it too.
tku...@diabloresearch.com
nao...@uhs.umass.edu wrote:
> tku...@diabloresearch.com wrote:
> >
> > In article <19981223092344...@ng27.aol.com>,
> > tecno...@aol.com (Tecnociclo) wrote:
> > > From the Dedaccai catalog:
> > >
> > > Head tubes
> > > 18MCDV6 31.7/1.0
> > >
> > > Material spec is all 24CrMo4, 900 N/mm 13% Elongation.
> >
> > The elongation probably infers the heat treatment of the tube. Is this
> > a heat treated tube or not? More importantly, did Dedaccia even bother
> > to make the differentiation? After all, it isn't very important.
>
> as it is made with 18MCDV6, which has specs of 1250 N/mm2 with 12%
> elongation. The rest of the Ded Zero set is 18MCDV6HT, which bumps
> the claim that I in particular was responding to was that "no quality
> bicycles use heat treated tubing", not "no quality bicycles use heat
> treated head tubes".
I thought from the previous postings that it was clear that I was
talking about the head tube. I think that you'll agree that the
18MCDV6 material at 1250 N/mm2 is close enough to the heat treated
version in strength that it would make no practical difference in
the head tube.
You've given lots of good information and all of it, it seems to
me, validates what I've been saying -- that all (OK, most) of the
head tubes made in the world are nearly identical in size and the
materials vary from cheap, cheap, cheap steel to the highest quality
steels in the world today. If the cheap versions do not deform from
road loads or even from serious accidents, it is not likely that you'll
find the higher quality steels distorting either. No matter what the
heat treatment or lack thereof.
It has been brought to my attention that if the headset was improperly
adjusted it CAN act as a hammer. I think I probably agree with this
but how could the rider ever stand the noise from a headset that loose?
How could he ride long enough to seriously damage the head tube without
the bike ending up in a shop long before the damage was done?
tku...@diabloresearch.com
rpb...@mmm.com (Bob Brown) wrote:
> OK, this discussion is going too far. But as an Engineer, I love it when
> technical discussions go too far, so I'll jump back in here and add a few
> more comments.
>
> Prestige head tubes, and the area of debate was the heat treatment of such
> tubes.
By golly I thought that we were talking about head tube ovalization
and someone brought up Prestige tubing as a side issue. After all,
most Bridgetones were build of Ishiwata tubing and Tange #1 and #2
tubes. I think that the only frames made of Prestige were the MB-0
and these frames were built super light (stupid light as someone
suggested). They were also only built in the smaller sizes.
Since the MB-0 was a TIG welded bike I suggest that that wasn't the
model that suffered from heat weakening of the head tube from copper
brazing of the lugs.
> As I have said, Tom, you're wrong! The heat treatment does matter.
> Why do you keep saying it doesn't, or that tubes that are heat treated
> aren't?
To whom? Head tubes of the same dimensions and from greatly inferior
material do not ovalize from road shocks. Why do you insist that heat
treating would somehow make a difference when the HAZ is still much
stronger than materials used traditionally?
> It' been said all along that it was limited to a few frames that had a
> mistake in the manufacturing processs. The are rare, but did happen.
> Manufacturing process mistakes do happen. That's all this was.
And this information is what makes me extremely suspicious. Would you
consider it the fault of the material if you found out that the rider
had ridden for a year over rought terrain with a very loose headset?
> Tom, how do forces from the front wheel get transmitted to the frame?
> Through the headtube of course, that's the only place it can happen. Any
> reaction force from the fork acting on the frame acts on the headtube in
> some form. Specifically, through the ends of the headtube, where the headset
> bearings are attached.
All of these forces are spread and moderated by the flexure of the materials
in between. Implying that road shocks (which admittedly are high) are
transmitted undiminished to the headset is inaccurate.
> Alright here there is also a good explaination. First, these frames
> you saw probably did not have the manufactuing flaw that the bridgestones in
> question did.
We are getting back to this "manufacturing flaw" that has never been
substantiated. When there are several go-betweens as there are in the
replacement of frames from a good sized company like Bridgestone I suggest
that you need to take any information being passed with a grain of salt.
> (OK, this part is long, and requires a knowledge of statics)
OK, I don't think we need repeat this -- but drawing a free-body
diagram only tells you the direction and relative size of the applied
forces. You do have some real figures to put in the model? If not
why argue this point.
> One more thing, Tom Kunich, what is diablo research other than your domain
> name? Do you work for a research company? If so, I'd think you could do
> more research before you keep making these posts.
You can find us on the web at www.diabloresearch.com. I think that if
you are going to criticize what I'm posting you ought to use facts and
figures that are in line with what I'm saying and not with what you
feel you could criticize were I to say whatever you want to argue.
Joshua_Putnam
>I think that you misunderstand the argument Jon. I don't dispute that
>these others have seen ovalized head tubes. I question their theories
>on how the tube GOT that way. It is my belief that someone putting
>together 100-400 bicycles a year isn't going to pay strict attention
>to the fit of pieces that are already installed. Bridgestones were
>shipped virtually fully assembled and needed only minor work to put
>them on the showroom floor.
But this fails to address Mark Bulgier's experience, reported
earlier in this thread, with headsets installed in the shop on
fresh, reamed, warranty-replacement frames, a case in which the
shop did verify proper dimensions and headset fit when the
headset was first installed.
Michael Challis
>By golly I thought that we were talking about head tube ovalization
>and someone brought up Prestige tubing as a side issue. After all,
>most Bridgetones were build of Ishiwata tubing and Tange #1 and #2
>tubes. I think that the only frames made of Prestige were the MB-0
>and these frames were built super light (stupid light as someone
>suggested). They were also only built in the smaller sizes.
At least the 92 and 93 MB-1 and MB-2 were made with Ritchey Logic
Tange Prestige main tubes (seat and chain stays on the MB-1). I owned
a 93 MB-1, recently stolen. It was a warrenty replacement frame for a
93 MB-2 frame. Yes the MB-2 suffered from head tube ovalization!