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  #11  
Old August 1st 03, 07:35 PM
Rick Onanian
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Default More on disk brakes and wheel ejection




I should put on lead armor before diving into this thread, but....

On Fri, 01 Aug 2003 17:20:24 GMT, wrote:
How about a closed dropout with a new standard for attaching the
front wheel?


I see, you are trying to make friends with the many bicyclists who
enjoy having easily changeable wheels. I don't think you are being any
more realistic about this than your tightening theory. At about this
point your admonition to "think about it" comes to mind.


Why is the current QR system the _only_ one that could be easy?

On my mountain bike, I have to flip the QR lever and then
hand-unscrew the opposite side of the skewer partway. Why not
close the dropout slots into holes, and make a skewer that's
just a little quicker to unscrew all the way off and pull out
of the wheel?

Then, no tools required, and pretty much the same time to
remove and replace the wheel. The only situation where it
could be a problem is in a race.

I imagine the only thing to change from the current system is
the dropout, and minor change to skewers (which could still fit
in existing wheels and be used in existing slotted dropouts).

Disclaimer: I don't know what I'm talking about, and am a damn
fool. There, I said it for you. G

Jobst Brandt

Palo Alto CA

--
Rick Onanian
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  #12  
Old August 1st 03, 08:35 PM
Stergios Papadakis
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Rick Onanian wrote:

Why is the current QR system the _only_ one that could be easy?

On my mountain bike, I have to flip the QR lever and then
hand-unscrew the opposite side of the skewer partway. Why not
close the dropout slots into holes, and make a skewer that's
just a little quicker to unscrew all the way off and pull out
of the wheel?

Then, no tools required, and pretty much the same time to
remove and replace the wheel. The only situation where it
could be a problem is in a race.

I imagine the only thing to change from the current system is
the dropout, and minor change to skewers (which could still fit
in existing wheels and be used in existing slotted dropouts).

Disclaimer: I don't know what I'm talking about, and am a damn
fool. There, I said it for you. G


I'm not sure what you are envisioning.
You would then have to flex the fork legs outward to
fit the axle, and most forks are too stiff to
be flexed easily by that amount.

This doesn't solve the problem anyway. There
will be some play when the axle is fit into
its hole. It would still get pushed up and down
to the extent of that play by braking and bump
forces. The play wouldn't result in wheel ejection,
but it still isn't good design.

Stergios
  #13  
Old August 1st 03, 08:42 PM
Chris Zacho The Wheelman
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(Stergios=A0Papadakis) wrote:
snipped

I'm with Jobst. The simplest calculation
shows that normal braking forces put a
load on the axle that is larger than the
ISO standard which the skewers are
designed to. That should be the end of
the discussion.


The fact that certain skewers, when used
on certain forks, exceed the standard by
enough that failures don't happen daily is
irrelevant. Nobody can know which
combinations are safe and which aren't
unless all permutations are tested. That
would obviously be stupid. Standards are
created in order to make such
foolishness unnecessary.


Fork makers, put the caliper where it
belongs and be done with it. Then, your
marketing division can come up with an
ad explaining how the altered CG of the
fork improves both control when
descending and front-wheel traction
when climbing.


Stergios


The only _other_ solutions would be to add a cap to the end of the
dropouts, look at a motorcycle fork for a heavyweight example of this,
or some sort of "locking skewer" that _couldn't_ unscrew without some
voluntary action by the rider first. Maybe something along the lines of
the freehub lockring?

But I also agree with Jobst. simply putting the brake calipers in front
would be the easiest solution. And you don't need any calculations to
see this, it can be easily demonstrated. Hold your arms out in front of
your body, like a front fork, hold a wheel in your hands and spin it
"forwards".

Now have someone grab the spokes where the present location of a disk
brake caliper would be. You can feel the axle trying to pull itself
downwards, out of your hands! Now, in your imagination, add the inertia
of the bike, rider, etc...

Now try the same thing again, but this time have him grab the wheel in
"front" of your arms.

Repositioning the calipers wouldn't cause any problems with retrofit on
older frames, as the brake mounting has nothing whatsoever to do with
the attachment of the forks to the frame. The brake may end up on the
opposite side of the front wheel than the back, but that would ba a
small price to pay, I would think.

Sure, many front disks haven't evicted their wheels, but many Ford
Pintos didn't explode, either!

May you have the wind at your back.
And a really low gear for the hills!
Chris

Chris'Z Corner
"The Website for the Common Bicyclist":
http://www.geocities.com/czcorner

  #14  
Old August 1st 03, 09:38 PM
Rick Onanian
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Default More on disk brakes and wheel ejection

On Fri, 01 Aug 2003 15:35:38 -0400, Stergios Papadakis
wrote:
I'm not sure what you are envisioning.
You would then have to flex the fork legs outward to
fit the axle, and most forks are too stiff to
be flexed easily by that amount.


No, you'd just pull the skewer right out of the wheel.

This doesn't solve the problem anyway. There
will be some play when the axle is fit into
its hole. It would still get pushed up and down
to the extent of that play by braking and bump
forces. The play wouldn't result in wheel ejection,
but it still isn't good design.


Well, I'm no engineer, but an engineer could probably
come up with something like my idea but better. Or,
just make the dropout holes the same size as the hole
in the hub -- the hub doesn't have any play up and down
on the skewer.

Stergios

--
Rick Onanian
  #15  
Old August 1st 03, 09:58 PM
Dave Lehnen
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Default More on disk brakes and wheel ejection

Sheldon Brown wrote:
Quoth Jobst:

We don't need no steenkin further research, as they say. All that is
needed is to move the caliper ahead of the fork, nothing more. In my
estimation, this is the only reasonable solution that would
conclusively solve the problem.



That would require re-desining the calipers, n'es-ce pas?

snip

If the caliper is moved from the rear of the left fork to the front
of the right fork, the hydraulic line or cable would still exit in
about the correct (upwards) direction.

Dave Lehnen

  #16  
Old August 1st 03, 10:25 PM
Stergios Papadakis
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Default More on disk brakes and wheel ejection

Rick Onanian wrote:


No, you'd just pull the skewer right out of the wheel.


You should go look at your bike.
The front wheel's axle fits into the dropouts.
It is not just the skewer in the dropouts.
Go ahead and pull your skewer out with someone
sitting on the bike. The skewer is a skinny
piece of metal because it is only supposed to
be loaded in tension. The outside of the axle
presses against the top of the dropout slot when
the skewer is removed.



The skewer has enough play that it slides through the
hole in the axle. That is enough.

What you are proposing is dangerous.
You are proposing eliminating the part of the axle that
extends into the dropout. That would not only make
it difficult to line up the axle with the little holes
and get the skewer through, but it would load the
skewer in shear if you ever adjusted it with any load
on the bike.

Stergios
  #17  
Old August 1st 03, 10:43 PM
Rick Onanian
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Default More on disk brakes and wheel ejection

On Fri, 01 Aug 2003 17:25:53 -0400, Stergios Papadakis
wrote:
No, you'd just pull the skewer right out of the wheel.


You should go look at your bike.
The front wheel's axle fits into the dropouts. It is not just the skewer
in the dropouts. Go ahead and pull your skewer out with someone


I knew there was a reason why it wouldn't work...but I
figured I'd suggest it anyway.

As soon as I read this far, I remembered just how it
goes together, and why it wouldn't work.

What you are proposing is dangerous.


Agreed.

I guess a new system would, in fact, have to be made
which wouldn't be compatible with old skewers and hubs,
but I suspect it could be made compatible with old
dropouts...not that anybody would have any reason to use
a new, structural-skewer wheel with old, slotted dropouts.

All of that said, I bet a proper engineer, or even myself
on a more creative day, could come up with a workable
system that's more compatible.

And, even so, it wouldn't be worth it; it has been said
over and over in this thread that moving the caliper a
little bit, or changing the angle/direction of the
dropout, would eliminate the whole issue. Sounds like
a lot easier than redesigning the QR wheel attachment
system.

Stergios

--
Rick Onanian
  #18  
Old August 1st 03, 11:07 PM
Spider
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wrote in message ...
anonymous snipes rudely from cover:


Ahh, Mr. Brandt - already starting, from the first line with ad
hominem commentary.

1.) Ad hominem commentary is usually reserved for those who cannot
discussion issues logically,

2.) or whose argument is weak from first principles. The
distractions of attacking the writer does a fine job of deflecting
criticism from weak points.

Google up "spider" and "pseudonym" in rec.bicycles.tech for my reasons
for remaining anonymous in USENET. You will see that my credibility
with you is far down on my list of concerns.

I also recognize that my requests for information have been ignored -
either they do not exist, or they do not support your position.

The hand-wringing is over the solid fact that very few of these
failures occur. The fact that they DO occur does not imply that
there is a fundemental design flaw in the system. While I do agree
that the system is not optimal, the entire bicycle, from frame to
tires, is a compromise. Strength, weight, convenience, efficiency.
Everything.


Just because you are too lazy to review the tests and incidents that
have been presented doesn't mean there is no evidence and no obvious
design flaw in the current arrangement of disk brakes.


Two logical fallacies in one sentence. 1.) Another ad hominem
comment (it also happens to be a strawman; I'll show that later.) 2.)
A strawman. I did not claim that there was "no evidence." In fact,
I have agreed that there may indeed be a problem.

Just about any
moderately astute mechanical engineer recognizes the magnitude of this
flaw on inspection, without ever making a measurement.


Of course, this implies that the mechanical engineers employed in the
bicycle industry are not even moderately astute. Those employed by
the fork and brake manufacturers do not know what the heck they are
doing, according to Jobst Brandt. An interesting implication, but
we'll just dismiss it as hilariously false, OK?

I notice that in your book, open right here in front of me, are some
really nice tables and graphs. In particular, the graphs on p.125
(Fig. 68.)

Did you arrive at those graphs without making measurements? You imply
in your text on p. 124 that you actually, physically tested them, and
describe the apparatus. Why, might I ask, is this required for such a
simple mechanical system (a spoke), but not required for a more
complicated system like a fork/skewer/disk brake set-up?

There is also the inconvenient fact that the failures are not a
given, and do not happen 100% on all disk-brake/fork systems. This
implies that some PART of the system may be more at fault than
another, and that the design is adequate (if not optimal) but the
execution, in some cases, is inadequate. Dangerously so, in fact.


Talk to the rider in the wheelchair whose wheel separation brought
focus to this problem that was previously pushed aside because there
were no serious injuries YET.


Red herring. Nobody advocates solid seatposts or handlebars, etc,
etc, etc. If there is indeed a systematic problem, then I agree that
it must be solved. But iuntil such time as it's PROVEN, with
controlled, repeatable experiments, I will reserve judgement, as any
careful scientist should.

Mountain bikers are expected to fall.


Yes, and sometimes it happens due to user error (improperly tightened
stem bolts is one thing that jumps up first.) In fact, most falls
could probably be directly attributed to user error.

Why failures are less common than one might expect has also been
statistically explained here on this forum.


No, they actually have not. Neither the raw data nor the methods for
analysis are in evidence anywhere.

If you were interested,
you could look this up in deja news or Google.


Well, after about a half an hour of looking, I seem to be unable to
locate the raw data or the methods used to analyze them.

I will not do your
library search.


Of course not, especially when you're credibility is on the line.
Now, maybe you could supply a search string that makes this phantom
data appear. That might be helpful to everyone. BTW, since you make
the assertion, it is up to you to supply some evidence. Otherwise,
I'll just dismiss it as yet another red herring.

So, I have a solution that is easier than cheaper than your's:


If someone is worried about disk brakes and ejection, they should
convert to a non-disk-brake system. Cheap and easy.


Others can ride their booby trapped bicycles while remembering to not
leave the wheels in the frame over a longer number of rides and not to
make hard braking stops such as upon landing from a jump.


Non sequitur.

My front wheel has not left the frame all season. The register marks
scribed in the fork and the skewer ends match perfectly, not even as
much as 0.25mm rotation on either side. I make hard-braking stops
often, over quite rough terrain.

I'm not going to hold my breath over getting real data on this.
"Because I said so," or "because it's theoretically possible" aren't
good enough answers.


[ad hominem commentary snipped] manufacturers and merchant are giving
their liability serious thought.


Serious thought action. In the end, they could decide that
out-of-court settlements could be cheaper than re-design/recall. I
notice, again, that no real data is forthcoming.

Of course as a non combatant you can
offer all sorts of inane solutions to what you consider a non-problem.


Your name-calling is tedious and beneath you. Maybe you could explain
how name-calling bolsters your position?

I own disk brakes, and use them often, on a mountain bike. 1.) I do
not consider it a "non-problem," but a *potential* problem. Why would
you mischaracterize my postings on the subject? 2.) I am right in
the middle of it, and am laying my health and safety on the line.
Unlike you, Jobst, I am actually physically dependent on the system
working. All you have to lose is a little bit of your ego, and some
luster from your reputation. I could lose my life if I am wrong. But
I do not yet believe that I am in imminent danger.

I don't understand what motivates you to take this stance that
benefits no one.


I am an experiemental scientist, and I am demanding the same standard
of proof that you yourself applied to bicycle wheel spoke strength.
No more, no less. If I have to pay money to get a fork and disk
caliper that are more safe, I will do so. But not until it is proven.

I am also not convinced that all factors have been taking into
account, and that issues that may appear trivial on the surface are
actually important in the proper functioning of the system.

I'm sure you have not testified in a bicycle
liability suit but your smug style and off kilter advice would not be
seen favorably by the court or the jury.


Smug style? The irony is noted, Mr. Brandt. My advice to go to
V-brakes is solid, considering it is the only option open at this
moment. Tell me, Jobst - how is this advice "off-kilter" in any way?

In any case, I have read every piece of information I have seen on
this subject, since it directly effects me (or has that potential.)
Your "lazy" comment is just fluff and bluster. I suspect you would
not be so rude if you were not hiding behind the electronic curtain.

While I do not expect any hard data, or even a thoughtful reply from
you, comporting yourself in an adult fashion henceforth would be
appreciated.

Spider
  #19  
Old August 1st 03, 11:16 PM
Rick Onanian
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On 1 Aug 2003 15:07:55 -0700, Spider wrote:
I own disk brakes, and use them often, on a mountain bike.


Often?

Do you sometimes ride that bike without using them?

Spider

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Rick Onanian
 




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