Carlton Reid on QR safety

Discussion in 'Mountain Bikes' started by James Annan, Feb 4, 2006.

  1. David Martin

    David Martin Guest

    Ed Pirrero wrote:
    > David Martin wrote:
    > > Ed Pirrero wrote:
    > > > > > And how many incidents of bikes with rim brakes have had the same thing
    > > > > > happen?
    > > > >
    > > > > Zero, AFAIK.
    > > >
    > > > Of course, you haven't even bothered to look. When I was riding my
    > > > cruiser bike, I once came off a curb and had the wheel come out of one
    > > > of the drop outs. Turned the bars and threw me right onto the
    > > > sidewalk. That bike had no front brake at all.


    > > > There's one.


    > > So your cruiser bike with *no front brake at all* has the wheel drop
    > > out under gravity and you think this is an appropriate exampel to show
    > > that a front wheel drops out through the influence of braking with rim
    > > brakes?

    >
    > I didn't claim it had anything to do with braking forces. It had
    > everything to do with gravity and user error.


    You miss the point. When asked for an example of a bike with rim brakes
    showing a front wheel ejection you post an example of a bike without
    rim brakes.

    > > Bizarre. If you can't get simple things right, how could one trust a
    > > single thing you say.

    >
    > LOL. Irony.


    At least I know the difference between a rim brake and no brake.

    > > > I don't pretend - it's happened to me, before disk-brake bikes even
    > > > existed. And I've had other front wheel incidents after transport that
    > > > were quite obviously user error.
    > > >
    > > > All with rim brakes.

    > >
    > > No, one which you state with no brakes at all.

    >
    > Read what you're responding to before you respond.


    In the set of incidents which you have reported, not all of them were
    wheels equipped with rim brakes. Is (not all) != all too difficult to
    comprehend?

    ...d
     


  2. Marz

    Marz Guest

    Jay Beattie wrote:
    > "Marz" <[email protected]> wrote in message
    > news:1140109[email protected]
    > >
    > > Jay Beattie wrote:
    > > > In fact, most of the hard braking on an MTB is on the rear

    > wheel. ...
    > > > . -- Jay Beattie.

    > >
    > >
    > > Dude! Most of you braking should be appled to the front wheel.

    > If
    > > you're jamming on the rear brake, you're not slowing you're

    > slidding.
    > >
    > > Oh and the rest of your post was wrong too.

    >
    > Dude! You are not going to lock up your front wheel on loose dirt
    > because it is really hard, dude, to control a front wheel skid.
    > More back brake than front on loose terrain, dude. That's what
    > I'm getting at. In fact you lock up your rear even on purpose
    > sometimes to carve that big, dirt churning turn, dude. Try that
    > on the front wheel for a little fun sometime, dude. -- Jay
    > Beattie.



    0 for 2, you're not doing so good.

    If you want to stop on loose stuff quickly, use your front brake. Even
    if it's steep loose stuff, still use your front brake.

    If the front wheel starts to skid, modulate your braking.

    Try it on a flat piece of dirt road, get up to speed and try using
    front then back brake to stop. Which one stops you quicker? Don't
    forget to get your arse behind your saddle if you're really hammering
    that front brake.

    If you want a laugh, try taking an off camber loose corner at speed and
    locking both wheels. You'll need to weight the inside edge of your
    tyres while you slighty counter steer to drift around the corner. Only
    works at speed. It's more like skiing than riding.


    Laters dude,

    Marz
     
  3. dvt

    dvt Guest

    Ed Pirrero wrote:
    > David Martin wrote:
    >> Ed Pirrero wrote:
    >>>> - would
    >>>> take at least a week.


    >>> Actually, I thought up a test in my head in about thirty seconds. It
    >>> would actually require someone to do some real work, instead of tapping
    >>> on a keyboard, but I guess that's really the big impediment here,
    >>> right? Sheer laziness.


    >> How long would it take to *perform* the tests though?


    > Less time than it takes to [family newsgroup, buddy] in usenet.


    Sounds like an interesting test. Details?

    --
    Dave
    dvt at psu dot edu
     
  4. Jay Beattie

    Jay Beattie Guest

    "G.T." <[email protected]> wrote in message
    news:[email protected]
    > Jay Beattie wrote:
    > > "Marz" <[email protected]> wrote in message
    > > news:[email protected]
    > >
    > >>Jay Beattie wrote:
    > >>
    > >>>In fact, most of the hard braking on an MTB is on the rear

    > >
    > > wheel. ...
    > >
    > >>>. -- Jay Beattie.
    > >>
    > >>
    > >>Dude! Most of you braking should be appled to the front

    wheel.
    > >
    > > If
    > >
    > >>you're jamming on the rear brake, you're not slowing you're

    > >
    > > slidding.
    > >
    > >>Oh and the rest of your post was wrong too.

    > >
    > >
    > > Dude! You are not going to lock up your front wheel on loose

    dirt
    > > because it is really hard, dude, to control a front wheel

    skid.
    >
    > Dude! Have you ever ridden off-road? It's easy to control a

    front
    > wheel skid in loose dirt.


    Yes, I confess, most of my dirt riding is in mud on a cross-bike
    and only sometimes on my mountain bike. I bow to the dirt gods.
    I also agree that you can drift your front wheel in dirt, but the
    really simple point I was making is that it is more common to
    stop the rear wheel in loose terrain than the front. In my
    sheltered existence, I have not seen people routinely lock up
    front brakes as a steering technique but have seen them lock up
    rear brakes on purpose to slide around a corner -- or for some
    reason that escapes my non-dirt-god understanding. The more
    important point was that from a wheel ejection/disc brake
    standpoint, if your are sliding either wheel, then you are not
    getting the ejection forces theorized in this thread which,
    apparently, assume infinite traction. I was also making the point
    that I hate the word "dude," but that is another matter.-- Jay
    Beattie.
     
  5. Mike Causer

    Mike Causer Guest

    On Thu, 16 Feb 2006 12:36:31 -0800, Jay Beattie wrote:

    > The more important
    > point was that from a wheel ejection/disc brake standpoint, if your are
    > sliding either wheel, then you are not getting the ejection forces
    > theorized in this thread which, apparently, assume infinite traction.


    Yes and no. Infinite traction does not give infinite braking capability.
    Once above a coefficient of friction better than 0.6 - 0.7 any extra
    does no good because the rider will either be over the bars or using
    superior skill to pull a "stoppie". In either case the actual "G" is
    going to be 0.6 - 0.7 So assume infinite traction if you wish, it makes
    no difference to the forces we are discussing.


    Mike
     
  6. Ian Blake writes:

    >>> It is possible to generate more than 0.6g deceleration
    >>> momentarily. Others have written in this NG about the peak forces
    >>> possible on rough terrain. But I don't think many people ride
    >>> that hard.


    >> Racers and those into "xtreme" riding, yes. But those are a tiny


    > Everybody does extreme braking. Everyday I descend a steep hill
    > around a blind bend to a T-Junction with a busier road. The
    > slightest bit of exuberance might result in an urgent need for heavy
    > braking. (Its the reason I have disc brakes on a commuter bike.
    > Wet rim brakes were far too exciting for me).


    It doesn't take a "racer" or any other extreme user to cause a 1g
    retardation. Bumpy trails with embedded river bottom rock cause
    intermittent airborne travel and if descending, applying the brake
    will cause a hard rock skid, brief as that may be.

    Locally, in the Forest of Nisene Marks, I have met plenty of
    descending riders making the usual crunch-crunch bouncing skids as
    they head into turns. This is not unusual and occurs often.

    Jobst Brandt
     
  7. Ian Blake

    Ian Blake Guest

    On Thu, 16 Feb 2006 15:43:38 +0000, Tony Raven <[email protected]> wrote:

    >Tim McNamara wrote:
    >> Those calculations were based on real
    >> world numbers, published measurements of pull-out resistance, and
    >> minor things like the laws of physics.

    >
    >Your calculations are all fine except that you keep considering pull out
    >forces in the absence of lawyers lips. Now most disk brake forks have
    >lawyers lips. With them the pull out forces are probably at least an
    >order of magnitude higher because you need to physically push them out
    >the way or stretch the skewer so it passes over them.
    >
    >> I didn't even have to appeal
    >> to the issue of transverse cyclic forces to show that the problem
    >> exists.

    >
    >Only because you and everyone else keep ignoring the presence and
    >influence of the lawyers lips. If you include them you have to resort


    Lawyers Lips are a fail safe back up system. They are not the prime method of
    holding the axle in place. This thread is about failure of the primary system.

    No one is disputing that Lawyers Lips will prevent total release of the wheel
    even with a partially open QR.

    In my experience of Lawyers Lips on an old bike (my current bikes do not have
    them). There was certainly room between the fail safe stop position and the
    position I closed the QR. There may still be room for my problem with the
    disc brake to occur. (Wheel twists in dropout, The angle partially engages the
    brake, very annoying).
     
  8. Jay Beattie wrote:
    > . The more
    > important point was that from a wheel ejection/disc brake
    > standpoint, if your are sliding either wheel, then you are not
    > getting the ejection forces theorized in this thread which,
    > apparently, assume infinite traction.


    Forces at the front contact patch can be greater than what's usually
    assumed, especially off road.

    Usually, people think in terms of a deceleration limit imposed by
    pitchover. "You can't apply that much force, because you'll go over
    the bars."

    But you can have transient forces that are much larger than the force
    necessary for pitchover. On the road, it's much more unlikely, but on
    rough off-road, you can envision near-tangential impacts of rocks, etc.
    with the tire's perimeter. The force goes away as soon as the tire
    clears the rock, so the rotational inertia of the rider&bike prevents
    instantaneous pitchover. But the force the QR has to deal with (if
    it's a typical disk brake) can be momentarily very large.

    - Frank Krygowski
     
  9. James Annan

    James Annan Guest

    Tony Raven wrote:

    > Tim McNamara wrote:
    >
    >> Those calculations were based on real
    >> world numbers, published measurements of pull-out resistance, and
    >> minor things like the laws of physics.

    >
    >
    > Your calculations are all fine except that you keep considering pull out
    > forces in the absence of lawyers lips. Now most disk brake forks have
    > lawyers lips. With them the pull out forces are probably at least an
    > order of magnitude higher because you need to physically push them out
    > the way or stretch the skewer so it passes over them.



    Actually, it's been explained in some detail how a bolt will likely
    loosen under transverse slipping, and there have been several
    descriptions of riders who have regularly found their QRs loosened in
    exactly this way - ie with the lever still closed, but when installed on
    the LHS, rotated in an anticlockwise direction:


    "Both my G/f and I have had problems with Hopes.

    1) They were done up [email protected] tight.

    2) Every time they've come loose, the lever has been shut, but instead
    of being next to the fork leg, its pointing straight down to the floor,
    implying they've "wound" loose. Spin the lever back through 180° to its
    usual position and its "normal tight" again."


    James
    --
    James Annan
    see web pages for email
    http://www.ne.jp/asahi/julesandjames/home/
    http://julesandjames.blogspot.com/
     
  10. James Annan

    James Annan Guest

    Jay Beattie wrote:
    > "James Annan" <[email protected]> wrote in message
    > news:[email protected]
    >
    >>dvt wrote:
    >>
    >>
    >>>Tim McNamara wrote:
    >>>
    >>>
    >>>>One thing I wondered about was instantaneous loading versus

    >
    > static
    >
    >>>>loading, if those are the correct terms, which I have no

    >
    > idea how to
    >
    >>>>calculate. I would think- but don't know- that a quick jam

    >
    > on the
    >
    >>>>brake at 25 mph would result in a high sharp force compared

    >
    > to my more
    >
    >>>>static force based on a .6 g deceleration. Would the

    >
    > magnitude of the
    >
    >>>>force be raised with higher speeds, or just the time

    >
    > interval over
    >
    >>>>which the load develops? My understanding of physics

    >
    > suggests the
    >
    >>>>latter.
    >>>
    >>>
    >>>It is possible to generate more than 0.6g deceleration

    >
    > momentarily.
    >
    >>>Others have written in this NG about the peak forces possible

    >
    > on rough
    >
    >>>terrain. But I don't think many people ride that hard.
    >>>

    >>
    >>The cannondale "tests" measured a peak 235 ft-pounds of braking

    >
    > torque
    >
    >>on the front wheel, fromw hich you can work out about 950N

    >
    > deceleration
    >
    >>and 3800N ejection force, far in excess of the ballpark

    >
    > estimates I and
    >
    >>others have produced based on a steady 0.6g braking.
    >>
    >>

    >
    > http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/cannondale.html
    >
    > Do these calculations assume infinite traction and occupant
    > restraint? There is a point at which braking force will eject
    > the ride, and the ejection of the wheel will be irrelevant since
    > the rider already is airborne. I also wonder whether you can
    > generate those super high braking forces when your front wheel is
    > skidding down the road or sliding in soft dirt. In fact, most of
    > the hard braking on an MTB is on the rear wheel. Somebody should
    > rig a real bike with strain gauges or accelerometers (or whatever
    > the instrumentation should be) and find out what the real world
    > forces are. I had a broken frame case where we did that. Very
    > enlightening. -- Jay Beattie.



    The bit you apparently missed in my post:

    The cannondale "tests" MEASURED a peak 235 ft-pounds of braking torque

    If you'd bothered clicking on the link, you'd have seen what they did.

    James
    --
    James Annan
    see web pages for email
    http://www.ne.jp/asahi/julesandjames/home/
    http://julesandjames.blogspot.com/
     
  11. Jay Beattie writes:

    >>> In fact, most of the hard braking on an MTB is on the rear wheel.


    >> Dude! Most of you braking should be applied to the front wheel. If
    >> you're jamming on the rear brake, you're not slowing you're
    >> sliding.


    >> Oh and the rest of your post was wrong too.


    > Dude! You are not going to lock up your front wheel on loose dirt
    > because it is really hard, dude, to control a front wheel skid.
    > More back brake than front on loose terrain, dude. That's what I'm
    > getting at. In fact you lock up your rear even on purpose sometimes
    > to carve that big, dirt churning turn, dude. Try that on the front
    > wheel for a little fun sometime, dude.


    That may be your perception but in fact most heavy braking is done
    with the front wheel. If traction is miserable, then no heavy braking
    is done with either wheel. Just the same 1g braking occurs often on
    descending hard and dry trails with embedded river bottom (rounded)
    rocks. On such descents the bicycle is barely on the ground between
    bumps and on bumps maximum braking occurs as the suspension fork
    absorbs the rock. These are the jarring force reversals that cause
    axles to move in the dropout and only on the hub brake side, the other
    end having no ejection forces.

    Jobst Brandt
     
  12. Tim McNamara

    Tim McNamara Guest

    Tony Raven <[email protected]> writes:

    > Tim McNamara wrote:
    >> Those calculations were based on real world numbers, published
    >> measurements of pull-out resistance, and minor things like the laws
    >> of physics.

    >
    > Your calculations are all fine except that you keep considering pull
    > out forces in the absence of lawyers lips. Now most disk brake
    > forks have lawyers lips. With them the pull out forces are probably
    > at least an order of magnitude higher because you need to physically
    > push them out the way or stretch the skewer so it passes over them.


    I considered the lawyer lips in their correct role: they are there in
    case of *failure* of the QR to retain the axle in the dropout and are
    not part of the retention system proper. If they lawyer lips are
    what's holding your axle in the dropouts, that is because of a
    *failure* of the QR to retain the axle. Relying on the lawyer lips to
    hold in the wheel is simply horrendous incompetent design.

    >> I didn't even have to appeal to the issue of transverse cyclic
    >> forces to show that the problem exists.

    >
    > Only because you and everyone else keep ignoring the presence and
    > influence of the lawyers lips. If you include them you have to
    > resort to transverse cyclical forces and QR unscrewing or some other
    > mechanism to allow wheel ejection. That is the critical bit that
    > everyone avoids dealing with and has yet to show clear demonstration
    > of a mechanism preferring instead to rely on the post hoc fallacy
    > that because a wheel was lost it must have been ejected by the
    > brakes. When the mechanism can be demonstrated I will be persuaded
    > but at present it's the elephant in the room everyone is pretending
    > is not there.


    Given how often lawyer lips have come up in this and the previous
    threads on the topic, there is no chance that anyone has forgotten the
    lawyer lips. The intent of laywer lips is not to provide axle
    retention for disk brakes, it is to prevent people who don't know how
    to use QRs from losing their front wheels.

    The elephant is actually the size of a cat, and we all know it's
    there. Those of us advocating change are just prudent enough not to
    rely on the cat to save us.

    Going back to the first principles of the discussion: there is a
    reactive force that results from using disk brakes. That force has a
    specific direction dictated by the location of the brak caliper. With
    many if not most current designs which mount the front brake on the
    trailing side of the fork, the direction of that reactive force is
    towards the opening of the dropouts. This force attempts to push the
    axle out of the dropout, hence it is called an "ejection force." The
    magnitude of the force is large- per Cannondale's numbers up to 854
    pounds. Even using my more conservative numbers, as corrected by dvt,
    the net ejection force can easily be over 400 lbs acting on one
    dropout. That's more than the pull-out resistance measured by Howat
    et al for quite a few skewers.
     
  13. A Muzi a écrit :

    > -Rolled thread on brake bolts?-


    > jim beam wrote:


    > > eh? like this?
    > > http://www.flickr.com/photos/[email protected]/99524699/


    > The Shimano bolt referenced is indeed rolled. That is
    > not at all common to our industry.


    As I wrote yesterday, the first three examples of caliper brakes that
    came to hand appear to have rolled threads on a stepped shaft. I've
    just found a fourth - a modern Shimano BR-A550 57mm dual pivot. The
    bolt is of exactly the same form as the Shimano 600 bolt pictured, with
    one rolled thread on the narrower, swaged portion of the shaft, and a
    second rolled thread on the broader portion.

    > I pulled one of those Shimano bolts and a loupe. It is also
    > the only brake bolt here without a center pip for turning.


    All three of the Shimano brakes that I have on had (1050, 6208, A550)
    have an irregular, concave end, like the end of an ordinary rolled M6
    screw. The Superbe Pro BRS shows signs of milling along the shaft and
    on both ends. The step in the shaft of the Suntour looks cut, while the
    Shimanos look swaged. But all the threads look rolled.

    James Thomson
     
  14. Tony Raven

    Tony Raven Guest

    Tim McNamara wrote:
    >
    > I considered the lawyer lips in their correct role: they are there in
    > case of *failure* of the QR to retain the axle in the dropout and are
    > not part of the retention system proper. If they lawyer lips are
    > what's holding your axle in the dropouts, that is because of a
    > *failure* of the QR to retain the axle. Relying on the lawyer lips to
    > hold in the wheel is simply horrendous incompetent design.
    >



    Its called fail safe design. If the primary retention device fails, the
    secondary takes over preferably in a way that ensures it is clear to the
    user that there has been a primary system failure.

    For an unsafe condition to occur both the primary and secondary systems
    have to have failed. All the calculations you are doing only show how a
    primary failure might occur by the QR slipping. What they have failed
    to address other than by speculation is how the secondary system also
    fails which is a necessary condition for the wheel to be ejected.


    >
    > Given how often lawyer lips have come up in this and the previous
    > threads on the topic, there is no chance that anyone has forgotten the
    > lawyer lips. The intent of laywer lips is not to provide axle
    > retention for disk brakes, it is to prevent people who don't know how
    > to use QRs from losing their front wheels.
    >


    Correct but by default it should prevent a QR from exiting the fork for
    forces many times the highest calculated here for an ejection force.
    Unless you can demonstrate rather than speculate the mechanism by which
    this also fails you have failed to show the two necessary conditions for
    wheel ejection to occur - a slipping QR and a verified mechanism for the
    QR to pass the lawyers lips.


    --
    Tony

    "The best way I know of to win an argument is to start by being in the
    right."
    - Lord Hailsham
     
  15. Luke

    Luke Guest

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

    > Tim McNamara wrote:
    > >
    > > I considered the lawyer lips in their correct role: they are there in
    > > case of *failure* of the QR to retain the axle in the dropout and are
    > > not part of the retention system proper. If they lawyer lips are
    > > what's holding your axle in the dropouts, that is because of a
    > > *failure* of the QR to retain the axle. Relying on the lawyer lips to
    > > hold in the wheel is simply horrendous incompetent design.
    > >

    >
    >
    > Its called fail safe design. If the primary retention device fails, the
    > secondary takes over preferably in a way that ensures it is clear to the
    > user that there has been a primary system failure.


    The primary device, unlike the secondary, does not simply retain, it
    secures. The difference between these two functions is the difference
    between having and losing control of the bike.

    >
    > For an unsafe condition to occur both the primary and secondary systems
    > have to have failed.


    <snip>

    That's an amusing contradiction. The secondary retention device,
    'preferably' takes over in such a manner as to clearly inform that the
    QRs have failed to secure the wheel (what if the Lawyers' Lips cite
    client privilege, keeping mum?), which in of itself constitutes an
    unsafe condition, but is not considered so until the secondary
    retention system fails also.

    Luke
     
  16. Tim McNamara

    Tim McNamara Guest

    Tony Raven <[email protected]> writes:

    > Tim McNamara wrote:
    >> I considered the lawyer lips in their correct role: they are there
    >> in case of *failure* of the QR to retain the axle in the dropout
    >> and are not part of the retention system proper. If they lawyer
    >> lips are what's holding your axle in the dropouts, that is because
    >> of a *failure* of the QR to retain the axle. Relying on the lawyer
    >> lips to hold in the wheel is simply horrendous incompetent design.

    >
    > Its called fail safe design. If the primary retention device fails,
    > the secondary takes over preferably in a way that ensures it is
    > clear to the user that there has been a primary system failure.
    >
    > For an unsafe condition to occur both the primary and secondary
    > systems have to have failed. All the calculations you are doing
    > only show how a primary failure might occur by the QR slipping.
    > What they have failed to address other than by speculation is how
    > the secondary system also fails which is a necessary condition for
    > the wheel to be ejected.


    That's where we disagree, Tony. You seem to think that it is
    acceptable for the QR to fail under the reaction force resulting from
    disk brakes, because the lawyer lips are there to save you. I don't
    think that it is acceptable for the design to be such that it makes it
    possible that the QR will fail. No other brake design does this, just
    disk brakes with the caliper mounted on the trailing side.

    The laywer lips exist to prevent an *abnormal* occurrence- losing the
    front wheel because the rider failed to properly close the QR. And
    even then, the lawyer lips may very well never come into play during
    riding, unless the rider tries to lift the front wheel. With disk
    brakes, the ejection force is a normal occurrence and happens every
    time the rider brakes. The primary retention system- the QR- must be
    able to retain the wheel 100% of the time, no exceptions.

    >> Given how often lawyer lips have come up in this and the previous
    >> threads on the topic, there is no chance that anyone has forgotten
    >> the lawyer lips. The intent of laywer lips is not to provide axle
    >> retention for disk brakes, it is to prevent people who don't know
    >> how to use QRs from losing their front wheels.

    >
    > Correct but by default it should prevent a QR from exiting the fork
    > for forces many times the highest calculated here for an ejection
    > force. Unless you can demonstrate rather than speculate the
    > mechanism by which this also fails you have failed to show the two
    > necessary conditions for wheel ejection to occur - a slipping QR and
    > a verified mechanism for the QR to pass the lawyers lips.


    We are apparently never going to agree on this. By default the lawyer
    lips should not be required to keep the brakes from pushing the front
    wheel out of the dropout. Period. There should be no way whatsoever
    for the brake to create and ejection force on the axle. Period. As a
    result I will never own a bike with disk brakes of this design.
     
  17. Mike Causer

    Mike Causer Guest

    On Fri, 17 Feb 2006 09:19:21 +0000, Tony Raven wrote:

    >> Given how often lawyer lips have come up in this and the previous
    >> threads on the topic, there is no chance that anyone has forgotten the
    >> lawyer lips. The intent of laywer lips is not to provide axle retention
    >> for disk brakes, it is to prevent people who don't know how to use QRs
    >> from losing their front wheels.
    >>

    > Correct but by default it should prevent a QR from exiting the fork for
    > forces many times the highest calculated here for an ejection force.


    Sadly not. British Standard 6102-1:1999 (which is based on ISO
    4210:1996 but has advanced in some respects) requires wheel retention by
    the QR mechanism of 2300N (517lbf) for 30 seconds, but with open QR the
    lips have to withstand a load of just 100N (22.5lbf). [Section 9.4.4]



    Mike
     
  18. Tony Raven wrote:
    >
    > I thought everyone here was was arguing against me that a loose QR was
    > not detectable by the rider until it got to the point the wheel was
    > ejected. Now you are trying to argue that a loose QR will be more than
    > detectable - it will loose you control of the bike. Which is it?


    Be careful what you ascribe to "everyone." There can be differences of
    opinion on such matters, even among people who agree that brakes should
    not be trying to eject the front wheel from the dropouts.

    FWIW, I don't know of anyone interested in bicycling safety issues who
    feels it's fine to ride a bike with a loose QR, whose axle is held in
    place only by the lawyer lips. If you feel such riding is fine, you'll
    have very few members on your team.

    > Having a loose but
    > retained front wheel is not of itself unsafe.


    Again, I think that's a VERY uncommon attitude. Can you find any
    safety literature that agrees with you?

    > I've ridden that way with
    > disk brakes through my mistake a number of times although unlike many
    > here I pretty quickly knew something was wrong by the feel of the
    > steering and the knocking sound from the front wheel as the QR hit the
    > lawyers lips.


    Under what conditions were you riding? It may be one thing to ride on
    ordinary pavement under ordinary speeds with a loose QR (although,
    again, I doubt you'll find anyone else who says so); but I suspect it's
    quite another thing to be barrelling hell-bent-for-leather down a steep
    rocky hillside with a loose QR. I don't do such riding, but I suspect
    the sounds and sensations would be severely muddied by the general
    chaos involved.

    And of course, if you _were_ pounding your way down a super-steep,
    rocky hill and felt something funny in your front wheel, what would you
    do about it? Slam on the front brake even harder so you could stop to
    inspect? Good luck!

    - Frank Krygowski
     
  19. Tim McNamara

    Tim McNamara Guest

    Mike Causer <[email protected]> writes:

    > On Fri, 17 Feb 2006 09:19:21 +0000, Tony Raven wrote:
    >
    >>> Given how often lawyer lips have come up in this and the previous
    >>> threads on the topic, there is no chance that anyone has forgotten
    >>> the lawyer lips. The intent of laywer lips is not to provide axle
    >>> retention for disk brakes, it is to prevent people who don't know
    >>> how to use QRs from losing their front wheels.
    >>>

    >> Correct but by default it should prevent a QR from exiting the fork
    >> for forces many times the highest calculated here for an ejection
    >> force.

    >
    > Sadly not. British Standard 6102-1:1999 (which is based on ISO
    > 4210:1996 but has advanced in some respects) requires wheel
    > retention by the QR mechanism of 2300N (517lbf) for 30 seconds, but
    > with open QR the lips have to withstand a load of just 100N
    > (22.5lbf). [Section 9.4.4]


    Wow. Of course, those are the legal standards and not actual
    measurements. Laywer lips do vary in design from just a couple of
    small bumps at the tips of the dropouts to flanges that are almost
    half the height of the QR nuts.

    But do the math. Since the ejection force is applied to only one
    dropout, the British Standard requirements are effectively that the QR
    has to withstand a pullout force of 108.5 lbf and the lawyer lips only
    11.25 lbf! I can't help but think that decent quality skewers and
    forks would exceed this handily, hopefully anyway since even moderate
    braking with a current design disk brake would create a force that
    would exceed those numbers.
     
  20. GWood

    GWood Guest

    I believe his point was that a reader may indeed be interested, but having
    no added information, would not post uselessly.

    I also find it interesting and would like the option to read or plonk as it
    suits me. The idea of posting to merely say "I find this interesting" is
    kinda lame.

    Oh crap, I just did that.

    "Andy H" <[email protected]> wrote in message
    news:[email protected]
    >
    > Then do just that, you have no potential problems do you? Do you have the
    > statistics to hand?
    >
    > Andy H
    >
    >
     
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