More on disk brakes and wheel ejection

TTT

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

Tim McNamara writes:


Well, this is still preliminary research and whilst it will
undoubtedly put a bit of a rocket up the proverbial of many fork
manufacturers from our point of view as riders of disc equipped
bikes a little perspective is in order. Whilst it is looking like
there seems to be an emerging problem the incidences of actual
accidents that can be attributed to skewers undoing are clearly very
small. Common sense coupled with a routine of skewer checking
whilst out on the trails will most likely be enough to limit the
problem to a very small risk. In short there is nothing here that
suggests mountain bikers with disc brakes should panic and revert
back to V-brakes. As they say in the science world, more research is
needed.

I disagree. A free body diagram shows that forces from a "rear of
fork mounted" brake caliper exerts a downward force on the axle and
that it is greater than a dropout without retention lips will hold
under "normal" closure force. How QR skewers unscrew from vertical
axle motion caused by these brake forces has been explained and
proven by tests, leaving the "you didn't close it right" apologists
out of the running.

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.

I cannot understand what all the hand wringing is about. Just do it!
This is fretting at its worst.

Jobst Brandt

Palo Alto CA

wrote in message
...
Tim McNamara writes:


Well, this is still preliminary research and whilst it will
undoubtedly put a bit of a rocket up the proverbial of many fork
manufacturers from our point of view as riders of disc equipped
bikes a little perspective is in order. Whilst it is looking like
there seems to be an emerging problem the incidences of actual
accidents that can be attributed to skewers undoing are clearly very
small. Common sense coupled with a routine of skewer checking
whilst out on the trails will most likely be enough to limit the
problem to a very small risk. In short there is nothing here that
suggests mountain bikers with disc brakes should panic and revert
back to V-brakes. As they say in the science world, more research is
needed.

I disagree. A free body diagram shows that forces from a "rear of
fork mounted" brake caliper exerts a downward force on the axle and
that it is greater than a dropout without retention lips will hold
under "normal" closure force. How QR skewers unscrew from vertical
axle motion caused by these brake forces has been explained and
proven by tests, leaving the "you didn't close it right" apologists
out of the running.

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.

I cannot understand what all the hand wringing is about. Just do it!
This is fretting at its worst.

Whether or not the calliper is moved on the forks there's a lot of expensive
bikes out there that will not or cannot get retrofitted. How about Salsa or
someone coming out with a front skewer with left handed threads for these
bikes. Would that help?
John Rees

John Rees writes:

Well, this is still preliminary research and whilst it will
undoubtedly put a bit of a rocket up the proverbial of many fork
manufacturers from our point of view as riders of disc equipped
bikes a little perspective is in order. Whilst it is looking like
there seems to be an emerging problem the incidences of actual
accidents that can be attributed to skewers undoing are clearly
very small. Common sense coupled with a routine of skewer
checking whilst out on the trails will most likely be enough to
limit the problem to a very small risk. In short there is nothing
here that suggests mountain bikers with disc brakes should panic
and revert back to V-brakes. As they say in the science world,
more research is needed.

I disagree. A free body diagram shows that forces from a "rear of
fork mounted" brake caliper exerts a downward force on the axle and
that it is greater than a dropout without retention lips will hold
under "normal" closure force. How QR skewers unscrew from vertical
axle motion caused by these brake forces has been explained and
proven by tests, leaving the "you didn't close it right" apologists
out of the running.

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.

I cannot understand what all the hand wringing is about. Just do
it! This is fretting at its worst.

Whether or not the caliper is moved on the forks there's a lot of
expensive bikes out there that will not or cannot get retrofitted.
How about Salsa or someone coming out with a front skewer with left
handed threads for these bikes. Would that help?

I didn't mention anything about prior equipment nor did the above
comments. The question is what to do about the problem for the
future. How the recall and retrofit occurs is a separate matter.
That people are wringing their hands about whether it is a real
problem and whether it even needs repair is the main problem here.
There are many in this forum that are still defending the status quo.

Left handed thread??? Please explain what effect that should have.
We already discussed that inserting the skewer from the other side
doesn't help much and only then when the lever snags something when it
unscrews. However, the reason it unscrews is that it isn't holding
and moves up and down in the dropout between braking and riding over
bumps.

Jobst Brandt

Palo Alto CA

John Rees writes:

Well, this is still preliminary research and whilst it will
undoubtedly put a bit of a rocket up the proverbial of many fork
manufacturers from our point of view as riders of disc equipped
bikes a little perspective is in order. Whilst it is looking like
there seems to be an emerging problem the incidences of actual
accidents that can be attributed to skewers undoing are clearly
very small. Common sense coupled with a routine of skewer
checking whilst out on the trails will most likely be enough to
limit the problem to a very small risk. In short there is nothing
here that suggests mountain bikers with disc brakes should panic
and revert back to V-brakes. As they say in the science world,
more research is needed.

I disagree. A free body diagram shows that forces from a "rear of
fork mounted" brake caliper exerts a downward force on the axle and
that it is greater than a dropout without retention lips will hold
under "normal" closure force. How QR skewers unscrew from vertical
axle motion caused by these brake forces has been explained and
proven by tests, leaving the "you didn't close it right" apologists
out of the running.

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.

I cannot understand what all the hand wringing is about. Just do
it! This is fretting at its worst.

Whether or not the caliper is moved on the forks there's a lot of
expensive bikes out there that will not or cannot get retrofitted.
How about Salsa or someone coming out with a front skewer with left
handed threads for these bikes. Would that help?

I didn't mention anything about prior equipment nor did the above
comments. The question is what to do about the problem for the
future. How the recall and retrofit occurs is a separate matter.
That people are wringing their hands about whether it is a real
problem and whether it even needs repair is the main problem here.
There are many who are still defending the status quo in this forum.

Left handed thread??? Please explain what effect that could have.
We already discussed that inserting the skewer from the other side
doesn't help much and only then when the lever snags something when it
unscrews. However, the reason it unscrews is that it isn't holding
and moves up and down in the dropout between braking and riding over
bumps.

Jobst Brandt

Palo Alto CA

wrote in message ...
Tim McNamara writes:


Well, this is still preliminary research and whilst it will
undoubtedly put a bit of a rocket up the proverbial of many fork
manufacturers from our point of view as riders of disc equipped
bikes a little perspective is in order. Whilst it is looking like
there seems to be an emerging problem the incidences of actual
accidents that can be attributed to skewers undoing are clearly very
small. Common sense coupled with a routine of skewer checking
whilst out on the trails will most likely be enough to limit the
problem to a very small risk. In short there is nothing here that
suggests mountain bikers with disc brakes should panic and revert
back to V-brakes. As they say in the science world, more research is
needed.

I disagree.

Why? AFAIK, there has been *no* experiemental research done on this
system. If there are published articles, could you please post a
link? I am very interested.

A free body diagram

A free-body diagram is useful in showing the *potential* problem, but
it in no way proves anything.


shows that forces from a "rear of
fork mounted" brake caliper exerts a downward force on the axle and
that it is greater than a dropout without retention lips will hold
under "normal" closure force.

"Without retention lips" is a key line. I wonder - how many
disk-brake-capable forks lack retention lips? I do not count
user-removed lips in this.

How QR skewers unscrew from vertical
axle motion caused by these brake forces has been explained and
proven by tests, leaving the "you didn't close it right" apologists
out of the running.

Sorry, but I have not seen the tests that were run on QR skewers in
disk-brake-equipped forks. Could you point out those articles?

The fact is that until very recently, nobody enven thought of such a
thing. Using cyclic movement in other systems does *suggest* the
possiblity, but does not *prove* that it happens in the system that we
are discussing. Hypothesis proof.

The unproven "you didn't close it right" hypothesis is co-equal with
the same, unproven cyclic-motion hypothesis.

We don't need no steenkin further research, as they say.

The fact that no experimental research has been published makes this
statement hilarious. All that exists are the free-body diagram that
may or may not be an accurate description of all the forces involved,
and an extention of a known phenomenon of cyclic loading which may or
may not promote asymmetric "unscrewing forces" on skewers.

All that is
needed is to move the caliper ahead of the fork, nothing more.

Finally, we agree on something, at least in part. Non-QR axle
retention systems (QR20, or some such) might also solve the problem.

Or a stronger skewer.


In my
estimation, this is the only reasonable solution that would
conclusively solve the problem.

Assuming, of course, that the problem actually exists. I have yet to
see anything more than connect-the-dots hypotheses.

I cannot understand what all the hand wringing is about. Just do it!
This is fretting at its worst.

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.

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.

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.

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.

Spider

anonymous snipes rudely from cover:

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

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. Mountain bikers are expected to fall.
Why failures are less common than one might expect has also been
statistically explained here on this forum. If you were interested,
you could look this up in deja news or Google. I will not do your
library search.

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.

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.

As you snipe from the sidelines, manufacturers and merchant are giving
their liability serious thought. Of course as a non combatant you can
offer all sorts of inane solutions to what you consider a non-problem.
I don't understand what motivates you to take this stance that
benefits no one. 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.

Jobst Brandt

Palo Alto CA

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

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
--
Rick Onanian

In article ,
(Spider) wrote:

Why? AFAIK, there has been *no* experiemental research done on this
system. If there are published articles, could you please post a
link? I am very interested.

I did. The very first article in this thread was by me posted July
17th, prompted by seeing publication of experimental research that
confirms there *is* a problem with current disk brake fork design.
The doubting Thomases promptly ignored it.

You can find it at Google. You can also find the reference article at:

http://www.singletrackworld.com/article.php?sid=1063