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  #271  
Old February 13th 07, 07:27 AM posted to rec.bicycles.tech
G.T.
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Posts: 1,403
Default x-post: Bike Biz: Wheel ejection theory goes legal

wrote:
On Mon, 12 Feb 2007 18:37:47 -0800, "G.T."
wrote:

wrote in message
news
On Mon, 12 Feb 2007 17:40:08 -0800, "G.T."
wrote:

wrote in message
...
On Mon, 12 Feb 2007 16:41:08 -0800, "G.T."
wrote:

wrote in message
...
On Mon, 12 Feb 2007 15:49:57 -0800, "G.T."
wrote:

"Ed Pirrero" wrote in message
ups.com...
On Feb 12, 3:02 pm, "G.T." wrote:
"Ed Pirrero" wrote in message

oups.com...





On Feb 12, 2:27 pm, "G.T." wrote:
"Ed Pirrero" wrote in message
ups.com...
On Feb 11, 7:54 pm, Gary Young wrote:
This is a variant of the
my-uncle-was-a-smoker-and-he-lived-until-95
argument.
Except for the small details that smoking will most definitely
cause
some harm, and, so far, disk brakes have caused none due to
the
ejection force being present.
None? You're sure about that?
Greg
The answer to both questions is in the part you trimmed.
"(Qualifier: if some harm has occurred, it certainly hasn't been
distinguished from user error.)"

So now you're omniscient?
Strawman.

If you've got any, and I mean ANY, credible data that any of the
incidents involving wheel ejection have been proven as disk-brake
caused, go ahead and cite it.

It's sad that you and jb are such untrusting fools.

"Missy's QR popped. She had definitely tightened it before the ride
as
she
was doing some goofy stuff. The Skareb had the lawyer lips intact.
[The]
XT skewer [was] really tight."

"QR WAS done up - I had checked it at the top and had not stopped,
crashed
or clipped anything that may have undone it."

Greg
Dear Greg,

For the rest of us fools, trusting or otherwise, could you add the
missing citation?

That is, who is saying that someone else's QR "popped"?

And where can we find it--a web page, a magazine, a newspaper?

The first can be found by searching "missy giove wheel ejection" on
Google
and the other is on someone's site who y'all don't trust.

Greg
Dear Greg,

Wouldn't it be common courtesy to just provide the links?
See below.

Your Google suggestion provides 42 places to look:

http://www.google.com/search?as_q=mi...&safe=imag es

See how easy it is?

Why make it hard for people who are interested to look at whatever
you're talking about? It gives the impression that whatever you're
citing can't stand examination, which is scarcely your intent.
Because I don't believe that you, jb, or EP are interested or you would
have
found references to wheel ejections in the past.

Greg
Dear Greg,

I'm asking where I can find what you quoted, which shows interest on
my part.

Ok, my bad. When I searched just a little while ago this recounting was at
the top of the Google results:

http://www.bikebiz.com/Missy-Gioves-QR-pops-open-

Greg


Dear Greg,

Now there's something to look at.

Sorry, but it's not very credible as it stands.

"Missy's QR popped. She had definitely tightened it before the ride as
she was doing some goofy stuff."

Does that mean that the speaker thinks that Missy must have tightened
it because she was doing some goofy stuff and he assumes that she
would have "definitely tightened" it?

Or does it mean that he saw her tighten it before she went riding and
began doing goofy stuff? Who watches another rider slapping a wheel
into the fork? It's possible, but strange.

"The Skareb had the lawyer lips intact. [The] XT skewer [was] really
tight. I'd actually mentioned your story to Rick when we were leaving
the office."

How does he know how tight Missy's skewer was if she was the one who
tightened it?

You may not like such questions, but they're the ones that any lawyer
or expert trying to reconstruct an accident would ask. Whatever Jobst
may think about the principles, here's his timely comment in another
current thread on plaintiffs and accident reconstruction:

"I would like to have seen the bicycle [another bike, not Missy's]
right after the incident. It has been my experience that
reconstruction of what occurred is often easier than first
indications. That has been so, in every case in which I was called to
testify. That is to say, the event did not occur as plaintiff
described."

In these anecdotes mentioned in this thread, people insist that they
had just definitely checked a really tight quick release because
they'd been reading that the QR might pop open unexpectedly--and sure
enough, the QR that had no previous history of popping open obligingly
pops open on the ride.

Isn't it odd that there's no history of Missy's QR popping open while
she did "goofy stuff" in redwood forest rides with two friends, one of
whom just read an article about QR's popping open?

Maybe Missy's QR had been popping open all the time, but she just
never mentioned it to friends? It could be, but it would be odd that
she never mentioned such startling behavior.

Maybe Missy had never previously ridden so goofily? It could be, but
it seems unlikely that a world-class downhill rider suddenly exceeded
all her previous efforts on a casual ride.

Or maybe the other usual (and less flattering) explanations apply? "On
Any Sunday" cruelly shows Malcom Smith, arguably that era's greatest
desert racer, attacking the Widowmaker hill-climb on his Husqvarna
with the cameras rolling and huge audience, only to sputter to an
embarrassing stop because he forgot to turn his fuel tap on.

Of course, there may be a more detailed article somewhere about
Missy's QR that would lay the obvious questions to rest.

And this story and every other story mentioned in this thread could be
perfectly true and accurate.

But the strange pattern of QR's that pop open as soon as someone hears
they might do so raises reasonable doubts.

So does the rest of the article that you quoted, which doesn't even
mention the possibility that the QR might just not have been tightened
as claimed afterward:

"On One's Brant Richards is not convinced the 'Missy incident' is the
Annan theory found in the field."

"'We don't know how Missy's QR popped open. She could have caught it
trailside on something. It might well have been tight, but might not
have been locked over centre.'"

"'It could have been incorrectly installed, with the clamping surface
not sitting properly in the dropout, and have settled loose, then
flopped open.'"

"'The problem now is people are now suspecting an Annan-type QR/disc
problem, not the fact that something else - several other things -
could have happened!'"

"'We have a rear disc mount on our singlespeed jump frames, and the
relationship of the disc and dropout slot means that certain riders
have noticed the wheel being moved backwards by the force of the disc
brake due to the forces involved. This is only when the wheel is
clamped in place by a chaintug - a device to stop the wheel moving
forwards - which spreads the clamping force over a large area. Use of
just a good old track nut usually stops this in its tracks.'"

"'I therefore don't discount the fact that the physics and my
experience show that a wheel can be shifted in the dropout under
braking load. But I do discount that a correctly installed QR of a
correct over-centre-clamp type lock won't come undone unless it's
disturbed on the trail.'"

"And Richards has a cheap solution:"

"'Surely something as simple as zip tieing the QR in a closed position
would stop all this. It's the bicycle equivalent of the axle nut split
pin.'"

http://www.bikebiz.com/Missy-Gioves-QR-pops-open-

For anyone unfamiliar with axle nut split pins, front and rear
motorcycle axles often (if not invariably) come with a hole drilled
sideways through the threads and use a turret nut that allows a large
cotter pin to be inserted and prevent the nut from unscrewing.

The cotter pins rarely survive the first wheel removal, and the empty
holes usually plug up with mud and even tiny rock fragments on trials
machines.

As for the notion that racers (and sincere amateurs) are somehow above
simple mistakes, remember that during major surgery a nurse is
required to count the instruments and sponges because experience (and
x-rays) show that extraordinarily well-trained and dedicated surgeons
keep leaving things inside patients.

And despite this precaution, instruments and sponges still keep
turning up inside patients.


Yep, you're right. Just like jb and EP, you're right, it's always the
user's fault. As a techie at work I should know that by now. It's
always the users fault.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons
Ads
  #272  
Old February 13th 07, 08:49 AM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default x-post: Bike Biz: Wheel ejection theory goes legal

On 2007-02-11, wrote:
[...]
I'd rather not go to the numbers because they are irrelevant. What is
relevant is a coefficient of traction enough to cause an endo on solid
pavement and that this can be as much as 1g considering the rider CG
(belly button) can be on a 45° line from tire contact with the road.

Half of that load is on each dropout pushing up and rearward at 45°.
At the same time a downward force of the entire front wheel load times
the ratio o f wheel diameter to disk diameter (up to 4x) is pulling
one side of the wheel downward. Therefore, roughly 8x times the
upward force on that one dropout.


This is correct, but I misunderstood it.

If we consider the direction of the net force on the front wheel, it's
[1, 0] from braking, [0, 1] from ground reaction, and [sin(theta),
-cos(theta)] * R/r from the disk. Not 2R/r.

We're assuming maximum braking here, and so the net torque on the wheel
is 0. The fact that the disk is only one side makes no difference to
that calculation.

Jobst's description is considering net force on the axle, which is
pushing the rider back along 45 degrees with both dropouts, but is
resisted at only one.

Correcting my calculations again, I get 34 degrees from vertical for Ben
Micklem's wheel (which is 54 degrees from the dropout exit angle), and
17 degrees from vertical for the wheel with the caliper at 3 o'clock.

I think the numbers do matter, particularly the difference in angle
between the direction of the ejection force and the exit direction
provided by the dropout. If the difference is 45 degrees, it seems to
me the wheel would certainly not eject however large the magnitude of
the force. This is because the component pushing it out of the dropout
will be exceeded by the component burying it into the steel/aluminium of
the dropout.

function phi = ejection_angle(theta, R, r)
% theta is angle of caliper in radians, measured anticlockwise with 0 at 3
% o'clock. R is tyre radius, r is disk radius. phi is angle of ejection
% force from vertical in degrees.

% The caliper force. x +'ve is rearward, y -'ve is downward.
c = [sin(theta), -cos(theta)];

% Its magnitude is scaled by difference in radius between disk and tyre,
c *= R / r;

% Add the braking force and the contact force (friction coefficient is 1.0)
% to give the net force f on the wheel under braking.
f = c + [1, 0] + [0, 1];

% Work out that vector's direction from vertical
phi = atan(f(1) / f(2));
phi *= -360 / (2*pi);
endfunction

% Caliper at 2:30.
theta = (0.5 / 12) * 2*pi;
disp(ejection_angle(theta, 675.14, 160));

% Caliper at 3:00
disp(ejection_angle(0, 675.14, 160));
  #273  
Old February 13th 07, 08:58 AM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default x-post: Bike Biz: Wheel ejection theory goes legal

On 2007-02-12, Tim McNamara wrote:
In article ,
Ben C wrote:

[...]
I think front mounted calipers is overkill, and has the drawback of
putting the mountings in tensile fatigue as you've explained.


And yet it is done successfully on other vehicles, so that is a
surmountable problem and a straw man raised by jim.


It was also interesting to read the reaction of Ben Micklem's frame
builder to the suggestion of front-mounting the caliper. They didn't
think it sounded like a good idea.

But moving the dropout angle forwards and the caliper upwards a bit,
as some designs already do-- wouldn't that solve the theoretical
and/or real problems?


It could. Look at motorcycle disk brakes, which often place the caliper
up tight against the fork leg. The caliper ends up nearly at the top of
the disk. The vector of the reaction force from braking would be in a
much more benign direction.


As I said in another thread, if the difference in direction is 45
degrees or better, I don't think you're going to get ejection. Unless my
calculations are still wrong (it's been known...) Ben Micklem has a 54
degree difference with a 2:30 caliper and 20 degree forwards dropout.
Should be perfectly safe.

Placing the caliper in from of the fork would result in the reaction
force driving the axle into the dropout and eliminating the ejection
force altogether.


Of course true, but although not impossible, undesirable.

The 2007 range of "Ben C" mountain bikes will use rear calipers mounted
at 2:30 and slightly forward-opening dropouts. And no tapering on the
forks.
  #274  
Old February 13th 07, 10:06 AM posted to rec.bicycles.tech
Andrew Lee
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Posts: 44
Default x-post: Bike Biz: Wheel ejection theory goes legal

A Muzi wrote:
p.s. - Jobst makes a good point about hub brakes (disc, drum whatever) on
undersized/lightweight fork blades or stays. The occasional tinkerer
discovers this with great surprise.


Imagine what would happen if someone Chalo-sized had to do hard braking on
this bike:

Skinny fork, brake calipers about 90 degrees from the dropout opening
http://www.hampsten.com/Tournesol/po...teur05_pop.htm

No lawyer lips that I can see, but maybe they are really small
http://www.hampsten.com/Tournesol/po...teur04_pop.htm

Hole midway up the fork on the brake side
http://www.hampsten.com/Tournesol/po...teur02_pop.htm




  #275  
Old February 13th 07, 04:00 PM posted to rec.bicycles.tech
Mike Causer
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Posts: 301
Default x-post: Bike Biz: Wheel ejection theory goes legal

On Mon, 12 Feb 2007 23:27:33 -0600, Tim McNamara wrote:

Other pictures on other pages of that site work correctly on my browser,
just not that page. Odd.


Do a "view image", which will get the small picture with a URL like
http://materials.open.ac.uk/mem/imag...s_cc/ccf7r.jpg
then take the "r" out of the name of the jpeg.
http://materials.open.ac.uk/mem/imag...es_cc/ccf7.jpg


Something is borked in their javascript, which is completely unnecessary
for a simple link to a picture.


Mike
  #276  
Old February 13th 07, 04:41 PM posted to rec.bicycles.tech
dvt
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Posts: 435
Default x-post: Bike Biz: Wheel ejection theory goes legal

jim beam wrote:
but the retention force exceeds payload by at least 3 times worst case
scenario.


Worst case?

--
Dave
dvt at psu dot edu
  #277  
Old February 13th 07, 05:40 PM posted to rec.bicycles.tech
Mike Causer
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Posts: 301
Default x-post: Bike Biz: Wheel ejection theory goes legal

On Mon, 12 Feb 2007 16:23:21 -0600, Ben C wrote:

Here is my working in the form of a GNU Octave script if anyone has the
energy to check it.


I haven't gone through it thoroughly (downloading Octave now), but
there are a couple of assumptions that I think are incorrect:


% Its magnitude is scaled by difference in radius between disk and tyre,
% and multiplied again by 2 since the disk is only on one side of the axle.


This factor is only relevant when the weight of bike + rider is
included, which isn't part of this calculation. Instead of doubling the
braking load I think you should halve the gravitational load (when it's
used), and if you will grant some stiffness in the hub and axle that
transfers part of the braking load to the other side, reduce the braking
load by some percentage.


% Add the braking force and the contact force (friction coefficient is 1.0)
% to give the net force f on the wheel under braking.


Once the rear wheel has lifted a greater friction coefficient has no
effect, and I think you'll find that the actual value required for
maximum braking is between 0.6 and 0.65 (Wilson gives 0.56 but I think
he is assuming a crouched rider for his CoG location).

I have a program that allows some experiment with friction and CoG
position, but it's pretty crude and written in Awk, so I might rewrite
it in Octave as a way of learning something about Octave. If you want
to see the Awk version send me an email.



Mike
  #278  
Old February 13th 07, 05:48 PM posted to rec.bicycles.tech
Ed Pirrero
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Posts: 785
Default x-post: Bike Biz: Wheel ejection theory goes legal

On Feb 12, 4:06 pm, Tim McNamara wrote:
In article .com,
"Ed Pirrero" wrote:





On Feb 11, 8:55 pm, "G.T." wrote:
Ed Pirrero wrote:
On Feb 11, 8:37 am, jim beam wrote:
Tim McNamara wrote:


snip underinformed opinion


1. there are no reported accidents that can be definitely
distinguished from user error.


Exactly. Tim like to throw bombs around about these reported
incidents, but never once has anyone proven that it was actually
the forces in question vs. user error.


So because it hasn't been proven yet you guys are 100% certain that
it's been user error?


Strawman.


No, it looks like just a poorly formed question.

"A straw man argument is a logical fallacy based on misrepresentation of
an opponent's position. To "set up a straw man" or "set up a straw-man
argument" is to create a position that is easy to refute, then attribute
that position to the opponent. A straw-man argument can be a successful
rhetorical technique (that is, it may succeed in persuading people) but
it is in fact a misleading fallacy, because the opponent's actual
argument has not been refuted." Given the question mark at the end of
Greg's post, I think it is reasonable to give him the benefit of the
doubt. Were it a sentence, then I would agree that it is a straw man.

However, you do appear to simply disregard any evidence that contradicts
your theory. That may not be an accurate assessment of your thinking
process but it is the impression I get from reading your posts. Your
logic- and jim's- looks like this to me:

A. It has been postulated that disk brake can cause wheel ejection.
B. Uncertainty can be cast upon the evidence that A is true.
C. Therefore A is false.

That may or may not be what you intend. On my screen, that's how it
reads.


A reasonable reply! I am surprised, and pleased.

OK, here's how it goes:

A. Yes, I agree.

B. Sort of - I think that because there is a force, that the
possibility exists that a wheel could be ejected.

C. No, not true at all.

I'm still an agnostic on whether this "problem" is real, or just
theoretical. Because, as Frank writes, so many conditions have to
line up right for ejection to occur, it gets into the realm of doing a
fix on something that's not broken.

As I have said, to you and to others, I am willing to look at real
data, and evaluate it for what it is. I don't dismiss data out of
hand, I dismiss conclusions based on opinion rather than hard data.
While to you the difference may be subtle, for me it makes all the
difference in the world.

Unfortunately, I don't consider the anecdotes "data", because the
initial conditions are unknown. It is *possible* that the initial
conditions are normal, but it is possible that they are not. Not
exactly a dismissal, but not exactly full acceptance as data points.

I consider any attempt to put me in the position of defending some
absolute denial as strawman logical fallacy, for all of these reasons.

I hope this clears things up.

E.P.

  #279  
Old February 13th 07, 05:49 PM posted to rec.bicycles.tech
Ed Pirrero
external usenet poster
 
Posts: 785
Default x-post: Bike Biz: Wheel ejection theory goes legal

On Feb 12, 3:49 pm, "G.T." wrote:
"Ed Pirrero" wrote in message

ups.com...





On Feb 12, 3:02 pm, "G.T." wrote:
"Ed Pirrero" wrote in message


groups.com...


On Feb 12, 2:27 pm, "G.T." wrote:
"Ed Pirrero" wrote in message


roups.com...


On Feb 11, 7:54 pm, Gary Young wrote:


This is a variant of the
my-uncle-was-a-smoker-and-he-lived-until-95
argument.


Except for the small details that smoking will most definitely cause
some harm, and, so far, disk brakes have caused none due to the
ejection force being present.


None? You're sure about that?


Greg


The answer to both questions is in the part you trimmed.


"(Qualifier: if some harm has occurred, it certainly hasn't been
distinguished from user error.)"


So now you're omniscient?


Strawman.


If you've got any, and I mean ANY, credible data that any of the
incidents involving wheel ejection have been proven as disk-brake
caused, go ahead and cite it.


It's sad that you and jb are such untrusting fools.


Logical fallacy - ad hominem.

E.P.

  #280  
Old February 13th 07, 05:59 PM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default x-post: Bike Biz: Wheel ejection theory goes legal

On 2007-02-13, Mike Causer wrote:
On Mon, 12 Feb 2007 16:23:21 -0600, Ben C wrote:

Here is my working in the form of a GNU Octave script if anyone has the
energy to check it.


I haven't gone through it thoroughly (downloading Octave now), but
there are a couple of assumptions that I think are incorrect:


% Its magnitude is scaled by difference in radius between disk and tyre,
% and multiplied again by 2 since the disk is only on one side of the axle.


This factor is only relevant when the weight of bike + rider is
included, which isn't part of this calculation.


Yes, exactly right, and I realized this and pointed it out in an earlier
post. You need to get rid of the factor of two.

Instead of doubling the braking load I think you should halve the
gravitational load (when it's used), and if you will grant some
stiffness in the hub and axle that transfers part of the braking load
to the other side, reduce the braking load by some percentage.


I'm just considering the forces on the wheel: road force (horizontally
backwards), ground reaction force (vertically upwards, same magnitude--
friction coefficient of 1.0), and caliper force. Add those three up and
you get the net force on the wheel. Then you can see if its direction is
within 45 degrees of the way out.

The caliper force is computed so as to give zero net torque on the
wheel.

Now I'm thinking there's another error there. Ground reaction force
should not be included, as it is opposed by the weight of the rider/bike
pushing down on the wheel. This means I'm right back to my original
version of the calcuation (no ground reaction force or factor of two)
and I get 27 degrees from vertical for the caliper at 2:30 (which is 47
deg from the dropout if the dropout is 20 deg forwards), and 13 deg from
vertical for caliper at 3:00 (or 14 deg if the disk/rim ratio is exactly
4 instead of 4.2).

% Add the braking force and the contact force (friction coefficient is 1.0)
% to give the net force f on the wheel under braking.


Once the rear wheel has lifted a greater friction coefficient has no
effect, and I think you'll find that the actual value required for
maximum braking is between 0.6 and 0.65 (Wilson gives 0.56 but I think
he is assuming a crouched rider for his CoG location).


1.0 was meant to be sort of "worst case", although actually the friction
coefficient can get slightly higher than 1.0.

I have a program that allows some experiment with friction and CoG
position, but it's pretty crude and written in Awk, so I might rewrite
it in Octave as a way of learning something about Octave. If you want
to see the Awk version send me an email.


I might do that. Thanks for looking through my version.
 




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