More on disk brakes and wheel ejection

Discussion in 'Cycling Equipment' started by Tim McNamara, Jul 18, 2003.

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  1. Tim McNamara

    Tim McNamara Guest

    Following the link from http://www.eland.uklinux.net/cgi-bin/articledb_list.pl?DBmode=full&DBfo
    rm=HTML&DBstorynumber=527

    to

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

    From Bikebiz:

    A German product safety lab's testing rig has found axle slippage thanks to disc brake ejection
    forces. Ernst Brust of Velotech.de, a privately-owned, industry-respected testing lab, has tested
    Annan's theory on Velotech's suspension fork testing rig and found clear cause for concern.
    According to Brust, 'The industry can no longer afford to ignore the questions raised by passing
    them off as users' mistakes.' image

    This has possible ramifications for fork makers and bike suppliers who spec the kind of forks that
    appear to allow the theoretical possibility of wheel ejection under extreme loads. Moulds for 2004
    forks are now done and dusted, and many 2004 bikes are being equipped with forks that may be subject
    to recalls.

    Some fork makers now say they are taking Annan's theories very seriously and are making design
    changes but will not be drawn on when their modified forks will be ready for market. The US Consumer
    Product Safety Commission (CPSC), and other international consumer safety bodies, are already
    conducting their own tests, doing literature searches and seeking consumer accounts of wheel
    ejections thanks to potential disc-brake/fork design flaws.

    Bike expert Jobst Brandt from America, author of the classic book The Bicycle Wheel, supports
    Annan's theories:

    'The mechanism has been clearly stated, the forces have been identified in magnitude and direction,
    and credible descriptions of failures have been presented. What's going on here? There is no Easter
    Bunny. Believe it!'

    Velotech, also known as Dienstleistungszentrum für Produktsicherheit, the Institute for Product
    Safety, is a Schweinfurt-based testing lab with bike-specific testing rigs that replicate real world
    riding conditions. The company was founded in 1991 by Ernst Brust, a former employee of FAG bearings
    and then technical director of Winora, the German cycle manufacturer.

    Brust believes design mistakes have been made:

    'Development in the field of components has taken place in leaps and bounds. At the same time
    established dimensions in components have been retained in order to facilitate the introduction of
    new sub-assemblies to the market. The use of these new developments without due consideration has
    frequently led to new safety problems in other areas.

    'Drop-outs on forks have been optimised for the use with rim brakes. Without the necessary critical
    re-examination, new disc brakes have been introduced ­ and this has led to problems.'

    In fact, Brust has been aware of disc-brake/fork axle-slippage since 2001, long before Annan raised
    the issue on his website.

    'Tests which we have carried out since the end of 2001 have shown that front wheels can be pulled
    out of forks under certain circumstances. This has been known to happen to rear wheels as well, but
    accidents involving rear wheels seldom have serious consequences. Accidents involving front wheels
    inevitably lead to falls.

    'The manufacturers concerned have hitherto denied that risks were involved, while at the same time
    improving the design of their forks.'

    Brust doesn't believe the industry has yet made enough design changes to eliminate the axle slippage
    problem. His attempts to interest fork manufacturers in the potential for slippage due to some
    current fork designs have not been wholly successful.

    And now Brust is working on new, more exhaustive tests:

    'The very first hard braking loads led to movement in the axle. Fatigue testing on a roller drum
    test rig will demonstrate whether or not the drop-outs are adequately designed for the loads to be
    expected in long-term use. Road jolting and brake loading are tested in combination. Since testing
    is not yet completed we cannot as yet comment on any results.'

    Velotech's testing rigs simulate the impact from the road surface through strips of varying height
    on a roller drum, at varying speeds, and can simulate out-of-saddle riding, rapid descents, jumps
    and braking loads.

    Much of Ernst Brust's work has been illuminated by co-operation with Dr Eric Gross of the technical
    university of Hamburg-Harburg. Gross is an expert on the determination of operational loads on
    mountain bikes (see, VDI Verlag GmbH, Düsseldorf, Reihe 12, Nr 308). And Brust helped to devise the
    DIN cycle standard (DIN 79100) in 1997 and later introduced the certification programme ³DIN plus
    for bicycles and components² for DIN CERTCO Ltd.

    Brust's business partner is Klaus Massek, former technical director of the German bicycle federation
    and former chairman of the German bicycle standards committee.

    http://www.velotech.de/html/english.html

    At the same time as lab based testing was taking place, Ben Cooper of Kinetics, a Glasgow-based
    retailer of recumbents, electric bikes and other specialist machines and Physics Degree holder, has
    been conducting more real world testing of Annan¹s theory.

    'My usual commuting bike is equipped with disc brakes. It has titanium quick release skewers, and
    forks with no 'lawyer tabs'. In over a year of use, I have never had to adjust the quick release. It
    was tightened as hard as I could get it by hand.

    'I retightened the skewer using the '90 degree rule'. This rule is often quoted for quick releases -
    you tighten the nut so the lever starts to get tight when the lever is at 90 degrees to the wheel.
    So this was looser than I previously had it, but still hand tight. The lever was on the right side
    (opposite to where I normally have it, but consistent with advice from SRAM and others).

    'I then rode the bike on my usual commuting journey - 6 miles per day, on and off road, including
    cattle grids and speed bumps taken at speed. Every day I loosened then tightened the lever, and
    recorded the angle at which the lever began to bite.

    'I repeated the experiment on a V-brake-equipped bike - the same skewer was used over the
    same route.'

    On the V-brake equipped bike the QR's bite point was found to be still at 90 degrees after a week of
    riding. However, on the disc-brake equipped bike, Cooper halted the experiment after three days when
    he discovered the bite point had shifted to 80 degrees.

    His conclusion?

    'There seems to be an effect from the disc brake which causes the quick release to loosen. Since
    this disc bike was used with the same skewer for over a year with no adjustment, it is apparent that
    this effect only occurs if the skewer is not tight enough. There is a certain critical limit. Below
    this limit, the skewer can loosen. Above this limit, it won¹t. The limit is dependent on skewer
    design and rider weight.'

    But Cooper isn't convinced there's a massive safety issue at stake:

    '[Annan's] initial analysis is correct, the force diagrams and calculations he details are accurate,
    and as someone with a degree in physics, I have no problem with that part of his theory. I am less
    sure about the consequences of the basic maths.

    'In Annan's analysis, the two forks legs are assumed to be independent - the force from the disc
    brake is assumed to only act on the left dropout. I do not believe that this is correct in practice.
    Imagine what happens if the axle starts to come out on one side only. First, the disc rotor will
    have to be deflected - this requires quite a bit of force. Then the skewer will also need to be
    stretched by an amount proportional to the displacement of the axle. Thirdly, the axle cannot move
    far before the rim of the wheel contacts the inside of the fork leg - in most case I tested, it is
    not possible to remove the axle on the left side only.

    'So, basically, the force generated must be enough to overcome the strength of the serrations on
    both sides of the fork, not just the left side.

    'I have talked to a number of technical people at various manufacturers, and they have never seen
    this problem with their products. Yes, they could be covering up - but these were off-the-record
    discussions with non-lawyers so I do not think so.

    'I believe that there is a possibility of a problem with some combinations of components. Unlike
    James Annan, I do not believe that there is a fatal design flaw with all combinations of disc brake,
    fork and quick release.'

    The full scope of Ben¹s research can be seen here..

    http://www.kinetics-online.co.uk/html/disc_brakes___qrs.html

    So what do we do now?

    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.
     
    Tags:


  2. 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
     
  3. Jobst Brandt

    Jobst Brandt Guest

    Tim McNamara <[email protected]> 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 [email protected] Palo Alto CA
     
  4. John Rees

    John Rees Guest

    <[email protected]> wrote in message news:[email protected]...
    > Tim McNamara <[email protected]> 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
     
  5. Jobst Brandt

    Jobst Brandt Guest

    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 [email protected] Palo Alto CA
     
  6. > <[email protected]> wrote in message news:[email protected]...
    > >
    > >
    > > 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.
    >

    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
     
  7. John Rees

    John Rees Guest

    <[email protected]> wrote in message news:[email protected]...
    > 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.

    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..

    > 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.

    Think about it. Why does the motion only LOOSEN the QR thread? If it was random, and just up and
    down movement, why doesn't it sometimes also TIGHTEN the QR? Putting the skewer in from the other
    side does not reverse the threads. I agree the skewers are not up to the stress imposed by a disk on
    the suspension fork. I'm also not convinced that moving the calliper to the fork front is going to
    completely solve the problem. Why not also make the front dropout horizontal, rear entry?

    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?

    How about a closed dropout with a new standard for attaching the front wheel? 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 .

    John Rees
     
  8. Spider

    Spider Guest

    [email protected] wrote in message news:<[email protected]>...
    > Tim McNamara <[email protected]> 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
     
  9. Jobst Brandt

    Jobst Brandt Guest

    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 [email protected] Palo Alto CA
     
  10. Jobst Brandt

    Jobst Brandt Guest

    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 [email protected] Palo Alto CA
     
  11. Jobst Brandt

    Jobst Brandt Guest

    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 on cars that open to the rear
    and many other things that have shown their worth pragmatically over millions of vehicles. Maybe we
    should revive the air cooled car engine, solid axles and king pin steering again.

    I'm sure you should think about it!

    Jobst Brandt [email protected] Palo Alto CA
     
  12. Rick Onanian

    Rick Onanian Guest

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

    On Fri, 01 Aug 2003 17:20:24 GMT, <[email protected]> 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 [email protected] Palo Alto CA
    --
    Rick Onanian
     
  13. 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
     
  14. John Rees

    John Rees Guest

    <[email protected]> wrote in message news:[email protected]...
    > John Rees writes:
    >
    > >>>> I disagree. A free body diagram shows that forces from a "rear
    > > 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.

    Sigh. I see that your tone is different for different people. I guess it's also my newsreaders fault
    that I see duplicate posts from you only and no other person? I did not realise this had been a long
    running thread, and it's not my fault that I didn't see the first 1k posts about it. Neither you nor
    I 'own' the thread. You're more willing to agree with Sheldon Brown, who has more personality in his
    thumbnail than you appear to have in your entire body, than you are with
    me. Even though his suggestions are similar to (and quite likely much better than) mine.

    > 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.

    You have made an incorrect assumption my smug tongued expert. I ride plenty enough and own plenty of
    bikes. And if you're ever in NC, why don't you join us for a ride and we will be happy to drop you
    on our beautiful rolling hills. I never said anything about a wrench. My point is if there is
    concern that the current popular design causes wheels to be shed, then the current design needs to
    be re-thought. And, if you are not open minded enough to considers another's ideas, then it only
    reinforces the smug label you have earned with
    mf.

    > > 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.

    Yes. Please consider why it would be a big deal for it to take an extra 30 seconds to remove a front
    wheel from a disc braked bike. The only issue I can think of where having a different mounting
    system for disc wheels is that maybe it would be a hassle to swap wheels between disc and non disc
    bikes. But we have long ago departed true compatibility in this area since many disc only wheels no
    longer even HAVE braking surfaces so you already can't swap.

    > > 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.

    This point would make sense if we all still rode rigid forked, lightweight mountain bikes with canti
    brakes. But we don't, do we? The modern mountain bike has undoubtedly evolved significantly in the
    last 20 years. An evolution that far outstrips anything that's happened to road bikes, and for that
    matter automobiles. When cars evolved from their horse carriage origins, and become heavier, faster
    and more powerful, wasn't there a switch from wooden wheels to pneumatic tires? Weren't the wooden
    wheels well proven and pragmatic for maybe centuries? So why on earth don't we still have wooden
    wheels on cars (or bikes for that matter)? You're the wheel expert, so please share with us.

    > I'm sure you should think about it! Jobst Brandt

    Every day. John Rees
     
  15. Maki

    Maki Guest

    In article <[email protected]>, [email protected] wrote:

    > 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.

    Redesigning the QR so that it cannot unscrew is easier, cheaper, and backwards compatible.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  16. Dave Lehnen

    Dave Lehnen Guest

    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
     
  17. Rick Onanian

    Rick Onanian Guest

    On Fri, 01 Aug 2003 15:35:38 -0400, Stergios Papadakis <[email protected]> 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
     
  18. 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
     
  19. Rick Onanian

    Rick Onanian Guest

    On Fri, 01 Aug 2003 17:25:53 -0400, Stergios Papadakis <[email protected]> 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
     
  20. Spider

    Spider Guest

    [email protected] wrote in message news:<[email protected]>...
    > 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
     
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