More on disk brakes and wheel ejection

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

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  1. James Annan

    James Annan Guest

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

    >
    > I don't think it is as bad as you describe. If manufacturers acted now, modified their forks and
    > recalled existing models, a solid defense would be that the current design was general practice
    > for all bicycles and that no one found fault with it until a large user field had established with
    > a large variety of rider demands and operator skills. This would demonstrate a good faith response
    > to a belated discovery that should be without major criticism.

    Maybe, but I haven't heard of any forks being recalled with this problem in the past 4 months, and
    in the meantime riders keep on getting seriously hurt.

    James
     


  2. Rick Onanian

    Rick Onanian Guest

    On Sat, 09 Aug 2003 07:00:40 GMT, <[email protected]> wrote:
    >> Redesigning the QR so that it cannot unscrew is easier, cheaper, and backwards compatible.
    >
    > Could you outline how such a device would work and how it would

    I don't know how it works, but I saw skewers with a button that must be pressed before they will
    screw/unscrew, in a LBS the other day.

    > prevent the axle from moving up and down alternately with braking and normal load, the mechanism
    > by which QR's are unscrewed?

    I suspect that preventing them from being unscrewed, along with screwing them tight in the first
    place, would prevent any issue; at least, that's the impression that I got from this thread. It
    could be a wrong impression.

    > As long as the attachment is a "dropout", having braking forces trying to pull the wheel downward
    > is a threatening condition that makes a reasonably cautious rider worry about how tight is tight
    > enough. The less skilled or forgetful riders could fare worse. With the caliper ahead of the fork,
    > all these concerns are removed.

    I agree that changing the position of the caliper and/or changing the design of the existing open
    dropout system would eliminate the safety need for a skewer that won't unscrew.

    > Jobst Brandt [email protected] Palo Alto CA
    --
    Rick Onanian
     
  3. Rick Onanian

    Rick Onanian Guest

    On Sat, 09 Aug 2003 07:13:13 GMT, <[email protected]> wrote:
    > Rick Onanian writes:
    >> No, you'd just pull the skewer right out of the wheel.
    >
    > When you propose that, I take it you are not capturing the axle in the dropout, as is customary
    > with a QR, but are expecting the QR to hold the wheel alone. In that case, the skewer would need
    > to be about 10mm in diameter as axles are now. What sort of axle for mounting bearings, do you
    > have in mind? I see these various suggestions as incomplete designs and not practical solutions.
    <snip>
    > Since I cannot visualize what you have in mind, I suspect your method has not yet been thought out
    > to practical completion.

    Very much true; somebody else mentioned similar questions, and indeed, I realized that I did not
    think out the idea to practical completion. It may be possible to create a system similar to what I
    proposed, but there are certainly better ways around the issue (like moving the caliper).

    That is why I made it clear that I'm no engineer. <G>

    > Jobst Brandt [email protected] Palo Alto CA
    --
    Rick Onanian
     
  4. Robin Hubert

    Robin Hubert Guest

    I'm going to have some fun at Interbike with this one. Fox, Manitou, RockShox, watch out!

    --
    Robin Hubert <[email protected]
     
  5. In article <[email protected]>, Rick Onanian <[email protected]> wrote:

    > On Sat, 09 Aug 2003 07:00:40 GMT, <[email protected]> wrote:
    > >> Redesigning the QR so that it cannot unscrew is easier, cheaper, and backwards compatible.

    > > As long as the attachment is a "dropout", having braking forces trying to pull the wheel
    > > downward is a threatening condition that makes a reasonably cautious rider worry about how tight
    > > is tight enough. The less skilled or forgetful riders could fare worse. With the caliper ahead
    > > of the fork, all these concerns are removed.
    >
    > I agree that changing the position of the caliper and/or changing the design of the existing open
    > dropout system would eliminate the safety need for a skewer that won't unscrew.

    Marzocchi already makes a quickly-releasable through-axle design called the QR20:

    http://www.marzocchi.com/eng/spa/products/mtb/catalogs/2003/popfeatures/q
    r20.htm

    It does require a hub built for a 20 mm axle, though. It's not really aimed at disc ejection, but
    rather at preventing axles from breaking under the abuse of freeriding and dirt-jumping maniacs.

    --
    Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
     
  6. Jobst Brandt

    Jobst Brandt Guest

    Rick Onanian writes:

    > I agree that changing the position of the caliper and/or changing the design of the existing open
    > dropout system would eliminate the safety need for a skewer that won't unscrew.

    This is a recurring theme that misses the point as I see it. A hand installed wheel, one without a
    wrench tightened conical "lug nut" as on automobile wheels, WILL move, either because it is not
    tight enough to restrain all movement, or because it was inadvertently not tightened sufficiently.
    As long as the disengaging force on the axle remains, the problem remains with any manually
    tightened QR mechanism that I can visualize. In this respect, I find suggestions for a modified QR
    or dropout are wishful thinking.

    As I said, moving the caliper ahead of the fork is an absolutely effective solution while any
    modification of the dropout without it can only appeal to riders who do not believe that the current
    configuration is dangerous or that it is operator error of not tightening the wheel sufficiently.

    Jobst Brandt [email protected] Palo Alto CA
     
  7. Maki

    Maki Guest

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

    > > Redesigning the QR so that it cannot unscrew is easier, cheaper, and backwards compatible.
    >
    > Could you outline how such a device would work and how it would prevent the axle from moving up
    > and down alternately with braking and normal load, the mechanism by which QR's are unscrewed?

    Did I say "prevent the axle from moving up and down"? No, I said "cannot unscrew" and that means
    that the nut and the QR are locked, i.e. they cannot turn. In that case they can go up and down as
    long as you want and unscrewing will not happen. I posted in a past thread one possible locking
    device, if you can't find it with google I'll do it for you. I'm not saying that this is an optimal
    solution, but it would easily give a lot more safety to those who already have a disk equipped MTB
    at a very low cost; I would buy such a skewer for myself even if I'm not currently using disks. Then
    better designs can be made for the future, but if you expect manufacturers to recall all existing
    forks and calipers you are a dreamer.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  8. Maki

    Maki Guest

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

    > > Calipers are fine where they are, the weak link is the wheel/hub interface.
    >
    > No, the problem is that the fork design is flawed. Not the wheel/hub interface, not the QRs, etc.

    Sorry, it was a typo, actually wheel/hub interface doesn't have any sense since the hub is part of
    the wheel. :) Read "fork/hub interface". The fork is obviously involved.

    > The fork puts the caliper in exactly the right place to push the wheel out of the dropout. Annan
    > has demonstrated this quite clearly, yet people like yourself insist on shilly-shallying around
    > looking for some kludge to try to overcome a significant design flaw.

    > Why is this so difficult to comprehend?

    It isn't difficult at all and I don't disagree on James theory. Where did I say that? I proposed a
    closed dropout, did you read it?

    We discussed this before, do you remember? Calipers are there because handling is better in this
    way. Also, calipers ahead of the fork will pull the fork instead of pushing it. Years of motorcycle
    experience shows that most people is unconfortable with that, no matter how hard you try to convince
    them that the fork is solid enough.

    The problem *is* the QR. Is sucks. It was designed for road bikes. Todays MTBs have extremely high
    performance, that means higher stresses. The fact that high-end freeride forks and all DH ones use
    different systems proves that, brakes apart, the standard QRs are weak. If you change the caliper
    position the QR is still weak. If you change the dropout direction the QR is still weak. The QR
    *needs* to be made stronger. I'm sure that not only the braking reaction, but general vibrations,
    bumps, torsions and thermal stresses have a role in loosening QRs. Did I say that the QR is weak
    and sucks?

    What I did want to say (and sorry if I'm not always clear, but English is not my mother tongue
    especially in technical field) is that if we have to redesign forks and calipers, that are an order
    of magnitude more expensive than an hub, then it makes a lot of sense to redesign everything,
    starting from the real weak link, that is the QR. It make no sense to throw away half a bicycle to
    save the silliest and cheapest part of it. Manufacturers have already started to do that on DH and
    FR bikes, XC ones resists because the typical XC usage is lighter and the appeal of a really quick
    relase is strong for users.

    The motorcycle style hub with closed dropout that I suggested and you didn't read isn't a kludge,
    but a perfectly safe (and already working on motorcycles) solution that can be easily done with a
    little modify to the fork and without touching the calipers. Then the same modified wheel can be
    used *also* on existing forks: if they have lawyer lips it will provide a sensible increment in
    safety, especially if threadlocking devices are used. Not the best, but better than nothing. If you
    have any criticism to this solution please tell. But don't say "it's a kludge", tell me *why* it is.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  9. Maki

    Maki Guest

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

    > > James, it's you that linked the QR tests on your website. When the standard asked for 500N some
    > > reached 4000N or so. The current generation is probaly much better.
    >
    > I think that's a misinterpretation. The standard had already been updated to 2300N rather than the
    > earlier 500N, and I do not believe the skewers changed either before or since (I don't even know
    > for which, if any, countries, the ISO standard is a legally-adopted requirement).

    Maybe I'm wrong, but IIRC the tests were made in the early 90s and the standard changed in 1996. I
    don't have any document proving that, but a fellow on an italian NG said that Shimano updated their
    QRs in 1996. He is usually very reliable.

    > > one can redesign the hubs, no need to rework the fork [snip]
    > This 'backwards compatibility' appears to require a new front wheel (hub with larger hole for
    > fatter skewer) - is this correct?

    Of course. Since I premised that "at worst one can redesign the hubs" it is quite obvious that a new
    hub is needed, but it costs 1/10 of a fork. The backwards compatibility is referred to the existing
    forks and calipers. I tried to explain better the rationale behind this approach in response to Tim.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  10. Jobst Brandt

    Jobst Brandt Guest

    Maki Tartamillo writes:

    >> Why is this so difficult to comprehend?

    > It isn't difficult at all and I don't disagree on James theory. Where did I say that? I proposed a
    > closed dropout, did you read it?

    And did you read the explanation why that is still not a solution? As long as this is a QR hub
    without conical "lug nuts" the axle will move in the dropout and compromise the adjustment of the
    clamping force. To get a better feel for these motions consider the pedal attachment in the cranks.
    In spite of being tightened so tight that one can sense the smell of onions (tears in the eyes),
    pedals always move. That is why we have left hand threads on left pedals and why there is always a
    large worn fretting ring on the face of the crank. The only thing that will prevent this, as
    automotive people discovered in the 1930's is to use a conical lug nut, something that is long
    overdo on pedal faces... the next subject that we need to bring to the attention of the bicycle
    industry after disk brake caliper positioning.

    > We discussed this before, do you remember? Calipers are there because handling is better in this
    > way. Also, calipers ahead of the fork will pull the fork instead of pushing it. Years of
    > motorcycle experience shows that most people is uncomfortable with that, no matter how hard you
    > try to convince them that the fork is solid enough.

    Both of the effects you mention are urban legend. If you want to make these points, you'll need to
    explain the mechanical difference between a caliper ahead or behind the fork and how this has any
    effect on handling or braking. It isn't so! We don't need to transplant M/C urban legends into
    bicycling. We already have more than we need.

    > The problem *is* the QR. Is sucks. It was designed for road bikes. Todays MTB's have extremely
    > high performance, that means higher stresses.

    You speak like a real MTB'er who believes that the MTB is a motorcycle and necessarily flies off
    great jumps onto the rocks. Even the best dirt M/C's can be destroyed with such antics. In fact
    road QR's are adequate. What can break is the axle. That you can pull a wheel out with enough force
    is also true but such forces do not come from riding but from a misplaced brake caliper. The
    retention force of the QR needs to be only a small fraction of the upwards forces, in fact only
    enough to keep the wheel from falling out from gravitational loads and lateral torque loads that
    cannot get large because spoked wheels collapse long before axle disengagement forces are high
    enough to dislodge the wheel.

    > The fact that high-end freeride forks and all DH ones use different systems proves that, brakes
    > apart, the standard QR's are weak. If you change the caliper position the QR is still weak. If you
    > change the dropout direction the QR is still weak. The QR *needs* to be made stronger. I'm sure
    > that not only the braking reaction, but general vibrations, bumps, torsion and thermal stresses
    > have a role in loosening QR's. Did I say that the QR is weak and sucks?

    If you use the QR's that you mention, they will still be a hazard with a rear mounted caliper so
    there is no gain in your solution. What I have asked before is why do people make these argument
    unless they are defending their own product or identify with the choice of bicycle they have mad to
    a degree that exceeds logic. "Hey, I bought this bike so it's got to be good!" We see that with car
    buffs all the time. So what's your angle in belittling the only effective solution to the disk
    brake problem?

    > What I did want to say (and sorry if I'm not always clear, but English is not my mother tongue
    > especially in technical field) is that if we have to redesign forks and calipers, that are an
    > order of magnitude more expensive than an hub, then it makes a lot of sense to redesign
    > everything, starting from the real weak link, that is the QR. It make no sense to throw away half
    > a bicycle to save the silliest and cheapest part of it.

    This is also an empty argument because the solution will require a major design change no matter hoe
    ineffective the one chosen is. Therefore, moving the caliper to the front and changing nothing else
    is the easiest and lest expensive solution, besides being the only effective one I have seen.

    > The motorcycle style hub with closed dropout that I suggested and you didn't read isn't a
    > kludge, but a perfectly safe (and already working on motorcycles) solution that can be easily
    > done with a little modify to the fork and without touching the calipers. Then the same modified
    > wheel can be used *also* on existing forks: if they have lawyer lips it will provide a sensible
    > increment in safety, especially if threadlocking devices are used. Not the best, but better than
    > nothing. If you have any criticism to this solution please tell. But don't say "it's a kludge",
    > tell me *why* it is.

    Because it requires a large wrench and great force. The motorcycle coincidentally has a large enough
    axle, due to its greater weight, to permit using such a large nut. The bicycle does not and any such
    massive change is not going to be taken 'lightly' by the market. This nut should be a tapered face
    nut like a wheel lug nut of a car to be truly safe. Thread locking compounds have their place but
    this is not one of them.

    Jobst Brandt [email protected] Palo Alto CA
     
  11. A Muzi

    A Muzi Guest

    > Rick Onanian writes:
    > >> 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.

    <[email protected]> wrote in message news:[email protected]...
    > When you propose that, I take it you are not capturing the axle in the dropout, as is customary
    > with a QR, but are expecting the QR to hold the wheel alone. In that case, the skewer would need
    > to be about 10mm in diameter as axles are now. What sort of axle for mounting bearings, do you
    > have in mind? I see these various suggestions as incomplete designs and not practical solutions.

    > >> 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.

    [RO]> > 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.

    [JB]> If you are not an engineer then you probably should consider axles in
    > holes without clearance a press fit and after some use a loose fit. Since I cannot visualize what
    > you have in mind, I suspect your method has not yet been thought out to practical completion.

    Well, just thinking aloud, I can imagine a system with a hole not a slot at the end of a fork and a
    sleeve that is stepped to fit a large fork hole and capture the 10mm axle end. That way you wouldn't
    have to spring the fork so far apart. That sleeve would be slipped from the outside through the fork
    and over the axle ends, then a skewer through all.. A positive lock ( some variant of a castellated
    nut?) of some type could be used on the skewer itself since the movement would be less, and less
    critical. Obvioosly I haven't even drawn such a thing but the idea is that a closed opening for the
    axle is desirable. I'm thinking along those lines because right now the caliper is forced against
    the fork but reversing it would put the caliper's mounting fasteners in tension which may introduce
    another set of problems.

    We all agree the present setup is not ideal. Simply moving the calipr to the front strikes me as
    inviting trouble as the installation fasteners become critical. I am not arguing that a sleeve
    through a pireced fork end is a solution , just that some such approach might be workable.

    --
    Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
     
  12. Jobst Brandt

    Jobst Brandt Guest

    Andrew Muzi writes:

    > We all agree the present setup is not ideal. Simply moving the caliper to the front strikes me as
    > inviting trouble as the installation fasteners become critical. I am not arguing that a sleeve
    > through a pierced fork end is a solution, just that some such approach might be workable.

    The fasteners (bolts) currently retain caliper forces no differently than if the caliper were in any
    other position. They hold the caliper against its mounting bracket against motion with friction and
    ultimately bolt shear at he limit if the bolts were loose enough to allow slip, regardless of where
    the caliper is positioned.

    Whom are we trying to protect by not moving the caliper to where it should be? All these other
    solutions require at least as much change as repositioning the caliper.

    Jobst Brandt [email protected] Palo Alto CA
     
  13. Maki

    Maki Guest

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

    > Maki Tartamillo writes:

    "Maki Tartamillo" is not my name, nor my nickname, nor my email. Please stop transfiguring names.

    > >> Why is this so difficult to comprehend?
    >
    > > It isn't difficult at all and I don't disagree on James theory. Where did I say that? I proposed
    > > a closed dropout, did you read it?
    >
    > And did you read the explanation why that is still not a solution? As long as this is a QR hub
    > without conical "lug nuts" the axle will move in the dropout and compromise the adjustment of the
    > clamping force.

    I think I've been the first one to point out that changing the dropout angle would not work, so I
    have very clear in my mind that as long as there is clearance the axle *can* move. But you should
    remember that we are talking of extreme cases, most people is using disk brakes as they are without
    problems. In those extreme cases, with a closed dropout the wheel is not going to be ejected so, in
    that sense, is safe. You will notice the wheel is loose and tighteen it. Personally I believe that
    solutions like QR20 or Tullio should be the standard, but since it is too expensive to convert all
    the existing forks I suggested a compromise. Being a compromise it cannot be optimal under all
    points of view.

    > > We discussed this before, do you remember? Calipers are there because handling is better in this
    > > way. Also, calipers ahead of the fork will pull the fork instead of pushing it. Years of
    > > motorcycle experience shows that most people is uncomfortable with that, no matter how hard you
    > > try to convince them that the fork is solid enough.
    >
    > Both of the effects you mention are urban legend. If you want to make these points, you'll need to
    > explain the mechanical difference between a caliper ahead or behind the fork and how this has any
    > effect on handling or braking. It isn't so! We don't need to transplant M/C urban legends into
    > bicycling. We already have more than we need.

    You answered the post of "A Muzi". Most people reason like that. Actually, pushing has better load
    spreading than pulling, but with proper sizing you can work around it. As said it is a psycological
    thing. For the handling part I already explained it too but I'll redo it for you: the closer the
    caliper is to the steering center line the lower is its inertia when you turn the handelebar. How
    much it is noticable is open to debate, but the mechanic principle is there. MX motorcycles started
    with the calipers in front but soon changed. Maybe they all are not a bunch of losers?

    > > The problem *is* the QR. Is sucks. It was designed for road bikes. Todays MTB's have extremely
    > > high performance, that means higher stresses.
    >
    > You speak like a real MTB'er who believes that the MTB is a motorcycle and necessarily flies off
    > great jumps onto the rocks. Even the best

    Oh! And I tought that disk brakes are used by mommies to reach the mall. Go figure... Have you ever
    seen a mountain bike in action? And a motorcycle? It's not that flying off great jumps is the norm
    for everybody, but nor it is braking at 0,6g. How do you explain the fact that every manufacturer
    sells alternative solutions for locking the front wheel? Maybe someone found that the standard QR
    isn't all that stiff?

    > If you use the QR's that you mention, they will still be a hazard with a rear mounted caliper so
    > there is no gain in your solution. What I have asked before is why do people make these argument
    > unless they are defending their own product or identify with the choice of bicycle they have mad
    > to a degree that exceeds logic. "Hey, I bought this bike so it's got to be good!" We see that with
    > car buffs all the time. So what's your angle in belittling the only effective solution to the disk
    > brake problem?

    What's yours? I don't work in the bicycle industry, I've nothing to defend, I don't use disk brakes
    on bicycles and I'm not belittling anyone or anything. I'm sharing my ideas in the spirit of Usenet.
    If I find a fault in your reasoning I tell you, if you find a fault in mine you tell me. At the end
    we are both richer. If you don't believe that I don't know why you are wasting your time on Usenet.

    > This is also an empty argument because the solution will require a major design change no matter
    > hoe ineffective the one chosen is. Therefore, moving the caliper to the front and changing nothing
    > else is the easiest and lest expensive solution, besides being the only effective one I have seen.

    Changing noting else??? The only part that you save is a 5$ QR!!! It's two days that I'm trying to
    communicate with you but either I'm not able to express myself or you are not able/willing to
    understand. I'll repeat once more, then I'll give up. I have two objections to your solution:

    a) it costs too much for the industry to recall every existing fork. It is far cheper to defend
    themselves in the court and show the users are sloppy. If you can convince Mr Rockshox to give me
    a new fork for free I'm happy, but I'm not holding my breath. From James' page: |James, it seems
    that, at least in the US 'operator error' has been the |prominent call from the legal world.
    That's Rockshox speaking. Do you really believe they will do it?

    b) I'm not sure your solution is complete. What's sure is that it will nullify the braking force
    reaction, which is important. However we still have the wimpy QR. So far we have always talked
    about the disengaging force, but that's only the most evident phenomenon. What about torsion?
    When you brake you generate a couple that twists (not sure this is the correct term, but you get
    the idea) the left leg. When it is twisted the two dropouts are no longer aligned and this means
    that either the axle bends or the QR and nut may slip (depending on the amount of torsion). Since
    the axle is not firmly hold by the dropout my guess is that the QR can easily slip. Of course
    this has to be verified in practice, but I'm pretty confident that the effect of cyclic fork
    torsion has similar effects to that of the disengaging force. We'll still end up with an
    unscrewing effect. Since your solution in any case requires to rebuild the fork (and most likely
    the calipers) I can't see a reason not to rebuild the hub/fork too and get rid of all those
    worries. The solutions already exist, and their only, common, fault is that they are all
    proprietary. IMHO manufacturers should meet and came out with a new system that finally works,
    without "but" and "if". That's a bolt-through design.

    > > devices are used. Not the best, but better than nothing. If you have any criticism to this
    > > solution please tell. But don't say "it's a kludge", tell me *why* it is.
    >
    > Because it requires a large wrench and great force. The motorcycle coincidentally has a large
    > enough axle, due to its greater weight, to permit using such a large nut. The bicycle does not and
    > any such massive change is not going to be taken 'lightly' by the market. This

    It will still allow more tension than a conventional QR. Or not?

    > nut should be a tapered face nut like a wheel lug nut of a car to be truly safe. Thread locking
    > compounds have their place but this is not one of them.

    So you aren't reading me... "Thread locking compounds"... whoever talked about that? I'm speaking of
    a QR that enters the dropout slot so that it cannot turn once close. It's easy to do. It's less easy
    on the nut side, but it can be done. And in any case it should be almost unnecessary since according
    to James' theory the force on the nut is really low.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  14. Maki

    Maki Guest

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

    > b) I'm not sure your solution is complete. What's sure is that it will nullify the braking force
    > reaction, which is important. However we still have the wimpy QR. So far we have always talked
    > about the disengaging force, but that's only the most evident phenomenon. What about torsion?
    > When you brake you generate a couple that twists (not sure this is the correct term, but you
    > get the idea) the left leg. When it is twisted the two dropouts are no longer aligned and this
    > means that either the axle bends or the QR and nut may slip (depending on the amount of
    > torsion). Since the axle is not firmly hold by the dropout my guess is that the QR can easily
    > slip. Of course this has to be verified in practice, but I'm pretty confident that the effect
    > of cyclic fork torsion has similar effects to that of the disengaging force. We'll still end up
    > with an unscrewing effect.

    Forgot to add...
    | There are three common causes of the relative motion occurring in the threads:
    |
    |1. Bending of parts which results in forces being induced at the
    |friction surface. If slip occurs, the head and threads will slip which |can lead to loosening.
    |
    |2. Differential thermal effects caused as a result of either
    |differences in temperature or differences in clamped materials.
    |
    |3. Applied forces on the joint can lead to shifting of the joint
    |surfaces leading to bolt loosening.

    This is from James' page, quoting <http://www.boltscience.com/pages/vibloose.htm> I'm specifically
    referring to point 1. Since disk brakes generate an insane amount of heat point 2 is a cause of
    serious concern too.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  15. James Annan

    James Annan Guest

    Maki wrote:

    > |James, it seems that, at least in the US 'operator error' has been the |prominent call from the
    > legal world. That's Rockshox speaking. Do you really believe they will do it?

    Do you really believe that ultimately they will have a choice? Just because they have money, does
    not mean that they can prove black is white, even in a US court. IMO a few unequivocal statements
    from independent testing labs (such as the German one that is investigating the problem) will put
    intolerable pressure on them. At some point they may have to start worrying about the unlimited
    punitive damages rather than merely compensation - this is the fault with the 'cheaper to
    compensate' line of thought.

    The manufacturers might be able to pull the wool over the eyes of the CPSC for some time, but not
    indefinitely. Those guys also have a duty to investigate and have their own reputation to worry
    about if they miss such glaring fault as this.

    Not sure about the USA law, but in the UK, the level of proof required is 'on the balance of
    probabilities' not 'beyond reasonable doubt'. IMO we are already well beyond this lower threshold
    for many of the failures I have heard about.

    James
     
  16. Jobst Brandt

    Jobst Brandt Guest

    Maki Tartamillo writes:

    >>> It isn't difficult at all and I don't disagree on James theory. Where did I say that? I proposed
    >>> a closed dropout, did you read it?

    It isn't a "theory." It is a straight forward measurable fact and is obvious by inspection,
    geometrically knowing that forces have actions and reactions. The way you say that, I
    detect skepticism. You don't disagree with... sounds like the reassuring, "some of them are
    my best friends."

    >> And did you read the explanation why that is still not a solution? As long as this is a QR hub
    >> without conical "lug nuts" the axle will move in the dropout and compromise the adjustment of the
    >> clamping force.

    > I think I've been the first one to point out that changing the dropout angle would not work, so I
    > have very clear in my mind that as long as there is clearance the axle *can* move. But you should
    > remember that we are talking of extreme cases, most people is using disk brakes as they are
    > without problems. In those extreme cases, with a closed dropout the wheel is not going to be
    > ejected so, in that sense, is safe. You will notice the wheel is loose and tighten it.

    We are not talking about "extreme cases" but rather reasonably predictable failures among normal
    distributions of users. Why wheels do not separate more often has been explained. The greatest
    number of riders assemble their bicycles after arriving by car at the trailhead. This assures a
    tight QR at the beginning of each ride. Of those that do not do that, only a small number experience
    any loosening and don't question that the wheel was rattling in the retention ridges and tighten it.
    This is not a reasonable way to offer a product to users.

    > Personally I believe that solutions like QR20 or Tullio should be the standard, but since it is
    > too expensive to convert all the existing forks I suggested a compromise. Being a compromise it
    > cannot be optimal under all points of view.

    In other words, you would not fix the problem but just use "a bigger hammer" as it is often
    referred to.

    >>> We discussed this before, do you remember? Calipers are there because handling is better in this
    >>> way. Also, calipers ahead of the fork will pull the fork instead of pushing it. Years of
    >>> motorcycle experience shows that most people is uncomfortable with that, no matter how hard you
    >>> try to convince them that the fork is solid enough.

    >> Both of the effects you mention are urban legend. If you want to make these points, you'll need
    >> to explain the mechanical difference between a caliper ahead or behind the fork and how this has
    >> any effect on handling or braking. It isn't so! We don't need to transplant M/C urban legends
    >> into bicycling. We already have more than we need.

    > You answered the post of "A Muzi". Most people reason like that. Actually, pushing has better
    > load spreading than pulling, but with proper sizing you can work around it. As said it is a
    > psychological thing. For the handling part I already explained it too but I'll redo it for you:
    > the closer the caliper is to the steering center line the lower is its inertia when you turn the
    > handlebar. How much it is noticeable is open to debate, but the mechanic principle is there. MX
    > motorcycles started with the calipers in front but soon changed. Maybe they all are not a bunch
    > of losers?

    >>> The problem *is* the QR. Is sucks. It was designed for road bikes. Todays MTB's have extremely
    >>> high performance, that means higher stresses.

    >> You speak like a real MTB'er who believes that the MTB is a motorcycle and necessarily flies off
    >> great jumps onto the rocks. Even the best

    > Oh! And I thought that disk brakes are used by mommies to reach the mall. Go figure...

    > Have you ever seen a mountain bike in action? And a motorcycle? It's not that flying off great
    > jumps is the norm for everybody, but nor it is braking at 0,6g.

    > How do you explain the fact that every manufacturer sells alternative solutions for locking the
    > front wheel? Maybe someone found that the standard QR isn't all that stiff?

    Some are patented and others are less expensive or have a lighter closure handle than others. These
    folks work hard to differentiate themselves from competitors. Just read their claims.

    >> If you use the QR's that you mention, they will still be a hazard with a rear mounted caliper so
    >> there is no gain in your solution. What I have asked before is why do people make these argument
    >> unless they are defending their own product or identify with the choice of bicycle they have mad
    >> to a degree that exceeds logic. "Hey, I bought this bike so it's got to be good!" We see that
    >> with car buffs all the time. So what's your angle in belittling the only effective solution to
    >> the disk brake problem?

    > What's yours?

    > I don't work in the bicycle industry, I've nothing to defend, I don't use disk brakes on bicycles
    > and I'm not belittling anyone or anything. I'm sharing my ideas in the spirit of Usenet. If I find
    > a fault in your reasoning I tell you, if you find a fault in mine you tell me. At the end we are
    > both richer. If you don't believe that I don't know why you are wasting your time on Usenet.

    Let me say it more succinctly. Why do you oppose moving the caliper to the front of the fork, placed
    exactly the same as it is now but the fork leg rotated 180 degrees... with any asymmetrical fork
    features remaining where they are?

    >> This is also an empty argument because the solution will require a major design change no matter
    >> hoe ineffective the one chosen is. Therefore, moving the caliper to the front and changing
    >> nothing else is the easiest and lest expensive solution, besides being the only effective one I
    >> have seen.

    > Changing noting else??? The only part that you save is a 5$ QR!!! It's two days that I'm trying to
    > communicate with you but either I'm not able to express myself or you are not able/willing to
    > understand. I'll repeat once more, then I'll give up.

    Your solution requires re-tooling the fork and if a new casting must be made then changing the brake
    bracket is no problem. In any case, old forks cannot be modified to meet the problem for the future.

    > I have two objections to your solution:

    > a) it costs too much for the industry to recall every existing fork. It is far cheaper to defend
    > themselves in the court and show the users are sloppy. If you can convince Mr Rockshox to give
    > me a new fork for free I'm happy, but I'm not holding my breath. From James' page:

    > |James, it seems that, at least in the US 'operator error' has been |the prominent call from the
    > legal world.

    > That's Rockshox speaking. Do you really believe they will do

    > b) I'm not sure your solution is complete. What's sure is that it will nullify the braking force
    > reaction, which is important. However we still have the wimpy QR. So far we have always talked
    > about the disengaging force, but that's only the most evident phenomenon. What about torsion?
    > When you brake you generate a couple that twists (not sure this is the correct term, but you
    > get the idea) the left leg. When it is twisted the two dropouts are no longer aligned and this
    > means that either the axle bends or the QR and nut may slip (depending on the amount of
    > torsion). Since the axle is not firmly hold by the dropout my guess is that the QR can easily
    > slip. Of course this has to be verified in practice, but I'm pretty confident that the effect
    > of cyclic fork torsion has similar effects to that of the disengaging force. We'll still end up
    > with an unscrewing effect.

    As you see, forks are now made as a single unit casting connected with an ever stronger bridge
    because one sided brake attachment causes differential fork leg displacement. They are working on it
    and will continue to do so. I don't think we should expect a disclosure of what is next or how the
    industry believes it is liable.

    > Since your solution in any case requires to rebuild the fork (and most likely the calipers) I
    > can't see a reason not to rebuild the hub/fork too and get rid of all those worries. The solutions
    > already exist, and their only, common, fault is that they are all proprietary. IMHO manufacturers
    > should meet and came out with a new system that finally works, without "but" and "if". That's a
    > bolt-through design.

    I don't understand what you mean by this. Do you now propose that the caliper be moved to the front
    along with your skewer proposal?

    If MTB users are agreeable with no QR for their wheels, that would not be a problem but I doubt that
    riders want to give up the ability to take a wheel out and change a tube or tire without tools on
    the trail.

    >>> devices are used. Not the best, but better than nothing. If you have any criticism to this
    >>> solution please tell. But don't say "it's a kludge", tell me *why* it is.

    I don't have a sufficiently clear picture of your design to analyze its faults but a 20mm diameter
    closed dropout has problems. I don't see how it is held and secured.

    >> Because it requires a large wrench and great force. The motorcycle coincidentally has a large
    >> enough axle, due to its greater weight, to permit using such a large nut. The bicycle does not
    >> and any such massive change is not going to be taken 'lightly' by the market. This

    > It will still allow more tension than a conventional QR. Or not?

    No doubt. A larger screw can exert larger force.

    >> nut should be a tapered face nut like a wheel lug nut of a car to be truly safe. Thread locking
    >> compounds have their place but this is not one of them.

    > So you aren't reading me... "Thread locking compounds"... whoever talked about that? I'm speaking
    > of a QR that enters the dropout slot so that it cannot turn once close. It's easy to do. It's less
    > easy on the nut side, but it can be done. And in any case it should be almost unnecessary since
    > according to James' theory the force on the nut is really low.

    There you go again calling a theory. These are all hard facts.

    Jobst Brandt [email protected] Palo Alto CA
     
  17. Fakhina Sohl

    Fakhina Sohl Guest

    [email protected] wrote in message news:<[email protected]>...
    > It isn't a "theory." It is a straight forward measurable fact and is obvious by inspection,
    > geometrically knowing that forces have actions and reactions.

    Let's not forget that Newtonian physics is only a theory...

    Seriously though, here's my A$0.03. The two sides of this argument are proposing,
    respectively, redesigning the system to be infallible under design loads, and redesigning the
    system to fail safely.

    I am very much in favour of the second approach - especially as a first-response solution.

    Especially on a mountain bike, "design loads" mean nothing. People will, and do, ride to the limits
    of their equipment.

    Even if we only consider manufacturing variability, there _will_ be failures in the field. It's a
    statistical certainty. Whether the QR skewers are as thick as your finger and located in recessed
    conical seats as Jobst proposes...there will be a defective part, and it will fail.

    WHEN that one-in-a-billion part fails, if the caliper is behind a vertical dropout, the axle WILL
    tend to be ejected under brakes. It is an unacceptable failure mode.

    The system needs to be re-designed so that if/when an axle slips, breaks, whatever, the wheel will
    not be ejected by braking forces. That means either re-directing the force (eg. caliper in front of
    fork leg) or providing support for the force as it is currently directed (eg. forward-facing
    dropouts, QR20/Tullio closed retention systems).

    I can only imagine one direction from here. Fork/brake manufacturers can't afford the legal
    implications of admitting that there's a problem. The lawsuits would break them. But the next design
    iteration of all fork models will either have closed retention systems, or no disc brake mounts.

    The reason given will be that the XC race forks are so light and cutting-edge that they can't handle
    disc brake loads without compromising performance; and the
    freeride/all-mountain/whatever-the-buzzword-is-this-week will be all Tullio or QR20 for increased
    stiffness.

    Dropout forks with disc brake mounts will be quietly dropped from the lineup. The axle-eject issue
    will be sidestepped.

    In any case, my next bike will have discs and clamped axles. I've just started using discs on my
    current dropout fork - mindful of the shortcomings in the design. I'd like it to be otherwise, but
    it's not going to happen with my budget.

    fs
     
  18. Dion Dock

    Dion Dock Guest

    In my experience, the QR is much easier to undo at the end of a long ride. (Yes, this is on a
    bike with a front disc brake.) When I first noticed this, I assumed it was because they were
    off-brand skewers.

    I have yet to find the QR completely loose, but it definitely takes less effort to open it than
    to close it.

    -Dion

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

    > We are not talking about "extreme cases" but rather reasonably predictable failures among normal
    > distributions of users. Why wheels do not separate more often has been explained. The greatest
    > number of riders assemble their bicycles after arriving by car at the trailhead. This assures a
    > tight QR at the beginning of each ride. Of those that do not do that, only a small number
    > experience any loosening and don't question that the wheel was rattling in the retention ridges
    > and tighten it. This is not a reasonable way to offer a product to users.
    CA
     
  19. Maki

    Maki Guest

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

    > > |James, it seems that, at least in the US 'operator error' has been the |prominent call from the
    > > legal world. That's Rockshox speaking. Do you really believe they will do it?

    > Do you really believe that ultimately they will have a choice? Just

    I'm not sure they can *afford* it. It is true that a lot of forks are sold as OEM parts so they can
    refuse to recall them unless the bike mounted disks right out of the factory, but there's still a
    hell of a lot of forks to update. And they have to pay for labour too, not only the parts that for
    them may be relatively cheap to produce. Popular pressure (i.e. people refusing to buy disk brakes,
    but I don't see it happen) can lead them to use better solutions in the future, but I'm not
    optimistic about existing stuff. I hope I'm wrong, but I think the scenario painted by Fakhina Sohl
    is the more realistic I've seen.

    > because they have money, does not mean that they can prove black is white, even in a US court. IMO
    > a few unequivocal statements from independent testing labs (such as the German one that is
    > investigating the problem) will put intolerable pressure on them. At some point they may have to
    > start worrying about the unlimited punitive damages rather than merely compensation - this is the
    > fault with the 'cheaper to compensate' line of thought.

    Read Pace arguments to see their defense line. For them it's always someone else's fault, their
    product is ISO compliant.

    --
    Fact of life #15: Heads bleed, walls don't.
     
  20. Maki

    Maki Guest

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

    >Maki Tartamillo writes:

    Why are you still calling me that way? You look really childish.

    >>>> It isn't difficult at all and I don't disagree on James theory. Where did I say that? I
    >>>> proposed a closed dropout, did you read it?

    >It isn't a "theory." It is a straight forward measurable fact and is obvious by inspection,
    >geometrically knowing that forces have actions and reactions. The way you say that, I detect
    >skepticism. You don't disagree with... sounds like the reassuring, "some of them are my best
    >friends."

    Should I apologize once more for my english? "James law" didn't sound as well to me. I'm not
    skeptical, ok? I'm convinced that there is a problem and I will not switch to disk brakes until it
    is solved. Suggest a better term than "theory" and I'll use that.

    >We are not talking about "extreme cases" but rather reasonably predictable failures among normal
    >distributions of users. Why wheels do not separate more often has been explained. The greatest
    >number of riders assemble their bicycles after arriving by car at the trailhead. This assures a
    >tight QR at the beginning of each ride. Of those that do not do that, only a small number
    >experience any loosening and don't question that the wheel was rattling in the retention ridges and
    >tighten it.

    Aneddoctal evidence shows that a *single descent* is enough to loosen the QR. The real reason is
    that people doesn't usually brake that hard. To get QR slipping you need to brake hard enough to
    generate a big force. 0,6g and 90Kg biker generate a force that is about what a properly used ISO QR
    can withstand, but 0.6g means stopping from 50Km/h in 14 meters. Try to do that downhill and off
    road! Most people just slows down with lower decelerations, and braking at 0.3g isn't that demanding
    and even a slightly misused QR works. So in normal use you need either a bad QR or some serious
    degree of misuse to have problems. Of course there are cases in which 0.6g can be reached (maybe
    more in peak performance) so the problem is real and need to be solved, but it is not common,
    basically only hardcore and sloppy users are affected.

    >This is not a reasonable way to offer a product to users.

    Agreed. But it seems pretty common in the bicycle industry. Ask a Rockshox dealer how many times he
    saw bent Sid forks.

    >> How do you explain the fact that every manufacturer sells alternative solutions for locking the
    >> front wheel? Maybe someone found that the standard QR isn't all that stiff?
    >Some are patented and others are less expensive or have a lighter closure handle than others. These
    >folks work hard to differentiate themselves from competitors. Just read their claims.

    Jobst, are you kidding? I'm talking of *users* that switch to other systems because the standard QR
    is not stiff enough to give them the steering precision they like. They have to spend *more* money
    to switch. I'm speaking of forks like the RS Psylo that are available with both systems. I'll save
    you a post: no, it's not just that users believe every marketing blurb without trying the products.

    >Let me say it more succinctly. Why do you oppose moving the caliper to the front of the fork,
    >placed exactly the same as it is now but the fork leg rotated 180 degrees... with any asymmetrical
    >fork features remaining where they are?

    I just don't think it would solve all the problems beyond any doubt. Only a clamped axle would, but
    if we have to use a clamped axle then the caliper position is no more an issue so why bother with it
    in the first place? And in any case because of rake you cannot simply rotate the existing fork legs,
    you have to redesign the mounts and make one of the two quite long. Also there is a high chance that
    existing calipers (at least some of them) will not work as well backwards. Have you checked that
    with brake manufacturers?

    >Your solution requires re-tooling the fork and if a new casting must be made then changing the
    >brake bracket is no problem.

    No, it doesn't. Obviously you haven't read it.

    >> b) I'm not sure your solution is complete. What's sure is that it will nullify the braking force
    >> reaction, which is important. However we still have the wimpy QR. So far we have always talked
    >> about the disengaging force, but that's only the most evident phenomenon. What about torsion?
    >> When you brake you generate a couple that twists (not sure this is the correct term, but you
    >> get the idea) the left leg. When it is twisted the two dropouts are no longer aligned and this
    >> means that either the axle bends or the QR and nut may slip (depending on the amount of
    >> torsion). Since the axle is not firmly hold by the dropout my guess is that the QR can easily
    >> slip. Of course this has to be verified in practice, but I'm pretty confident that the effect
    >> of cyclic fork torsion has similar effects to that of the disengaging force. We'll still end
    >> up with an unscrewing effect.
    >
    >As you see, forks are now made as a single unit casting connected with an ever stronger bridge
    >because one sided brake attachment causes differential fork leg displacement. They are working on
    >it and will continue to do so. I don't think we should expect a disclosure of what is next or how
    >the industry believes it is liable.

    Forks have always had a strong bridge, long before disk brakes. Without it the fork flexes so much
    that you cannot keep a straight line on good surfaces, let alone off road use. The bridge is so far
    from the caliper that it cannot do much to limit fork torsion due to braking and the standard axle
    is of no help. You didn't answer my objections. Have you thought about the effect of that torsion on
    the QR? Have you thought about the effect of heat on the QR?

    >I don't understand what you mean by this. Do you now propose that the caliper be moved to the front
    >along with your skewer proposal?

    No, I'm saying that moving the caliper isn't probably enough. As long as the QR as-we-know-it is
    there, there is still room for failure. You also need to close the dropout in some way.

    >If MTB users are agreeable with no QR for their wheels, that would not be a problem but I doubt
    >that riders want to give up the ability to take a wheel out and change a tube or tire without tools
    >on the trail.

    You start from the assumption that the current system is the only QR that can be made, but that's
    just not the case. Do you know how Tullio and QR20 work? No tools needed, at least on Tullio.

    >I don't have a sufficiently clear picture of your design to analyze its faults but a 20mm diameter
    >closed dropout has problems. I don't see how it is held and secured.

    Ah, so that's the problem. Couldn't you say it before, instead of trashing it?

    I just said that we can get a better clamping by using a bigger skewer, and this requires a
    different kind of hub. That hub is a scaled down version of a motorcycle hub. The skewer, that is
    also the axle, is a scaled up version of the skewer we are already using. Just make it the same
    diameter of the axles we have now. This will have the same faults of a standard QR, but much better
    performance and will work with existing forks. I don't recommend this a general solution, I think
    that the "safety net" we can get with a good quality lockable QR and a standard hub is enough for
    most people; the others (those who really brake hard and regularly find their QR loose) should
    switch to a clamped axle. If they can't or won't, then that solution may be a more affordable
    compromise. Note that hubs compatible with both the standard QR and 20mm clamped axles are already
    in production and it is really easy to adapt them to a 10mm axle/skewer. So that hub can be saved
    when eventually upgrading the fork.

    >>> nut should be a tapered face nut like a wheel lug nut of a car to be truly safe. Thread locking
    >>> compounds have their place but this is
    not
    >>> one of them.
    >> So you aren't reading me... "Thread locking compounds"... whoever
    talked
    >> about that? I'm speaking of a QR that enters the dropout slot so
    that it
    >> cannot turn once close. It's easy to do. It's less easy on the nut
    side,
    >> but it can be done. And in any case it should be almost unnecessary since according to James'
    >> theory the force on the nut is really low.

    >There you go again calling a theory. These are all hard facts.

    There you go again attaching to a single maybe-wrong word and ignoring the real contents.

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