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

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?

What about changing the angle of the wheel slot in the fork ends to make
it perpendicular to the braking reaction force? This would seem a lot
easier to do.

Forgive me if this has already been suggested and dismissed for some
good reason--I haven't been reading all of the posts in this looooong
thread.

Sheldon "Four O'Clock" Brown
+-----------------------------------------------------------+
| Sometimes the only thing more dangerous than a question |
| is an answer. --Ferengi Rule of Acquisition #208 |
+-----------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

John Rees writes:

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.

Well, I didn't see the rest of the discussion. Your post stands as
the first in the thread on my newsreader. The post you responded to
and quoted was undated, makes it tough for me to located the
original thread..

That's a problem between you and your newsreader. It has no effect on
presenting technical arguments, suggesting that others "think about
it" is a bit rude, especially when the writer hasn't done so.
Loosening screws is a common occurrence in machinery for sound
reasons. Tightening a screw takes more torque than loosening so with
random roughness and motion, loosening is the preferred direction of
rotation. By your logic screws should not be lying along roads where
they have unscrewed themselves from their designed position.

Why even have a dropout? Since there isn't a yellow motorcycle chasing XC
riders around in races to make quick wheel changes, why is there a need for
a super quick release on a mountain suspension fork in the first place?

I take it you don't ride bike. I for one prefer to change my flat
tires using a patch kit and not needing a wrench to remove the wheel.
When I start a ride I also like to grab a suitable wheel from by
"armory" and quickly and simply attach it to my bicycle.

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 stick with a design that predates:
- Mountain bikes.
- Suspension forks.
- Disc brakes.
The time seems to have arrived to rethink the entire front wheel
attachment.

That and the concept of four wheels on a car, front engines and doors
that open to the rear and many other things that have shown their
worth pragmatically over millions of vehicles. maybe we should review
the air cooled ace engine and solid axles again.

I'm sure you should think about it!

Jobst Brandt

Palo Alto CA

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

Sheldon Brown writes:

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-designing the calipers, n'es-ce pas?

What about changing the angle of the wheel slot in the fork ends to
make it perpendicular to the braking reaction force? This would
seem a lot easier to do.

I think we went through all that. As long as the braking forces are
down and the wheel loads are up, the axle will move and the QR will
unscrew. Therefore, changing the dropout slot orientation is only a
bandaid and does not attack the underlying problem. The caliper must
be in front so that its reaction forces are in the same direction as
the wheel load forces. Only then will the reliable retention of the
wheel be assured.

Forgive me if this has already been suggested and dismissed for some
good reason--I haven't been reading all of the posts in this
looooong thread.

Well, it hasn't been put this way before but it has been part of the
argument for caliper placement. I'm glad you brought it up again so
that that aspect does not get lost.

Jobst Brandt

Palo Alto CA