Disc brakes and QRs making headlines

Discussion in 'Cycling Equipment' started by Tim McNamara, May 13, 2003.

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  1. Tim McNamara

    Tim McNamara Guest

    James Annan's Web site about disc brakes and disengaging front wheels appears to have had an impact
    (no pun intended) and was mentioned today on Peter Eland's VeloVision Magazine Web site:

    http://www.velovision.co.uk/

    Eland mentions that the concern has been taken up on the BikeBiz industry Web site. I looked and
    there's nothing I could find in the consumer pages, but there seems to be possibly something in the
    industry pages.

    James's Web site is at:

    http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index. html
     
    Tags:


  2. Doug Huffman

    Doug Huffman Guest

    Just as the 'media' drives hysterical concerns in the US for its profit, the bike media drives
    hysteric concerns. Words no longer mean much unless they are piled high and deep. The conspiracy of
    ignorance masquerades as common sense.

    People have forgotten the significance of words like 'may' and 'possibly' and 'anecdote'. My disk
    brakes have been reliable for >20K miles.

    "Tim McNamara" <[email protected]> wrote in message
    news:[email protected]...
    > James Annan's Web site about disc brakes and disengaging front wheels appears to have had an
    > impact (no pun intended) and was mentioned today on Peter Eland's VeloVision Magazine Web site:
    >
    > http://www.velovision.co.uk/
    >
    > Eland mentions that the concern has been taken up on the BikeBiz industry Web site. I looked and
    > there's nothing I could find in the consumer pages, but there seems to be possibly something in
    > the industry pages.
    >
    > James's Web site is at:
    >
    > http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index. html
     
  3. James Annan

    James Annan Guest

    Tim McNamara wrote:

    > Eland mentions that the concern has been taken up on the BikeBiz industry Web site. I looked and
    > there's nothing I could find in the consumer pages, but there seems to be possibly something in
    > the industry pages.

    Yes, it's on the password-protected bit:

    http://www.bikebiz.co.uk/web/article.php?id=2899

    Is this the end of QRs for MTBs? A Scottish climate research scientist based in Japan has stirred up
    a hornet's nest of a safety topic. James Annan claims quick release skewers are no longer 'fit for
    purpose' on disc-brake equipped bikes. They can and do come undone, says Annan. Riders have so far
    put this down to their own sloppiness but a recent crash, which left an English rider disabled, has
    brought the issue into sharp focus. Manufacturers have been dismissive of Annan's emails to date but
    a growing number of engineering-trained bike experts are lining up behind Annan's theories.
    Cigarette companies, aware of tobacco-related illnesses since the 1950s onwards, were successfully
    sued in group actions because of the wilful disregard of evidence that tobacco harms. If the QR
    problem is ignored, could the bike trade be crippled by similar lawsuits?

    (etc, with more in the same vein - nothing factually different from what has been said on my website
    and rec.bicycles.tech)

    > James's Web site is at:
    >
    > http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index. html

    James
     
  4. David Kunz

    David Kunz Guest

    > "Tim McNamara" <[email protected]> wrote in message
    > news:timmcn-ED6E81.203715130520[email protected]...
    >
    >>James Annan's Web site about disc brakes and disengaging front wheels appears to have had an
    >>impact (no pun intended) and was mentioned today on Peter Eland's VeloVision Magazine Web site:
    >>
    >>http://www.velovision.co.uk/
    >>
    >>Eland mentions that the concern has been taken up on the BikeBiz industry Web site. I looked and
    >>there's nothing I could find in the consumer pages, but there seems to be possibly something in
    >>the industry pages.
    >>
    >>James's Web site is at:
    >>
    >>http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index. html

    Doug Huffman wrote:
    > Just as the 'media' drives hysterical concerns in the US for its profit, the bike media drives
    > hysteric concerns. Words no longer mean much unless they are piled high and deep. The conspiracy
    > of ignorance masquerades as common sense.
    >
    > People have forgotten the significance of words like 'may' and 'possibly' and 'anecdote'. My disk
    > brakes have been reliable for >20K miles.
    >

    Unfortunately, "may" and "possibly" means to lawyers that the companies know about the "problem" and
    therefore are liable for any consequences to the limit that a jury may make it reach into it's
    pockets (plus expenses). I'm really tired of the US legal system and the people who exploit if for
    their own selfish ends.

    David
     
  5. W K

    W K Guest

    "Doug Huffman" <[email protected]> wrote in message news:[email protected]...
    > Just as the 'media' drives hysterical concerns in the US for its profit,
    the
    > bike media drives hysteric concerns. Words no longer mean much unless
    they
    > are piled high and deep. The conspiracy of ignorance masquerades as
    common
    > sense.
    >
    > People have forgotten the significance of words like 'may' and 'possibly' and 'anecdote'. My disk
    > brakes have been reliable for >20K miles.

    Have you actually looked at the physics behind it? It definately makes sense, and is something the
    manufacturers should at least be thinking about.

    BTW its not actually a question of the reliability of the brakes.
     
  6. James Annan wrote:

    > > James's Web site is at:
    > >
    > > http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index. html
    >
    > James

    Hi James, Is there a reason you picked .6 g for your deceleration in your model calculation?
    Obviously on some surfaces the traction is limited, but an experienced MTBer who gets his weight way
    back, and chest nearly to the seat, could easily brake much harder if the traction is good.

    max braking force = rider weight/tan(angle) where "angle" is the angle above the horizontal of the
    line from the front contact patch to the rider's CG (neglecting the bike weight, of course). .6 g
    corresponds to 60 degrees, and I'd guess a rider could get pretty close to 45 on flat ground,
    resulting in a 70% greater force.

    Stergios
     
  7. Dave Kahn

    Dave Kahn Guest

  8. Jobst Brandt

    Jobst Brandt Guest

    Pete Cresswell writes:

    >>Have you actually looked at the physics behind it?

    > A question from the spatial-relationship-challenged: Does the force that wants to pop the wheel
    > out of the forks get greater or lesser as the diameter of the disk increases? (i.e. is it greater
    > for 165mm disks or 185mm disks given all other factors equal?)

    The force is translated the skid force on the road to a vertical force that wants to push the
    axle out of the dropout by a ratio of wheel diameter to disk diameter (if the caliper is behind
    the fork).

    That translates to the smaller the disc the greater the disengaging force. I see no physics astute
    contributors disagreeing with James's assessment of the problem, only disbelievers who show no
    reason why it is not so, other than they haven't crashed yet.

    Jobst Brandt [email protected] Palo Alto CA
     
  9. Chris B .

    Chris B . Guest

    On Thu, 15 May 2003 01:12:45 GMT, "(Pete Cresswell)" <[email protected]> wrote:

    >RE/
    >>Have you actually looked at the physics behind it?
    >
    >A question from the spatial-relationship-challenged: Does the force that wants to pop the wheel out
    >of the forks get greater or lesser as the diameter of the disk increases? (i.e. is it greater for
    >165mm disks or 185mm disks given all other factors equal?)
    >-----------------------
    >PeteCresswell

    I was corrected on just this point the last time this was discussed.

    For a given rate of deceleration, the extraction force will increase as the diameter of the rotor
    _decreases_. The larger rotor is a longer lever so less force needs to be applied to result in the
    same torque.

    Chris Bird
     
  10. James Annan wrote:
    >
    > Stergios Papadakis <[email protected]> wrote in message
    > news:<[email protected]>...
    >
    > > Hi James, Is there a reason you picked .6 g for your deceleration in your model calculation?
    >
    > It's a pretty standard estimate, and I didn't want to go to extremes - that would only have led
    > (even more) people to say I was exaggerating and scaremongering. It's not critical to the
    > calculation.
    >
    > James

    Fair enough. Nice work, by the way.

    Stergios
     
  11. Doug Taylor

    Doug Taylor Guest

    [email protected] (James Annan) wrote:

    >Doug Taylor <[email protected]> wrote in message
    >news:<[email protected]>...
    >
    >> I suppose, but since I've had zero problems with my QR in 2 years of hard riding with discs, I
    >> remain about as concerned as I am with mold in my house.
    >
    >That's ok, even stupid people deserve some protection from badly designed products (in fact if
    >anything it's the stupid people who need the protection more than those who understand the danger,
    >and may be able to mitigate it).
    >
    >> But once the liability lawyers get a hold of it, it will become another over hyped circus and it
    >> will end up costing the consumer. Forget the lawyer lips: coming soon to your drops: "lawyer
    >> latches"
    >
    >You might more accurately aim your animosity at the 'engineers' who built bicycles designed to spit
    >the front wheel out without warning on a fast descent. What's worse, some of them continue to deny
    >the problem even once it has been explained to them in words of one syllable. What does that tell
    >you about their competence and/or ethical standards? To me, that puts them comfortably lower than
    >lawyers, who are at least actually supposed to advocate the case of their client rather than seek
    >the truth.
    >
    >At least some of them are now starting to take the problem seriously. It remains to be seen whether
    >they are approaching the problem with a genuinely open mind, or merely trying to 'prove' that their
    >products are not at fault.

    I apologize for my stupidity, but until your theories are backed up by statistics which prove
    there is a cost benefit to re-engineering the system , I remain unconcerned and unconvinced. I
    certainly have no plans to change the components on my mountain bike as it is currently set up, or
    stop using it.

    Time will tell whether I am a lame brain or you are Chicken Little. --dt
     
  12. James Annan

    James Annan Guest

    Jon Isaacs wrote:
    >>Have you actually looked at the physics behind it? It definately makes sense, and is something the
    >>manufacturers should at least be thinking about.
    >
    >
    > What makes you think they are not thinking about it?
    >
    > One thing to realize is the website in question was the result of a crash involving a bike with no
    > retaining lips. It took a good deal of effort to get the site owner to be upfront about this.

    Readers are invited to read my FIRST posting on the subject:

    http://groups.google.com/groups?q=g:thl3236422428d&dq=&hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=images&selm-
    =c96ea403.0212011748.5f6ce80b%40posting.google.com

    and judge the validity of this complaint.

    Do you have anything relevant to say on the contents of the website, by the way? I remember you
    being rather sceptical at first, but as soon as I suggested that the QR could unscrew you seemed to
    go very quiet.

    James
     
  13. James Annan

    James Annan Guest

    Doug Taylor wrote:

    >
    > Time will tell whether I am a lame brain or you are Chicken Little.

    I make no strong claims about the magnitude of the problem, I'm only explaining what goes wrong when
    it does. I know is it quite rare in absolute terms, but it can have extremely serious consequences.
    I'm not sure how you get from there to Chicken Little.

    James
     
  14. Jose Rizal

    Jose Rizal Guest

    [email protected]:

    > Pete Cresswell writes:
    >
    > >>Have you actually looked at the physics behind it?
    >
    > > A question from the spatial-relationship-challenged: Does the force that wants to pop the wheel
    > > out of the forks get greater or lesser as the diameter of the disk increases? (i.e. is it
    > > greater for 165mm disks or 185mm disks given all other factors equal?)
    >
    > The force is translated the skid force on the road to a vertical force that wants to push the
    > axle out of the dropout by a ratio of wheel diameter to disk diameter (if the caliper is behind
    > the fork).
    >
    > That translates to the smaller the disc the greater the disengaging force. I see no physics astute
    > contributors disagreeing with James's assessment of the problem, only disbelievers who show no
    > reason why it is not so, other than they haven't crashed yet.
    >

    However, bear in mind that the larger the rotor diameter, the greater the load on the fork brake
    mounts. This is the reason that suspension fork manufacturers (eg Manitou, Fox) void the warranty on
    their "standard" (ie non-downhill) forks if larger than 6" rotors are used.
     
  15. Terry Morse

    Terry Morse Guest

    Jose Rizal wrote:

    > However, bear in mind that the larger the rotor diameter, the greater the load on the fork brake
    > mounts. This is the reason that suspension fork manufacturers (eg Manitou, Fox) void the warranty
    > on their "standard" (ie non-downhill) forks if larger than 6" rotors are used.

    Please explain. For a given braking force, a larger diameter rotor will lessen--not increase--the
    force on the brake mounts. There must be some other reason why fork manufacturers don't want large
    diameter rotors.
    --
    terry morse Palo Alto, CA http://www.terrymorse.com/bike/
     
  16. Doug Taylor

    Doug Taylor Guest

    James Annan <[email protected]> wrote:

    >> Time will tell whether I am a lame brain or you are Chicken Little.
    >
    >I make no strong claims about the magnitude of the problem, I'm only explaining what goes wrong
    >when it does. I know is it quite rare in absolute terms, but it can have extremely serious
    >consequences. I'm not sure how you get from there to Chicken Little.

    By the same token, I don't see how you get to I'm "stupid" because I'm not getting a big hard on
    worrying about my wheel (with snugly fastened QR and lawyer lips on fork dropout) falling off.

    --dt
     
  17. Jon Isaacs wrote:
    >
    > What makes you think they are not thinking about it?
    >
    > One thing to realize is the website in question was the result of a crash involving a bike with no
    > retaining lips. It took a good deal of effort to get the site owner to be upfront about this.
    >
    > Jon Isaacs

    I think this is a bad argument. The system should NOT rely on the retaining lips to keep the axle in
    position. Every fork's dropout shape will be slightly different, and QRs vary in their exact
    geometry. If the system is to rely on the lips to keep the axle in position, then the outer diameter
    of the face of the QR would have to exactly press against the tops of the retaining lips when the
    axle was fully in the dropouts (obviously, since the fork makers don't also supply the axle and QR,
    they aren't designing them this way). Otherwise, the axle could shift until the QR bears against the
    lips. That is not something you want.

    Perhaps a particular crash would have been prevented by using a fork with lips. That doesn't mean
    the QR + disk brake system is an OK design. You shouldn't have to reposition your front wheel QR
    unless you want to.

    Stergios
     
  18. Jose Rizal

    Jose Rizal Guest

    Terry Morse:

    > Jose Rizal wrote:
    >
    > > However, bear in mind that the larger the rotor diameter, the greater the load on the fork brake
    > > mounts. This is the reason that suspension fork manufacturers (eg Manitou, Fox) void the
    > > warranty on their "standard" (ie non-downhill) forks if larger than 6" rotors are used.
    >
    > Please explain. For a given braking force, a larger diameter rotor will lessen--not increase--the
    > force on the brake mounts. There must be some other reason why fork manufacturers don't want large
    > diameter rotors.

    A larger rotor will decrease the force required by the calipers to supply the same moment about the
    axle as a smaller rotor, but the bending moment on the fork mounts, which now see a larger moment
    arm despite the decreased force on the caliper, is increased.

    Quoted from a post I made some time ago on the subject:

    "Consider a free body diagram of a fork and disc brake system, and assume that the caliper mounting
    posts are parallel to the radial line from the axle to the center of the caliper contact area. This
    does not affect the validity of the analysis since the mounting posts can be looked upon as moment
    arms. Also assume that the caliper center is exactly between the tips of the mounting posts.

    Now in the case of a small rotor with diameter Ro, the force exerted by the caliper Fo is taken up
    by the two mounting posts. Assume that each post takes up exactly half the caliper force, or 0.5*Fo.
    The moment about the base of each post will then be

    1) 0.5 * Fo * Lo,

    where Lo is the length of the mounting post.

    Now consider the case of a larger rotor, say R1. Assume that the mounting posts are lengthened by
    the same amount as the increase in radius for the larger rotor, that is,

    2) R1 - Ro = L1 - Lo

    and the posts are still parallel to the axle-caliper radial line.

    Since the moment about the axle needs to be the same as with the smaller rotor, then

    3) F1 * R1 = Fo * Ro.

    and so

    4) F1 = Fo * Ro/R1.

    The moment about the base of each post will now be

    5) Moment = 0.5 * F1 * L1 = 0.5 * Fo * Ro/R1 * L1

    But L1 = (R1 - Ro + Lo) from 2) above, so the moment on each post is

    6) Moment = 0.5 * Fo * Ro/R1 * (R1 - Ro + Lo).

    Plugging in typical numbers show clearly that the larger the disc brake rotor, the greater the
    moment exerted on the fork leg brake mounts."

    Example: let Ro = 76.2mm (6" rotor), Lo = 15mm, and R1 = 101.6mm (8" rotor)

    Plug into 1) and 6) above and it's clear that the moment on each mounting post is about 2 times
    greater for the larger rotor than for the smaller rotor.
     
  19. Giganews

    Giganews Guest

    I have never, in several years and many thousands of miles of hard riding with disc brakes, had a QR
    become loose.

    I understand the force diagram, but fail to see what would cause the QR to loosen, unless it was
    already extremely loose to begin with and vibrated out. My QRs all have serrated faces so this is
    essentially a non-problem.

    I think a simple force balance will also tell you that the force pushing the wheel out of the
    dropout is dramatically smaller than the force required to move the wheel if the skewer is tightened
    properly or even anywhere near properly.

    you = Chicken little.

    "James Annan" <[email protected]> wrote in message news:[email protected]...
    > Tim McNamara wrote:
    >
    > > Eland mentions that the concern has been taken up on the BikeBiz industry Web site. I looked and
    > > there's nothing I could find in the consumer pages, but there seems to be possibly something in
    > > the industry pages.
    >
    > Yes, it's on the password-protected bit:
    >
    > http://www.bikebiz.co.uk/web/article.php?id=2899
    >
    > Is this the end of QRs for MTBs? A Scottish climate research scientist based in Japan has stirred
    > up a hornet's nest of a safety topic. James Annan claims quick release skewers are no longer 'fit
    > for purpose' on disc-brake equipped bikes. They can and do come undone, says Annan. Riders have so
    > far put this down to their own sloppiness but a recent crash, which left an English rider
    > disabled, has brought the issue into sharp focus. Manufacturers have been dismissive of Annan's
    > emails to date but a growing number of engineering-trained bike experts are lining up behind
    > Annan's theories. Cigarette companies, aware of tobacco-related illnesses since the 1950s onwards,
    > were successfully sued in group actions because of the wilful disregard of evidence that tobacco
    > harms. If the QR problem is ignored, could the bike trade be crippled by similar lawsuits?
    >
    > (etc, with more in the same vein - nothing factually different from what has been said on my
    > website and rec.bicycles.tech)
    >
    > > James's Web site is at:
    > >
    > > http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index. html
    >
    > James
     
  20. Mike S.

    Mike S. Guest

    "GigaNews" <[email protected]> wrote in message news:[email protected]...
    > I have never, in several years and many thousands of miles of hard riding with disc brakes, had a
    > QR become loose.
    >
    > I understand the force diagram, but fail to see what would cause the QR to loosen, unless it was
    > already extremely loose to begin with and vibrated out. My QRs all have serrated faces so this is
    > essentially a non-problem.
    >
    > I think a simple force balance will also tell you that the force pushing
    the
    > wheel out of the dropout is dramatically smaller than the force required
    to
    > move the wheel if the skewer is tightened properly or even anywhere near properly.
    >
    > you = Chicken little.
    >
    I've been wondering about this thread. Seems that there are two camps: one is that discs and QRs
    shouldn't mix, and the other says: properly used the QR should be fine.

    If discs and QRs are a bad combo, why is it that there are only a very, very small minority of
    riders ever having problems with the combo? I know in my experience with QRs and discs, that I
    haven't noticed anything different than if I was running rim brakes.

    Which led me to thinking about forces on the rear of the bike. Shouldn't the force of pedaling the
    bike do the same thing to the rear wheel as discs do to the front? Since most mtn dropouts are semi-
    to vertical, shouldn't the force of pedaling try to pull the rear wheel out of the dropout too? What
    about discs in the rear?

    So, if the rear dropouts are OK, why aren't the fronts?

    I'm still not convinced its not a case of "user error." I detect hints of the Audi "unintended
    acceleration" syndrome here. As y'all know, I'm NOT an engineer, just curious.

    Mike
     
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